predictive maintenance of a hydraulic system using axial...

,,DUNAREA DE JOS” UNIVERSITY OF GALATI

FACULTY OF ENGINEERING

DEPARTMENT OF MANUFACURING ENGINEERING

Predictive Maintenance of a Hydraulic

System Using Axial Piston Pump

Scientific supervisors: Master student:

Prof.Dr.Eng.Mohamed Rafik Sari

Assoc. Prof. Dr. Eng. Nicusor BAROIU Eng. Khaoula BERKAS

Galati – 2019

Dedication

Khaoula BERKAS

I

Acknowledgement

The work presented in the thesis was carried out at “Dunarea de Jos” Galati, Roumanie as part

of the Erasmus+ project. (ANL Med - Algerian National Laboratory for Maintenance

Education; Project No. 586035-EPP-1-2017-1-DZ-EPPKA2-CBHE-JP).

Especial thanks to my parents for sustaining effort, patience and inspiring me at all time with

their love.

I express my gratitude to my supervisors Pr. Dr. Sari Mohamed Rafik and Assoc. Prof. Dr.

Eng. Nicusor for providing guidance and pushing me forward during my research. Assoc.

I would like to express my indebtedness and deepest appreciation for Erasmus+ project

coordinators Prof. Dr. Eng. Viorel Paunoiu and Prof. Dr. Eng. Khelif Rabia, for his

kindness and cooperation.

I cover my thanks and respect to all advisers who represent their general and kind help

especially the Department of Chemistry, Physics, and Environment Prof. Dr. Chim. Rodica –

Mihaela Dinica, Assoc. Prof. Dr. Chim. Romica Cretu and Eng. Andreea Veronica Dediu

(Botezatu).

I am grateful for the technical support offered by Center MoRAS developed through Grant

POSCCE ID 1815, cod SMIS 48745 (www.moras.ugal.ro).

Last but not least, I would like to thank Erasmus + for this opportunity. All of you are

wonderful.

Dedication

Khaoula BERKAS

II

DEDICATION:

Thanks to all those who supported me to achieve my work successfully.

I dedicate this humble work in particular to:

My father who supported me

My beloved mother whose prayers and blessing spurred me to accomplish my work

successfully.

My brother and sister, may Allah bless them all. Everyone who helped and supported

me.

To you all I dedicate my love and gratitude and the outcome of my work

Abstract

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Abstract: Among the most efficient and modern means of mechanization and automation of machinery,

equipment and installations are hydraulic drive systems, the use of which has increased

considerably in recent years because of their advantages remarkable [1] [2].

Extensions of the service life of hydrostatic plants are gaining importance due to several

considerations, including the choice of hydraulic fluids. The use of the right hydraulic fluid is

essential to optimize the performance and life of the system. Hydraulic fluids are the

cornerstone of the hydraulic system.

The analysis of the oil, performed as part of a conditional preventive maintenance, will for

example, to detect the degradation of the oil and monitor the following possible malfunctions:

pollution of the circuit (solids, water etc.), wear of components (pumps, motors, distributors).

Changes in chemical structure and physical properties are followed by several techniques and

tests. The first objective of this work consists in submitting the experimental results of the

physicochemical analysis of mineral oil used in hydraustatic installations such as, the

refractive index, the kinematic viscosity, and flash point, then we will use another analysis

like the FTIR spectroscopy which allows the identification of functional groups and the

determination of molecular structures of the oil used in hydraustatic installation.

The second part of this work involves the use of another modern method which is

thermography for the purpose of controlling the temperature of the pump, since the pump is

the heart of the installation.

Keywords: Hydraulic oil, oil degradation, physicochemical properties, FT-IR analysis,

camera thermography.

Résumé

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Résumé Parmi les moyens les plus efficaces et les plus modernes de mécanisation et d'automatisation

des machines, des équipements et des installations figurent les systèmes de transmission

hydrauliques, dont l'utilisation a considérablement augmenté ces dernières années en raison de

leurs avantages remarquables [1] [2].

L'allongement de la durée de vie des installations hydrostatiques gagne de l'importance en

raison de plusieurs considérations, notamment le choix des fluides hydrauliques. L'utilisation

du bon fluide hydraulique est essentielle pour optimiser les performances et la durée de vie du

système. Les fluides hydrauliques sont la pierre angulaire du système hydraulique. L'analyse

de l'huile, réalisée dans le cadre d'une maintenance préventive conditionnelle, permettra par

exemple de détecter la dégradation de l'huile et de surveiller les éventuels dysfonctionnements

suivants : pollution du circuit (solides, eau, etc.), usure des composants (pompes, etc.)

moteurs, distributeurs). Les modifications de la structure chimique et des propriétés physiques

sont suivies de plusieurs techniques et tests. Le premier objectif de ce travail consiste à

présenter les résultats expérimentaux de l'analyse physicochimique des huiles minérales

utilisées dans les installations hydrostatiques telles que, l'indice de réfraction, , la viscosité

cinématique et le point d'éclair, puis nous utiliserons une autre analyse comme le FTIR

spectroscopie qui permet l'identification de groupes fonctionnels et la détermination des

structures moléculaires de l'huile utilisée dans une installation hydrostatiques. La deuxième

partie de ce travail implique l’utilisation d’une autre méthode moderne, la thermographie,

permettant de contrôler la température de la pompe, celle-ci constituant le cœur de

l’installation.

Mots-clés : Huile hydraulique, dégradation de l'huile, propriétés physicochimiques, analyse

FT-IR, thermographie par caméra.

ملخص

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ملخص

التي زاد الهيدروليكية،أنظمة القيادة والمنشآت،من بين أكثر الوسائل كفاءة وحداثة في الميكنة وأتمتة اآلالت والمعدات

.2][ ]1استخدامها بشكل كبير في السنوات األخيرة بسبب مزاياها الرائعة ]

بما في ذلك اختيار السوائل االعتبارات،تكتسب إطالة العمر التشغيلي للمصانع الهيدروستاتيكي أهمية نظًرا للعديد من

الهيدروليكية. يعد استخدام السائل الهيدروليكي الصحيح ضروريًا لتحسين أداء النظام وعمره. السوائل الهيدروليكية هي

سوف يقوم على المشروطة،الذي يتم تنفيذه كجزء من الصيانة الوقائية الزيت،حجر الزاوية في النظام الهيدروليكي. تحليل

تآكل المكونات (،الماء الصلبة،مثال باكتشاف تدهور الزيت ومراقبة األعطال المحتملة التالية: تلوث الدائرة )المواد سبيل ال

المحركات والموزعين(. التغييرات في التركيب الكيميائي والخصائص الفيزيائية تتبعها العديد من التقنيات المضخات،)

العمل في تقديم النتائج التجريبية للتحليل الفيزيائي الكيميائي للزيوت المعدنية واالختبارات. يتمثل الهدف األول من هذا

ثم سنستخدم تحليًًل آخر ،االشتعال والكثافة واللزوجة الحركية ونقطةالمستخدمة في المنشآت المائية مثل مؤشر االنكسار

الهياكل الجزيئية للزيوت المستخدمة في التحليل الطيفي الذي يسمح بتحديد المجموعات الوظيفية وتحديد FTIR مثل

التركيب الهيدروستاتيكي. يتضمن الجزء الثاني من هذا العمل استخدام طريقة حديثة أخرى هي التصوير الحراري بغرض

.أن المضخة هي قلب التركيب نظرا المضخة،التحكم في درجة حرارة

، التصوير الحراري FT-IR تحليل والكيميائية،الخواص الفيزيائية الزيت،تدهور الهيدروليكي،: الزيت الكلمات المفتاحية

للكاميرا

List of figures

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List of figure:

Fig.I. 1.Hydraulic Application Trend and Milestone. ................................................................ 1

Fig.I. 2.Excavatore. .................................................................................................................... 3

Fig.I. 3.Machine tools ................................................................................................................ 3

Fig.I. 4.Compact wheel loader buckets. ..................................................................................... 4

Fig.I. 5.steel mill. ....................................................................................................................... 4

Fig.I. 6.NC press. ....................................................................................................................... 4

Fig.I. 7.Injection- molding machine. .......................................................................................... 4

Fig.I. 8.Classification of pumps. ................................................................................................ 9

Fig.I. 9.Swach plate type. ......................................................................................................... 10

Fig.I. 10.Bent axis type. ........................................................................................................... 11

Fig.I. 11.Radial pistos pumps. .................................................................................................. 11

Fig.I. 12.Vane pump. ............................................................................................................... 13

Fig.I. 13.External gear pumps. ................................................................................................. 14

Fig.I. 14.Internal gear pumps. .................................................................................................. 14

Fig.II. 1.Objectif of maintenance. ............................................................................................ 18

Fig.II. 2.Maintenance activities. ............................................................................................... 18

Fig.II. 3.Wear in hydraulic systems. ........................................................................................ 21

Fig.II. 4.Cavitation in gear pump. ............................................................................................ 22

Fig.II. 5.Foaming phenomena in gear pump. ........................................................................... 23

Fig.II.6 Flow chart depicting the process of

faultfinding.…………………………………………………………………………………...27

Fig.III. 1.Classification of hydraulic fluids. ............................................................................. 32

Fig.III. 2.Volume and velocity of flow. ................................................................................... 36

Fig.III. 3.Causes and effects of ageing (Sourse: Asaff et al., 2014)......................................... 39

Fig.III. 4.Infrared spectroscopy. ............................................................................................... 39

Fig.III. 5.Mode of operation of FT-IR analysis. ....................................................................... 40

Fig.III. 6.Spectroscopy analysis .............................................................................................. 40

Fig.III. 7.UV-Vis Double PC 8 Spectro-Scan 50 Apparatus. .................................................. 42

Fig.III. 8.Engler viscometer. .................................................................................................... 43

Fig.III. 9.Flash Point Apparatus. .............................................................................................. 45

Fig.III. 10.Light crossing from any transparent medium into another. .................................... 46

Fig.III. 11.Refractometer diagram. ........................................................................................... 47

Fig.III. 12.Refractometer apparatus. ........................................................................................ 47

Fig.III. 13.A peek through the measuring telescope shows scales of Refractive Index. ......... 47

Fig.III. 14.Drawing shows the actual appearance of the image as seen through the focusing

telescope. ........................................................................................................................... 47

Fig.III. 15..Spectrum 03 oils before use pH=4-5. .................................................................... 48

Fig.III. 16.Used hydraulic oil in difference spectrum. ............................................................. 49

Fig.III. 17.The same oil used 18months. .................................................................................. 50

List of figures

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Fig.III. 18.degradation of hydraulic oil. ................................................................................... 50

Fig.III. 19.Transmitance spectrum of new oil. ......................................................................... 51

Fig.III. 20.Transmitance spectrum of oil after 6 months. ........................................................ 51

Fig.III. 21.Transmitance spectrum of oil after 12 months. ...................................................... 51

Fig.III. 22.Transmitance spectrum of oil after 18 months. ...................................................... 51

Fig.III. 23.Evolution of the viscosity at 25 °C and 40 °C. ....................................................... 52

Fig.III. 24.Evolution of the flash point. .................................................................................... 53

Fig.III. 25.Measured refractive index. ...................................................................................... 54

Fig.IѴ. 1.Continuous quality control on welds. ....................................................................... 57

Fig.IѴ. 2.Medical Infrared Imaging of hand of human. .......................................................... 57

Fig.IѴ. 3.Vehicle maintenance. ............................................................................................... 57

Fig.IѴ. 4.Medical Infrared Imaging of animals. ...................................................................... 57

Fig.IѴ. 5.Thermal images of a district heating pipeline. ......................................................... 57

Fig.IѴ. 6.Electromagnetic spectrum. ....................................................................................... 59

Fig.IѴ. 7.Schematic representation of the method of thermography. ...................................... 60

Fig.IѴ. 8.Hydrostatic installation with camera thermography. ............................................... 62

Fig.IѴ. 9.ThermoVision A20M ThermoVision Camera. ........................................................ 63

Fig.IѴ. 10.The properties of the pump material. ..................................................................... 63

Fig.IѴ. 11.Choice of the temperature measurement range. ..................................................... 63

Fig.IѴ. 12.Temperature variation for p = 20 bar after 15 minutes. ......................................... 65

Fig.IѴ. 13.Temograph taken with the FLIR camera after 15 minutes. .................................... 65







Fig.IѴ. 20.Temperature variation for p= 20 bar after 50 minutes. .......................................... 66


Fig.IѴ. 22.The hottest area of the pump. ................................................................................. 67

Fig.IѴ. 23.Temperature variation for p= 50 bar after 5 minutes. ............................................ 67

Fig.IѴ. 24.Temograph taken with the FLIR camera after 5minutes. ....................................... 67






Fig.IѴ. 30.Temograph taken with the FLIR camera after 30 minute. ..................................... 69

List of tables

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List of tables: Table.I. 1.The fluid used in hydraulic systems .......................................................................... 7

Table.I. 2.Characteristics of pumps .......................................................................................... 14

Table.I. 3.Specification. ........................................................................................................... 15

Table.II. 1.Causes of noise in hydraulic installations and reduction solutions. ....................... 25

Table.III. 1.Classification of hydraulic fluids based on ISO Viscosity grade. ...................................... 30

Table.III. 2.Examples for density at 15 °C [59 °F]. ................................................................. 34

Table III. 3.Technical data of hydraulic oil HLP 46. ............................................................... 36

Table.III. 4.Hydraulic oil parametr Prista® MHMb type . ...................................................... 37

Table.III. 5.Classification of mineral oils for hydraulics systems. .......................................... 38

Table.III. 6 .Experimental measurement table of viscosity. ..................................................... 52

Table.IѴ. 1.Time used for the selected room. .......................................................................... 61

Table.IѴ. 2.The parameters of the pump. ................................................................................ 64

List of tables

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General introduction

Nowadays, it is well established that the hydraulic systems have gained considerable interest

due to their wide engineering applications such as aerospace, chemical and mechanical

engineering. “Hydraulics” is one of drive systems to control machinery and equipment,

comparable with pneumatics and electricity.

The components of hydraulic systems work together intimately. As a result, damage to one

component may cause further damage to others. For instance, overheated oil caused by a

leaky cylinder seal can break down and cause damage to other cylinders or the pump. That is

why it pays to perform regular maintenance and preventative inspections to eliminate

problems before they occur. The reliability of these systems must be supported by efficient

“maintenance regimes”.

Hydraulic fluid is the medium of power transfer in hydraulic equipment, it is important to

know the properties of hydraulic fluids and its influence on system performance. There are

different types of fluids based on their availability, working purpose etc. Therefore, selection

of fluid depends on the working conditions of the hydraulic equipment. The oil analysis,

performed as part of a conditional preventive maintenance, will allow, for example, detecting

and monitoring the following potential malfunctions: pollution of the circuit (solids, water

etc.), wear of components (pumps, motors, distributors etc.).

The first chapter of this work was devoted to a bibliographic study focused on hydraulic

systems in a general way.

In the second chapter, we have been particularly interested in the maintenance of hydraulic

systems.

The third chapter is divided into two parts:

The first part presents the analysis carried out on the hydraulic oil as well as the various

experimental devices set up in this work.

The second part gathers the experimental results of the measurements carried out with the

laboratories with a discussion.

The fourth chapter, which is the last in the thesis, concerns the assessment of temperature of

pump by infrared camera thermography.

Finally, we end our work with a general conclusion.

Algerian National Laboratory for Maintenance Education

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- Objectives:

The goal of the ANL-MEd is to provide Algerian industry with a new generation of skilled

personnel, especially at mid- and higher levels, along with ensuring flexible and continuing

education and training of industry personnel at all levels. Flexibility is necessary to adapt and

update the knowledge according to the day-to-day progress of science and technology. The

partners in the project have been selected above all to suit to the genuine structure of Algerian

academia and industry and to align it to a modern and dynamic European standard. The

reference line is represented by the two main characteristics of the Algerian industry

- Description:

For Algerian economy, Africa's fourth economy, to be able to compete successfully both at

national and international levels, production systems and equipment must perform at much

better levels. Requirements for increased product quality, reduced throughput time and

enhanced operating effectiveness within a rapidly changing customer demand environment

continue to demand a high maintenance performance. Unfortunately, few companies in

Algeria address the significant synergies of knowledge and skills in maintenance and

maintenance operations. Currently, there are no any maintenance programmes at academic

level while training in maintenance is isolated being performed solely in few large companies.

Today, the universities are further stressed by huge classes, overstressed infrastructures,

inadequate and unskilled supervisors, insufficient and old equipment, and a lack of up-to-date

educational and scientific materials. Vocational education suffers from problems with the

language of instruction, poor teaching, haphazard job placement (lack of systematization),

lack of industrial linkages, and lack of flexibility. These problems produce graduates with

inadequate skills in unwanted areas and the inability to adapt. Investing in education and

training in maintenance engineering and management at all professional levels, engineers,

managers and technical personnel in various industries, will boost the Algerian economic

competitiveness and will create thousands of new jobs in universities, training centres, and for

engineers, managers and technicians in all economic sectors. Youth, men and women, will

find a rewarded carrier path and professional satisfaction in Algerian economic sector.

The Algerian National Laboratory in Maintenance Education, ANL-MEd, has the mission to

create the next generation educated workforce in industry. There are two major driving forces

for the ANL-MEd project proposal: i) Matching the educational and training programmes at

universities to the needs of industry and generally of the Algerian economy, for creation of

new jobs. ii) Creation of a strong coalition between university - industry - governmental

organizations for long-term collaboration in education, training and research, for revitalization

of Algerian economy and in particular of Algerian industry.


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ANL-MEd assembles for 36 months a consortium with 14 partners with unique combination

of skills and expertise. The consortium, coordinated by USTHB, has a hierarchical structure

that ensures an efficient communication and cooperation. Four European universities with

solid competence in maintenance engineering and management will contribute to

development of teaching material and training students, teacher, trainers and industry staff.

The four Algerian universities will collaborate with EU partners and the Algerian industrial

partners to develop and implement the specialization and training programmes, and to create

the ANL-ORG, the national laboratory which will coordinates all activities related to

maintenance education. The key factor for implementation of the project objectives is the

active collaboration between academic and industrial partners. Therefore, important resources

have been allocated for creating a harmonious working environment – ANL-ORG – with

activities for creating synergies between project partners and stakeholders. This will

contribute to strengthening the active cooperation between university and industry, as well

between Algeria and EU. The project activities are distributed in 7 work packages according

to a detailed work plan that adequately structures the efforts into manageable work packages

with clear responsibilities and objectives. For improved effectiveness in the project for

organization of implementation, the partners are grouped in three clusters: ANL-EDUC –

cluster for education, ANL-VET – cluster for vocational education and training and ANL-

ORG for organization of the ANL, coordinating the resources for integration, communication

and exploitation.

Presentation of the working environment

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Presentation of the working environment

- The University of Dunarea de Jos de Galati:

My internship took place in Galati, Romania, an extreme eastern town with about 230 000

people, on the Danube river. This town is in the Galati county, very close from the border of

Rep. Moldova and Ukraine. It contains also old and important industries like ArcelorMittal or

the shipyard company Damen.

It is an old division of the school, from the former Technical Institute of Galati. It was initially

well-known for naval building and technology of ships and ports. Then, it expanded with new

specializations: - Refrigeration and technology of machinery building in 1960 - Thermal

machines and welding technology in 1978 - Metallurgical engineering in 1990 The objectives

of the faculty of mechanical engineering is the development of scientific research centers,

promoting the national and international cooperation of inter-university and economic

environment, and contributing to the universal knowledge’s. The Faculty of Engineering has

created strong ties with national industries such as Dacia but also with international industries

such as Fiat or ArcelorMittal.

- The Faculty of Engineering:

I performed my internship in the Faculty of Engineering, in the Department of Manufacturing

Engineering.

Symbol of the Faculty of Engineering.

Plagiarism declaration

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Plagiarism declaration 1- I know that plagiarism means taking and using the ideas, writings, works or inventions

of another as if they were one’s own. I know that plagiarism not only includes

verbatim copying, but also the extensive use of another person’s ideas without proper

acknowledgement (which includes the proper use of quotation marks). I know that

plagiarism covers this sort of use of material found in textual sources and from the

Internet.

2- . I acknowledge and understand that plagiarism is wrong.

3- I understand that my research must be accurately referenced. I have followed the rules

and conventions concerning referencing, citation and the use of quotations as set out in

the Departmental Guide.

4- This assignment is my own work, or my group’s own unique group assignment. I

acknowledge that copying someone else’s assignment, or part of it, is wrong, and that

submitting identical work to others constitutes a form of plagiarism.

5- I have not allowed, nor will I in the future allow, anyone to copy my work with the

intention of passing it off as their own work.

Student Name: Khaoula BERKAS

Signes, Date:

22.07.2019


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Dedication .................................................................................................................................. II

Abstract .................................................................................................................................... III

Résumé ..................................................................................................................................... IV

V .......................................................................................................................................... ملخص

List of figure ............................................................................................................................. VI

List of tables .......................................................................................................................... VIII

General introduction ................................................................................................................. IX

Algerian National Laboratory for Maintenance Education ....................................................... X

Presentation of the working environment ............................................................................... XII

Plagiarism declaration ........................................................................................................... XIII

Chapter I: Generalities of hydraulic systems ........................................................................ 1

I. Introduction ............................................................................................................................. 1

I.1. Definitions ........................................................................................................................ 2

I.1.1. Hydraulics .................................................................................................................. 2

I.1.2. Hydrostatics ............................................................................................................... 2

I.2. Fields of application of hydraulic..................................................................................... 3

I.3. Advantages and disadvantages of using hydraulic systems ............................................. 4

I.4. Fluids used in hydraulic systems ...................................................................................... 5

I.5. Generality of hydraulic pumps ......................................................................................... 8

I.5.1. Definition ................................................................................................................... 8

I.5.2. Classification of pumps ............................................................................................. 9

I.5.3. Piston pumps.............................................................................................................. 9

II.5.4. Vane pumps ............................................................................................................ 11

I.5.5. Gear pumps .............................................................................................................. 13

I.5.6. Comparison of the pumps ...................................................................................... 14

Chapter II: Maintenance and troubleshooting for hydraulic systems. ............................. 16

II. Introduction ......................................................................................................................... 16

II.1. Definitions .................................................................................................................... 16

II.1.1. Maintenance ........................................................................................................... 16

II.2. Types of maintenance ................................................................................................... 18


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II.2.1. Preventive maintenance .......................................................................................... 19

II.2.2. Corrective maintenance .......................................................................................... 19

II.2.3. Predictive maintenance .......................................................................................... 19

II.2.4. Improvement maintenance ..................................................................................... 19

II.3. Hydraulic system problems .......................................................................................... 20

II.3.1. The phenomenon of wear due to fluid contamination............................................ 20

II.3.2. Problems due to entrained gas in fluids ................................................................. 21

II.3.3. Cavitation ............................................................................................................... 21

II.3.4. Foaming .................................................................................................................. 22

II.4. Common causes for hydraulic system breakdown ....................................................... 23

II.5. Noise in hydraulic installations ..................................................................................... 24

II.5.1. Causes of noise in hydraulic systems ..................................................................... 24

II.6. Troubleshooting ............................................................................................................ 27

II.6.1 Fault finding process ................................................................................................... 27

II.7. Conclusion ........................................................................................................................ 29

Chapter III: Materials and methods for hydraulic oils analysis ....................................... 30

III.1. Introduction ..................................................................................................................... 30

III.1.1. Classification of hydraulic fluids based on ISO viscosity grade .................................. 30

III.2. Types of hydraulic fluids................................................................................................. 31

III.2.1. Mineral-Oil based Hydraulic fluids .......................................................................... 31

III.2.2. Fire Resistant Fluids ................................................................................................. 31

III.2.3. Environmental Acceptable Hydraulic Fluids (EAHF) ............................................. 31

III.3. Fluid properties and comparative performances ............................................................. 32

III.3.1. The types of oils used in the hydraulic system ..................................................... 36

IIII.4. Methods of predictive maintenance that promote the energy efficiency of hydraulic

systems ..................................................................................................................................... 38

III.4.1. Spectroscopic method ............................................................................................... 38

III.4.1.1. Oil degradation mechanisms .............................................................................. 38

III.4.1.2. FT-IR Analysis of Used Lubricating Oils .......................................................... 39

III.4.1.3. Transmittance: ....................................................................................................... 41

III.4.2. Physic-chemical analysis for hydraulic oil (prista MHM) ....................................... 42

III.4.2.1. Measuring the viscosity of oils .......................................................................... 42

III.4.2.2. Flash point for hydraulic oil ............................................................................... 44


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III.4.2.3. Effects of oil degradation on Refractive Index .................................................. 45

III.5. Results ............................................................................................................................. 48

III.5.1. FT-IR analysis .......................................................................................................... 48

III.5.2. Observation and calculation of the viscosity: ....................................................... 51

III.5.3. Flash point ................................................................................................................ 53

III.5.4. Refractive index ........................................................................................................ 54

Chapter IѴ: Assessment of temperature of pump by infrared thermography ................ 55

IѴ.1. Objective ......................................................................................................................... 55

IѴ.1.1. Introduction: ............................................................................................................. 55

IѴ.1.2. History and development ......................................................................................... 56

IѴ.1.3. Application ............................................................................................................... 56

IѴ.1.4. Advantages and disadvantages of thermography infrared ....................................... 57

IѴ.1.5. Effects of Emissivity on Thermal Imaging .............................................................. 58

IѴ.2.Obtained results ............................................................................................................... 58

Ѵ.2.1. Measuring the temperature of the pump ................................................................... 58

IѴ.2.2.The equations of the thermography chamber ............................................................ 59

IѴ.2.3. Experimental equipment .......................................................................................... 62

IѴ.2.4. Diagrams obtained ................................................................................................... 64

IѴ.3. Conclusion ...................................................................................................................... 69

Chapter Ѵ: conclusions ......................................................................................................... 70

References

Annex

Chapter I: Generalities of hydraulic systems

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I. Introduction: “Hydraulics” is one of drive systems to control machinery and equipment, comparable with

pneumatics and electricity. It was in the early 1900’s that practical hydraulic

applications were first seen in the marketplace. A hundred years before that, water

hydraulics,” the origin of the fluid power systems, emerged. Figure 1.1 traces the

development history of some typical water and oil hydraulics. Recently, production

machinery and their drive systems have been required to be environmentally friendly; “water

hydraulics” is attracting attention again because of its cleanliness and safety [1].

With a variety of applications, hydraulic systems are used in all kinds of large and small

industrial settings, as well as buildings, construction equipment, and vehicles. Paper mills,

logging, manufacturing, robotics, and steel processing are leading users of hydraulic

equipment [2].

As an efficient and cost-effective way to create movement or repetition, hydraulic system-

based equipment is hard to top. It’s likely several companies has hydraulics in use in one or

more applications for these reasons [2]. Hydraulics, which owes much to the high lubricity of

mineral oils being used as working fluids, offer compact, high- power, and easy-to-control

system components in various industrial fields [1].

Fig.I. 1.Hydraulic Application Trend and Milestone[1].


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1- Hydrostatics principles: Archimedes

(287～212 B.C.)

2- Bases of hydrodynamics: Galileo

(1564～1642)

3- Hydrostatic laws: Blaise Pascal

(1623～1662) Force multiplier

[Pascal,s principle; 1653]

4- Patent application for the water

hydraulic press machine： Joseph

Bramah + Henry Maudsley (self-

seal)

5- Water hydraulic crane, water

hydraulic accumulator,

manufacturing plant using water

hydraulic drive systems:

1845-1849, William Armstrong

(1810～1900)

6- Fluid power (water hydraulics) supply

company： 1884, The London Hydraulic

Power Company.

7- Power transmission system: J.W.Hall,

Pittler, Lentz, Manley

8- Axial piston pump: 1902-1906, Harvey

Williams + Reynolds Janney

9- Radial piston pump: H.S.Hele-Shaw

10- Pressure balanced vane

pump：1925, Harry F.Vickers

I.1. Definitions:

Hydraulics is a branch of engineering concerned mainly with moving liquids. The term is

applied commonly to the study of the mechanical properties of water, other liquids, and even

gases when the effects of compressibility are small. Hydraulics can be divided into two areas,

hydrostatics and hydrokinetics.

I.1.1. Hydraulics: The Engineering science pertaining to liquid pressure and flow.

The word hydraulics is based on the Greek word for water and originally covered the study of

the physical behavior of water at rest and in motion. Use has broadened its meaning to include

the behavior of all liquids, although it is primarily concerned with the motion of liquids.

Hydraulics includes the manner in which liquids act in tanks and pipes, deals with their

properties and explores ways to take advantage of these properties [3].

I.1.2. Hydrostatics:

Hydrostatics, the consideration of liquids at rest, involves problems of buoyancy and flotation,

pressure on dams and submerged devices, and hydraulic presses. The relative

incompressibility of liquids is one of its basic principles.

Hydrostatics is about the pressures exerted by a fluid at rest. Any fluid is meant, not just

water. Research and careful study on water yields many useful results of its own, however,


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such as forces on dams, buoyancy and hydraulic actuation, and is well worth studying for

such practical reasons [3].

I.2. Fields of application of hydraulic:

Hydraulics is applied in a wide range of industries: from construction machinery,

automobiles, and airplanes (outdoor) to machine tools and press machines (indoor). Typical

applications in each industrial field are listed below:

1- Construction machinery: excavators, cranes, wheel loaders, and bulldozers;

2- Agricultural/forestry machinery: tractors, combines, rice planting machines, lawn

mowers, and logging machines;

3- Material processing/forming machinery: steel mill, machine tools, and plastic

processing, die casting, press and sheet metal processing machines;

4- Automobiles: power steering, transmissions, brake systems, and accessories for

transport vehicles;

5- Industrial and special-purpose vehicles: fork lifts, platform vehicles, garbage trucks,

concrete mixer trucks, concrete pump trucks, and accessories for transport vehicles

(wing roofs and tail lifts);

6- Ships/fishing machinery: steering, propulsion machinery, and deck cranes;

7- Aerospace machinery: steering, brake systems, and landing gear;

8- Testing machinery/simulator: vibration testers, flight simulators, and amusement

machines;

9- Special equipment: hydraulic lifts, vibration control systems for high-story buildings

and trains, sluice gates, crushers, and compactors [1] [3].

Fig.I. 2.Excavator [4].

Fig.I. 3.Machine tools [65].


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Fig.I.4.Compact wheel loader

buckets [5].

Fig.I. 6.NC press [6].

Fig.I. 7.Injection- molding machine [7].

I.3. Advantages and disadvantages of using hydraulic systems:

Advantages of using hydraulic systems:

A hydraulic system has many advantages, which makes it quite efficient in transmitting power

as:

- Higher density of transferred energy;

- Possible command and control performance;

- High safety, control and protection. System protection features prevent damage in

overload situations;

- High reliability;

- Possibility of centralized service [8].

Fig.I. 5.Steel mill [66].


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Disadvantages of using hydraulic systems:

- Hydraulic systems also have certain drawbacks, some of which are:

- Low return compared to other shareholders;

- Variable viscosity as a function of temperature;

- Instability of the hydro-motor movement at low speed;

- The cost of the equipment. [8].

I.4. Fluids used in hydraulic systems:

The working fluid is the single most important component of any hydraulic system. It serves

as a lubricant, heat transfer medium, Sealant and most important of all, a means of energy

transfer. Fluid characteristics play a critical part in determining the equipment performance

and life. Hydraulic fluids are basically non-compressible in nature and can therefore take the

shape of any container. This tendency of the fluid makes it exhibit a certain advantage in the

transmission of force across a hydraulic system. Use of a clean, high-quality fluid, is an

essential prerequisite for achieving efficient operation of the hydraulic system. Although early

hydraulic systems employed the medium of water for transferring hydraulic energy, there are

serious limitations attached to it such as: Its relatively high freezing point (water freezes at 0

°C or 32 °F when the pressure is atmospheric).

- Its tendency to expand when frozen;

- Its corrosive nature;

- Its poor lubrication properties;

- Its capacity to dissolve more oxygen leading to phenomena such as oxygen pitting

[9].

Although hydraulic fluid types vary according to application, the four common types are:

1- Petroleum-based fluids which are the most common of all fluid types and widely

used in applications where fire resistance is not required.

2- Water glycol fluids used in applications which require fire resistance fluids.

3- Synthetic fluids used in applications where fire resistance and non-conductivity is

required;

4- Environment-friendly fluids that end up causing minimal effect on the

environment in the event of a spill.

As discussed earlier, hydraulic fluids have the four essential primary functions of power

transmission, heat dissipation, lubrication and sealing to accomplish which, they should

possess the following properties:

1- Ideal viscosity;

2- Good lubricity;

3- Low volatility;

4- Non-toxicity;

5- Low density;

6- Environmental and chemical stability;

7- High degree of incompressibility;

8- Fire resistance;

9- Good heat-transfer capability;


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10- Foam resistance and most importantly;

11- Easy availability and cost-effectiveness [9] .

Although hydraulic fluid types vary according to application, the four common types are:

1- Petroleum-based fluids which are the most common of all fluid types and widely

used in applications where fire resistance is not required;

2- Water glycol fluids used in applications which require fire resistance fluids;

3- Synthetic fluids used in applications where fire resistance and non-conductivity is

required;

4- Environment-friendly fluids that end up causing minimal effect on the

environment in the event of a spill. As discussed earlier, hydraulic fluids have the

four essential primary functions of power transmission, heat dissipation,

lubrication and sealing to accomplish which, they should possess the following

properties:

- Ideal viscosity;

- Good lubricity;

- Low volatility;

- Non-toxicity;

- Low density;

- Environmental and chemical stability;

- High degree of incompressibility;

- Fire resistance;

- Good heat-transfer capability;

- Foam resistance and most importantly;

- Easy availability and cost-effectiveness.

It is quite obvious that no single fluid can meet all the above requirements and it is therefore

essential that only the fluid that comes closest to satisfying most of these requirements be

selected for a particular application [9].


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Table.I. 1.The fluid used in hydraulic systems [9].

The fluid used

Characteristics

The water

Benefits:

- Invariance of viscosity with temperature;

- Low compressibility;

- Non-flammability.

Disadvantages:

- Limited temperature range (<100 C);

- High frost;

- Inappropriate lubrication;

- Low viscosity, etc.

Water mixed

with glycerine

Benefits:

- High density (1,2 ... 1,7) kg / dm3;

- Lower frost point (-30 ... -40) ° C.

Disadvantages:

- low lubricant;

- hygroscopic - variable in time;

- Good electrolyte – produces corrosion.

Mineral oil

Benefits:

- good lubrication and adhesion properties;

- Temperature range between freezing point and increased

flammability (-35 ... 260) ° C;

- Density approx. 0.9 kg / dm3;

- Used at temperatures (-20 ... 85) ° C;

- Used at pressures of (50 ... 300) bar.

Additive and

blended oils

- Additive and blended oils

- Extreme pressure additives:

- Used at temperatures (-8 ... 90) ° C;

- Used at pressures of (200 ... 500) bar.

- Oil Transformer Oil:

• Used at pressures> 900 bar.

- Silver chloride, talc and polyfluoride:

• used at pressures (200 ... 400) Kbar.

Other

- Synthetic liquids (esters, silicate esters, silicones, etc.)

- Izopentanul - temperaturi foarte scăzute (-40 ... -150)°C.

- Liquid helium - temperatures up to -210 ° C.


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The fluid used

Characteristics

- NaK Metallic Liquid - temperatures up to 760 ° C.

The working fluid is the single most important component of any hydraulic system. It serves

as a lubricant, heat transfer medium, Sealant and most important of all, a means of energy

transfer. Fluid characteristics play a critical part in determining the equipment performance

and life. Hydraulic fluids are basically non-compressible in nature and can therefore take the

shape of any container. This tendency of the fluid makes it exhibit a certain advantage in the

transmission of force across a hydraulic system. Use of a clean, high-quality fluid, is an

essential prerequisite for achieving efficient operation of the hydraulic system. Although early

hydraulic systems employed the medium of water for transferring hydraulic energy, there are

serious limitations attached to it such as:

Its relatively high freezing point (water freezes at 0 °C or 32 °F when the pressure is

atmospheric).

• Its tendency to expand when frozen;

• Its corrosive nature;

• Its poor lubrication properties;

• Its capacity to dissolve more oxygen leading to phenomena such as oxygen pitting. This has

necessitated [1] [3].

I.5. Generality of hydraulic pumps:

I.5.1. Definition:

The mechanical device that is used to convert mechanical power into hydraulic energy is

known as a hydraulic pump. The load that is responsible for the pressure is overcome with

this device by creating sufficient power and generating a flow.

The hydraulic pump has two functions to perform during operation, allowing atmospheric

pressure to push liquid into the inlet line from the reservoir to the pump by the mechanical

action created vacuum at the pump. The other function it performs is that the pumps

mechanical action supplies the liquid to the pump outlet and then forced into the hydraulic

system [10].


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I.5.2. Classification of pumps:

Fig.I. 8.Classification of pumps [11].

Volumetric pumps assure high performance in high-pressure operation, compared to the other

types, and are easy to convert to the variable displacement type. Thus, they can operate with

various control types. The piston pumps provide advantages including:

1- high efficiency;

2- ease of operation at high pressure;

3- ease of conversion to the variable displacement type;

4- various applicable control types.

The pumps are categorized into axial, radial, and reciprocal piston types. This section explains

the axial piston type, which is most widely applied in industrial machinery, from low-/middle-

pressure general industrial machines to high- pressure press machines and construction

machines [1] [11].

I.5.3. Piston pumps:

Piston pumps are meant for the high-pressure applications. These pumps have high-efficiency

and simple design and needs lower maintenance. These pumps convert the rotary motion of

the input shaft to the reciprocating motion of the piston. These pumps work similar to the four

stroke engines. They work on the principle that a reciprocating piston draws fluid inside the

cylinder when the piston retracts in a cylinder bore and discharge the fluid when it extends.

Generally, these pumps have fixed inclined plate or variable degree of angle plate known as

swash plate (shown in Figure I.9 and Figure I.10). When the piston barrel assembly rotates,

pumps

Volumetric

Rotary

To geared

To pallet

With lobes

To screw

Alternative

Piston

Membrane

Rotodynamic

Helico-centrifugal

Centrifugal

Helico-axial


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10

the swash plate in contact with the piston slippers slides along its surface. The stroke length

(axial displacement) depends on the inclination angle of the swash plate [12].

When the swash plate is vertical, the reciprocating motion does not occur and hence pumping

of the fluid does not take place. As the swash plate angle increases, the piston reciprocates

inside the cylinder barrel. The stroke length increases with increase in the swash plate angle

and therefore volume of pumping fluid increases. During one half of the rotation cycle, the

pistons move out of the cylinder barrel and the volume of the barrel increases. During another

half of the rotation, the pistons move into the cylinder barrel and the barrel volume decreases.

This phenomenon is responsible for drawing the fluid in and pumping it out. These pumps are

positive displacement pump and can be used for both liquids and gases. Piston pumps are

basically of two types [12]:

a) Axial Piston Pumps:

These pumps have pistons installed in parallel, or axially, with the pump shaft. The pumps are

sub categorized into the swash plate type and the bent axis type according to the piston stroke

mechanism, as shown in figure I.9 and figure I.10 alternate suction and discharge strokes.

Some of the swash plate type axial piston pumps have a fixed cylinder block and a rotating

swash plate, which rotates so that the piston moves. This type uses a check valve in each

cylinder to switch suction and discharge.

The displacement of the piston pumps can be changed by adjusting the angle of the swash or

bent axis. The swash plate type allows easier adjustment of the angle; thus, it is generally used

as a variable displacement piston pump.I.10 shows the appearances of the swash plate type

variable displacement pumps (A and A3H series) and a graphic symbol of the variable

displacement piston pump [1] [11].

Fig.I. 9.Swach plate type [1].


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Fig.I. 10.Bent axis type [1].

b) Radial Piston Pumps:

These pumps have pistons installed in a pattern radial to the pump-rotating shaft. The pumps

are more suitable for high-pressure operation than the axial type. Figure I.11 shows the

structure of a typical radial piston pump. Piston stroke is achieved with an eccentricity of the

piston-sliding ring to the pump rotating shaft. These pumps switch suction and discharge per

piston stroke in the ring. With a mechanism for ring eccentricity change added, the pumps

allow their displacement to be adjusted [1].

II.5.4. Vane pumps:

These pumps intake and discharge fluid according to the change of space enclosed by the

vanes and the cam ring that rotates by means of the rotor. Vane pumps in a low/middle

pressure range from approximately 7 to 25 MPa (1 015 to 3 626 psi) and with middle

displacement; for example, the single middle-pressure type has a displacement of

approximately 300 cm3/rev. These pumps provide the following advantages:

Fig.I. 11.Radial pistos pumps [13].


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- Minimized discharge pressure pulsation;

- Compactness and light weight for high output;

- Less efficiency degradation due to vane wear;

- Reliability and ease of maintenance [1] [14].

The pumps are quieter because of the structure and are less susceptible to working fluid

contamination than piston pumps. Therefore, they are conveniently used in a wide range of

applications. The pumps typically have a structure where the vane is pressed against the cam

ring by inducing pressurized flow to the bottom of the vane. With the improved structure,

pumps capable of operating at a high pressure of up to 42 MPa (6 092 psi) are also

commercially available. Vane pumps are categorized into fixed and variable displacement

types. Each type is further subcategorized into single and multiple pumps. With vane pumps,

it is easy to construct double and triple pumps by mounting pump elements (components such

as rotors, vanes and cam rings) in tandem to the pump shaft. Such multiple pumps with

displacements of 300 to 500 cm3/rev have been commercialized. Variable displacement type

vane pumps, with changing ring eccentricity, are also available. These pumps, with displace-

ments of 30 cm3/rev or less, are widely used as hydraulic pressure sources for small machine

tools [1], [14].

How Vane Pumps Work:

Despite the different configurations, most vane pumps operate under the same general

principle described below.

1. A slotted rotor is eccentrically supported in a cycloidal cam. The rotor is located close to

the wall of the cam so a crescent-shaped cavity is formed. The rotor is sealed into the cam by

two side plates. Vanes or blades fit within the slots of the impeller. As the rotor rotates

(yellow arrow) and fluid enters the pump, centrifugal force, hydraulic pressure, and/or

pushrods push the vanes to the walls of the housing. The tight seal among the vanes, rotor,

cam and side plate is the key to the good suction characteristics common to the vane pumping

principle.

2. The housing and cam force fluid into the pumping chamber through holes in the cam (small

red arrow on the bottom of the pump). Fluid enters the pockets created by the vanes, rotor,

cam, and side plate [15] [3].

3. As the rotor continues around, the vanes sweep the fluid to the opposite side of the crescent

where it is squeezed through discharge holes of the cam as the vane approaches the point of

the crescent (small red arrow on the side of the pump). Fluid then exits the discharge port

[14].


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Fig.I. 12.Vane pump [14].

Advantages:

- Handles thin liquids at relatively higher pressures;

- Compensates for wear through vane extension;

- Sometimes preferred for solvents, LPG;

- Can run dry for short periods;

- Can have one seal or stuffing box [14].

Disadvantages:

- Can have two stuffing boxes;

- Complex housing and many parts;

- Not suitable for high pressures;

- Not suitable for high viscosity;

- Not good with abrasives [14].

I.5.5. Gear pumps:

These pumps operate with two gears engaged with each other and rotating to feed a hydraulic

fluid from the suction area to the discharge area. They all have fixed (constant) displacement

capacities. They are categorized into external and internal gear pumps; the internal type

generally has smaller discharge pulsation and lower noise level than the other. The gear

pumps are relatively resistant to working fluid contamination. Pumps operate at 20 to 25 MPa

and offer a displacement of 100 cm3/rev for the single type. Similar to vane pumps, double

type gear pumps are easy to construct. High-pressure gear pumps often adopt involute gears,

which allow highly accurate processing, bringing about high system operation efficiency.

Contacting with each other at two points, the gears rotate to entrap oil in the engaging parts,

resulting in vibration and noise, which are reduced by a groove on the side plate allowing the

oil to escape. Some low-pressure gear pumps use trochoidal gears. Figure I.13 and figure I.14

shows the external and internal gear pumps [15].

The displacement of external gear pumps is determined by a chamber between the

neighboring gear teeth and the inner surface of the casing; the displacement of the internal

gear pump is determined by a chamber between the external and internal gears and a dash

board. The crescent-shaped dash board (filler piece) separates the suction and discharge areas.

For both the types, the sides of the gear teeth are sealed with side plates. The high-pressure

external gear pumps have a movable side plate by which high-pressure flow is led to the rear

side to press against the gear and keep a suitable clearance.


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Gear pumps consist of relatively simple parts. They offer high suction performance at a low

cost and are used in various fields: forklifts, industrial platform vehicles, construction

machines such as excavators and wheel loaders, and supporting pumps for primary pumps.

Compact packages containing the gear pump, safety and check valves, oil reservoir, and DC

motor are popular in automobiles [16].

Fig.I. 13.External gear pumps [17]. Fig.I. 14.Internal gear pumps [18].

I.5.6. Comparison of the pumps:

Typical hydraulic pumps fall into three categories: piston, vane, and axial table I.2 and table

I.3 show characteristics, structures, and specifications of the respective pumps.

Table.I. 2.Characteristics of pumps [1-2].

Type Piston pumps Vane pumps Gear pumps

Structure

Operation

Principe

Expansion and compression of a

volume in a cylinder block with

the piston stroke

Expansion and

compression of

volumes between

the vanes and the

cam ring.

Movement of

volumes between

tooth spaces and the

casing (the external

gear pump is shown.)

Efficiency - Generally the highest.

- The valve plate is easily

damaged and efficiency drops as

the plate wears out.

- Generally low.

- Can be

compensated when

the vane wears out.

Generally low.

Drops as the gear

wears out.

Contamination

Resistance

Highly susceptible to foreign

substances in oil.

Susceptible to

foreign substances

in oil, but less so

Susceptible to

foreign substances in

oil, but hardly


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Type Piston pumps Vane pumps Gear pumps

than piston pumps. susceptible when the

pumps are low-

pressure types.

Suction Ability Low. Middle. High.

Variable

Displacement

Type

Easy to convert by changing the

angle of the swash plate or bent

axis.

Can be converted

by changing the

eccentricity of the

cam ring for the

unbalanced type.

Difficult.

Table.I. 3.Specification [1-2].

Max. Operating

Press.

[MPa]

Max.

Displacement

[cm3/rev]

Max. Shaft

Speed [r/min]

Overall

Efficiency

%

Axial piston pump 45 1 000 5 600 85～95

Radial piston pump 70 500 2 900 80～92

Vane pump 40 350 4 200 75～90

Gear pump 35 500 6 000 75～90

Chapter II: Maintenance and troubleshooting for hydraulic systems

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Chapter II: Maintenance and troubleshooting for hydraulic systems.

II. Introduction:

Maintenance was an area that was often thought of an area that did not need much attention.

However, with the greater focus on safety, environment, energy efficiency and profitability

Maintenance has now become an area where there is renewed attention. Maintenance in the

past was thought in terms of Breakdown and Preventive Maintenance. Starting from the late

eighties and early nineties, there have major developments in Maintenance [19].

The components of hydraulic systems work together intimately. As a result, damage to one

component may cause further damage to others. For instance, overheated oil caused by a

leaky cylinder seal can break down and cause damage to other cylinders or the pump. That's

why it pays to perform regular maintenance and preventative inspections to eliminate

problems before they occur [20]. Due to component wear or failure, some system parameters

may change causing abnormal behavior in each component or in the overall circuit itself.

Therefore, if the accurate and reliable performance of the system is an objective, it is

necessary to monitor the condition of the main components of the system. To do so, it is

necessary to understand what kind of failures can exist in each component and how those

failures affect both the component’s performance and that of the complete system [1].

Hydraulic systems are becoming more complex in design and in function. The reliability of

these systems must be supported by efficient “maintenance regimes”. There are three such

regimes: breakdown maintenance (most expensive), time based maintenance, and condition

based maintenance (least expensive). Choosing a maintenance regime depends on the system.

If the systems do not require high reliability or if economics or safety is not the issue, the

breakdown maintenance approach may be sufficient. However, for maximum reliability and

safety, the condition based maintenance approach should be implemented. In general, most

hydraulic systems do require high reliability and thus the latter condition monitoring approach

is most desirable [1].

Condition based maintenance of a system can be very cost effective. Hibberd (1988)

estimated that it would save about £100M to £150M per year to apply condition-based

maintenance of pumping systems alone in industry. Thus, the condition monitoring of a

hydraulic system can bring benefits other than just reliability and improved safety [1].

II.1. Definitions:

II.1.1. Maintenance:

British Standard Glossary of terms (3811:1993) defined maintenance as:

The combination of all technical and administrative actions, including supervision actions,

intended to retain an item in, or restore it to, a state in which it can perform a required

function [21].

Maintenance is a set of organized activities that are carried out in order to keep an item in its

best operational condition with minimum cost acquired.


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Ignoring for the moment the strictness of a standardized definition we can define maintenance

as the set of activities developed to ensure proper running of equipment and systems, ensuring

that technical intervention is taken at the right opportunities with the right scope and in

accordance with good technical practices and legal requirements, in order to avoid loss of

function or reduction of efficiency and, should any of these occur, ensure that they are

returned to good operating conditions at the earliest possible delay, all at an optimized overall

cost. [11,12].

In the early years of fluid power systems, maintenance was frequently performed on a hit or

miss basis. The prevailing attitude then was to fix the problem only after the system broke

down. With today's highly sophisticated machinery and with the advent of mass production,

industry can no longer afford a failure, as the cost of downtime is prohibitive [22].

II.1.2. Reliability:

Or operational reliability of a hydraulic system (s) is its ability to operate in the design

parameters without failures over a period of time [22].

II.1.3. The availability:

(According to SR EN 62308/2007) is the system's suitability, in terms of reliability,

maintenance and organization of the maintenance actions, to perform its specific functions at

a given time or within a required time frame [22].

II.1.4. Failure:

Or loss is the total or partial loss of the performance or performance of a hydraulic equipment

or system, and may occur accidentally or over time, due to changes in working parameters

below the allowable level [22].


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Fig.II. 1.Objectives of maintenance [11].

II.2. Types of maintenance:

Maintenance activities are classified as shown:

Fig.II. 2.Maintenance activities [3].

maintenance

preventive

systematic

condition based

corrective intrinsic failure

extrinsic failure

improvement

Maximising Production

Minimising Energy

Usage

Optimising Useful Life

of Equipment

Providing Budgetary

Control

Optimising Resources

Utilisation

Reduce Breakdowns

Reduce Downtime

Improving Equipment

Efficiency

Improving Inventory

Control

Implementing Cost

Reduction

Maintenance


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II.2.1. Preventive maintenance:

Is a schedulable type of maintenance that aims at preventing failures, loss or reduction of

function. Prevention is always the prime objective of management. Preventive maintenance

can be further classified in accordance with the nature of the originating conditions [23]:

Systematic maintenance: also designated pre-determined maintenance, when the opportunity

for the intervention is blindly determined, based on pre-defined frequency: calendar or

running units (hours, km, cycles, etc). Typical title descriptions: weekly inspection; monthly

lubrication; 10000 hours overhaul; 20000 km service [23].

Condition based maintenance: when the opportunity to carry out the work is based on

symptoms detected along an inspection or running parameters, before loss or significant

reduction of function. Typical title descriptions: replace slack driving belt; adjust valve;

Replace bearing [23].

II.2.2. Corrective maintenance:

Is a non-schedulable maintenance action following a failure or unexpected loss of function,

which may have occurred as a result of:

Intrinsic failure: a loss of function due to a cause intrinsic to the maintenance item:

equipment broke down; pipe broke; overheated bearing.

Extrinsic failure: a loss of function due to a cause external to the maintenance item: accident,

collision, poor operation. Although penalizing the operational availability of the equipment

this failure does not contribute to the theoretical maintenance indicators or intrinsic reliability

of the item [23].

II.2.3. Predictive maintenance:

The term predictive maintenance (PdM) refers to a maintenance policy that triggers

maintenance activities by predictions of failures. To obtain accurate predictions, PdM is

typically based on a set of activities that inform (the owner, service provider or operator)

about the current, and preferably also the future state of their physical assets. For this, PdM

employs analytics, methods and techniques (denoted as maintenance analytics, MAs, or

synonymous: maintenance techniques, MTs) that use asset data, such as condition and loading

data or experience, to detect or predict changes in the physical condition of equipment (signs

of failure). Thus, the term PdM covers a set of maintenance policies (pointed out by the

dashed region in Figure 1) that are based on the condition of the asset. These condition-based

policies can be subdivided in policies that use the measured condition of the asset and policies

that use the calculated condition of the asset. Traditionally, the measured policies are regarded

as condition-based maintenance (CBM) and the calculated as truly predictive maintenance. In

this work however, all condition-based policies are regarded as predictive maintenance. This

is first to create clarity since a wide variety of definitions for PdM tend to be used in both

practice as in the academic literature. Second, it thereby also recognizes the large variety in

types of analytics that are used for PdM [3].

II.2.4. Improvement maintenance:

Nowadays is a recognized and stimulated maintenance approach aimed at improving the

performance of the equipment in its context. It is schedulable. Typically, an improvement is

identified and a modification is studied and planned to improve the running conditions,


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20

energy efficiency, and/or maintainability, among many others. Indeed, there is usually much

scope for improvements in any industrial or facilities plant, as long as there is a basic positive

attitude towards this approach: introducing automation; equipment monitoring; improving

running efficiency; energy saving; reducing emissions; noise; improving accesses for

maintenance; reducing maintenance necessities. Further to its strictly technical scope,

maintenance covers nowadays a wide spectrum of activities related to the fulfilment of legal

requirements, certification, safety, security and social sustainability – understood as the

capability of the organization to exhibit and be in a position to demonstrate at any time that it

runs its activities using practices that are safe, preserve the environment and are socially

acceptable [23].

These considerations and the technological profile of modern equipment explain why the

maintenance function has become a first line activity requiring multi-disciplinary expertise,

training of technicians and managers, involving a wide range of responsibilities in any

organization. The times where maintenance was considered the poor partner in an

organization and we had to convince the boss that managing it properly would bring

significant advantage are far away. Neglecting maintenance management to-day may simply

condemn the whole organization [23].

II.3. Hydraulic system problems:

Hydraulic systems are part of the fluid power industry. These systems will use hydraulic

fluids to create pressure. At present, hydraulics is an area for research and the growth is

visible for us. Almost every industry utilize some applications of hydraulics. Control accuracy

is one of the benefits of the hydraulic system over others.

Careless usage and lack of maintenance will create hydraulic problems. Most of the problems

in the hydraulic system can be eliminated with proper care and maintenance.

The important symptoms of system failures include abnormal noise, high fluid temperature

and slow operation etc [24].

II.3.1. The phenomenon of wear due to fluid contamination:

Impurities in the hydraulic oil and oxidation product in the hydraulic oil of course will effect

the function of the hydraulic system. Particles are very harmful to pumps, valves and so on.

Especially when these particles have the same size as the slot between piston and cylinder. In

this case the particle will be pressed with the oil between piston and cylinder. The particle will

touch both surfaces at the same time. Because the piston moves in the cylinder hard solids

will create abrasion or scratches. Because of the abrasion the particle will create new

particles. In modern hydraulic systems, the slot between piston and cylinder has a size of 0.5

µm – 4.0 µm (servo valves). For proper operation of the hydraulic system particles in this size

have to be removed from the oil [9] [25].


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Fig.II. 3.Wear in hydraulic systems [6].

II.3.2. Problems due to entrained gas in fluids:

Entrained gas or gas bubbles in the hydraulic fluid is caused by the sweeping of air out of a

free air pocket by the flowing fluid and also when pressure drops below the vapor pressure of

the fluid. Vapor pressure is that pressure at which the fluid begins changing into vapor. This

vapor pressure increases with increase in temperature. This results in the creation of fluid

vapor within the fluid stream and can in turn lead to cavitation problems in pumps and valves.

The presence of these entrained gases reduces the effective bulk modulus of the fluid causing

unstable operation of the actuators [9].

II.3.3. Cavitation:

Cavitation, defined simply as the formation of bubbles in a liquid, can have detrimental

effects on a hydraulic pump. In an incorrectly designed hydraulic system, a vacuum may form

on the hydraulic fluid, pulling trapped air out of the fluid to form small bubbles [26].

The phenomenon of cavitation is in fact the formation and subsequent collapse of the vapor

bubbles. This collapse of the vapor bubbles takes place when they are exposed to the high-

pressure conditions at the pump outlet, creating very high local fluid velocities, which impact

on the internal surfaces of the pump. These high-impact forces cause flaking or pitting on the

surface of components such as gear teeth, vanes and pistons leading to premature pump

failure. Additionally the tiny metal particles tend to enter and damage other components in the

hydraulic system. Cavitation can also result in increased wear on account of the reduced

lubrication capacity [9].

A variety of factors within the system could produce such a vacuum. When fluid enters the

hydraulic pump and is compressed, the small air bubbles implode on a molecular level. Each

implosion is extremely powerful and can remove material from the inside of the pump until it

is no longer functional. Cavitation can destroy brand new pumps in a matter of minutes,

leaving signs of physical damage including specific wear patterns. The process of cavitation

destroying a hydraulic pump also has a distinctly audible sound similar to a growl [26].

The good news is that cavitation need not be a common problem in hydraulic systems. A few

design flaws are largely responsible for causing cavitation: improper configuration of pump

suction lines and the use of suction-line filters or strainers. To prevent these causes of

cavitation and ensure the creation of a quality hydraulic system with a long, productive life,

seven design elements must be properly executed [26].

- Correctly design the hydraulic reservoir;

- Use a breather filter on the reservoir;


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- Install properly sized and configured suction lines;

- Remove any suction-line filtration;

- Use a properly sized pump;

- Maintain proper fluid temperature;

Use a flooded suction for the pump [26] [27].

Fig.II. 4.Cavitation in gear pump [28].

II.3.4. Foaming:

The phenomenon consists in dissolving (mixing) the air with hydraulic fluid from the

hydraulic system. The causes of foaming are as follows:

- Leakage of pump suction pipe: in this situation, the pump sucks air from the atmosphere and

dissolves it in the working fluid. As the suction cup is not under pressure, most of the time

these leaks are not visible (no leakage is recorded), so a thorough examination is required to

detect them [29].

- The absence of soothing that delimits the suction area in the oil tank; the role of soothing is

even to soothe the oil in the tank, thus allowing separation of the dissolved air eventually in

the oil before it is sucked into the plant. In the absence of soothing, the agitation caused by

the flow of the oil sucked by the pump, driving the mixture into the plant [29].

- Filling the liquid in the tank with foamed oil during the operation of the pump.

- Switching on the machine (after a long time or commissioning) without having previously

deactivated the hydraulic system. It can be said that foaming is, in fact, a contamination of

the working fluid, this contamination results in a biphasic, liquid-gas mixture, its properties

and behavior in operation undergoing major changes: the liquid becomes compressible,

decreases its viscosity. The presence of foaming is manifested by noisy operation, shock and

pressure oscillations, excessive heating, movement of the non-uniform speed elements and

in the case of precise positioning / tracking systems there are found unacceptable deviations

from tolerances admitted [29].


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Fig.II. 5.Foaming phenomena in gear pump [30].

II.4. Common causes for hydraulic system breakdown:

The most common causes of hydraulic system failures are:

• Clogged and dirty oil filters;

• An inadequate supply of oil in the reservoir;

• Leaking seals;

• Loose inlet lines, which cause pump cavitations and eventual pump damage;

• Incorrect type of oil;

• Excessive oil temperature;

• Excessive oil pressure.

A majority of these problems can be overcome through a planned preventive maintenance

regime. The overall design of the system is another crucial aspect. Each component in the

system must be properly sized, compatible with and form an integral part of the system.

It is also imperative that easy access be provided to components requiring periodic inspection

and maintenance such as strainers, filters, sight gages, fill and drain plugs and the various

temperature and pressure gages. All hydraulic lines must be free of restrictive bends, as this

tends to result in pressure loss in the line itself [9].

The three maintenance procedures that have the greatest effect on system life, performance

and efficiency are:

1- Maintaining an adequate quantity of clean and proper hydraulic fluid with the correct

viscosity;

2- Periodic cleaning and changing of all filters and strainers;

3- Keeping air out of the system by ensuring tight connections.

A vast majority of the problems encountered in hydraulic systems have been traced to the

hydraulic fluid, which makes frequent sampling and testing of the fluid, a vital necessity.

Properties such as viscosity, specific gravity, acidity, water content, contaminant level and

bulk modulus require to be tested periodically. Another area of vital importance is the

training imparted to maintenance personnel to recognize early symptoms of failure.

Records should also be maintained of past failures and the maintenance action initiated

along with data containing details such as oil tests, oil changes, filter replacements, etc

[9].

Oxidation and corrosion are phenomena which seriously hamper the functioning of the

hydraulic fluid. Oxidation, which is caused by a chemical reaction between the oxygen

present in the air and the particles present in the fluid, can end up reducing the life of the fluid


Khaoula BERKAS

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quite substantially. A majority of the products of oxidation are acidic in nature and also

soluble in the fluid, thereby causing the various components to corrode. [9].

Although rust and corrosion are two distinct phenomena, they both contribute a great deal to

contamination and wear. Rust, which is a chemical reaction between iron and oxygen, occurs

on account of the presence of moisture-carrying oxygen. Corrosion on the other hand is a

chemical reaction between a metal and acid. Corrosion and rust have a tendency to eat away

the hydraulic component material, causing malfunctioning and excessive leakage [9].

II.5. Noise in hydraulic installations:

In machinery and equipment that has moving parts, such as hydraulic equipment, there are

shocks and vibrations that are either directly transmitted to the whole system or generate air

oscillations, which means noises and which in any case have a negative effect on of the entire

machine. These effects, sometimes capital, can be in many situations prevented if specialists

can establish clear relations between the type of noise and the functional state of the

equipment, [2]. The frequency of sound that the human ear can perceive is between 20Hz and

16000Hz. Noise below 20Hz is called infrasound, and over 16000Hz is they are called

supersonic and can be detected with special equipment, which can be included in the list of

special facilities of maintenance workers.

Here are some interesting examples of sounds:

- The sounds emitted by a trumpet are in the range of 220Hz and 1046Hz;

- Flute sounds between 260Hz and 2200Hz;

- The bass sounds are in the range of 41Hz and 400Hz;

- The human voice is between 60Hz (low bass) and 1300Hz (soprano).

The unit of sound intensity (acoustic pressure) is the dB (decibel). As a rule, not all noises

indicate malfunction and, as such, for the protection of people, a certain level is to be

observed. Thus, for housing, hotels, guest houses the limit allowed by law is max. 50 dB, for

schools 55 dB and for industrial spaces 85 dB. These allowable limits allow deviations that

establish failures to be immediately detected and, after a specialized analysis, be able to

interfere with in line with existing procedures (methodologies) at the firm level. In many

cases the hydraulic system is the element that generates the noises above the level admitted in

a hall and, therefore.

II.5.1. Causes of noise in hydraulic systems:

o Noise caused by pressure variation: working fluid pressure pulses, which occurs

primarily at the pump level, but also at the level of the distribution and adjustment

equipment. Because by redesigning the pump this noise can not be ruled out but possibly

reduced, it is it is recommended to apply the solution of the use of noise dampers, in pre-

established areas, from the design phase of the system [2].

o The noise created by the pumping: unit, which adds engine noise drive, thermal or

electric, at the pump noise. If the drive motor is thermal, try all methods to reduce it noise

by isolating and limiting transmission. If the engine is electric, you can not do much in

general, but the level noise is only 15-20 dB in the system. The problems with these

engines are caused by heating and cooling them. The most "noisy" equipment in the

system is the pump. The best ones are with screws and wheels, but unfortunately the most

used are those with axial or radial pistons. Into the In general, volumetric pumps that


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close and open high-speed work cameras generate pulses, which produce noises and can

only be reduced during the design phase. The greatest noise reduction is made from the

design phase, because then flexible tubing connections between the pumping unit and the

pool can be included and between the pumping unit and the control and adjustment unit

subassembly, on the other hand [2]. A simple but not sufficiently efficient method is to

introduce noise absorbers based on the idea of limiting by reflection and not by

absorption;

o Noise caused by the supply of fluid from the battery to the system: Accumulated

energy, if supplied suddenly, causes large flows, but especially pressure, which produces

quite well-known noises. The hammer blow, which usually occurs when closing or

suddenly opening a hydraulic distributor, is another reason to produce noise. The

preferred solution for specialists is the introduction of a pneumohydraulic accumulator in

the pipeline. Since this solution is insufficient, in recent years, hydraulic devices that can

vary the fluid velocity in the closing and opening phases of the pipe;

o The noise level: emitted by an object is directly proportional to the radiant area and

inversely proportional to its mass. If the mass of the hydraulic system subassemblies can

intervene from the design phase, by increasing the tank mass or by strengthening the

electropump support, on the surface may be quite small, practically insignificant. In

practice, remove the basin electropump (about 0.5m) or use an electropump immersed in

the basin [2];

o Another reason: for the occurrence of noise is related to the working fluid compression

performance expressed in Bulk's module. At compression, but especially at

decompression, fluid volume changes create shocks and noises, which can be predicted

from the design phase and usually resolved by introducing flexible ducts by using

accumulators placed in critical areas or simply by creating decompression holes [2]

ASSOFLUID specialists have classified the main causes of noise and noise reduction

solutions in Table II.1 [2].

The noise sources from pump construction can not be eliminated or limited by

maintenance, but only kept under control. It is very important for the engine and the

pump to be insulated with elastic elements in the coupling area. An optimal solution is

also the one where the electropump is mounted vertically, with the engine out and the

submerged pump. The modern solution of the noise that generates special noises is

related to the use of proportional and servovalve devices, which can be controlled as

movement and flow with a high precision, following a flow-increasing or decreasing

curve, theoretically or experimentally predetermined.

Table.II. 1.Causes of noise in hydraulic installations and reduction solutions [2].

The cause of

generation

The specific reason for the

occurrence of noise

Noise reduction solution

Pump cavitation

Clogging or filter suction section too

low.

Clean or replace.


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The cause of

generation

The specific reason for the

occurrence of noise

Noise reduction solution

Suction conductor diameter too

small.

Widening the diameter.

The suction line has too many curves

or too wide; the pipe diameter is too

large.

Change pipes.

Restraint in suction line; semi-closed

devices, too hard springs on non-

return sensors.

Changes or opens

complete the appliances,

repair or

replace pipelines and

hoses

The fluid is too cold. Heat the fluid.

Inappropriate fluid. Replace the fluid.

Penetration air

in the fluid

Low fluid level in the tank. Fill the tank.

Improper cleaning of fluid and

system

Clean the system and fluid

again.

Damage to flexible suction tubes. Replace hoses.

Air entry near the pump shaft. Replace the seal.

The return line is above the level. Arrange the return.

Mechanical

vibrations

Vibration des pipelines. Replace connections

(fixings).

Pump

Worn or defective. Worn or defective.

Incorrect pump. Replace.

Valves

Unstable. Replace.

Fluid velocity too high. Replace with a pipe and a

valve with larger diameter.

Ventilation line too long. Add a restrictor.

Motor Worn or defective. Repair or replace.

Inappropriate engine. Replace.


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II.6. Troubleshooting:

Troubleshooting or faultfinding as we call it is often performed in a random and haphazard

manner, leading to items being changed for no logical reason. Such an approach may

eventually work but it is hardly the quickest and cheapest way of getting a faulty system back

into operation. There must be better and more systematic approaches to correcting a problem.

Fault finding has been rather simplistically, represented in the form of a flow chart below

(Figure II.6) [31].

Fig.II. 6 Flow chart depicting the process of faultfinding [31].

II.6.1 Fault finding process:

A) Noisy Pump or Excessive Pump Vibration

o Cavitation caused by air entering pump inlet caused by:

- Dirty inlet suction strainer – clean or replace;

- Loose connection on suction line or suction strainer – tighten;

- Low hydraulic fluid level – check level, observe level variation through entire

machine cycle, add oil if needed;

- Excessive pump speed – check specifications of pump and motor;

- Incorrect hydraulic fluid being used ;

- Oil is foaming – low or old oil – replace or add anti-foaming agent;

- Very large volume actuator causing periodic low levels in tank;

- Clogged reservoir air breather vent causing vacuum in tank -replace breather vent

filter [31] [6].

o Excessive oil viscosity causing cavitation – check viscosity replace as necessary, change

with season;

Analyze knowledge to date

Decide on test to localize fault further

Conduct test

Fault located?

Repair

Test operation

Record fault and diagnosis

Analyze fault records


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- Temperature is too low for oil – change oil or add oil heater for cold weather operation

- Damaged or worn pump – repair or replace, check filters,

- Misalignment of Pump and Motor – check alignment;

- Pump and/or motor mounts worn or loose – tighten or replace mounts and coupler;

- Relief valve chattering – check setting – may be too low, may need resizing;

- Relief valve operating continuously- pump flow passing continuously over relief valve

back to tank when system not being used – change to tandem center directional control

valve or add other unloading method [31] [6] [7].

B) Low or Erratic Pressure Output

Air in System caused by:

- Actuators need to be bled of air;

- High point in system needs to be bled of air;

- Pump is cavitating – see point A;

- Air being sucked in through loose fitting or hole in hose;

- Defective or worn pump – repair or replace;

- Incorrect Pump Speed or Size – check specifications and compatibility of pump and

motor – speed, displacement, and power;

- Incorrect drive motor power input – check that all electrical power phases are

operating – check all fuses and breakers;

- Defective or loose shaft coupling between pump and motor – repair or replace or

tighten;

- Defective or worn cylinder or other actuator – replace seals and/or bearings;

- Pressure relief valve or pressure regulating valve set too low – adjust setting;

- Pressure relief valve or pressure regulating valve is dirty and not seating – clean or

repair;

- Leak in hydraulic pressure line – check all lines, fittings and hoses – tighten or repair

[6].

C) No Output Pressure

- No power – check electrical supply to motor, check fuses and breakers, check wire

connections, check PLC out puts & solenoids, reset emergency stop switches;

- No or low hydraulic fluid in reservoir – check level and add as required;

- Pump is turning in wrong direction – check and correct rotation;

- Pump or motor shaft or shaft coupling is stripped or broken – check and repair or replace;

- Pressure relief valve stuck open – check and adjust setting or repair or replace

- Pump outlet flow bypassing directly to tank – check for faulty valving or circuit error;

- Hydraulic pressure line is ruptured or not connected – check lines, look for large leaks [6].

D) Hydraulic Cylinder Not Moving

- Directional valve failure – check power to solenoids, determine if it is shifting, valves may

need cleaning or repair, coil or solenoid armature may be burned out, check electrical wires

and connections;

- Insufficient pressure supplied – check system pressure ;


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- Hydraulic line problem – check for kinked, dented or crushed hoses and tubes, check for

damaged fittings;

- Defective actuator – check cylinder condition – piston rod bent or cylinder barrel dented

causing binding, barrel id is scored or corroded causing excessive friction, seals worn causing

oil bypassing piston;

- Load exceeds capacity of actuator – check system pressure and size of piston and calculate

forces and compare to load, allow for friction, force vector geometry and pressure loss;

- Hydraulic circuit error – valve installed incorrectly, check valve backwards, lines installed

incorrectly, breather port on single acting cylinder plugged [6] [7].

E) Hydraulic Cylinder Slow, Shuddering or Erratic

- Air in system – bleed air from system, bleed from highest point;

- Pump is cavitating – see point a;

- Pressure supply is fluctuating – see point b;

- Defective actuator – check cylinder condition – piston rod bent, cylinder barrel dented,

barrel id is scored or corroded, seals worn, oil bypassing piston;

- Defective or worn pump – repair or replace;

- Hoses are kinking as cylinder moves;

- Control valve failure – valves may need cleaning or repair, coil or solenoid armature may be

burned out, check electrical wires and connections;

- Load exceeds capacity of actuator – check system pressure and size of piston and calculate

forces and compare to load, allow for friction, force vector geometry and pressure loss [6] [7].

F) Hydraulic Fluid Overheating

- Oil reservoir too small – check tank size versus pump flow – optimum reservoir size is at

least 3 times pump gpm without heat exchanger;

- Oil level too low – check and add as required;

- Incorrect fluid – wrong viscosity, change in season – oil not changed with season;

- dirty hydraulic fluid – check condition, check maintenance records, replace filter cartridges,

replace oil with new if necessary;

- Heat exchanger faulty – check if running, clean, check id of radiator, check temperature

switch and wires and connections;

- Heat exchanger turned off – not switched on for change of season;

- Hydraulic line sizes too small – compare line id with flow capacity chart and actual flow

being seen – flow can be much greater than pump flow on return lines;

- Relief valve operating continuously – pump flow passing continuously over relief valve

back to tank when system not being used;

- System overload – check system capacity, workload percentage rating versus actual use;

- Excessive pump speed – check specifications of pump and motor to ensure compatibility of

speeds [6-8].

II.7. Conclusion:

This chapter focuses on the maintenance of hydraulic systems. Indeed, we tried to give an

overview on the different types of failures encountered in hydraulic systems, as well as the

main causes of each failure.

Chapter III: Materials and methods for hydraulic oils analysis

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III.1. Introduction:

To meet the increased requirements on higher efficiency and better functionality of hydraulic

systems, new components and system concepts have been developed over the years. However,

the most important component in a hydraulic system, which has a major impact on system

efficiency and wear are the fluid itself. The last decades, major attention on hydraulic fluid

development, have been set upon environmental adaption [32].

Hydraulic fluid is the medium of power transfer in hydraulic equipment, it is important to

know the properties of hydraulic fluids and its influence on system performance. There are

different types of fluids based on their availability, working purpose etc. So selection of fluid

depends on the working conditions of the hydraulic equipment. So to select a fluid one has to

be clear about the operating conditions of hydraulic equipment and this can be achieved by

testing the equipment with different fluids and select the fluid that gives the best performance.

To know about the properties (like viscosity, operating temperature range) of fluids available

there should be some standardisation of hydraulic fluids and one such type is ISO

(International Organization for Standardization). Though there are many this is followed by

most. By this standardization, the fluid manufacturer can categorize the fluids and the user

can easily select the fluid according to their requirement [33].

III.1.1. Classification of hydraulic fluids based on ISO viscosity grade:

Most of the fluids used are classified with ISO standards. The ISO standard fluids are mainly

classified based on the kinematic viscosity at 40 °C. The fluid is mainly taken at 40 °C which

is taken as a reference temperature between the maximum operating and the ambient

temperatures. The ISO classification is done on 18 main fluids based on their viscosity grade

[33].

Table.III. 1.Classification of hydraulic fluids based on ISO Viscosity grade [2].

ISO Viscosity Grades based on

kinematic Viscosity [centistokes/cSt] at 40 0C

ISO VG Minimum [cSt]

Maximum [cSt]

2 1.98 2.42

3 2.88 3.52

5 4.14 5.06

7 6.12 7.48

10 9.0 11

15 13.5 16.5

22 19.8 24.2

32 28.8 35.2

46 41.4 50.6


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ISO VG Minimum [cSt] Maximum [cSt]

68 61.2 74.8

100 90 110

150 135 165

220 198 242

320 288 353

460 414 506

680 612 748

1000 900 1100

1500 1350 1650

III.2. Types of hydraulic fluids:

According to ISO, there are three different types of fluids according to their source of

availability and purpose of use [34].

III.2.1. Mineral-Oil based Hydraulic fluids:

As these have a mineral oil base, so they are named as mineral-oil-based hydraulic fluids.

This kind of fluids will have high performance at lower cost. These mineral oils are further

classified as HH, HL and HM fluids [33].

Type HH fluids are refined mineral oil fluids which do not have any additives. These fluids

are able to transfer power but have less properties of lubrication and unable to withstand high

temperature. These types of fluid have a limited usage in industries. Some of the uses are

manually used jacks and pumps, low pressure hydraulic system etc [33].

Type HL fluids are refined mineral oils which contain oxidants and rust inhibitors which help

the system to be protected from chemical attack and water contamination. These fluids are

mainly used in piston pump applications [33].

HM is a version of HL-type fluids which have improved anti-wear additives. These fluids use

phosphorus, zinc and sulphur components to get their anti-wear properties. These are the

fluids mainly used in the high pressure hydraulic system [33].

III.2.2. Fire Resistant Fluids:

These fluids generate less heat when burnt than those of mineral oil based fluids. As the name

suggests these fluids are mainly used in industries where there are chances of fire hazards,

such as foundries, military, die-casting and basic metal industry. These fluids are made of

lower BTU (British Thermal Unit) compared to those of mineral oil based fluids, such as

water-glycol, phosphate ester and polyol esters. ISO have classified these fluids as HFAE

(soluble oils), HFAS (high water-based fluids), HFB (invert emulsions), HFC (water glycols),

HFDR (phosphate ester) and HRDU (polyol esters) [33].

III.2.3. Environmental Acceptable Hydraulic Fluids (EAHF):

These fluids are basically used in the application where there is a risk of leakage or spills into

the environment, which may cause some damage to the environment. These fluids are not

harmful to the aquatic creatures and they are biodegradable. These fluids are used in forestry,

lawn equipment, off-shore drilling, dams and maritime industries. The ISO have classified


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these fluids as HETG (based on natural vegetable oils), HEES (based on synthetic esters),

HEPG (polyglycol fluids) and HEPR (polyalphaolefin types) [33].

Fig.III. 1.Classification of hydraulic fluids [4].

III.3. Fluid properties and comparative performances:

While selecting a hydraulic fluid one has to be aware of hydraulic fluid properties and its

effect on hydraulic system. Generally, the hydraulic fluids have many properties and some of

the important properties are explained in detail below [33]:

a) Viscosity :

A hydraulic fluid has a low viscosity when it is thin and a high viscosity when it is thick. The

viscosity changes with the temperature [35].

• If the temperature increases, viscosity is reduced.

• If the temperature decreases, viscosity is increased. Hydraulic units work under extreme

temperature changes, especially in heavy duty vehicles. The viscosity range of the hydraulic

fluid is extremely important. The hydraulic fluid must be thin enough to flow through the

filter, inlet and return pipes without too much resistance. On the other hand, the hydraulic

fluid must not be too thin, in order to avoid wear due to lack of lubrication and to keep

internal leakage within limits [35].

o Dynamic viscosity µ:

Hydraulic fluids

Based on mineral oil and related hydrocarbons

Standard

HH

HL

HM

HG

HV

Fire resistant hydraulic fluids

ISO 11158

HFAE

HFAS

HFB

HFC

HFDR

HFDU

Environmentally acceptable

hydraulic fluids

ISO 15380

HETG

HEPG

HEES

HEPR


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The units of dynamic viscosity µ are N.s/m2. It is normal in the international system (SI) to

give a name to a compound unit. The old metric unit was a dyne .s/cm2 and this was called a

POISE after Poiseuille. The SI unit is related to the Poise as follows [36]

10 Poise = 1 N.s/m2 (3.1)

Which is not an acceptable multiple. Since, however, 1 Centi Poise (1cP) is 0.001 N s/m2

then the cP is the accepted SI unit. [36]

1 cP = 0.001 N.s/m2 (3.2)

o Kinematic viscosity ν:

This is defined as:

ν = dynamic viscosity /density ν = µ/ρ (3.3)

The basic units are m2/s. The old metric unit was the cm2/s and this was called the STOKE

after the British scientist. The SI unit is related to the Stoke as follows [36].

1 Stoke (St) = 0.0001 m2/s and is not an acceptable SI multiple. The centi Stoke (cSt),

however, is 0.000001 m2/s and this is an acceptable multiple [36].

1 cSt = 0.000001 m2/s = 1 mm2/s (3.4)

b) Shear stability:

Fluids using polymer viscosity index improver may noticeably shear down (> 20 %) in

service. This will lower the viscosity at higher temperatures below the originally specified

value. The lowest expected viscosity must be used when selecting fluids. Consult your fluid

supplier for details on viscosity shear down [35].

c) Pour point:

The pour point according to ISO 3016 defines the temperature when the fluids stops to

flow. The pour point according to ISO 3016 defines the temperature when the fluids

stops to flow. Start up temperature is recommended to be approximately 15 °C [59 °F]

above hydraulic fluid pour point [35].

d) Density:

The density has to be specified by the manufacturer of the hydraulic fluid. Using

hydraulic fluid with a high density requires the sufficient diameter of the suction line

and/or elevated tank to provide positive inlet pressure [35].

m

V (3.5)

Density is approximately a linear function of pressure (P) and temperature (T)

(Anderson, 1988) [37].

0(1 aP bT) (3.6)


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In engineering practice, the manufacturers of the hydraulic fluids often provide the relative

density (the specific gravity) instead of the actual density. The specific gravity of a fluid is the

ratio of its actual density to the density of water at the same temperature.

Table.III. 2.Examples for density at 15 °C [59 °F] [4].

Hydraulic fluid type Density at 15 °C [59 °F]

Petroleum (mineral) based fluids 0.86 — 0.90 g/ml

Syntetic ester 0.92 — 0.926 g/ml

Rape seed oil 0.92 g/ml

Water 1.00 g/ml

Polyalkylenglykol 1.02 g/ml

HFC 1.08 g/ml

Polyethylenglykol 1.10 g/ml

HFD (phosphate ester) 1.13 g/ml

e) Bulk Modulus:

Bulk modulus is a measure of the compressibility or the stiffness of a fluid. The basic

definition of fluid bulk modulus is the fractional reduction in fluid volume corresponding to

unit increase of applied pressure, expressed using the following equation (McCloy and

Martin, 1973):

p

vT

(3.7)

The bulk modulus can either be defined as the isothermal tangent bulk modulus if the

compressibility is measured under a constant temperature or as the isentropic tangent bulk

modulus if the compressibility is measured under constant entropy. In analyzing the dynamic

behavior of a hydraulic system, the stiffness of the hydraulic container plays a very important

role. An effective bulk modulus, e

, is often used to consider both the fluid’s compressibility

ßf, and container stiffness,ßc , at the same time (Watton, 1989) [37].

e c f

1 1 1

(3.8)

f) Pressure and force:

The terms force and pressure are used extensively in the study of fluid power. It is essential

that we distinguish between the terms. Force means a total push or pull. It is the push or pull

exerted against the total area of a particular surface and is expressed in pounds or grams.

Pressure means the amount of push or pull (force) applied to each unit area of the surface and

is expressed in pounds per square inch (lb/in2) or grams per square centimeter (gm/cm2).

Pressure maybe exerted in one direction, in several directions, or in all directions .


Khaoula BERKAS

35

- Computing Force, Pressure, and Area:

A formula is used in computing force, pressure, and area in fluid power systems. In this

formula, P refers to pressure, F indicates force and A represents area. Force equals pressure,

times area. Thus, the formula is written [38]:

F p.A (3.9)

Pressure equals force divided by area. By rearranging the formula, this statement may be

condensed into [38]:

F

pA

(3.10)

Since area equals force divided by pressure, the formula is written [38]:

F

Ap

(3.11)

g) Volume and velocity of flow:

The volume of a liquid passing a point in a given time is known as its volume of flow or flow

rate. The volume of flow is usually expressed in gallons per minute (gpm) and is associated

with relative pressures of the liquid, such as 5 gpm at 40 psi [38].

The velocity of flow or velocity of the fluid is defined as the average speed at which the fluid

moves past a given point. It is usually expressed in feet per second (fps) or feet per minute

(fpm). Velocity of flow is an important consideration in sizing the hydraulic lines.

Volume and velocity of flow are often considered together. With other conditions unaltered

that is, with volume of input unchanged—the velocity of flow increases as the cross section or

size of the pipe decreases, and the velocity of flow decreases as the cross section increases.

For example, the velocity of flow is slow at wide parts of a stream and rapid at narrow parts,

yet the volume of water passing each part of the stream is the same. In figure III.2, if the

cross-sectional area of the pipe is 16 square inches at point A and 4 square inches at point B,

we can calculate the relative velocity of flow using the flow equation [38]:

𝑄 = 𝑣 ∙ 𝐴 (3.12)

Where Q is the volume of flow, v is the velocity of flow and A is the cross-sectional area of

the liquid. Since the volume of flow at point A, Q1 , is equal to the volume of flow at point B,

Q2 , we can use equation 2-7 to determine the ratio of the velocity of flow at point A, v1 , to

the velocity of flow at point B, v2 [38].


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36

Fig.III. 2.Volume and velocity of flow [38].

III.3.1. The types of oils used in the hydraulic system:

A) First type: Hydraulic oil motor HLP 46: ISO VG 10 at ISO VG 150 = HVB

hydraulic oil according to DIN standard 51524/T2

Table III. 3 Technical data of hydraulic oil HLP 46 [39].

Technical data Typical Value

• Viscosity class • 46

• Color • light yellow

• Density 20 0C (g/ml) • 0.873

• Viscosity at 100 0C (mm2/s) • 46

• Viscosity at 100 0C (mm2/s) • 7.0

• Viscosity index • 110

• Flow point (0C) • -27

• Flash point • 228

o Areas of application:

For stationary and mobile applications in hydraulic systems in construction, forestry and

agricultural machinery such as excavators, tractors etc., hoists, industrial machinery and

machine tools, wood splitters, lifting platforms and presses etc. it has good compatibility with

materials, this LIQUI MOLY hydraulic oil can be used in the most common pump systems in

hydraulic systems. This hydraulic oil can also be used with all mineral oil compatible sealing

materials and coatings [39].

o Specifications:

B) Second type: Hydraulic oil motor HVB 46 ISO VG 10 at ISO VG 150 = HVB

hydraulic oil according to DIN standard 51524/T2.

o Properties:

- Outstanding thermal stability;

- Outstanding corrosion protection;

- Highest thermal stability;

- Excellent wear resistance;

- does not attack common sealing materials;

- High lubrication reliability [39].


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C) Third type: Prista® MHMb hydraulic oil: ISO 11158 –HM (AFNOR NF E 48-

603).

PRISTA MHMb: hydraulic oils are formulated from highly refined mineral base stocks

exhibiting very good demulsibility and air-release properties blended with a highly efficient

additive system, free from zinc or other metals, including rust, oxidation and corrosion

inhibitors and anti-wear agents PRISTA MHM-b hydraulic oils are developed for use as

working media in hydrostatic lubrication systems and moving parts in circulating systems,

hydraulic vane pumps, hydraulic gear pumps and hydraulic piston units [40].

One of the advantages of ashless additives is that they improve oil filterability especially

when contamination with water is expected. Therefore, these oils can successfully be used as

working fluid in systems with high temperature loads and where contaminations with water

are expected to occur such as paper presses. The oils are well suited for hydraulic system

operated at very high pressures exceeding 25 MPa and oil temperatures exceeding 90°C [40].

o Benefits:

- Improved operating and filtration performance in water contaminated systems,

- High resistance to oxidation;

- Maximum equipment protection of rust and corrosion;

- Extremely stable in presence of water [40].

Table.III. 4.Hydraulic oil parametr Prista® MHMb type [40] .

Parameter

Test

Method

Typical Value at 32

10 15 22 32 46 68 100

Density at 20 °С, g/ml EN ISO

3675

0.881 0.866 0.867 0.868 0.875 0.879 0.883

Kinematic viscosity at

40°С, mm2/s

EN ISO

3104

10 15 22 32 46 68 100

Viscosity index ISO 2909 100 100 100 100 100 95 95

Flash point, COC, °С EN ISO

2592

125 140 160 190 200 210 220

Pour point °C ISO 3016 -36 -36 -33 -30 -27 -27 -18

Copper strip corrosion,

3h, 100 °C

EN ISO

2160

Water separability time

to 3 ml emulsion,min

ISO 6614 10 10 10 10 15 15 15

Air release properties ,

min

ISO 9120 2 3 3 4 6 8 10


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Parameter

Test

Method

Typical Value at 32

Oxidation stability after

1000h TAN

increase, mg KOH/g

ASTM D

4310

<1

FZG EP Wear Test (A

8.3/90)

- Failure Load Stage

DIN

51354-2

- 12 12 12 12 12

Table.III. 5.Classification of mineral oils for hydraulics systems.

ISO symbol properties

HL Improved refined mineral oils with very high antioxidant

and anti-corrosion properties.

HM Improved refined mineral oils with very high anti-

oxidation, anti-corrosion and anti-wear properties.

HV Refined HM mineral oils with improved viscosity /

temperature properties.

Part 1: Material and methods

The part of this chapter aims at presenting the experimental results of the analysis done on

some physicochemical characteristics of the new and used HMM hydraulic oil, in order to

follow its operation as well as its degradation in a hydraulic installation, according to the time.

IIII.4. Methods of predictive maintenance that promote the energy

efficiency of hydraulic systems

III.4.1. Spectroscopic method:

III.4.1.1. Oil degradation mechanisms:

Mineral oils oxidise during their service-lifetimes and this causes significant increases in

friction and wear that affects the performance of the machine. The main effect of oxidation is

a gradual rise in the viscosity and acidity of the oil. The general mechanism of oil oxidation is

believed to be a free-radical chain reaction [41] ,[42].


Khaoula BERKAS

39

Fig.III. 3.Causes and effects of ageing (Sourse: Asaff et al., 2014) [43].

III.4.1.2. FT-IR Analysis of Used Lubricating Oils:

General Considerations:

Infrared spectroscopy is a widely used technique for the analysis of lubricating oils. The

Thermo Scientific Nicolet™ FT-IR spectrometer, coupled with OMNIC™ Integra™

software, provides modern laboratories with an intuitive package for routine infrared analysis

of liquid samples. This application note details the application and the parameters used to

derive the highest quality data [43].

Fig.III. 4.Infrared spectroscopy.

Analysis Considerations :

As a trending and screening tool, FT-IR analysis of used lubricants has limitations and must

be applied with appropriate measures to assure proper generation and interpretation of data.

First and foremost, numeric results from all of the parameters being determined (with the

exception of soot), are affected by the molecular fingerprint of the base lubricant and additive

package. That is to say, the additives an base oil have spectral features that interfere with the

peaks that develop as the lubricant is contaminated or oxidized during use. The magnitude of


Khaoula BERKAS

40

the peaks that develop are typically smaller than, or of similar magnitude to, those found in

the unused oil [43].

Mode of operation of FT-IR analysis:

32 scans were co-added over the range of 4000–400 cm−1 with a resolution of 4 cm−1. Air was

taken as the reference for the background spectrum before each sample. After each spectrum,

the ATR plate was cleaned with ethanol solution. In order to verify that no residue from the

previous sample remained, a background spectrum was collected each time and compared to

the previous background spectrum. The FT-IR spectrometer was sited in a room that was air

conditioned with controlled temperature (21°C).

Fig.III. 5.Mode of operation of FT-IR analysis.

Fig.III. 6.Spectroscopy analysis [43].

Considerations for Specific Analysis Parameters of Interest:

- Carbonyl Oxidation Products: the broad feature centered around 1730 cm-1The point

of maximum intensity will vary as the oil and conditions of its use are changed. The


Khaoula BERKAS

41

increase in peak height that occurs as the number of hours the oil has been run in the

engine increases has a greater significance in the measurement of degradation than total

acid number (TAN) or viscosity [43].

- Nitrogen Oxidation Products the sharp feature at 1630 cm-1 is the result of nitrogen

oxide fixation into the oil [43] .

- Sulfur Oxidation Products Another broad spectral feature, centered around 1150 cm-1,

is the result of sulfate compounds as well as overlap with oxidation products [43].

- Water and Glycol Contamination: water is detected as a broad feature, centered around

3400 cm-1 that is caused by the hydroxyl (-OH) group. Glycol has a characteristic peak

around 880 cm-1 as well as peaks at 1040, 1080 and 3400 cm-1. The peak at 880 cm-1 is

used to quantify because it is not subject to interferences to the same extent as the other

bands [43].

III.4.1.3. Transmittance:

Description of the device used:

Spectro UV-Vis Double PC 8 Auto and 1 Fixed Cell (Model UVD-3200) is a high

performance UV-Vis double beam automatic scanning spectrophotometer. It is an automatic

eight (8) cell spectrophotometer for precise testing with a variable bandwidth of 0.5, 1.0, 2.0,

and 5.0 nm. Model UVD-3200 spectrophotometer offers high performance, ease of use and

reliability, which can be used in various applications as oils analysis.

Spectro UV-Vis Double PC 8 Auto Cell (Model UVD-3200) utilizes a new optical system

design and is microcomputer controlled. With its focused-beam design, the system provides

optimal and reproducible results for small samples. The sample beam and the reference beam

are provided within the same sampling space, facilitating wider and longer scan of data

providing a more detailed view of the results in an easy to use environment.

Spectro UV-Vis Double PC 8 Auto Cell (Model UVD-3200) has a large LCD screen which

displays the menu screen and makes the device easier to use. Additionally, this instrument

permits the apparatus to be linked to a computer and a printer to display the photometric and

spectral data on the PC monitor, using the new UVWin 6.0 UV-VIS application software,

offering a wide range of uses and applications.

Labomed Inc. is certified by ISO 9001-2013, has CE Conformity and is FDA Licensed.

Mode of operation:

- Carefully spread a drop of oil between two glass slides.

- Introduce a blank blade into the first compartment to have the reference spectrum.

Insert the coverslips into the sampling compartments of the UVVisible spectrometer.

- Obtain spectra on the screen.


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Fig.III. 7.UV-Vis Double PC 8 Spectro-Scan 50 Apparatus.

III.4.2. Physic-chemical analysis for hydraulic oil (prista MHM):

III.4.2.1. Measuring the viscosity of oils:

At commercial scale:

Commercially it is measured by three makes of commercial viscometers:

Redwood viscometer (Used in common wealth countries).

Saybolt viscometer (Used in U.S.A).

Engler viscometer (Used in Europe).

Apparatus description:

The Engler Viscometer is mainly used in Germany. It generally measures the viscosity of oil.

It is the viscometer with tumultuous relative regimens and it measure the viscosity referred to

the water. It is showed in Engler Degree and represents the ratio between the down flow time

in seconds of 200ml of the sample through to calibrate capillary hole and the 200 time taken

by milliliter distilled water [44], [15].

Basic parts of the viscometer:

Thermostat: (A)

The basic function of the thermostat used in this apparatus is to maintain the constant

temperature for the heating of oil taken in the bath placed within the thermostat Bath

Thermostat bath is made of Brass and servers the required temperature [44].

Thermostat is arranged coaxially to the first one and it is equipped with thermometer and

agitator to shovels to set in action by hand. In this container the heating liquid comes place

that it will have to carry the oil to the temperature of test [44] [15].

Thermometer: (B)

There are two thermometer are used in this apparatus One is placed in the oil bath for the

measurement of the temperature of the oil used. The second thermometer is placed is the

thermostat bath which shows the temperature is then can be adjusted [44],[15].


Khaoula BERKAS

43

Cover: (C)

The container is fortified of wall cover double with two holes one for thermometer that

measure the temperature of the liquid and the other for a valve pin in wood, in order to close

the outflow hole [44] ,[15].

Valve: (D)

The valve pin passed through the cover and seats in the discharge pipe. When the pin is lifted

the oil start flowing through the platinum discharge tube and time of flow of 200ml of oil is

measure [44] [15].

Stirrer: (E)

Stirrer is use for the uniform distribution of the heat supplied to the fuel placed in the metal

bath [44] [15].

Jet: (F)

The oil container is constituted from brass metal with to the center of the base a hole,

communicating with a small calibrated with platinum capillary through wish the liquid will

have to flow down. The capillary allows the oil to flow through it and time a flow of oil is

used for the measurement of viscosity [44] ,[15].

Level Gauge: (G)

Three needle point gauges are fixed in the oil bath placed to 120° one from the other, mark it

the level that must catch up the liquid for measuring the oil on the one hand, and on the other

to serve for the correct adjustment of the horizontal position of the apparatus [44] ,[15].

Leveling Screw: (T)

Leveling screw is used for the correct horizontal position of the viscometer and it also help in

keeping the correct level of the oil in the bath [44] [15].

Fig.III. 8.Engler viscometer.


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44

Arrangement of apparatus:

It consists of two metal basins, one placed within the other, one serving as an oil reservoir and

the other as a thermostat. The oil bath is fixed in to the thermostat by support and by the

discharge pipe F. A valve pin D passed through the lid and seats in the discharge pipe. Three

needle-point gauges are fixed in the oil bath equidistance from the bottom for measuring the

oil on one hand and the other to serve for the correct adjustment of horizontal position of the

apparatus. When the oil bath is filled to gauge level it should contain 240 ml. A tripod

supports the apparatus. A measuring flask having on its neck two marks, one registering 200

ml, the other 240 ml is placed under the platinum discharge tube when a determination to be

made [44] ,[15].

To test the correctness of the apparatus the time taken for 200 ml of water at 20˚C flow out of

the bath and is filled to gauges, is noted. Before removing the valve the water should be

allowed to acquire a state of rest after being stirred by rotating the lid with the thermometer in

position. Exactly time same procedure is adopted when the oil is being tested [44], [15].

Experimental work:

Apparatus:

- Thermometer;

- Beaker;

- Specific Gravity Bottle and Engler Viscometer.

Procedure:

Clean the oil cup with soft tissue to remove any oil already present in cup.

Pour the water in the cup to filling marks, keeping pointed rod in the vertical position

(and cover up) which act as ball valve to close the orifice.

When cup has been filled with water up to the level gauge, lower the cover and insert

a thermometer into the cup (make sure the vertical rod is closing the orifice when you

cover down the cup).

Collect 200 ml of water in the beaker (after placing beaker beneath the orifice) and

note the time to out flow (in seconds) at room temperature by up lifting the vertical

rod.

Repeat the same procedure with the sample of oil and measure the time of flow for

200 ml of oil sample.

Heat the sample to achieve the required temperature and note the time (seconds) of

outflow of sample at 35 °C, 45 °C, 55 °C and 65 °C respectively.

III.4.2.2. Flash point for hydraulic oil:

The flash and fire points of a liquid fuel specimen are the indicators of its flammability.

European directives [45, 46] and other documents [1, 5, 6, 8] emphasis the necessity of

reducing the flammability risk when using industrial fluids (hydraulic fluids, lubricants,


Khaoula BERKAS

45

processing fluids like those used in steel treatment and cutting etc.), especially in explosive

atmosphere [47].

Apparatus required:

1. Pensky Martens closed Cup Apparatus;

2. Thermometers;

3. Electric heating arrangement;

4. Sample of oil.

The objective is to determine the flash and fire point temperatures of the hydraulic oil sample

(MHM-32), before and after 03 periods of operating using the Pensky Martens closed cup

apparatus [47].

Procedure:

1- Keep the device at 230V, 50Hz, 5 amps power source.

2- Clean the oil cup with a soft cloth and the oil to be tested in the cup up to the mark.

3- Place the oil filled cup on heater; insert the thermometer into the clip, until the bulb

thermometer sensor just dip into the oil surface.

4- Switch on the heater and heat the oil at a faster rate for a few minutes (2 to 3 min) and

control of the heating rate (100°C rise in 60 seconds).

5- Apply a test at 15°C rise in temperature.

6- Record the temperature at which first flash occurs and flash point of the sample oil.

7- To obtain the fire point, continue heating at the same rate and keep applying the flame

test to the surface of oil.

Fig.III. 9.Flash Point Apparatus.

III.4.2.3. Effects of oil degradation on Refractive Index:

Definition:

The speed of light in vacuum is a universal constant, but when light travels through any other

medium its speed slows down as it gets constantly absorbed and reemitted by the atoms in the

material. The ratio of the speed of light in vacuum to its speed in another medium/material is

called as the refractive index of the medium/material and is denoted by ‘n’ [1]. Refractive

index of a transparent solid or liquid, which is a measure of its interaction with

electromagnetic radiation, can be determined by various methods [48].


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46

𝑅𝑒𝑓𝑟𝑎𝑐𝑡𝑖𝑣𝑒 (𝑛) =𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 𝑖𝑛 𝑎 𝑣𝑎𝑐𝑢𝑢𝑚

𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 𝑖𝑛 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒

Whenever light changes speed as it crosses a boundary from one medium into another its

direction of travel also changes, i.e., it is refracted (Figure .III.10). (In the special case of the

light traveling perpendicular to the boundary there is no change in direction upon entering the

new medium.) The relationship between light's speed in the two mediums (vA and vB), the

angles of incidence (𝜃A) and refraction (𝜃B) and the refractive indexes of the two mediums

(nA and nB) is shown below [49]:

𝑉𝐴

𝑉𝐵=

𝑠𝑖𝑛𝜃𝐴

𝑠𝑖𝑛 𝜃𝐵=

𝑛𝐵

𝑛𝐴

Fig.III. 10.Light crossing from any transparent medium into another [49].

Apparatus required:

The main parts and controls of the Abbe Refractometer are:

1- Focusing telescope;

2- Colour compensator with graduated circle;

3- Setting knob for colour compensator;

4- Standard prism body;

5- Setting knob for prism and graduated circle turn;

6- Reading microscope,

7- Calibration screw - special wrench needed;

8- Control thermometer.


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Fig.III. 11.Refractometer

diagram [50].

Fig.III. 12.Refractometer

apparatus.

A B

Fig.III. 13.A peek through the measuring telescope shows scales of Refractive

Index.

Fig.III. 14.Drawing shows the actual appearance of the image as seen through the

focusing telescope.


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Part 2: Results

III.5. Results:

III.5.1. FT-IR analysis:

New hydraulic oils:

- Hydraulic oil motor HLP 46;

- Hydraulic oil motor HVB 46;

- Prista® MHMb hydraulic oil.

Fig.III. 15..Spectrum 03 oils before use pH=4-5.

FIND PEAKS:

Spectrum: MHM(p)-32 before use

pH=4-5

Region: 4000.19 400.16

Absolute threshold: 98.994

Sensitivity: 50

Peak list:

Position Intensity

721.76 93.470

1376.90 88.929

1460.11 81.886

2852.26 68.254

2920.98 55.626

HLP46 before use pH4-5

HVB46 BEFORE USE pH =4-5

MHM(p) -32 befo re use pH=4-5

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0.30

Ab

so

rba

nc

e

500 1000 1500 2000 2500 3000 3500 4000

Wav enumbers (cm-1)

Frequency

area to

search for

carbonyl

peaks.


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49

2953.35 78.423

Figure.III.15 shows three different new oils. The plot shows the differences in spectral

features resulting from the variation in base oils and additives used to make the lubricants.

These differences must be taken into account, or they will cause errors in the numeric values

obtained from the analysis. Because of this, spectral subtraction of the proper new oil

reference spectrum is applied to obtain correct used oil analysis results.

The ASTM D 7414 method measures, as an indicator, the peaks of oxidation absorbance by

Fourier transform infrared spectroscopy or FTIR spectroscopy. This measurement highlights

the oxidation byproducts, as indicated by the detected carbonyl peaks between 1800 and 1660

cm-1 (usually centered around 1709 cm-1). FigureIII.15 clearly shows an absence of carbonyl

peaks in this frequency, as can be expected for an oil that has not been oxidized (new oil).

Used oils:

FTIR analysis for used hydraulic oil (prista MHM-32)

Fig.III. 16.Used hydraulic oil in difference spectrum.

The spectral plot in this Figure III.16 shows a used oil difference spectrum and labels the

peaks of interest.

42

6.2

944

2.5

9

72

1.7

8

10

29

.71

11

56

.44

13

01

.62

13

76

.63

14

59

.64

17

14

.08

28

52

.43

29

21

.23

29

52

.29

oil after 6 months H32

oil after 12 months

new oil

oil after 18 months

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

Ab

so

rba

nc

e

500 1000 1500 2000 2500 3000 3500 4000

Wav enumbers (cm-1)


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Fig.III. 17.The same oil used 18months.

Figure III.17, displays a plot of a new oil, the same oil used 18months and the subtraction

result (difference spectrum).

Carbonyl Oxidation Products:

The broad feature centered around 1714 cm-1 is due to the presence of carbonyl-containing

degradation products of oil. These have been identified in the literature as lactones, esters,

aldehydes, ketones, carboxylic acids and salts, as well as others. The broadness of the peak is

because of the wide variety of materials present. The point of maximum intensity vary as the

oil and conditions of its use are changed. The increase in peak height that occurs as the

number of hours the oil has been run in the engine increases has a greater significance in the

measurement of degradation than total acid number (TAN) or viscosity (figure III.18)

(annex).

Fig.III. 18.degradation of hydraulic oil.

new oil

0.00

0.02

0.04

0.06

0.08

Ab

s

oil after 18 months

0.00

0.02

0.04

0.06

0.08

Ab

s

Subtraction Res ult:o il after 18 months

0.000

0.005

0.010

Ab

s

600 800 1000 1200 1400 1600 1800 2000

Wav enumbers (cm-1)


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III.5.2. Transmittance:

The type of hydraulic oil Prista MHM

Fig.III. 19.Transmitance spectrum of

new oil.


oil after 6 months.


oil after 12 months.


oil after 18 months.

- The results, obtained using a laboratory grade spectrometer, indicates that he

maximum transmittance is 87.5% for the new oil (before use);

- After 6 months of operation, the transmittance decreases to 75.5% as shown in Figure

20;

- After 12 months of operation, the transmittance is 11%;

- It is clear that after 18 months of operation the transmittance is almost zero;

Which explains the change of color of the hydraulic oil during its use.

III.5.2. Observation and calculation of the viscosity:

- Room Temperature T1=25 °C

- Heat at T2=40 °C.


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Table.III. 6 .Experimental measurement table of viscosity.

Oil H-32 C time (s) Degree engler

𝐸 =𝑡

𝑐

ʋ =7.58×E

(mm2/s)

25 0C 40 0C 25 0C 40 0C 25 0C 40 0C

New 56.08 600 253 10.7 4.51 81.09 34.2

After 6 months 56.08 840 285 14.98 5.08 136.28 38.52

After 12months 56.08 1177 388 20.99 6.92 159.08 52.44

After 18 months 56.08 2280.2 477 40.65 7.97 308.20 60.41

Fig.III. 23.Evolution of the viscosity at 25 °C and 40 °C.

According to their viscosity the mineral hydraulic oils are divided into viscosity grades (VG)

relating to the reference fluid temperature 40 °C at ambient pressure. The viscosity grades are

defined in the DIN E 51524 standard, which is also adopted by the international ISO standard.

The actual value of the oil viscosity can deviate from the rated value by ±10 %. Table.III.1

indicates the viscosity grades more often used in hydraulic systems and their minimum and

maximum values, permissible deviation.

Discussion:

If we take a closer look at the graph shown in figure III.23, we can compare the oils (MHM-

32 type) in four (04) different times:

- New oil;

- After 6 months of function;

- After 12 months of function;

0

50

100

150

200

250

300

350

New oil After 6months

After12months

After 18months

Kin

emat

ic v

isco

sity

, m

m²/

s

25°C

40°C


Khaoula BERKAS

53

- After 18 months of function.

Figures III.23 show, the evolution of the viscosity as a function of time, (again new oil until

18 months of function) at 40 °C and 25 °C, on the histogram obtained the viscosity of the oil

increases as a function of time, this increase is mainly due to the wear and contamination of

the particles in running time of operation of the installation, it can also come from mechanical

shear which causes a malfunction.

In addition to that, the fluid has mechanical strengths:

Too viscous, the passage in the pipes and through the components is difficult, the efficiency

of the installation is poor. Pumps may deteriorate under the effects of cavitation.

If we compare the results of the viscosity (after 12 and 18 months of operation) that we

obtained, with Table III.1 it is remembered that the value of the viscosity exceeds the max

value of the ISO standard.

III.5.3. Flash point:

Fig.III. 24.Evolution of the flash point.

Figure (III.24) shows the evolution of the flash point as a function of time, according to the

results obtained, we notice a drop in the flash point of the hydraulic oil after 18 months of

operation, this decrease could be the result of the presence of the new particles, or the thermal

cracking of the oil molecules, which has a negative influence on the lifetime of the hydraulic

installation.

There is a risk of ignition at 214 °C after 18 months of operation.

Therefore, it is necessary to control the temperature during operation to minimize any risk of

ignition.

224225 225,5

214

208

210

212

214

216

218

220

222

224

226

228

new oil after 6m after 12 m after 18m

Flas

h p

oin

t [0 C

]

Time


Khaoula BERKAS

54

III.5.4. Refractive index:

Fig.III. 25.Measured refractive index.

As shown in the Figure III.25 the refractive indices increased over time, and after 18 months

changed by 0.016. The color of the samples also changed over time. This can be explained by

the electronic absorption edge of the oils being shifted into the visible.

1,467

1,48 1,4805

1,483

1,46

1,465

1,47

1,475

1,48

1,485

New oil After 6 months After 12months After 18 months

Re

frac

tio

n in

de

x

CHAPTER IѴ: Assessment of temperature of pump by infrared

thermography

Khaoula BERKAS

55

Chapter IѴ: Assessment of temperature of pump by infrared

thermography

IѴ.1. Objective: When a hydraulic system has problems, it is common practice to first look at the pump. The

pump is arguably the heart of almost every hydraulic system and, as such, has traditionally

been blamed for almost every operating problem. Obviously, this cannot be true, but when

preliminary troubleshooting analysis focuses on the pump, a series of steps can pinpoint the

specific problem and lead to the cure [52].

This chapter aims to present a modern diagnosis method of specific malfunctions of

hydrostatic drive systems equipment’s. The diagnostic technique described is using the

infrared thermography and can be considered a non destructive examination practice of

hydraulic systems. The thermovision cameras, along with the computer equipment’s prove

their full efficiency in all industrial maintenance activities, when punctual intervention is

desired, quickly and inexpensively.

IѴ.1.1. Introduction:

Thermography (or Thermovision) is a technique for measuring the thermal field of a physical

body, which uses the infrared radiation, for recording and visualization of temperature

distribution on the surfaces. Termography is a non-destructive method that does not require

direct contact with the analyzed surface and is particularly useful in malfunctions diagnosing

in the industrial systems, because it is not necessary to interrupt the technological flow.

Thermography is an application that derives from the military techniques and it has found,

since the mid of the ‘50 years of the last century, a wide application in science, technique,

industry, biology, agriculture or medicine. The energy conservation involves the optimum use

of resources and represent an imperative when it comes to the application of measures to

develop an economy based on healthy growth. For this reason, it is necessary to obtain

accurate some informations about the energy performances of equipment’s, installations or

machinery. The information is obtained by drawing of energy balances or analysis based on

data resulting from the inspection of selected objectives. The industrial equipments presents

energy losses which depend on configuration, quality and sealing installation [53].

The evaluation of all energy losses susceptible to reduce the efficiency of a system, requires a

good vision on the thermal distribution of its components. This is achieved by thermography

technique, which allows to monitor the temperature distribution on the equipments surface, by

a method of measuring the infrared radiation [54].

The effective use of a modern methods of diagnosis and prevention is necessary when the

objective of the maintenance is the extending of lifetime and the proper functioning of

equipment’s and machineries. The proper use of the specialized instruments in nondestructive

diagnosis can detect and recognize the equipment malfunctions, with a high degree of

accuracy, if it is known the principle of functioning of these instruments [55],[1].

Thermography is one of the safest methods of predictive maintenance that could be used in

hydraulic drives. Currently, the method of thermography is successfully worldwide used in


thermography

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56

building maintenance and electrical wires maintenance. Our aim is to adapt the thermography

method to the hydraulic (system test bench) [1].

IѴ.1.2. History and development:

1960’s-development of cooled forward-looking infrared (FLIR):

1970’s-US Army develops uncooled irt technology module;

1980’s-Industries first commercial IR camera introduced;

1990’s-Succesful demonstration of 256,512 pixel cameras and introduction of

nightlights and surveillance cameras;

2000’s-Inroduction of 1st automotive thermal imaging driving aid by Cadillac and 1st

development of IR camera with zoom.

Future plans:

Infrared vision for everyday life;

Making the technology cheaper;

Resolution of display to be increased;

Increasing accuracy and longevity.

IѴ.1.3. Application:

Worldwide, the infrared thermography usage is in continuous expansion and

development both in material science and in engineering as:

Condition monitoring;

Medical imaging;

Veterinary thermal imaging;

Night vision;

Surveillance;

Research;

Process control;

Non-destructive testing;

Surveillance in security, law enforcement and defense;

Chemical imaging;

Buildings.


thermography

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57

IѴ.1.4. Advantages and disadvantages of thermography infrared:

Advantage

It is a non-contact type technique.

Fast, reliable & accurate output.

A large surface area can be scanned in no time.

It is capable of catching moving targets in real time

Presented in visual & digital form. Software back-up for image processing and

analysis.

Requires very little skill for monitoring.

It can be used to detect objects in dark areas.

Fig.IѴ. 1.Continuous quality

control on welds [56].

Fig.IѴ. 2.Medical Infrared Imaging

of hand of human [56].

Fig.IѴ. 3.Vehicle maintenance [56].

Fig.IѴ. 4.Medical Infrared Imaging

of animals [56].

Fig.IѴ. 5.Thermal images of a district heating pipeline [56].


thermography

Khaoula BERKAS

58

It can be used to measure or observe in areas inaccessible or hazardous for other

methods.

Disadvantages:

Cost of instrument is relatively high.

Unable to detect the inside temperature if the medium is separated by glass/polythene

material etc.

Difficult to interpret even with experience.

Training and staying proficient is time consuming.

IѴ.1.5. Effects of Emissivity on Thermal Imaging:

It is worthwhile to note that an object with high emissivity will appear hotter as compared to

an object with low emissivity, when placed together under same conditions of temperature,

moisture, and other environmental conditions. The object with low emissivity will appear dull

to thermal imaging camera, in the same way as it will appear to a human eye. Consequently,

the object’s temperature cannot be calculated by just measuring its emitted infrared radiation

and it is important to gain knowledge about the emissivity of the object [57], [58].

This problem of emissivity can be overcome by the following two methods [59]:

1. Identify and analyze the object, in terms of emissivity, whose thermal profile is required to

be measured for predictive maintenance. As modern day thermal imaging cameras provide

scope for temperature compensation, it is required to choose a suitable numerical value for

compensation, depending upon the study of emissivity of the object under consideration.

These thermal imagers provide a user interface to easily set the compensation value; this

value is further utilized by the signal processor of the thermal imager to correct the

temperature measurement value [6].

2. Another method is to paint the surface of low emissivity object with a high and constant

emissivity coating, but this is not a feasible method on all manufacturing plants/ buildings.

An alternative to this second method is to make a comparison of heat profile patterns,

between objects of similar emissivity, operating under similar conditions/ load [60]. This

alternative method will help to obtain the absolute temperature values of each individual

object, thereby, identifying the faulty object in an equipment/ manufacturing plant; this can

be analyzed and repaired or replaced, as desired, before the equipment fails to operate and

causes more damage.

IѴ.2.Obtained results:

Ѵ.2.1. Measuring the temperature of the pump:

Electromagnetic spectrum

The electromagnetic spectrum is arbitrarily divided into a number of wavelength regions,

called bands, distinguished by the methods used to produce and detect radiation. There is no

fundamental difference between the radiation in the various electromagnetic spectrum bands.

They are all governed by the same laws, and the only differences are those due to wavelength

values [60].


thermography

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59

Thermovision or Infrared Visualization (IR) is a technique by which a camera detects and

displays a radiation intensity map on a range of electromagnetic spectrum. The term thermal

imaging defines the image obtained by the thermal camera and is used particularly in military

or civilian applications, while thermography also involves temperature measurement in

industrial or scientific applications.

It is known that anybody with a temperature above zero Kelvin emits electromagnetic

radiation. Cold and very cold substances: liquid nitrogen, ice and snow also emit infrared. The

intensity of this radiation varies depending on the temperature of the object and its ability to

emit energy.

Infrared has a wide range within the electromagnetic spectrum, from 0.8 μm (micrometers) to

200μm, but only a small part is usable by IR measuring and visualization equipment. For

thermal imaging (thermography), only the range between 0.75 μm and 15 μm is of interest. In

fact, three (or two) subdomains are recognized by the manufacturer:

- short waves (SW - ShortWaves) or near infrared: 0.8 ÷ 1.5 μm;

- where average (MW - MidWaves): 2 ÷ 5 μm;

- long waves (LW - LongWaves): 7 ÷ 15 μm.

Fig.IѴ. 6.Electromagnetic spectrum.

1 - X-ray; 2 - UV; 3 - the visible spectrum; 4 - IR; 5 - microwaves; 6 - radio

waves.

Although wavelengths are given in μm (micrometers), other wavelength measurement units in

this spectral region are often used, eg nanometers (nm) and Angstrom (A) - 10000 = 1000 nm

= 1 μm.

IѴ.2.2.The equations of the thermography chamber:

When viewing an object, the camera receives radiation not only from the object itself but also

collects radiation reflected in the surroundings of the object surface. Both radiation are

somewhat attenuated by the measurement atmosphere. In addition, a third radiation to be


thermography

Khaoula BERKAS

60

considered is the radiation in the atmosphere. This is a real description of the measurement

conditions. What can be neglected, however, is the light of the sun and the scattering of

uncontrolled radiation from the sources of intense radiation out of the field of vision into the

atmosphere. Such perturbations are difficult to quantify, however, in most cases, they are

fortunately small enough to be neglected. If these are not negligible, setting up the

measurement is uncertain, even for a trained operator. It is the task of the operator to modify

situations where measurements may be disturbed: for example, by changing the viewing

direction, protection, etc [61].

Fig.IѴ. 7.Schematic representation of the method of thermography.

1- environment; 2 - object; 3 - Atmosphere; 4 – camera.

To obtain an object temperature calculation formula using the calibrated calibration chamber,

it is assumed that a power radiation W of a black body with the Celsius temperature is

assumed to be at a short distance. The camera will generate a Usource output signal proportional

to the input power (linear power of the camera). Thus, the equation can be written [61]:

sursa sursaU CW T 4.1

Or simplified:

sursasursa CWU 4.2

Where: C - constant.

If the radiation source is considered for a gray body with the emissivity ε, then the received

radiation will consequently be a source. Under these conditions, it is possible to define:

1- Emissivity of the object = ετWobj,

Where ε is the emissivity of the object, and τ is the atmospheric transmittance. The

temperature of the object will be Tobj.

2- Reflected emissivity of external sources = (1 - ε) τWrefl,


thermography

Khaoula BERKAS

61

Where (1 - ε) is the reflection coefficient of the object. The temperature of external

sources considered is Trefl.

It is assumed that the Trefl temperature is the same for all surfaces emitting from the

environment. This, of course, is for the simplification hypothesis.

It is also assumed that the emissivity of the environment is equal to 1. This is imposed

by the prism of Kirchhoff's Law.

3- atmospheric radiation= (1 – τ)τWatm,

Where (1 - τ) is atmospheric emissivity. Atmospheric temperature is considered Tatm.

Total radiation can be written as follows:

atmreflobjtot W1W1WW 4.3

By solving equation (4.3) for Uobj we obtain:

atmrefltotobj U

1U

1U

1U

4.4

The formula resulting from equation (4.4) is the measurement formula used by the FLIR

Systems series of cameras. The voltages used in Equation (4.4) are shown in Table (IѴ.1).

Table.IѴ. 1.Time used for the selected room.

Uobj Calculated output voltage of the Tobj black body temperature camera.

Utot The measured voltage of the thermal imaging chamber for particular

cases

Urefl Theoretical output voltage of the thermal body temperature sensor for

the Trefl black body according to the calibration

Uatm Theoretical output voltage of the thermal body temperature sensor Tatm

black body according to the calibration

The operator must introduce the following parameters in the camera settings in the actual

thermography situation: emissivity of the object ε, relative humidity, Tatm, distance to the

object (Dobj), actual temperature Trefl, atmospheric temperature Tatm. This task may sometimes

be quite difficult for the operator, as there are no easy ways to find the right values for

emissivity and atmospheric transmittance for real cases. The two temperatures are not

normally a problem provided the environment does not contain large and intense sources of

radiation. The figures below illustrate the relative importance of the proportion of radiation

for three different object temperatures, two emissivity values and two spectral ranges: SW and

LW. The other parameters have the following values [62]:

- τ = 0.88

- refl = +20 °C (+68 °F)

- Tatm = +20 °C (+68 °F)


thermography

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62

IѴ.2.3. Experimental equipment:

The experiments were carried out on a hydrostatic installation (test bench) in a laboratory in

the manufacturing engineering department, "in Galati Romania, Figure IѴ.8 shows the

equipment needed to determine the recorded sizes.

Fig.IѴ. 8.Hydrostatic installation with camera thermography.

- Axial piston pumps (1);

- FLIR ThermoVision A20M infrared thermal imaging room (2);

- ThermaCAM Researcher Professional (3) specialized software for acquisition and

processing of thermograms.

Infrared ThermoVision A20M from Flir Systems has been connected to a portable computer

terminal, allowing it to be ordered from both the computer and an integrated keyboard (TI), in

the form of buttons placed accessible at the top of the camera.

The most important features of the thermographic camera have been set:

1

2

3


thermography

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63

- Measuring range: 20 ÷ 900 °C;

- Image frequency: 50 Hz;

- Image resolution: 160x120 pixels;

- Thermal sensitivity <0.1 °C;

- Digital Video Interface: FireWire;

- Spectrum wavelength: 7.5 ÷ 13 μm.

Fig.IѴ. 9.ThermoVision A20M

ThermoVision Camera.

In order to obtain a true infrared image, it is also necessary to consider the parameters

describing the physical properties of the material to be processed (emissivity, reflected

temperature), ambient temperature, relative humidity, distance from the lens of the camera to

th pump.

Fig.IѴ. 10.The properties of the

pump material.

Fig.IѴ. 11.Choice of the

temperature measurement range.

Specialized software ThermaCAM Researcher Professional

ThermaCAM Researcher Professional is the ThermoVision A20M ThermoVision thermo-

imaging software - capable of measuring and capturing images of objects that emit infrared

radiation. Due to the fact that radiation is a function dependent on the surface temperature of

an object, the software allows the camera to make it possible to record the temperature in real

time, but it can also be used for the acquisition and processing of thermograms that include

the temperature range recorded at the cutting tool interface to be processed, the images


thermography

Khaoula BERKAS

64

obtained showing the thermal state at a certain moment during the cutting process.

Subsequently, it is possible to analyze the phenomena recorded with the thermographic

camera after it has been disconnected, as well as transferring text or image file information to

various other programs, such as MS Excel or MS Word [63] .

Through the ThermaCAM Professional Professional software, the recordings of the

thermography camera are captured and can be expressed numerically or graphically in the

form of images, profiles, histograms etc. All results are based on an infrared image with a

temperature scale, the program being able to display a single image at a pre-selected time

interval. For the numerical analysis of the temperature and statistical information in the

images, obtained either on the basis of the absolute measurements (the result is a real

temperature) or the relative ones (the result is a difference in temperature), markers (evolution

lines) were used on the image in infrared, which highlights the areas where the radiation of

the object is equal. This is true only if the emissivity of the object is the same throughout the

image, and the limits of the evolution line can not exist outside the maximum or minimum

temperatures of the initially set interval (0 °C ÷ 250 ° C). Markers can be punctual -

temperature is measured in one place on the image, zonal - temperature, maximum, minimum,

average and standard deviation in a perimeter chosen in the image or linear - measure the

minimum temperature, maximum temperature, average and standard deviation along a

straight line within the image [62].

Table.IѴ. 2.The parameters of the pump.

The parameters of the pump

pn (nominal pressure) [daN /cm2] 150

Qn (nominal flow) [l/min] 17

n (rotation speed) [rpm] 1450

The experiments were carried out on two pressure levels: 25 bar and 50 bar

IѴ.2.4. Diagrams obtained:

On the basis of the operating values of the pump n = 1275 rpm and p = 20 bar, images of the

temperature variation with the infrared camera FLIR represent in Figures 13, 15, 17, 19, 21.

In the present study, it was chosen to draw the evolution lines (L01, L02, ..., L05), Figures

(12, 14, 16, 18, 20), represent graphs to plot from the recorded values opting for the maximum

temperature.


thermography

Khaoula BERKAS

65

Fig.IѴ. 12.Temperature variation for p = 20 bar

after 15 minutes.

Fig.IѴ. 13.Temograph taken with

the FLIR camera after 15 minutes.


after 25 minutes.



40,6

40,8

41

41,2

41,4

41,6

41,8

42

1 2 3 4 5 6 7 8 9 10

tem

per

atu

re [

°C]

Time [s]

T[C] L1 L2 L3 L4 L5

42,5

43

43,5

44

44,5

1 2 3 4 5 6 7 8 9 10

Tem

per

ature

[°C

]

Time [s]

L1 L2 L3 L4 L5


after 35 minutes.



46

46,2

46,4

46,6

46,8

47

1 2 3 4 5 6 7 8 9 10Tem

pe

ratu

re [

°C]

Time [s]L1 L2 L3 L4 L5


thermography

Khaoula BERKAS

66

Fig.IѴ. 18.Temperature variation for p = 20

bar after 45 minutes.

Fig.IѴ. 19.Temograph taken with the

FLIR camera after 45 minutes.

Fig.IѴ. 20.Temperature variation for p= 20



FLIR camera after 50 minutes.

Fig IѴ.22 below shows the hottest area of the pump. The camera was fixed on this zone to see

the variation of the temperature for p=50 bar and n = 1700 rpm.

48,2

48,4

48,6

48,8

49

49,2

1 2 3 4 5 6 7 8 9

Tem

per

atu

re [

°C]

Time [s]

L1 L2 L3 L4 L5

49

49,5

50

50,5

51

1 2 3 4 5 6 7 8 9 10

Tem

per

atu

re [

°C]

Time [s]

L1 L2 L3 L4 L5


thermography

Khaoula BERKAS

67

Fig.IѴ. 22.The hottest area of the pump.

Fig.IѴ. 23.Temperature variation for p= 50 bar

after 5 minutes.


FLIR camera after 5minutes.

43,544

44,545

45,546

46,547

47,5

1 2 3 4 5 6 7 8 9 10 11 12

Tem

per

ature

[°C

]

Time [s]

L1 [C] L2[C] L3 [c] L4 [c] l5[c]

2 1


thermography

Khaoula BERKAS

68


after 15 minutes.



57

57,5

58

58,5

59

59,5

60

1 2 3 4 5 6 7 8 9 10

Tem

per

atu

re [

°C]

Time [s]

l1 l2 l3 l4 l5


after 10 minutes.



45

46

47

48

49

50

51

52

53

1 2 3 4 5 6 7 8 9 10

tem

per

atu

re [

C]

Time [s]

L1 L2 L3 L4 L5


thermography

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69

Fig.IѴ. 29.Temperature variation for p= 50



FLIR camera after 30 minute.

IѴ.3. Conclusion: Thermal imagers produce heat-based images, where the colors in the image show a

relationship between every pixel of the hydraulic equipment image and a reference surface

temperature. This thermal imaging technology serves an important purpose for predictive

maintenance of hydraulic pump .In mechanical drives, overheating is a general problem,

which indicates breakdown in near future.

Following the experimental research presented on the demonstration of the possibility of

using infrared thermography to predict the behavior of hydrostatic systems, to evaluate the

state of wear and the operation of hydrostatic pumps, a series of numerical and graphics was

obtained.

Some conclusions and comments regarding the thermography method used in maintenance

prevention:

Concerning with the carried out tests the punctual following conclusions are appropriate:

The first test was done at p= 20 bar:

- The thermogram analysis of Fig. IѴ.20 shows that the pump tested in Fig. IѴ.8 is operating

normally. Thus, we see that on the lower side of the pump, corresponding to the piston block

(area 2 in fig IѴ.22), the temperature is about 51ºC and on the upper side, where are the

pistons (area 1 in fig IѴ.22) ,the measured temperature is d about 46 ºC. The temperature

difference recorded at the pump heads is 5 °C, which is below the critical value of 10 °C.

- For the second test, which concerns the hottest zone (1 in Fig IѴ.22) of the pump, the

temperature rises to 78.1 °C at p = 50 bar after 30 minutes of operation (Fig IѴ.29).

72

73

74

75

76

77

78

79

1 2 3 4 5 6 7 8 9 10

Tem

per

atu

re [

°C]

Time [s]

l1 l2 l3 l4 l5

Conclusions

Khaoula BERKAS

70

Chapter Ѵ: conclusions The main function of hydraulic fluids is to transmit energy in the form of pressure. Other

functions are to ensure good lubrication of moving parts and to protect them against

corrosion.

An important part of the performance of an installation is related to the choice of fluid. In-

service monitoring by complete analysis is essential. A regularly controlled fluid (1 to 3 times

/ year depending on the case) is a fluid with a longer duration in time, which allows

significant savings. Effective monitoring increases the lifespan of the entire installation.

The first objective of experimental work was carried out by analysis of the used hydraulic oil

and the results obtained were compared with the new oil.

The oil analysis include:

- Spectroscopic analysis showed us the structure of the engine oil and its various components

by FTIR spectroscopy, and the color change of the oil by the UV-Visible spectrophotometry

method.

- Physicochemical characteristics:

The determination of the physicochemical characteristics ensures the identification of the

wear problems, it makes it possible to involve the dysfunction of the installation in order to

optimize the maintenance costs (direct and indirect) by a better knowledge of the state of the

machines.

According to the results of the analysis, it was found considerable change in the physico-

chemical properties of the oil after 18 months of operation.

If we compare the results of the viscosity (after 12 and 18 months of operation), with (table

III.1) it is remembered that the value of the viscosity exceeds the max value of the ISO

standard. In addition to that, the flash point of the hydraulic oil (after 18 months of operation)

decrease at 214 °C there is a risk of ignition at 214 °C. Therefore, it is necessary to control the

temperature during operation to minimize any risk of ignition (which is the objective of the

fourth chapter).

The second objective, which is assessment of temperature of pump by infrared thermography

the following general conclusions are available:

- The malfunctions diagnosis using infrared thermovision cameras provide to the staff

involved in predictive maintenance works an effective analytical method of hydraulic

drive systems, in a very short time, at low cost and with minimal effort.

- Alongside the classical methods of diagnosis, the thermography can be successfully

used as often are balances and energy analyzes for each class of hydraulic apparatus

analyzed.

- It is a particularly sensitive measurement technique that can record temperature

variations of tens of degrees, both spatially and temporally if there are known the

factor emissivity of the materials.

Conclusions

Khaoula BERKAS

71

- Are possible real-time analysis both before and after the intervention to the hydraulic

equipment, in order to obtain necessary information for a forecasting of their evolution

in time.

The application of infrared thermography method to the maintenance of hydraulic systems,

allows detection and correction of potential damages since in primary phase, prior to

production of the failures. In this way reduces the breaks in the operation of machines by

eliminating downtimes and by optimizing the operations for repair and maintenance.

References

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72

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Hamamatsucho Seiwa bld.4-8 Shiba Daimon1- Chorme Minato ku, Tokyo 105-0012-

JAPON, Overseas Business Department.

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Annex

Khaoula BERKAS

78

Table of Characteristic IR Absorptions

Frequency, cm–1 Bond Functional group

3640–3610 (s, sh) O–H stretch, free

hydroxyl

alcohols, phenols

3500–3200 (s,b) O–H stretch, H–bonded alcohols, phenols

3400–3250 (m) N–H stretch 1 ˚, 2˚ amines, amides

3300–2500 (m) O–H stretch carboxylic acids

3330–3270 (n, s) –C≡C–H: C–H stretch alkynes (terminal)

3100–3000 (s) C–H stretch aromatics

3100–3000 (m) =C–H stretch alkenes

3000–2850 (m) C–H stretch alkanes

2830–2695 (m) H–C=O: C–H stretch aldehydes

2260–2210 (v) C≡N stretch nitriles

2260–2100 (w) –C≡C– stretch alkynes

1760–1665 (s) C=O stretch carbonyls (general)

1760–1690 (s) C=O stretch carboxylic acids

1750–1735 (s) C=O stretch esters, saturated aliphatic

1740–1720 (s) C=O stretch aldehydes, saturated aliphatic

1730–1715 (s) C=O stretch α, β–unsaturated esters

1715 (s) C=O stretch ketones, saturated aliphatic

1710–1665 (s) C=O stretch α, β–unsaturated aldehydes, ketones

1680–1640 (m) –C=C– stretch alkenes

1650–1580 (m) N–H bend 1 ˚ amines

1600–1585 (m) C–C stretch (in–ring) aromatics

1550–1475 (s) N–O asymmetric stretch nitro compounds

1500–1400 (m) C–C stretch (in–ring) aromatics

1470–1450 (m) C–H bend alkanes

1370–1350 (m) C–H rock alkanes

1360–1290 (m) N–O symmetric stretch nitro compounds

1335–1250 (s) C–N stretch aromatic amines

1320–1000 (s) C–O stretch alcohols, carboxylic acids, esters,

ethers

1300–1150 (m) C–H wag (–CH2X) alkyl halides

1250–1020 (m) C–N stretch aliphatic amines

1000–650 (s) =C–H bend alkenes

950–910 (m) O–H bend carboxylic acids

Annex

Khaoula BERKAS

79

910–665 (s, b) N–H wag 1 ˚, 2˚ amines

900–675 (s) C–H “oop” aromatics

850–550 (m) C–Cl stretch alkyl halides

725–720 (m) C–H rock alkanes

700–610 (b, s) –C≡C–H: C–H bend alkynes

690–515 (m) C–Br stretch alkyl halides

predictive maintenance of a hydraulic system using axial...

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