basic hydraulic by sanjay humania

Basic hydraulicsTraining program

Objective

• The object of this subject is to teach more about hydraulics and its areas of application.

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Introduction

• The controlled movement of parts or a controlled application of force is a common requirement in the industries.

• These operations are performed mainly by using electrical machines or diesel, petrol and steam engines as a prime mover.


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Power source

Energy medium

Control system

Prime mover

Load

What is Fluid Power?

• Fluid power is the engineering science and technology that deal with the generation, control, and transmission of energy through the use of pressurized fluids.

• Or

• Fluid power technology is to convert, transmit, control & apply fluid energy to perform useful work. Fluid can be either a liquid or gas.


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Hydraulics

• The study of hydraulics deals with system operated with hydraulic oil media to impart power or to control power.

• Hydraulic power is the power that is transmitted by pressurized oil.

• It may be used to power machines or to control or to regulate machines.


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Oil tank / reservoir

Power source (Pump)

Pressurized oil

Control valve

Actuator

Basic principles

Historical review

• Actual advancement of ‘Oil Hydraulics’ started from the end of 17th Century. In 1648, a French Physicist, Pascal, discovered a fundamental law underlying the whole science of Hydraulics.

• It’s a two-part statement as given here:

▫ Pressure at any point in a static fluid is the same in every direction,

▫ Pressure exerted on a confined fluid is transmitted equally in all directions, acting with equal force on equal areas.


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formula:


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AREA

PRESSURE

FORCE

PRESSURE = FORCE ÷ AREA

FORCE = PRESSURE X AREA

Pressure

• Pressure is defined as the force per unit area.

• P = F / A

• The SI unit for pressure is Pascal (Pa),

• 1Pa =1N /m^2• The unit for pressure is also Bar (bar), kg / cm2,

▫ 1 bar=1.019368kg/cm2

▫ 1kg/cm2=0.9810bar

▫ 1bar = 105 Pa


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Pressure

• Pressure occurs in fluid when it is subjected to force.

• A force ‘F’ is applied to an enclosed fluid via a piston area ‘A’

• This result in a pressure ‘P’ in the fluid.• Increasing the force increase the pressure ‘P’ in

direct proportion.• Decreasing the area also increase pressure ‘P’

▫ Pressure in the fluid can therefore be define as the force acting per unit are, or:


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Pascal's law & its applications

• Basic law can be applied to an enclosed hydraulic system having a cylinder p1 with a piston area of 10cm2 & another cylinder p2 with 100cm2.

• Both are connected & filled with water.


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Pascal's law & its applications

• Now assume a force of 50N is applied downward on p1,

• The Pressure created by P1=Force/Area

• =50N/10cm2 = 5N/cm2

• A/c to Pascal's law, pressure acts equally in all direction.

• So, the pressure acting on p2 is also 5N/cm2 . As the p2 has the area of 100cm2 .

• So, Force available on p2 =Pressure X Area

• = 5N/cm2 X 100cm2 =500N

“The force applied to piston 1 is multiplied 10 times, this advantage is utilised in fluid power system !!!”


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Principle of hydraulic system

• The force given by fluid is given by the multiplication of pressure and area of cross section.

• As the pressure is same in all the direction, the smaller piston feels a smaller force and a large piston feels a large force.

• Therefore, a large force can be generated with smaller force input by using hydraulic systems.


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Hydraulic systems.

• The hydraulic systems consists a number of parts for its proper functioning.

• These include storage tank, filter, hydraulic pump, pressure regulator, control valve, hydraulic cylinder, piston and leak proof fluid flow pipelines.

• It consists of: ▫ cylinder

▫ storage tank

▫ Filter

▫ electric pump

▫ pressure regulator

▫ control valve

▫ leak proof closed loop piping.


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Schematic of hydraulic system


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Hydraulic systems components


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Hydraulic systems...

• The storage/fluid tank is a reservoir for the liquid used as a transmission media.

• The liquid used is generally high density incompressible oil. It is filtered to remove dust or any other unwanted particles and then pumped by the hydraulic pump.

• The capacity of pump depends on the hydraulic system design. These pumps generally deliver constant volume in each revolution of the pump shaft. Therefore, the fluid pressure can increase indefinitely at the dead end of the piston until the system fails.


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Hydraulic systems....

• The pressure regulator is used to avoid such circumstances which redirect the excess fluid back to the storage tank.

• The movement of piston is controlled by changing liquid flow from port A and port B.

• The cylinder movement is controlled by using control valve which directs the fluid flow.

• The leak proof piping is also important due to safety, environmental hazards and economical aspects.


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Types of Hydraulics

• The place held by hydraulics in (modern) automation technology illustrates the wide range of applications for which it can be used.

• A basic distinction is made between:

▫ Stationary hydraulics

▫ Mobile hydraulics


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Stationary hydraulics

• Stationary hydraulics is fixed at one station where all the activities are carried out at the same station. Stationary hydraulics is used in machine tool applications.

• The following application areas are important for stationary hydraulics: ▫ Production and assembly machines of all types

▫ Transfer lines

▫ Lifting and conveying devices

▫ Presses

▫ Injection moulding machines

▫ Rolling lines

▫ Lifts


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Mobile hydraulic

• Mobile hydraulic systems move on wheels or tracks, for example, unlike stationary hydraulic systems which remain firmly fixed in one position.

• A characteristic feature of mobile hydraulics is that the valves are frequently manually operated.

• Typical application fields for mobile hydraulics include: ▫ Construction machinery ▫ Excavators, elevating platforms ▫ Lifting and conveying devices ▫ Agricultural machinery


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Applications of hydraulic systems

• The hydraulic systems are mainly used for precise control of larger forces.

• The main applications of hydraulic system can be further classified in five categories:


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Industrial hydraulics

• Industrial: Plastic processing machineries, steel making and primary metal extraction applications, automated production lines, machine tool industries, paper industries, loaders, crushes, textile machineries, R & D equipment and robotic systems etc.


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In modern CNC controlled machine tools, tools and

work pieces are clamped by means of hydraulics.

Feed and spindle drives may also be effected

using hydraulics.

Mobile hydraulics

• Mobile hydraulics:Tractors, irrigation system, earthmoving equipment, material handling equipment, commercial vehicles, tunnel boring equipment, rail equipment, building and construction machineries and drilling rigs etc.


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Automobile hydraulics

• Automobiles: It is used in the systems like breaks, shock absorbers, steering system, wind shield, lift and cleaning etc.


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Marine hydraulics

• Marine applications: It mostly covers ocean going vessels, fishing boats and navel equipment.


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Aerospace hydraulics

• Aerospace equipment: There are equipment and systems used for rudder

• control, landing gear, breaks, flight control and transmission etc. which are used

• in airplanes, rockets and spaceships.


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Comparison of hydraulics with other

control media• There are other technologies besides hydraulics

which can be used in the context of control technology for generating forces, movements and signals:

▫ Mechanics

▫ Electricity

▫ Pneumatics


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HYDRAULIC OPERATION


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HYDRAULIC OPERATION


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HYDRAULIC OPERATION


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HYDRAULIC OPERATION


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HYDRAULIC OPERATION


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Hydraulic Pump

• A pump is the heart of the hydraulic system, convert mechanical energy into hydraulic energy.

• Main purpose of the pump is to create the flow of oil through the system & thus assist transfer of power & motion.

• The combined pumping and driving motor unit is known as hydraulic pump.

• The hydraulic pump takes hydraulic fluid (mostly some oil) from the storage tank and delivers it to the rest of the hydraulic circuit.

• In general, the speed of pump is constant and the pump delivers an equal volume of oil in each revolution.


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Hydraulic Pump

• The hydraulic pumps are characterized by its flow rate capacity, power consumption, drive speed, pressure delivered at the outlet and efficiency of the pump.

• The pumps are not 100% efficient. • The efficiency of a pump can be specified by two ways:

▫ One is the volumetric efficiency which is the ratio of actual volume of fluid delivered to the maximum theoretical volume possible.

▫ Second is power efficiency which is the ratio of output hydraulic power to the input mechanical/electrical power.

• The typical efficiency of pumps varies from 90-98%.


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Hydraulic Pump

• The hydraulic pumps can be of two types:

▫ centrifugal pump

▫ reciprocating pump


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Centrifugal pump

• Centrifugal pump uses rotational kinetic energy to deliver the fluid.

• The rotational energy typically comes from an engine or electric motor.

• The fluid enters the pump impeller along or near to the rotating axis, accelerates in the propeller and flung out to the periphery by centrifugal force as shown in figure.

• In centrifugal pump the delivery is not constant and varies according to the outlet pressure.


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Centrifugal pump

• These pumps are not suitable for high pressure applications and are generally used for low-pressure and high-volume flow applications.

• The maximum pressure capacity is limited to 20-30 bars.

• Most of the centrifugal pumps are not self-priming and the pump casing needs to be filled with liquid before the pump is started.


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Reciprocating or positive displacement

pump• The reciprocating pump is a

positive plunger pump. It is also known as positive-displacement pump or piston pump.

• It is often used where relatively small quantity is to be handled and the delivery pressure is quite large. The construction of these pumps is similar to the four stroke engine as shown in figure.


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Reciprocating or positive displacement

pump• The crank is driven by some external rotating motor. • The piston of pump reciprocates due to crank rotation.

The piston moves down in one half of crank rotation, the inlet valve opens and fluid enters into the cylinder.

• In second half crank rotation the piston moves up, the outlet valve opens and the fluid moves out from the outlet.

• At a time, only one valve is opened and another is closed so there is no fluid leakage.

• Depending on the area of cylinder the pump delivers constant volume of fluid in each cycle independent to the pressure at the output port.


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Classification of Hydraulic Pumps

• These are mainly classified into two categories:


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Pump

Hydrostatic

(Positive displacement)

Hydrodynamic

(Non-Positive displacement)

Positive displacement pumps

• This pump ejects fixed quantity of fluid per revolution of the pump shaft. The pump outlet flow is constant & is not depended on the system pressure. So they are suited for fluid power system.

• Positive displacement pumps must be protected against overload. The reason is that, it continues to eject fluid (even though it has no place to go) causing an extremely rapid build up of pressure.

• Example: Gear pump, Vane pump, piston pump.


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Advantages of positive displacement

pumps• PD pumps are widely used in hydraulic system

• They generate high pressure

• They are relatively small & enjoy very high power to weight ratio.

• They have greater flexibility of performance under varying speed pressure requirement.


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Construction & Principal of PD pumps..

• Reciprocating pump are generally cylinders with operating as a pump. They are available in various size, shape & driving mechanisms. Due to high pressure they are used for specialized applications. A pump using this principle is known as piston pump.

• Rotary pump are most common in oil hydraulics system when low to medium pressure is the prime consideration. ▫ The 3 prime types are: ▫ 1) Gear, 2) Vane, 3) Screw


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Gear Pumps

• Gear pump is a robust and simple positive displacement pump. It has two meshed gears revolving about their respective axes.

• The rigid design of the gears and houses allow for very high pressures and the ability to pump highly viscous fluids.

• They are suitable for a wide range of fluids and offer self-priming performance.


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Gear Pumps

• Based upon the design, the gear pumps are classified as:

▫ External gear pumps

▫ Lobe pumps

▫ Internal gear pumps

▫ Gerotor pumps


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External Gear pump

• External gear pumps have two mating gear in a closed fitted housing. One of the gear is connected to a drive shaft connected to the prime mover. The 2nd one, the follower gear is driven as it meshes with the driver gear.


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How external gear pump work !


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Generally gear pumps are used to

pump• Petrochemicals: Diesel oil, crude oil, lube oil etc.

• Chemicals: Sodium silicate, acids, plastics, mixed chemicals etc.

• Paint and ink

• Resins and adhesives

• Pulp and paper: acid, soap, lye, black liquor, lime, sludge etc.

• Food: Chocolate, cacao butter, fillers, sugar, vegetable fats and oils, animal food etc.


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Lobe Pump

• Lobe pumps work on the similar principle of working as that of external gear pumps.

• However in Lobe pumps, the lobes do not make any contact like external gear .

• Lobe contact is prevented by external timing gears located in the gearbox.


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Lobe Pump


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Lobe Pump

• Similar to the external gear pump, the lobes rotate to create expanding volume at the inlet.

• Now, the fluid flows into the cavity and is trapped by the lobes. Fluid travels around the interior of casing in the pockets between the lobes and the casing.

• Finally, the meshing of the lobes forces liquid to pass through the outlet port.


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Applications

• Lobe pumps are frequently used in food applications because they handle solids without damaging the product.

• Large sized particles can be pumped much effectively than in other positive displacement types.

• As the lobes do not make any direct contact therefore, the clearance is not as close as in other Positive displacement pumps.

• This specific design of pump makes it suitable to handle low viscosity fluids with diminished performance.


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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.

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


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Piston pumps types

• Piston pumps are basically of two types:

▫ Axial piston pumps

Bent axis piston pumps

Swash plate axial piston pump

▫ Radial piston pumps


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Axial Piston Pump

• Axial piston pumps are positive displacement pumps which converts rotary motion of the input shaft into an axial reciprocating motion of the pistons.

• These pumps have a number of pistons (usually an odd number) in a circular array within a housing which is commonly referred to as a cylinder block, rotor or barrel.


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Bent-Axis Piston Pumps

• In these pumps, the reciprocating action of the pistons is obtained by bending the axis of the cylinder block.

• The cylinder block rotates at an angle which is inclined to the drive shaft. The cylinder block is turned by the drive shaft through a universal link. The cylinder block is set at an offset angle with the drive shaft.

• The cylinder block contains a number of pistons along its periphery. These piston rods are connected with the drive shaft flange by ball-and socket joints. These pistons are forced in and out of their bores as the distance between the drive shaft flange and the cylinder block changes.

• A universal link connects the block to the drive shaft, to provide alignment and a positive drive.


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Swash Plate Axial Piston Pump


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Bent-Axis Piston Pumps Swash Plate Axial Piston Pump

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Sanjay Humania

Radial Piston Pump


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• The piston pump has pistons aligned radially in a cylindrical block.

• Pistons are placed in radial bores around the rotor. The piston shoes ride on an eccentric ring which causes them to reciprocate as they rotate.

• The eccentricity determines the stroke of the pumping piston.

• The radial piston pump works on high pressure (up to 1000 bar).

Combination Pump

• Two basic requirements for load lifting or load applying by a hydraulic ram.

• First, there is a need of large volume of fluid at a low pressure when the cylinder extends or retracts. The low pressure is required to overcome the frictional resistance.

• The second requirement is that a high pressure is needed, when the load is gripped.


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Combination Pump


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Combination Pump

• In this system two separate pumps are driven by a common electrical motor.

• Pump P1 is a high pressure low volume pump and pump P2 is a high volume low pressure pump.

• The hydraulic system is associated with relief valves RV1 and RV2 and a one-way check valve CV1.

• This kind of arrangement allows the fluid flow from left to right.

• This kind of arrangement saves energy as the large volume of fluid from pump P2 is returned to the tank at a very low pressure, and only a small volume of fluid from pump P1 is returned at a high pressure.


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Hydraulic Fluid & Properties

Job perform by the hydraulic oil

• They have the following primary tasks:▫ Power transmission (pressure and motion

transmission)▫ Signal transmission for control

• Secondary tasks:▫ Lubrication of rotating and translating components to

avoid friction and wear▫ Heat transport, away from the location of heat

generation, usually into the reservoir▫ Transport of particles to the filter▫ Protection of surfaces from chemical attack, especially

corrosion


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Hydraulic fluids requirements

• Functional▫ Good lubrication characteristics▫ Viscosity should not depend strongly on temperature

and pressure▫ Good heat conductivity▫ Low heat expansion coefficient▫ Large elasticity modulus

• Economic▫ Low price▫ Slow aging and thermal and chemical stability long

life cycle


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Hydraulic fluids requirements

• Safety▫ High flash point or in certain cases not

inflammable at all▫ Chemically neutral (not aggressive at all against

all materials it touches)▫ Low air dissolving capability, not inclined to foam

formation

• Environmental friendliness▫ No environmental harm▫ No toxic effect


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Properties of Hydraulic Fluid.

• Good Lubricity

• Stable Viscosity Characteristics

• Good Heat Dissipation

• Flash Point

• Low Foaming Tendency

• Fire Resistant

• Prevent Rust Formation

• Non-toxic, Easy to handle & Available


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Good Lubricity

• The component in a hydraulic system contain many surface which are in close contact and which move in relation to each other. The hydraulic fluid must separate and lubricate such surfaces. Protection against wear is a principal reason for selecting a fluid having good lubrication characteristics as a hydraulic medium.


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Good Heat Dissipation

• An important requirement of the fluid is to carry heat away from the working parts.

• Pressure drops, mechanical friction, fluid friction, leakages, all generate heat.

• The fluid must carry the generated heat away and readily dissipate it to the atmosphere or coolers.

• Therefore high thermal conductivity and high specific heat values are desirable in the fluid chosen.


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Flash Point

• The flash point of a hydraulic oil is defined as the temperature at which flashes will be generated when oil is brought into contact with any heated matter, e.g., a heat stick.

• Low flash point oils are not use as Hydraulic Oil.


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Low Foaming Tendency

• Foam results from air or other gases becoming entrained in the hydraulic fluid. Air enters a hydraulic system through the reservoir or through air leaks within the system.

• A hydraulic fluid under high pressure can contain a large volume of dissolved or dispersed air bubbles. When this fluid is depressurized, the air bubbles expand and produce foam. Because of its compressibility and poor lubricating properties, foam can seriously affect the operation and lubrication of machinery.

• Proper foam inhibitors modify the surface tension on air bubbles so they more easily break up.


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Fire Resistant

• Fire resistance is one of the properties that is optional in a good usable hydraulic fluid.

• The commonly used hydraulic liquid are petroleum derivative, and consequently they burn vigorously once they pass the point.

• For critical application, artificial or synthetic hydraulic fluid are used which have high fire resistances. Various grades of fluids with high water content are also available now a days for oil hydraulic system.


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Stable Viscosity Characteristics

• Viscosity is a measure of a hydraulic fluid's resistance to flow. It is a hydraulic fluid's most important characteristic and has a significant impact on the operation of the system.

• When a hydraulic oil is too thin (low viscosity), it does not seal sufficiently. This leads to leakage and wear of parts. When a hydraulic oil is too thick (high viscosity), the fluid will be more difficult to pump through the system and may reduce operating efficiency.

• All hydraulic fluids must be able to retain optimum viscosity during operation in cold or hot temperatures, in order to consistently and effectively transmit power


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Prevent Rust Formation

• In many systems, water can enter as condensation or contamination, and mix with the hydraulic oil. Water can cause rusting of hydraulic components.

• In addition, water can react with some additives to form chemical species which can be aggressive to yellow metals.

• Hydraulic oil formulations contain rust and corrosion inhibitors which prevent the interaction of water or other chemical species from attacking metal surfaces.


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Non-toxic, Easy to Handle & Available

• These characteristics refer to the interaction of the fluid with people who repair, handle, use or pay for hydraulic system fluid.

• Obviously, it is desirable that the fluid be as simple to handle and as available and cheap as possible.


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Hydraulic oil used in India.

• Indian oil corporation limited(IOCL) has marked oil used for hydraulic system are termed as Circulating and Hydraulic Oils.

• These oils are recommended for hydraulic system, circulation system of industrial gearboxes, air compressors requiring turbine quality oil and for plain and anti-friction bearings of turbo feed pumps, turbo blowers, etc.

• These Oils can be used for lubrication of intermittently operating turbo generator sets where oil is changed after short duration.


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Fluid power systems20-01-2016Sanjay Humania

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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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PUMP ACTUATOR

HYDRAULIC MACHINE


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Hydraulic POWER PACK

Power Pack

• The hydraulic power unit (power supply unit) provides the energy required for the hydraulic installation. Its most important components are

▫ The reservoir (tank) ,

▫ Drive (electric motor),

▫ Hydraulic pump,

▫ Pressure relief valve ,

▫ Filter and cooler.

• The hydraulic power unit may also act as a carrier for other devices (gauges, directional control valves).


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P T

Ts

Hydraulic SymbolsWhy we need Hydraulic Symbols ?

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M


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M


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Tank

DCV

Filter

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Graphical representation of hydraulic

and pneumatic elements• The hydraulic and pneumatic elements such as cylinders and

valves are connected • through pipelines to form a hydraulic or a pneumatic circuit. It is

difficult to represent the • complex functioning of these elements using sketches. Therefore

graphical symbols are • used to indicate these elements. The symbols only specify the

function of the element • without indicating the design of the element. Symbols also indicate

the actuation method, • direction of flow of air and designation of the ports. Symbols

are described in various • documents like DIN24300, BS2917, ISO1219 and the new

ISO5599, CETOP RP3 and • the original American JIC and ANSI symbols.


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and pneumatic elementsThe symbol used to represent an individual element display the following characteristics:

▫ Function

▫ Actuation and return actuation methods

▫ Number of connections

▫ Number of switching positions

▫ General operating principle

▫ Simplified representation of the flow path


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and pneumatic elementsThe symbol does not represent the following characteristics:

▫ Size or dimensions of the component

▫ Particular manufacturer, methods of construction or costs

▫ Operation of the ports

▫ Any physical details of the elements

▫ Any unions or connections other than junctions


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Symbols for ports

• Earlier the ports were designated with letter system. Now as per ISO5599 the ports are designated based on number system.


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Symbols for ports


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Graphical symbols of hydraulic

elements and equipment


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Circuit symbols for


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Directional control valves


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4/3way directional control valves


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Circuit symbols for manual operation


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Circuit symbols for manual operation


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Circuit symbols for flow control valves


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Circuit symbol for pressure valves


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Circuit symbols for non-return valves


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Hydraulic Actuators

Hydraulic Actuators

• The fluid discharged by the pump is directed to the ‘hydraulic actuator’. The actuator convert the pressure energy of the fluid into mechanical energy. There are 3 basic type of hydraulic actuator.

• The actuators convert the fluid pressure to a suitable linear or rotary motion.

• Linear motion – Hydraulic cylinder• Rotary motion – Hydro motor• Rotary motion – Semi-rotary actuator


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Hydraulic cylinders

• A hydraulic cylinder is a device, which converts fluid power into linear mechanical force and motion. It usually consists of a movable element, a piston and a piston rod operating within a cylindrical bore.


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Parts of a hydraulic cylinder

• A hydraulic cylinder consists of the following parts

• Cylinder barrel

• Piston

• Piston rod

• Bush

• Cylinder head and cap


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Type of hydraulic cylinder


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Hydraulic cylinder

Single acting cylinders

Double acting cylinders

Single acting cylinder

• In the case of a single acting cylinder, only the piston side is pressurized with hydraulic fluid. The cylinder can thus carry out work only in one direction. The fluid which flows into the piston chamber causes a pressure to build up the surface of the piston. The piston travels into its forward end position. The return stroke is effected by a spring, the dead weight of the piston rod or an external load


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Single acting cylinder.


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Plunger type single acting cylinder

• In the case of plunger cylinders, the piston and rod form a single component. Due to the design of the cylinder, the return stroke can only be effected by external forces. The cylinders can therefore generally be installed only vertically.


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Application of single acting cylinder


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• In the case of double acting cylinders, both piston surfaces can be pressurized. A working movement can thus be performed in both directions.

• With double acting cylinders with a single-sided piston rod, different forces and speeds are obtained on the advance and return strokes due to the difference in area between the piston surface and annular piston surface.


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Application of double acting cylinders


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Double acting cylinder with end

position cushioning • Cylinder with end position cushioning are used

to brake high stroke speeds smoothly and prevent hard impacts at the end of the stroke. Shortly before the end position is reached, the cross- section for the outflow of fluid is reduced by the built-in cushioning pistons and then finally closed. The hydraulic fluid is then forced to escape through a flow control valve.


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Cushioning Cylinder


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End position cushioning

• The piston is a short distance before its end position; the hydraulic fluid on the piston-rod side must escape via the adjustable flow control valve above the piston rod

• This type of end position cushioning is used for stroke speed between 6 m/min and 20 m/min. At higher speed, additional cushioning or braking devices must be used


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End position cushioning

• The piston rod is on its return stroke; in this flow direction, the non-return valve below the piston rod is opened, thus by-passing the flow control valve. The piston rod retracts at maximum speed.


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Double-acting cylinder with cushioning


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Telescopic cylinder

• Often cylinder & rod length does not fit in the machine. In that case the piston rod is also used as a piston barrel and a second piston rod is used.

• These kinds of cylinders are called telescopic cylinders. If we call a normal rod cylinder single stage, telescopic cylinders are multi-stage units of two, three, four, five or more stages.

• In general telescopic cylinders are much more expensive than normal cylinders. Most telescopic cylinders are single acting (push). Double acting telescopic cylinders must be specially designed and manufactured.


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Telescopic cylinder


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Hydraulic Motors

Hydraulic Motors

• In hydraulic system generally hydraulic motor provide rotational movement. A hydraulic motor transform hydraulic energy into mechanical energy which is applied to a resistance object by means of a shaft connected with the motor.

• Hydraulic motor closely resemble hydraulic pumps in construction & size. The only difference is that instead of pushing the fluid as the pump does, in hydraulic motor the rotating elements(i.e. vanes, gear, piston, etc.) are pushed by the oil pressure to enable the motor shaft to rotate & thus develop the necessary turning torque & continuous rotational motion.


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Construction of External Gear Motor


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Construction of Radial Piston Motor.


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Hydraulic motor used in FESTO training

kit


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Semi rotary actuator

• The limited angle rotary actuator is applied when the shaft has to rotate over a limited angle. The animation shows how this simple actuator works: in this case the shaft can rotate over an angle of about 270 degrees. This type of actuator is, among others, used as a rotator actuator on (small) cranes and excavators


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Hydraulic valves

Hydraulic valves

• The pressure energy is fed to the actuator through a number of control block called valves.

• Various type of valve are used in hydraulic system to control or regulate the flow medium. Basically valves are expected to control:

▫ Direction

▫ Pressure

▫ Flow

▫ Other special functions.


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• These valves control the direction of flow of the hydraulic fluid and, thus, the direction of motion and the positioning of the working components. Directional control valves may be actuated manually, mechanically, electrically, pneumatically or hydraulically. They convert and amplify signals(manual, electric or pneumatic) forming an interface between the power control section and the signal control section.


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Symbol design of valves.

• Method of designation of valve

• The basic symbol for control valve is a square.

• Two or more squares are used.

• Each square representing the switching position provided by the valve.

• 1. Two position valve.

• 2.Three position valve.


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Symbol design of valves..

• Lines in the boxes are used to show flow path with arrow indicating direction of flow.

• The shut off position is indicated by the line drawn at right angle to the horizontal line inside the rectangle.


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FLOW

SHUT OFF / NO FLOW

Pipe connections

• The pipe connections i.e. inlet and outlet ports to the valve are indicated by lines drawn on outside of the box and right angle to the horizontal line .

• The first position from left indicates the rest, initial or neutral position when the valve is not actuated.

• The second position or square from left indicates actuated position.


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Pipe connections

• Single position (initial)

• Two position valve

• Three position valve


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Commonly used direction control

valves• Direction control valve is used to control or to

change the direction or to start or stop the fluid flow only on the receipt of any signal which may be mechanical, electrical or a fluid pressure pilot signal.

• Direction control valves are described by number of ports and number of positions

▫ n / n way valve

▫ ( n = 1, 2, 3,……)


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Way/position

• Way Valve Ports Positions

• 2/2 2 (1 input , 1 output) 2

• 3/2 3 (1 input, 1 output, 1 tank) 2




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(2/2 ) On/off valve

• The most basic direction control valve is the simple on/off valve. A simple version is shown symbolically below.


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(2/2 ) On/off valve

• 2/2 way valve normally closed

• Not actuated


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(2/2 ) On/off valve

• 2/2 way valve normally closed

• Actuated


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(2/2 ) On/off valve

used in FESTO training kit


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(3/2 ) direction control valve

• The three way version of the above valve which allows the outlet port to be connected to either the pump or the reservoir is shown below


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• Normally closed

• Not activated


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• Normally close

• Activated


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(3/2 ) direction control valve in FESTO

training kit


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• Normally close

• Not Activated


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• Normally close

• Activated


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(4/2 ) direction control valve in FESTO

training kit


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• 4/3 way mid-position recirculation / tandem mid-position

• Middle position is activated


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• Position 1 is activated





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• 4/3 way mid position cutoff / all ports blocked mid position



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(4/3) direction control valve in FESTO

training kit


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(4/3) direction control valve



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(4/3) direction control valve



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Non-Return /Check valve


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(Direction control valve)• Check Valves are simply valves which provide

reasonably unrestricted flow in one direction and stop the flow in the other direction. A light spring is generally used to retain the valve to a closed position on near zero flow.


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(Direction control valve)


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Non-Return /Check Valves



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Pilot operated check valves

• As opposed to the simple non return valve, pilot operated check valve may also be operated in the direction of close.

• These valves are used, for example:▫ To isolated work circuits

under pressure

▫ To prevent the load from dropping, if a line should break

▫ To prevent creep movements hydraulically loaded actuators


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Pilot operated check valve


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Pilot operated check valve


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Pre-fill valve


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Pre-fill valve

• Pre-fill valve are large size hydraulic pilot operated check valve. They are used mainly to pre fill large cylinder volumes and to isolate the main working circuit under pressure.


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Flow rate

• Flow rate is the term used to describe the volume of liquid flowing through a pipe in a specific period of time. For example, approximately one minute is required to fill a10 litre bucket from a tap. Thus, the flow rate amounts to 10 l/min.


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Flow rate


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In hydraulics, the flow rate is designated as Q. The following equation applies:

Q =Flow rate

V = Volume

t = time

Flow control valves

• The speed of the actuators needs to be altered as per operational requirement. For this purpose hydraulic systems use flow control valves.

• These interact with pressure valves to affect the flow rate. They make it possible to control or regulate the speed of motion of the power components. Where the flow rate is constant, division of flow must take place. This is generally effected through the interaction of the flow control valve with a pressure valve.


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Flow control valves


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Flow control valve

• The main classification of the flow control valve are:


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Flow control valve

Non – pressure

compensated

Pressure

compensated.

Non-pressure compensated flow control valve

• The simplest type of flow control valve is a needle valve. The needle valve has a pointed stream that can be adjusted manually to control the rate of flow through the valve.


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Non-pressure compensated flow

control valve


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Non-pressure compensated flow

control valve


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Non-pressure compensated

unidirectional flow control valve• In most fluid power

application needle valve with integrated check valve is used to control the flow rate. This enable a regulated flow in one direction with free flow in the reverse direction.


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Non-pressure compensated

unidirectional flow control valve


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Pressure compensated flow control

valve• The flow through the valve varies as the square

root of the pressure drop across it. So any changes in pressure at the outlet and inlet changes the flow through the valve.

• But pressure compensation flow control automatically adjust to pressure changes and maintain a constant pressure drop from inlet to outlet, thus providing constant flow.


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valve


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valve


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Location of flow control valves

• The location of flow control valves with respect to other component & the work is quit important because it has an effect on the characteristics of the circuit performance.

• There are 2 basic type of location of a flow control valve in any hydraulic system.

▫ Meter – in circuit

▫ Meter – out circuit

▫ Bleed off circuit


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Meter – in circuit

• In this type of circuit, the valve is located in the pressure line leading to the work cylinder.

• The flow entering into the work cylinder is first controlled through the valve.

• Meter – in circuit are generally used when the load characteristics are constant & positive. For free reverse flow, generally a check valve is provided parallel to the flow control valve.

• For example: A hydraulic table feed on a surface grinder would require controlled rate of travel.


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Meter – out circuit

• In this type of circuits, the flow control valve is installed on the return side of the cylinder so that it controls the speed of the working cylinder by monitoring the discharge flow.

• The meter – out circuit is commonly used in machine tools that require precise control of fluid on discharge from the exhaust side of the cylinder.

• The machine tools like mills and drills often required large restraining force to prevent excessive pull on the cylinders.


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Pressure control valvesWhy we need Pressure control valves ?


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230


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234


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Pressure control valves

• Oil energy does the work due to pressure in the oil system. In a mechanical or hydraulic system there may be a need to increase or decrease the oil pressure depending on the specific requirement. Hence a group of valves called pressure control valve have been designed.


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Pressure control valves


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Pressure Relief Valves

• Relief valves are generally spring loaded valves which include a plug over a discharge port which is lifted against an spring force if the system pressure exceeds a certain value. This opens the flow to the discharge port relieving the pressure.


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(internal pilot operated version )• The pilot operated version enables more

accurate control of the setting and a lower relief setting can be accommodated


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(internal pilot operated version )


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(Externally controlled/remote pilot)


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The valve opens when pressure at X port is more than spring force.




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Application of Pressure Relief Valve

• It can be used

• To relive excessive pressure / to protect pump / other parts

• To limit the system pressure

• As a back pressure valve / counterbalancing valve

• As a sequence valve


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Pressure Reducing Valve

• This type of valve is used to maintain reduced pressure in specified location of a hydraulic system. Normally it is an open valve.

• A pressure reducing valve is one which used a spring loaded spool to control the downstream pressure.

• If the downstream pressure is below the value pressure, fluid will flow freely from the inlet to the out let.

• When the outlet pressure increases the valve setting , the spool moves to partially block the outlet port.

• If the valve is closed completely by the spool, it could cause the downstream pressure to buildup above the valve setting. To avoid this, a drain line is provided to drain the fluid to the tank.


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Application of Pressure Reducing

Valve• In oil driven spot welding guns, the control of the

pressure is important for good welding. In that hydraulic system both welding gun and the clamp are powered by the same pump/power pack.

• A pressure reducing valve which is placed in between the welding gun and main pressure, which will regulate the pressure on the spot welding gun.

• The clamp pressure is determined by the pump relief valve setting.


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3 way Pressure

Reducing & Relief valve • This valve is combination of 2 way pressure

regulator & PRV


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3 way Pressure

Reducing & Relief valve


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3 way Pressure



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Deceleration valve

• A deceleration flow control valve gradually reduce its flow rate to provide deceleration of the heavy loads. On some machine it is desirable to have a skip-feed arrangement. This is accomplished by having a cam operated deceleration valve.

• The cam operated deceleration valve is connected in parallel with the meter-out flow control valve to provide an adjustable minimum flow when the main flow path is closed.

• Rapid forward movement will take place when the valve is in the open condition. Cam on the slide act to close the valve gradually.


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Deceleration valve


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Deceleration valve

• Flow from the rod end of the cylinder is gradually restricted & this will slow down the movement & the feed phase starts.

• Return speed is at the maximum when flow from the pump to end bypasses the flow control valve by flowing through the check valve.


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Deceleration valve


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Shutoff valve


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Others components

Bourdon-tube pressure gauge


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PRESSURE GAUGE

• This gauge is sometimes known as Bourdon’s pressure gauge as it employs a ‘Burdon Pressure Tube’.

• It is a phosphor-bronze tube oval in section and circular in form. When pressure is applied to the tube, its tends to straighten and this move of the tube is transferred to a needle or pointer through a link, sector arm & a pinion assembly.

• The pressure can be read out from the pointer scanning a graduated dial.

• The accuracy of the pressure gauge should be within (+) or (-) 1 to 2% of the reading value.


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Components of Bourdon Tube Pressure

Gauge


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How Bourdon Tube Pressure Gauge

Works


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Why internal chamber of the gauge is

filled with liquid?• To maintain the accuracy of the pointer

movement and to avoid damage to the link mechanism, the entire internal chamber of the gauge is filled with transparent liquid like glycerin or any other oils.

• This will suppress any vibration and thus will ensure accuracy of the pressure reading.


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Accumulators

Accumulator

• Hydraulic accumulator is an accessory of a hydraulic system

• A hydraulic accumulator is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source.

• The external source can be a spring, a raised weight, or a compressed gas. An accumulator enables a hydraulic system to cope with extremes of demand using a less powerful pump, to respond more quickly to a temporary demand, and to smooth out pulsations. It is a type of energy storage device.


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Types of Hydraulic Accumulator

• The function of hydraulic accumulator is to store pressurized oil.

• Types:

▫ Weighted accumulator

▫ Spring loaded accumulator

▫ Gas-charged accumulator


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Weight loaded type accumulator

• This is the oldest type of accumulator. This consist of a vertical, heavy steel cylinder which incorporates a piston with packing to prevent leakage.

• A dead weight is attached to the top of the piston.

• The force of gravity of the dead weight provides the potential energy in the accumulator.

• The main disadvantages of this of accumulator is its large size and heavy weight makes it unsuitable for mobile equipment.


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Weight loaded type accumulator


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Spring loaded accumulator

• A spring loaded accumulator is similar to the weight loaded type, except that the piston is preloaded with a spring.


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Bladder type

• The three types of gas-charged accumulators are bladder, piston and diaphragm.

• The most popular of these is the bladder type. Bladder accumulators feature fast response (less than 25 milliseconds), a maximum gas compression ratio of around 4:1 and a maximum flow rate of 15 liters (4 gallons) per second.


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Accumulator used in FESTO kit


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Design of hydraulic circuits

Simple hydraulic circuit

• Make a double acting cylinder forward and backward.


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Simple hydraulic circuit

• Rotate a hydraulic motor clockwise and anti-clockwise.


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Regenerative Circuit

• A regenerative circuit is used to speed up the extending speed of a double acting hydraulic cylinder. Both ends of the hydraulic cylinder are connected in parallel so that one port of the four way valve is blocked.

• When the DCV is shifted to its left mode, the fluid bypasses the DCV and enters into the rod end of the cylinder. Fluid in the blank end drains back to the tank through the DCV as the cylinder retracts.


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Regenerative Circuit

• Normal circuit:


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Pilot operated Check Valves-

Application 1


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Application 2


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Application


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Meter – in circuit


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Meter – out circuit


281

PRESSURE COMPENSATED FLOW

CONTROL VALVE APPLICATION


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Application of pressure reducing valve


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3 way Pressure



284

Counterbalance Application


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Automatic cylinder reciprocating

circuit using sequential valve


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Counterbalance Application 2


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Sequence vale application “A+b+ then

AB-”


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Sequence vale application


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Remote relief valve – sequence valve

“A+B+ then AB-”


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HYDRAULIC MOTOR CONTROL

SEQUENCE APPLICATION


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Industrial Hydraulic Systems

Calender feeding device

Single-acting cylinder [Ex 1]• Rolls of paper are lifted into a

calender by a lifting device. The lifting device is driven by a plunger cylinder (single-acting cylinder). When the hydraulic power pack is switched on, the pump output flows directly to the cylinder. A 2/2-way valve, which is closed in its normal position, is fitted in a branch line leading to the tank. A non-return valve is used to ensure that the pump is protected against the oil back pressure. A pressure relief valve is fitted upstream of the non return valve to safeguard the pump against excessive pressures.


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Calender feeding device

Single-acting cylinder [Ex 1]


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Hardening furnace

Single-acting cylinder [Ex 2]• The cover of a harden furnace

is to raised by a single acting cylinder. The cylinder is activated by a 3/2 way valve. A 9 kg weight is attached to the cylinder to represent the load.

• What are the necessary components?

• Draw the hydraulic circuit diagram.

• Practical assembly of circuit.


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Hardening furnace

Single-acting cylinder [Ex 2]


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Furnace door control

Double-acting cylinder [Ex 3]• A furnace door is

opened and closed by a double acting cylinder. The cylinder is activated by a 4/2 way valve with spring return. Speed of opening and closing are to be controlled separately.


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Furnace door control

Double-acting cylinder [Ex 3]


298

Conveyor tensioning device

4/3-way valve with bypass to pump

[Ex 4]• Parts are fed through a drying oven on a steel

chain conveyor belt. It must be possible to correct the tracking of the belt by means of a tensioning device to ensure that the belt does not run off its rollers. This device consists of a steel roller fixed at one end and movable at the other by means of a double-acting cylinder. Hydraulic power must be available continuously.

• The hydraulic system must switch to the recirculation (H in mid-position 4/2 way valve) condition when the directional control valve is not actuated. The clamping station causes a continuous counter force to act on the cylinder.

• A piloted non-return valve is used to prevent creepage of the piston rod of the positioning cylinder as a result of oil leakage losses in the directional control valve.


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Conveyor tensioning device

4/3-way valve with bypass to pump

[Ex 4]


300

Drilling machine [Ex 5]

• In a automated drill machine, first the clamp cylinder should extend and clamp the work piece. Then the work cylinder should extend to drive a spindle to drill a hole in the work piece. Then the work cylinder retracts the drill spindle and the clamp cylinder retracts to release the work piece for removal.


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Drilling machine [Ex 5]


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Bulkhead door

Hydraulic clamping of a cylinder [Ex 6]• A double-acting cylinder is

used to open and close a bulkhead door. Closing must be carried out smoothly and at a constant adjustable speed. The speed is adjusted by means of a one-way flow control valve. A pressure relief valve must be fitted to provide counter-holding and prevent the heavy door from pulling the piston rod out of the cylinder during the closing operation.


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Bulkhead door

Hydraulic clamping of a cylinder [Ex 6]


304

Skip handling Varying load [Ex 7]

• The loading and unloading of skips from a skip transporter is carried out using two double-acting cylinders. Each cylinder is subject to varying loads – tractive load during unloading and compressive load during loading. The skip should be raised and lowered at a slow constant speed. Each cylinder must therefore be hydraulically clamped on both sides.


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Skip handling Varying load [Ex 7]


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Cold-store door Accumulator [Ex 8]

• A heavy cold-store door is opened and closed by a hydraulic cylinder. A hydraulic accumulator is to be installed to allow the door to be closed in the case of an electrical power failure. This will permit the cold-store door to be opened and closed a number of times. A 4/2-way valve is to be used to activate the cylinder. This valve should be connected up in such a way that the piston rod is advanced with the valve in its normal position.


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Cold-store door Accumulator [Ex 8]


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Thank You !

basic hydraulic by sanjay humania

Engineering