Download - Loader Hydraulic Training Courseware
Loader Hydraulic Training Courseware
2011
Main Content
� Suitable Group
� Contents
� Training Objectives
19/05/2015
� Evaluation Topics
� Contents
Suitable Group
This course is suitable for domestic and foreign intermediate and above technical service personnel
It also applies to…
19/05/2015
Main Content
� Suitable Group
� Contents
� Training Objectives
19/05/2015
� Evaluation Topics
� Contents
Training Objectives
1. This training course is expected to have 12 hours.
2. After training of this course, students should master the following main knowledge points:
(1)Basic knowledge of hydraulic system
(2)Structure and principle of LG hydraulic system
19/05/2015
(2)Structure and principle of LG hydraulic system
(3)Common failure and troubleshooting of systems and components
1
Basic Knowledge of Hydraulic Transmission
1
Contents
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Hydraulic System Introduction of LG Loader
2
1
Basic Principle of Hydraulic Transmission
Composition of Hydraulic Transmission System
1
2
Part 1 Basic Knowledge of Hydraulic
Transmission
3
4
Advantages of Hydraulic Transmission System
Disadvantages of Hydraulic Transmission
System
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5
6
7
8
System
Hydraulic Medium
Hydraulic Power Components
Hydraulic Control Components
Hydraulic Actuating Components
●●●● A machine is basically made up of four parts, including prime motor,
transmission device, working mechanism, and assistant mechanism.
The purpose of prime motor is to change various forms of energy into
mechanical energy, which is power supply of the machine. Working
mechanism works outside with mechanical energy. Transmission device
ⅠⅠⅠⅠ. Basic Principle of Hydraulic Transmission
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mechanism works outside with mechanical energy. Transmission device
between prime motor and working mechanism transfers power and
controls.
There are many transmission types. Transmission can be divided into
mechanical transmission, power transmission, pneumatic transmission and
liquid transmission by parts or working medium.
●●●● Transferring and controlling energy with liquid as working medium is
called liquid transmission.
It can be divided into hydraulic pressure transmission and hydraulic
transmission by principle. Hydraulic pressure transmission mainly
ⅠⅠⅠⅠ. Basic Principle of Hydraulic Transmission
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transmission by principle. Hydraulic pressure transmission mainly
delivers power with liquid pressure. Hydraulic transmission mainly
transfers power with kinetic energy of liquid.
●●●● Take hydraulic jack for example to
illustrate principle and features of
hydraulic transmission.
1. Force transmission follows Pascal's
Principle
1))))Thrust on piston equals oil pressure times
ⅠⅠⅠⅠ. Basic Principle of Hydraulic Transmission
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piston area.
2))))P, oil pressure, depends on external load.
2. Loading speed transfers according to the
principle of equal liquid volume after
changes. Its speed depends on quantity
of flow. Ignoring loss, hydraulic
transmission force is irrelevant with
speed.
Pressure::::P=F1/A1=F2/A2;;;;(Pascal's Principle)
Quantity of flow::::Q=A1V1=A2V2; (V=S/t)
(the Principle of Continuity );;;;
Power::::P====V1F1=V2F2=PQ ;;;;
Figure 1-1 Working Principle of Oil Jack
1-oil tank 2-control valve 3,6-cylinder 4,7-plunger 5-lever
8,9-one-way valve 10,11-pipelines
1. Hydraulic Power Supply
Components converting mechanical energy into liquid pressure. Typical
component is hydraulic pump.
2. Control Components
Control force, movement speed and direction actuating components by
controlling pressure, flow quantity and direction of fluid. Pressure, flow
ⅡⅡⅡⅡ. Composition of Hydraulic Transmission System
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controlling pressure, flow quantity and direction of fluid. Pressure, flow
quantity and direction usually control hydraulic valve.
3. Actuating Components
Components converting liquid pressure into mechanical energy,
including hydraulic cylinder moving in a straight line and hydraulic
motor with rotation movement.
4. Assistant Components
Other devices besides the above three components to guarantee
normal operation of the system in the system have delivering, storage,
heating, cooling, filtration, measurement and other functions, such as
pipeline, connector, fuel tank, radiator, filter, etc.
ⅡⅡⅡⅡ. Composition of Hydraulic Transmission System
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pipeline, connector, fuel tank, radiator, filter, etc.
5. Working Medium
Deliver energy and signal with it.
1. Unit power is light in weight, which means large force and torque can be obtained with
lighter equipment weight.
2. Small inertia, fast starting and braking due to its small volume and light weight.
3. Stepless speed regulation is easy during operating process with a large speed regulation
range.
4. Linear reciprocating motion can be easily achieved with the help of hydraulic cylinder with
simple structure.
ⅢⅢⅢⅢ. Advantages of Hydraulic Transmission System
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5. Easy to realize automation
6. Easy to achieve overload protection. Work is safe and reliable.
7. Hydraulic transmission can layout transmission mechanism flexibly.
8. Liquid working medium with elasticity and vibration absorbing ability makes hydraulic
transmission smooth and reliable.
It can be lubricated by itself during operation. Easy heat dissipation and long service life.
9. Easy to realize standardization, serialization and universalization. Easy to design,
manufacture and market.
1. Low transmission efficiency (75% ~ 80%). Leakage and environmental pollution.
2. Largely influenced by temperature change during operation.
3. Reliability of hydraulic system is still not as good as that of power transmission and
mechanical transmission.
4. Hydraulic components have high requirements to manufacturing accuracy and high
manufacturing cost. Use and maintenance require a certain professional knowledge and
a higher level of skill.
ⅣⅣⅣⅣ. Disadvantages of Hydraulic Transmission System
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a higher level of skill.
5. Acquisition and transfer of hydraulic energy is not as convenient as that of electricity.
Due to pressure loss and other reasons, hydraulic energy should not be transmitted
over a long distance.
6. Components, accessories and working medium in the hydraulic system work in a
closed system. Failures are difficult to discover in time. Failure causes are difficult to
determine.
7. Hydraulic transmission is sensitive to pollution of hydraulic oil and easy to have
failures.
• Energy and signal transmission;
• Lubricate hydraulic components, and reduce friction and wear;
• Heat dissipation;
• Corrosion prevention;
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
1. Functions of Hydraulic Medium
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• Corrosion prevention;
• Sealing of clearance in hydraulic components to prevent dual friction;
• Transmission, separation and precipitation of non-soluble
contaminants; and
• Provide diagnosis information for component and system failure.
• One is flammable hydrocarbon hydraulic oil (mineral oil type and
synthetic hydrocarbon type);
• Another is nonflammable (or fire resistant) hydraulic fluid.
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
2. Types of Hydraulic Medium
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• Another is nonflammable (or fire resistant) hydraulic fluid.
• Nonflammable fluid includes aqueous (such as HFA, HFB and HFC)
and non-aqueous synthetic fluid((((HFD)))).
1))))Viscosity
2))))Abrasion resistance
3))))Oxidation stability and thermal stability
4))))Demulsibility and hydrolytic stability
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
3. Main Performance of Hydraulic Medium
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4))))Demulsibility and hydrolytic stability
5))))Defoaming
6))))Anti-corrosion
7)))) Shear stability
8)))) Material compatibility
9)))) Filtering property
10)))) Other performance requirements
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
3. Main Performance of Hydraulic Medium ((((Continued))))
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10)))) Other performance requirements
Other requirements include flame resistance, resistance to low temperature,
radiation resistance (radioresistant) stability, nonpoisonous and tasteless,
harmless to human body, easy processing of waste fluid and other
performance.
• HH Hydraulic Oil. HH Oil is refined mineral oil without any additives.
• HL Hydraulic Oil. HL Oil is made from neutral base oil with high refined depth,
and antioxidant and anti-rust . It is anti-corrosive and anti-oxidative type.
• HM Hydraulic Oil. HM Oil is developed from HL anti-corrosive and anti-oxidative
oil.
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
4. Classification and Features of Hydraulic Oil of Mineral Oil Type
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oil.
• HR Hydraulic Oil. HR Oil is HL Oil added with viscosity index additive, which
makes oil viscosity decrease with temperature change.
• HG Hydraulic Oil. HG Oil is HM Oil added with anti-sticking agent (oiliness
solvent or antifriction agent)
• HV and HS Oil. HV and HS Oil are both low-temperature hydraulic oil used over
wide range of temperature variation according to ISO Standard. HV Oil is mainly
used in cold area. HS Oil is mainly used in freezing area.
●●●● Key Points of Reasonable Use
1))))Identify variety and mark of oil;
2))))Hydraulic system should be thoroughly cleaned before
liquid filling;
3))))New oil must be filtered before use;
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
5. Reasonable Use and Maintenance of Hydraulic Medium
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3))))New oil must be filtered before use;
4))))Oil cannot be mixed optionally;
5))))Pollution should be strictly controlled to prevent moisture,
air and solid impurities from entering hydraulic system.
●●●● Monitoring of hydraulic oil of mineral oil type
Due to mechanical, chemical and physical effect, additive in oil will be
gradually consumed during use and oil will decay. Its performance will
gradually deteriorate, which is characterized by:
1))))Changes of oil state, such as odor, color and appearance;
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
5. Reasonable Use and Maintenance of Hydraulic Medium
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1))))Changes of oil state, such as odor, color and appearance;
2))))Point of flammability decreases. other oil may be mixed;
3))))Mechanical impurities increase;
4))))Viscosity changes;;;;
5))))Acid value increases;
6))))Demulsibility becomes bad; and
7))))Defoaming becomes bad.
●●●● Replacing of hydraulic oil of mineral oil type
• For some main performance parameters of oil should be monitored periodically
and frequently. When deterioration reaches a certain degree, oil must be
replaced. At present, there are generally 3 methods to determine the oil
replacing period.
1) Specify fixed oil replacing period
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
5. Reasonable Use and Maintenance of Hydraulic Medium
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1) Specify fixed oil replacing period
Specify fixed oil replacing period according to equipment, condition and type of
oil and oil injection quantity, such as half a year, one year or operation of 1000
to 2000h;
2))))Determine whether to replace oil according to experience and observation of oil
sample; and
3))))Specify oil drainage index. Determine whether to replace oil according to test
result of oil sample;
●●●● Pollution of hydraulic oil is mainly caused by the following reasons.
1))))If sand, scraps, abrasive materials, welding slag, rust slice, dust and other dirt in
pipelines of hydraulic system and hydraulic components are not removed in
washing before use, these dirt will enter hydraulic oil when hydraulic system
works.
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
6. Pollution and Protection of Hydraulic Oil
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2))))External dust and sand, and oil lead flowing back into the tank pass the
repeatedly stretching piston rod during operation of hydraulic system and enter
hydraulic oil. In addition, dust, cotton lint and other things may enter hydraulic oil
during maintenance due to carelessness.
3))))Hydraulic system itself also constantly produces dirt, which will directly enter
hydraulic oil, such as wear particles of metal and seal materials, particles
dropping form filter materials, jelly generated due to oxidative deterioration of
fiber and oil caused by oil temperature increase, etc.
●●●● Harms of oil pollution
Serious hydraulic oil pollution will directly influence work performance of
hydraulic system, cause frequent failure of hydraulic system , and shorten
service life of hydraulic components. Main reason causing these risks are
particles in dirt. For hydraulic components, if these solid particles enter
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
6. Pollution and Protection of Hydraulic Oil
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particles in dirt. For hydraulic components, if these solid particles enter
components, wear of sliding parts of components will be intensified, orifice and
damping hole in hydraulic components may be blocked, or spool will be stuck,
causing hydraulic system failure. Water and air mixing will reduce lubrication
capacity of hydraulic oil reduction, accelerate oxidative deterioration, cause
corrosion, accelerate corrosion of hydraulic components, and make hydraulic
system vibrate or craw.
●●●● Pollution prevention measures
1))))Keep hydraulic oil clean before use;
2))))Keep hydraulic system clean after assembling and before operation;
3))))Keep hydraulic oil clean during operation;
ⅤⅤⅤⅤ. Hydraulic Transmission Medium
6. Pollution and Protection of Hydraulic Oil
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3))))Keep hydraulic oil clean during operation;
4))))Use appropriate oil filter;
5))))Regularly replace hydraulic oil; and
6))))Control working temperature of hydraulic oil.
Hydraulic pump works on the principle of
Hydraulic power components provide power supply for the system. They are
indispensable core components of the system. Hydraulic pump is the power
component providing the system with certain flow quantity and pressure.
ⅥⅥⅥⅥ. Hydraulic Transmission Components
1. Working Principle of Hydraulic Pump
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Hydraulic pump works on the principle of
seal volume change, so it is generally
called volumetric hydraulic pump.
The operation principle is explained with
Figure and gear pump.
Figure
1))))With several seals and can periodically change space;
2))))Absolute pressure of liquid in the tank must be identical to or greater than
the atmospheric pressure, which is the external condition for volumetric
hydraulic pump to absorb oil.
3))))Have corresponding assignment mechanism to separate oil absorption
ⅥⅥⅥⅥ. Hydraulic Transmission Components
2. Features of Hydraulic Pump
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3))))Have corresponding assignment mechanism to separate oil absorption
cavity from liquid discharge cavity.
Ensure regular and continuous absorption and discharge of liquid of
hydraulic pump . Hydraulic pumps with different structure principle have
different assignment mechanism.
1))))Pressure
Working pressure, rated pressure and maximum permissible pressure.
2))))Discharge and flow
Theoretical flow, rated flow, and actual flow
ⅥⅥⅥⅥ. Hydraulic Transmission Components
3. Main Performance Parameters of Hydraulic Pump
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3))))Power and efficiency
●●●● Power loss of hydraulic pump includes volume loss and mechanical
loss.
●●●● Power of hydraulic pump: input power and output power
1))))By structure: Gear pump, vane pump, plunger pump, screw pump, etc.
①①①① Gear pump: Inner gearing gear pump and outer gearing gear pump;
②②②② Vane pump: Single acting vane pump and double acting vane pump;
③③③③ Plunger pump: Axial plunger pump, radial plunger pump and valve oil
distributing valve plunger pump;
ⅥⅥⅥⅥ. Hydraulic Transmission Components
4. Type of Hydraulic Pump
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distributing valve plunger pump;
2))))By function: Constant delivery pump and variable pump
gear pump axial plunger pump radial plunger pump
Hydraulic transmission control and regulating components are also
called control valve, valve for short. They are used to control
direction of flow and adjust pressure and flow of fluid of, in order to
satisfy start, stop, redirection, speed regulation, voltage
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
1. Concept
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satisfy start, stop, redirection, speed regulation, voltage
stabilization, unloading, pressurization, decompression and other
operational needs of actuating components.
1)))) In structure, all valves consist of valve body, valve spool (turn valve or
slide valve) and components of driven valve spool movements (such as
spring and electromagnet).
2)))) In working principle, relationship among opening size, pressure
difference between inlet and outlet of valve and flow through valve of all
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
2. Common Features
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difference between inlet and outlet of valve and flow through valve of all
valves comforts to orifice flow formula, but different valves have
different control parameters.
●●●● Performance Parameters
①①①① Nominal pressure Maximum working pressure allowed by long-term reliable
work of hydraulic control valve , which is limited by intensity of valve. Actual
permissible maximum working pressure is also related to other factors, such
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
3. Performance Parameters and Basic Requirements of Hydraulic Control Valve
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as reversing reliability of reversing valve and pressure regulating scope of
pressure valve.
②②②② Nominal diameter Unit of nominal diameter of hydraulic control valve is mm. A
certain nominal diameter represents a certain of flow capacity, which is
permissible maximum flow (nominal flow). It should be pointed out that, valves
with the same nominal diameter may have different nominal flow because of
their different functions.
●●●● Performance requirements
a. High action sensitivity. Reliable to use. Small impact and vibration during
operation. Low noise.
b. When valve port is closed, sealing should be good. When valve port is opened,
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
3. Performance Parameters and Basic Requirements of Hydraulic Control Valve
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direction valve should have small fluid flow pressure loss, direction valve
should have good core stability.
c. Controlled parameters (pressure or flow) should have high precision and
small fluctuation when influenced by outside interference.
d. Compact structure. Convenient to install, debug and maintain. High
universality.
There are many varieties of control valves used in hydraulic transmission, which can
be classified by characteristics. It is the most common to classify by purpose of
control valves.
((((1))))Directional control valve (such as one-way valve and reversing valve);
((((2))))Pressure control valve (such as overflow valve, pressure reducing valve and
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
4. Classification of Hydraulic Control Valve
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((((2))))Pressure control valve (such as overflow valve, pressure reducing valve and
sequence valve);
((((3))))Flow control valve((((such as throttling valve, flow speed control valve and flow
distributing and collecting valve );
They can also be classified by structure, operation mode, connection mode, control
mode, adjustability of output parameters, etc. Different combination valves can be
composed according to needs.
• Concept::::Valve used to control fluid flow pressure in the hydraulic system
or control.
• Common Points::::Work in the principle of balanced liquid pressure and
spring force on valve core.
• Classification::::
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
5. Pressure Control Valve
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• Classification::::
Overflow valve----safety valve and constant pressure valve;
Pressure reducing valve----fixed pressure reducing valve, fixed
differential reducing valve and proportional pressure reducing valve;
Sequence valve---- sequence valve, unloading valve, back pressure
valve, balanced valve, hydraulic switch, etc.
●●●● Main purpose of overflow valve is pressure leveling (constant pressure valve) or
security protection (safety valve) of hydraulic system.
Almost all the hydraulic systems need to use it. Its performance has very big effect on
normal operation of the whole hydraulic system.
●●●● System figure illustrates the role of overflow valve. Overflow Valve 2 in the left figure
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
1)))) Overflow valve
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●●●● System figure illustrates the role of overflow valve. Overflow Valve 2 in the left figure
is constant pressure valve. Overflow Valve 2 in the right figure is safety valve.
constant pressure valve
safety valve
●●●● Structure type: can be divided into directly
operated type and pilot operated type by form
of structure and basic action mode.
①①①① Directly operated overflow valve((((see figure))))
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
1)))) Overflow valve((((Continued))))
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Directly operated overflow valve controls on-off
movement with pressure oil in the system directly
acting on valve core which is balanced with spring
force.
Limited by structure and control precision, directly
operated overflow valve is commonly used in little
traffic system with low pressure (less than 2.5 MPa).
Function Symbol Map
Figure of Low-pressure Directly Operated Overflow Valve
1-nut 2-pressure adjusting spring 3-top cover 4-valve core 5-valve body
②②②② Pilot operated overflow valve ((((see figure
for operating principle))))
● Consist of main valve and pilot valve;
●●●● Damping hole has small diameter (0.6-1.2);
Easy to block. Will not operate normally.
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
1) Overflow valve((((Continued))))
Remote Control
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Easy to block. Will not operate normally.
● Advantages in performance (pressure
adjusting range, on-off characteristic,
dynamic performance, remote control, etc.).
Suitable for system with high pressure and
big flow.
Function Symbol Map
Principle Demo
Pilot Overflow Valve
1-spring of main valve 2-main valve core 3-damper hole
4-valve core of pilot valve 5-sping of pilot valve
Pressure reducing valve is a pressure control valve
which makes outlet pressure (secondary pressure)
below inlet pressure (primary pressure). Its function
is to provide two or several different pressure
output with one oil source.
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
2))))Pressure reducing valve
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output with one oil source.
In addition, when oil pressure is unstable, a stable
low pressure can be obtained by putting a pressure
reducing valve in the return circuit.
It can be divided into fixed pressure reducing valve,
fixed differential reducing valve and proportional
pressure reducing valve by pressure controlled by
pressure reducing valve.Function Symbol Map
Pressure Reducing Valve
1-main valve core 2-damper hole 3-vavle core of pilot valve V-flow speed of valve port
L-outside leakage port
As in the picture above, working principle of fixed pressure reducing valve can be considered according to
that of pilot operated overflow valve .
Compare pilot operated pressure reducing value and pilot operated overflow valve. They have the
following differences.
a. Pressure reducing valve keeps outlet pressure basically unchanged, and overflow valve keeps inlet
pressure basically unchanged.
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
2) Pressure reducing valve
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b. When not working, inlet opening and outlet opening of pressure reducing valve are connected. Inlet
opening and outlet opening of overflow are not connected.
c. To ensure pressure setting value of outlet of pressure reducing valve is constant, its spring cavity of
pilot valve needs to be connected to external oil tank separately through drain port. Outlet of overflow
valve is connected to oil tank, so its spring cavity and oil leakage of pilot valve can be connected to
outlet through pass on the valve. It doesn’t need to be connected to external oil tank separately.
★★★★ Other types of pressure reducing valves will not be described.
●●●● Sequence valve is a pressure valve which allows
actuating components to act successively with
pressure. See figure for working principle.
●●●● Sequence valve includes directly operated type
and pilot operated type. The former is generally
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
3))))Sequence valveRemote Control
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and pilot operated type. The former is generally
used in low pressure system. The latter is used in
middle or high pressure system.
●●●● Sequence valve and overflow valve have similar
structure. Compare pilot operated sequence valve
and pilot operated overflow valve. They have the
following differences.
Fu
nc
tion
Sym
bo
l M
ap
directly operated external control sequence valve
pilot operated sequence valve
Pilot Sequence Valve
①①①① Inlet pressure of overflow valve is basically unchanged
under through-flow condition. Inlet pressure of
sequence valve is determined by outlet pressure under
through-flow condition. If outlet pressure p2 is much
lower than inlet pressure p1, p1 will be basically
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
3))))Sequence valveRemote Control
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unchanged. When p2 increases to a certain degree, p1
will also increase. p1 = p2 + ∆ p. ∆ p is pressure loss
on sequence valve.
②②②② Overflow valve has internal leakage and sequence
valve needs to separately draw out leakage path,
which is external leakage.
③③③③ Outlet of overflow valve has to return to the oil tank.
Outlet of sequence valve can be connected to load.
Fu
nctio
n S
ym
bo
l Mapdirectly operated external
control sequence valve
pilot operated
sequence valve
Pilot Sequence Valve
Pressure switch is a electrohydraulic control
component converting oil pressure signal into
electrical signal. When oil pressure reaches setting
pressure of pressure switch, electrical signal will
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
4) Pressure switch((((hydraulic switch))))
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pressure of pressure switch, electrical signal will
be sent out to control movements of electromagnet,
electromagnetic clutch, relay and other
components, so as to realize sequential actions of
oil-way pressure relief, reversing and actuating
components, or close electromotor to stop
operation of system for safe protection, etc.
1—Plunger 2—Lever 3—Spring 4—Switch
Structure Chart
Concept: Function of directional control valve is to control flow direction of fluid. It
realizes connection or disconnection of pathways with relative motion between valve
core and valve body, to meet requirements of the system.
Type: Directional control valve includes one-way valve and reversing valve.
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
6. Directional control valve
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One-wayReversing Valve((((2-position
figure))))
Rig
ht p
ositio
n o
f thre
e-p
ositio
n
fou
r-join
t rev
ers
ing
valv
e
Left p
ositio
n o
f thre
e-p
ositio
n
fou
r-join
t rev
ers
ing
valv
e
●●●● Classification of one-way valve
①①①① By function: Common one-way valve and hydraulic controlled one-way valve.
②②②② By structure: Tubular (direct connection) and plate (right angle)
1))))One-way valve
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Tubular Plate
Oil Inlet P1
Oil Outlet P2
Oil Inlet P1 Oil Outlet P2
①①①① Common One-way Valve
●●●● Principle and performance: One-way valve only allows fluid flow to flow in one direction, but not reverse
flow. It can be used for outlet of hydraulic pump, to prevent system oil from flowing back; it can be used
to separate the connection between oil channels, to prevent oil from mutual interference; it also can be
used as the bypass valve to connect parallelly with sequence valve, pressure reducing valve, throttling
valve and speed control valve, so as to assemble into one-way sequence valve, one-way pressure
reducing valve, one-way throttling valve one-way speed control valve, etc.
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●●●● Structural form and
function symbol:
●●●● Opening pressure:
Generally 0.04~~~~0.1MPa;
opening pressure of back
pressure valve is 0.2~~~~
0.6 MPa
Oil Inlet P1Oil Outlet P2
Oil Inlet P1 Oil Outlet P2
Oil Inlet P1 Oil Outlet P2
(d) Symbol
Mode
Mode
Mode
●●●● Application:
①①①①Reverse protection of hydraulic pump
On one hand, prevent system pressure from influencing normal operation of pump. On the other hand, prevent the liquid from flowing back to oil tank through pump when stopped.
②②②②Separate oil channels prevent interference
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③③③③Comprise combination valve
One-way valve can comprise one-way combination valve with other valves
④④④④Installed in outlet oil line to produce back pressure
②②②②Hydraulic Controlled One-way Valve
●●●● Principle and performance: When the hydraulic controlled port K doesn’t connect pressure oil,
its function is same to common one-way valve. When the hydraulic controlled mouth
connects oil, valve can flow freely in two ways. The figure explains the working principle.
●●●● Structure: Hydraulic controlled piston, plunger, valve, spring etc.
●●●● Application::::Hydraulic controlled one-way valve has characteristics of common one-way
valve. It can also allow forward and reverse fluid flow to go through freely under certain
conditions. Therefore, it is commonly used in pressure maintaining, locking and balanced
circuit of hydraulic system.
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P1 P2
K
Function Symbol
Structure
Chart
symbol
Change flow direction and connect or cut off oil channels by relative motion of valve core in
valve body, so as to control reversing, start or stop of actuating components.
●●●● Classification of reversing valve
①①①① By motion mode of valve core relative to valve body:
Steering valve type, sliding valve type, ball valve type, etc.
②②②② By control method:
2))))Reversing Valve
Man
ual
Rev
ers
ing
Valv
e
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Manual, engine driven, electromagnetic, hydraulic, electric hydraulic, etc;
③③③③ By working position of valve core on valve body:
Two-position valve and three-position valve
④④④④ By number of main oil port on valve body:
Two-port valve, three-port valve, four-port valve and five-port valve.
Man
ual
Rev
ers
ing
Ele
ctro
mag
netic
Rev
ers
ing
Valv
e
●●●●Control mode symbols of commonly used sliding
reversing valve
Electric SpringManualEngine Drive (Roller
Type)
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HydraulicHydraulic Pilot
ControlElectromagnetic-Hydraulic Pilot
Control
●●●●Working principle of sliding reversing valve
Valve CoreValve Body
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Position of Valve Core Valve Port State Piston State
Middle Port A and Port B don’t connect oil Stop
Left P A Right
Right P B Left
Big Box Valve bodySmall Box
Station
Crossover point of arrow line in the small box or┴ symbol and bounding
Oil port
Oil channels connected ((((not always flow direction))))
●●●●Station and pathway symbols of main structure of reversing valve((((see figure))))
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always flow direction))))
┴ Oil channels disconnected
Functional chart of three-position four-port
reversing valve
Head of symbol
Normal position((((valve core without force);
A, B Oil ports connected to the oil tank;;;;
P, O Oil inlet and return opening
●●●● Principle and type symbols of main structure of reversing valve
Name Structure and Principle Chart Symbol
Two-position
two-port
A
P
A B
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Two-position
three-port
Two-position
four-port
A B
P O
A
P
B
Name Structure and Principle Chart Symbol
Two-position five-
port O1 O2
A B
P
A B
●●●● Principle and type symbols of main structure of reversing valve ((((continued))))
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Three-position
four-port
Three-position five-
port
P O
A B
PO1 O2
A B
●●●● The most commonly used six median functions of
three-position reversing valve
Function
Model
Median Symbols State, Features and Application of Median
Symbols
O
Port P, A, B and O are all closed;;;; Hydraulic
cylinder is locked. Hydraulic pump doesn’t
unload.
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H
Port P, A, B and O are Hydraulic pump ; Piston
of hydraulic cylinder is floating. Hydraulic
pump unloads.
Y
Port P is closed. Port A, B and O are
connected. Piston of hydraulic cylinder is
floating. Hydraulic pump doesn’t unload.
Function
ModelMedian Symbols
State, Features and Application of Median
Symbols
P
Port P, A and B are connected. Port O is
closed. Pump and hydraulic cylinder are
connected, which can comprise differential
motion and connect inlet.
●●●● The most commonly used six median functions of three-
position reversing valve((((continued))))
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motion and connect inlet.
M
Port P and Port O are connected. Port A and
Port B are closed. Piston of hydraulic cylinder
is locked. Hydraulic pump unloads.
K
Port P, A and B are connected. Port O is
closed. Piston of is locked. Hydraulic pump
unloads.
●●●● Several Commonly Used Reversing Valves
Armature
Coil
①①①① Electromagnetic reversing valve
Valve Body
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Valve Core
Function Symbol
Three-position four-port electromagnetic reversing valve
Two-position four-port electromagnetic reversing valve
★★★★ Performance of electromagnetic reversing valve
◆◆◆◆ AC power type: Convenient to use. Big starting force. Big reversing
impact. Noisy. Low frequency (about 30 times/min). Coil is easy to burn
out when valve is locked or voltage is low.
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◆◆◆◆ DC power type: Small reversing impact. High tolerance level of
reversing frequency. Due to constant current, coil is not easy to burn out.
Working reliability is high, but structure is complicated.
②②②② Hydraulic reversing valve
Hydraulic controlled pressure
port
Hydraulic controlled pressure port
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Hydraulic three-position four-port reversing valve
Function Symbol
★★★★ Performance of hydraulic reversing valve
Hydraulic reversing valve changes position of valve core with oil pressure. It has
big starting force. When flow of hydraulic controlled oil is big, reversing impact is
big. To control movement speed of valve core and reduce impact, one-way
throttling device (called damper regulator) is usually installed in front of
hydraulic controlled pressure port.
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Damper Regulator
③③③③ Electro-hydraulic reversing valve
Pilot valve
((((electromagnetic valve))))
Main valve
((((electromagnetic
valve))))
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Control oil channel
Main oil channel
★★★★ Principle drawing of electro-hydraulic reversing valve
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channel
Simplified Function Symbol
★★★★ Performance of electro-hydraulic reversing
valve
Electro-hydraulic reversing valve is combination of electromagnetic reversing
valve (pilot valve) and hydraulic reversing valve (main valve). Therefore, it can
control the high-power main valve with small-power electromagnet. Oil source and
return oil of pilot electromagnetic reversing valve can be established separately. It
can also be shared with main oil channel.
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④④④④ Engine driven reversing valve((((motion valve))))
Oil Inlet
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Lift type, two-port, normally closed
Lift type, two-port, normally opened
Roller type, three-port
Oil OutletBack-moving SpringValve Core
Roller Push Rod
Purpose of engine driven reversing valve is to move valve core with cam-action
strokedog installed on actuating mechanism, in order to control on-off of oil
channels and control stroke.
Appropriate reversing speed is obtained and reversing impact is reduced by
★★★★ Performance of electro-hydraulic engine driven
reversing valve
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changing appearance of cam.
⑤⑤⑤⑤ Manual reversing valve
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Self-restoring Type
Mechanical Positioning Type
Manual reversing valve is convenient to use. It is applicable to
occasion with small flow and longer interval.
★★★★ Performance of manual reversing valve
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◆◆◆◆ Student practice: draw out symbols of the following reversing valves
1. Two-position two-port electromagnetic reversing valve (normally closed);
2. Three-position four-port manual reversing valve((((Median function::::H);
3. Three-position four-port hydraulic((((with damper)))) reversing valve
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3. Three-position four-port hydraulic with damper reversing valve((((Median function::::P););););
Figure 3Figure 2Figure 1
●●●● Overview: Movement speed of actuating components in the hydraulic
system is determined by oil flow entering actuating components. Flow
control valve is a hydraulic valve controlling the flow by changing flow
area of port (local resistance of throttling port) or length of channels.
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
7. Flow Control Valve
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area of port (local resistance of throttling port) or length of channels.
●●●● Classification: Common throttling valve, pressure compensation speed control valve,
overflow throttling valve, temperature compensation speed control valve, flow
distributing and collecting valve, etc. Functional chart of all kinds of valves is shown
as below. Working principle of each flow control valve will not be described. See
ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)
7. Flow Control Valve (Continued)
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teaching material.
• Function::::Convert pressure of liquid into mechanical energy. Make linear,
swinging and rotating with motion drive working mechanism.
• Type: Hydraulic cylinder and motor.
1. Hydraulic Cylinder
ⅧⅧⅧⅧ. Hydraulic Actuating Components
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1))))Type of Hydraulic Cylinder
Hydraulic cylinder has the following types by structure and function.
●●●● Single-acting hydraulic cylinder ●●●● Double-acting hydraulic cylinder
●●●● Swinging hydraulic cylinder ●●●● Combination hydraulic cylinder
2))))Single-rod Piston Cylinder
The piston only has piston rod at one end.
There are cylinder fixed type and piston
rod fixed type. Single-rod piston cylinder
is a commonly used oil cylinder type.
2. Motor1))))Features of Motor
Sketch Map of Single-rod Piston Cylinder
ⅧⅧⅧⅧ. Hydraulic Actuating Components
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1))))Features of Motor
Hydraulic motor is a device converting fluid pressure into mechanical energy. In
principle, hydraulic pump can be used as hydraulic motor, and hydraulic motor
can be also used as hydraulic pump. In fact the same type of hydraulic pump
and hydraulic motor have similar structure, but by the two have different work
situation, which makes the two different in structure. Main differences are as
follows:
• Hydraulic motor generally needs forward and reversing rotating, so it should
have symmetry in the inside structure. Hydraulic pump usually rotates in single
direction. It doesn’t have this requirement.
• In order to reduce oil absorption resistance and radial force, inlet port of
hydraulic pump is generally larger than outlet port. Pressure in low-pressure
ⅧⅧⅧⅧ. Hydraulic Actuating Components
1))))Features of Motor
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hydraulic pump is generally larger than outlet port. Pressure in low-pressure
cavity of hydraulic motor is slightly above atmospheric pressure, so it doesn’t
have the above requirement.
• Hydraulic motor is required to operate normally at a wide speed range. Therefore,
we should adopt hydraulic bearing or hydrostatic bearing. Because when motor
is at low speed, if hydraulic bearing is used, it is not easy to formed lubrication
film.
• Vane pump rotates at high speed with blades to generate centrifugal force, so that
blades always adhere to the inner surface of stator to seal the oil and form working
volume. If it is used as motor, spring must be installed on root of blades of hydraulic
motor, in order to ensure that blades always adhere to the inner surface of stator and
motor can normally start.
• Hydraulic pump should have self-priming capacity in structure , and hydraulic motor
ⅧⅧⅧⅧ. Hydraulic Actuating Components
1))))Features of Motor (Continued)
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• Hydraulic pump should have self-priming capacity in structure , and hydraulic motor
doesn’t have this requirement.
• Hydraulic motor must have large starting torque. Starting torque is the torque that
can be output by motor axle when motor starts from static state. The torque is
generally larger than that under operation condition under the same operating
differential pressure. Therefore, in order to make the starting torque near to torque
under operation condition, it is required that motor torque has small pulsation and
small internal friction.
Hydraulic motor can also be divided into gear type, vane type, piston
type and other types by structure types.
ⅧⅧⅧⅧ. Hydraulic Actuating Components
2))))Type of Motor
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Structure of axial piston motor is basically
same to that of axial piston pump, so its
varieties are same to those of axial piston
pump. It can be also divided into straight axial
piston motor and bent axial piston motor. See
ⅧⅧⅧⅧ. Hydraulic Actuating Components
3))))Axial Piston Motor
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Working Principle of Swash-plate Axial Piston Motor
piston motor and bent axial piston motor. See
figure for working principle (see textbook for
content).
F1=p*A*tanγ
T1=F*r=F*R*conφ=p*A*R*tanγ*conφ
T=ηm*∆p*V/2π
Torque of cylinder generated by piston
Total torque actually output by motor
Torque force of cylinder generated by piston
1Basic Knowledge of Hydraulic Transmission
1
Contents of Training Courseware
19/05/20152015/5/19
Hydraulic System Introduction of LG Loader
2
1
Working Device Hydraulic System
Steering Hydraulic
1
2
Part 2 LG Hydraulic
System Introduction
19/05/20152015/5/19
Steering Hydraulic
System 2
3 Case Analysis
ⅠⅠⅠⅠ. Working Hydraulic System
1. Type
Loader working device hydraulic system has two types by control method of
multiple unit valve .
1) Manual (Flexible Axle) Control Working Hydraulic System;
918, 933, 936, 40F, 952, 953, 956 and other types of our company
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use this type.
2) Hydraulic Pilot Control Working Hydraulic System;
Exported 918, 936, 938, 958, 959, 968, 969, 979 and other types of our
company use this type.
2. Principle of Working Hydraulic System
Manual manipulation of flexible axel makes swing
arm slide valve and rotating bucket slide valve of
multiple unit valve do reciprocating movement,
connects ports of oil inlet and slide valve of multiple
unit valve, changes flow direction of hydraulic oil,
Working and Steering Hydraulic System Demo
ⅠⅠⅠⅠ. Working Hydraulic System
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unit valve, changes flow direction of hydraulic oil,
and realizes different actions of working device.
①①①①When flexible axel and rotating bucket reversing
valve of multiple unit valve are in the middle position,
flexible axel and bucket remain in the original
position. At this time, hydraulic oil in working oil
pump directly returns to oil tank through middle
channel of multiple unit valve.
Principle Drawing of Working Hydraulic System
②②②② Swing arm can lift, descent or float by controlling reversing slide valve on
swing arm.
③③③③ Bucket can turn forward and backward back controlling rotating bucket
ⅠⅠⅠⅠ. Working Hydraulic System
2. Principle of Working Hydraulic System (Continued)
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reversing valve. Double-acting safety valves are installed on oil channels in
front and back cavity of rotating bucket oil cylinder to protect from
overloading of big and small cavity of rotating bucket cylinder caused by
rotating bucket link mechanism.
3. Composition of Working Hydraulic System
●●●● Gear pump((((working
pump))))
●●●● Multiple unit valve
●●●● Oil cylinder (swing arm cylinder and rotating
ⅠⅠⅠⅠ. Working Hydraulic System
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cylinder and rotating
bucket cylinder))))
●●●● Oil tank((((shared with
steering system))))
●●●● Pipe, filter and other accessories
Describe the components according to system principle drawing
System Principle Drawing
Gear Pump((((Working Pump))))
●●●● Main parameters((((take LG953 and CBGj3166 for example))))
1))))Rated pressure ((((18MPa))))
2))))Rated rotate speed((((2200r/min))))
3))))Displacement((((166ml/r))))
★★★★ Liquid volume discharged per round of hydraulic pump
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Liquid volume discharged per round of hydraulic pump
4))))Flow((((265 l/min)
★★★★ Flow= Displacement××××Rotate speed
★★★★ Module of transfer gear with 42 gear teeth, working pump spindle
with 42 gear teeth and steering pump gear with 48 gear teeth are all 4.
●●●● Working Principle of Gear Pump
Gear pump is a hydraulic pump widely used in hydraulic system. It is generally made into quantitative
pump. By structure, gear pump can be divided into outer gearing gear pump and inner gearing gear pump.
Outer gearing gear pump is most widely used. working principle of outer gearing gear pump will be
explained with outer gearing gear pump.
It generally has separate three-piece structure. Three-piece
means front and back pump cover and pump body. A pair of gear
are installed in the pump body. They have the same number of
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are installed in the pump body. They have the same number of
gear teeth and gear into each other. Their width are close to that
of pump body. This pair of gear form a seal chamber with covers
at two ends and pump body. Tooth point of gear and gearing line
divide the seal chamber into two parts, which are oil absorption
cavity and oil pressure chamber. Two gears are respectively
fixed on driving axle and driven axle supported by needle roller
bearing with keys. Driving axle is driven by power machine.
Figure of Outer Gearing Gear
Demo Map
When driving gear of the pump rotates according to direction of arrow as shown in the figure,
teeth on the right of gear (oil absorption cavity) will throw out of gear and gear teeth will exit
tooth space, so that sealing volume will increase and partial vacuum will be formed. Under
the action of external atmospheres, oil in the oil tank will enter tooth space through oil
absorption channels and oil absorption cavity. With gear rotating, inhaled tooth between oil
was brought to the other side, into the pressure oil chamber. Then rotation of gear, oil
absorbed into tooth space will be brought to the other side and enter oil pressure cavity. At
this time, gear teeth are engaged each other, so that sealing volume will decrease and some
●●●● Working Principle of Gear Pump (Continued)
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this time, gear teeth are engaged each other, so that sealing volume will decrease and some
oil in the gear will be squeezed out, which forms oil pressure process of gear pump. During
gear engagement, tooth contact line will separate oil absorption cavity and oil pressure
cavity for oil distributing. When driving gear of gear pump is driven by power machine, the
gear meshing side, withdraw because sealing capacity greaten is constantly from tank in oil
absorption, gear meshing side, the side of teeth throwing out of gear will continually absorb
oil from oil tank because sealing volume increases. The side with gear engagement will
continually discharge oil because sealing volume decreases. This is the working principle of
gear pump.
●●●● Common fault analysis of loader gear pumpNo. Failure Reason Troubleshooting Method
1Hydraulic oil decreases. Transmission oil increases.
Oil seal is brokenTest pressure. Change working pump (or steering pump)
2Hydraulic oil increases. Transmission oil decreases.
Oil seal is brokenTest pressure. Change working pump (or steering pump)
3Oil leakage on joint surface of pump body
O ring or bolt is loose Change O ring or fasten bolt
4 Oil leakage of pump body Pump body cracks Test pressure. Change pump
Overwear of spline shaft Change spline shaft or pump
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5 Abnormal sound of pump
Overwear of spline shaft Change spline shaft or pump
Overwear of side plate Change side plate or pump
Poor size of spline shaft. Push the shaft.
Change spline shaft or pump
Bearing is brokenChange bearing or pump
6Insufficient flow of pump causes weak and slow lifting
Internal leakage caused by overwear of gear or side plate
Change pump (or broken parts)
Multiple Unit Valve
1))))Type
●●●● Double-joint multiple unit valve-used in loader with common
functions
●●●● Multiple unit valve-used in loader of multifunctional working device
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Multiple Unit Valve
2)))) Composition and Functions
●●●● Double-joint valve: Consisting of rotating bucket reversing slide valve, swing
arm reversing slide valve, safety valve, overload supplement valve, valve body,
etc.
●●●● Rotating bucket reversing slide valve is three-position valve. It controls middle
standing, front tilting and back tilting of bucket.
●●●● Swing arm reversing slide valve is four-position valve. It controls middle
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standing, lifting, dropping and floating of swing arm.
●●●● Reversing action of slide valve is realized by manual control of flexible axle (or
pilot oil pressure). Rotating bucket slide valve returns to the middle position with
spring. Swing arm slide valve returns to the middle position by manual control
and ball locking.
Piping Map of Working Device Hydraulic System
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Profile Map of Double-joint Multiple Unit Valve((((DF32))))
Action Demo
1 Swing arm slide valve
Tu
rn b
elo
w
Se
al o
ff
su
pra
ve
rge
nc
e
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2 Turning slide valve
3 Turn cylinder small cavityoverload valve
4 Turn cylinder big cavity overload valve
5 Safety valve
6 Valve body
Liftin
g
Se
al o
ff
De
sc
en
d
Flo
at
Safety Valve
1))))Safety valve of multiple unit reversing valve is between oil inlet cavity and returning
cavity. When system pressure is greater than setting pressure, safety valve will open
and overflow, so that working pressure of the system will be within the scope limited
by the setting pressure for safeguard of system. See structure chart for working
principle of safety valve.
2))))Pressure control: realized by adjusting pressure adjusting screw to change spring
preload.
3))))Setting pressure of safety valve
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3))))Setting pressure of safety valve
of different types of LG Loader
★★★★ LG956 and LG953 Loader
System setting pressure is 18MPa;
★★★★ LG952 Loader
System setting pressure is 16MPa;;;;
★★★★ LG933 and LG936 Loader
System setting pressure is 16MPa.Structure Chart of Safety Valve
Demo Map of Safety Valve
Overload Supplemental Valve
Overload supplemental valve (also called safety valve) is the combination of pilot type
overflow valve and on-way valve. It is installed on multiple unit reversing valve through
bolt. Two ports are respectively connected to oil channels in big and small cavity of turn
cylinder in multiple unit reversing valve . The other two ports are connected to oil-
returning circuit.
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Profile Map of Overload Supplemental Valve
Overload Supplemental Valve (Continued)
●●●● When turn reversing valve is in the middle position, front and back
cavity of turn cylinder are closed. At this time, if the bucket is affected by
external impact load, sharp rise of partial pressure can be effectively
1))))Functions of Overload Supplemental Valve
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external impact load, sharp rise of partial pressure can be effectively
prevented.
●●●● When swing arm lifts or drops, oil drainage and oil supplementation will be automatically
completed. If swing arm lifts to a certain position, piston rod of turn cylinder will be pulled
out, which will cause pressure rise in front cavity of turn oil cylinder. When the pressure
increases to a certain degree, hydraulic oil cylinder or hydraulic pipelines may be
destroyed. Due to double-acting safety valve, oil trapped in front cavity of hydraulic oil
cylinder can return to hydraulic oil tank through safety valve. When volume of front cavity
of oil cylinder reduces, volume of back cavity will increase, forming partial vacuum.
Supplemental valve of double-acting safety valve will be opened to supplement hydraulic
Overload Supplemental Valve
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oil for back cavity of turn oil cylinder and eliminate partial vacuum.
●●●● During unloading of loader, the bucket can quickly turn down by its weight. When the
bucket quickly turns down, after gravity center of the bucket goes over lower hinge point,
the bucket will turn faster by gravity, but movement speed of turn oil cylinder will be limited
by insufficient oil supple of oil pump. Because supplemental valve of double-acting safety
valve supplements oil timely for front cavity of turn oil cylinder, bucket can quickly turn
down, hit stop block, and realize unloading.
• Setting pressure of overload valve in big cavity of turn cylinder of LG953, LG956
and LG958 Loader is 21MPa. Setting pressure of small cavity is 12MPa.
• Setting pressure of overload valve in big cavity of turn cylinder of LG952, LG936
2))))Setting Pressure of Overload Supplemental Valve
Overload Supplemental Valve
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and LG933 Loader is 19 MPa. Setting pressure of small cavity is 12MPa.
• Setting pressure of overload valve in big cavity of turn cylinder of LG918 Loader
is 20 MPa. Setting pressure of small cavity is 12.5MPa.
Basic Failure and Troubleshooting of Multiple Unit Valve (DF)
No. Reason Failure Troubleshooting Method
1
Insufficient working pressure
Pressure setting of safety valve is low
Adjust pressure of safety valve
Slide valve of safety valve is locked Take apart, clean and reassemble
Pressure adjusting spring is broken
Change new spring
Pressure loss in system pipelines is too large
Change pipelines or adjust pressure of overflow valve within permissible pressure scope
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permissible pressure scope
2Insufficient working flow
Oil supply of system is not enough Check oil source
Port opening is not enough Adjust control mechanism
Oil temperature is too high. Viscosity drops
Take measures to reduce oil temperature
Improper selection of oil Change oil
Fit clearance between slide valve and valve body is too big
Change slide valve or assembly according to proper clearance
Basic Failure and Troubleshooting of Multiple Unit Valve (DF) (Continued)
No. Reason Failure Troubleshooting Method
3 Reset failureRestoring spring is broken or deforms Change spring or assembly
Restoring parts are not in the same axle, pulled, etc.
Change broken parts or assembly
4 Outside leakage
Seal ring is broken Change to new parts
Oil temperature is too high. Viscosity drops
Take measures to reduce oil temperature
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4 Outside leakagedrops temperature
Flange face installed on port is not well sealed.
Check fastening and sealing of corresponding parts
Fastening screws on joint surfaces are blocked or cap of pressure adjusting screw is loose
Fasten corresponding parts
5 Big deflection of swing arm
Clearance between valve body and valve rod of multiple unit valve increases
Change valve rod or assembly
Basic Failure and Troubleshooting of Multiple Unit Valve (DF) (Continued)
No. Reason Reason Troubleshooting Method
6 Bucket dropsInner leakage of overload supplemental valve in big cavity of turn cylinder (dirt blocked and broken)
Disassemble, clean, reassemble or replace
Wear and clearance between valve body and valve rod of multiple unit valve increases
Change valve rod or assembly
7 Bucket is put away Inner leakage of overload supplemental Change supplemental valve.
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7 Bucket is put away Inner leakage of overload supplemental valve in small cavity of turn cylinder (dirt blocked and broken)
Change supplemental valve. Low pressure
8
Front tire cannot support
Setting pressure of overload valve in small cavity of rotating bucketis low
Increase pressure of overload valve in small cavity
Large amount of leakage in small cavity of rotating bucket
Change slide valve according to proper clearance
Oil Cylinder• Type::::Hydraulic cylinder used in loader is single-rod piston double-acting oil cylinder.
• Classification: Swing arm oil cylinder, turn oil cylinder and steering oil cylinder.
• Composition::::Piston double-acting hydro-cylinder generally consists of oil cylinder
body, piston, piston rod guide sleeve, etc.
• Comments::::In order to analyze the problem, oil cylinder is usually divided into cavity
with rod (or small cavity, the side with piston rod) and cavity without rod (or big cavity).
Pressure oil enters left cavity of hydraulic cylinder from Port A and pushes piston to the
right. Hydraulic oil in the right cavity is discharged through Port B.
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right. Hydraulic oil in the right cavity is discharged through Port B.
Structure of Oil Cylinder1. Back cylinder cover2. Stop collar 3. Lantern ring 4. Snap ring5. Piston 6. O Ring 7. Back-up ring 8. Stop dog 9. Ax seal ring10. Oil cylinder body11. Port stand 12. Guide sleeve 13. Cylinder end 14. Dust ring 15. Piton rod16. 16. Screw Buffer Plunger
Hydraulic Pilot Control Working Hydraulic System
Working hydraulic system of LG918, LG933, LG936, LG956L, LG958L and other loaders, which
are export products of our company, uses pilot control working hydraulic system. main oil
channels with high pressure and big flow are controlled by pilot oil channels with low pressure
and small flow. Compared with mechanical control hydraulic system, this working hydraulic
system has the following features:
1))))Features of the System
●●●● Pilot control is light, flexible and efficient. Finger control can be realized.
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●●●● Pilot control is light, flexible and efficient. Finger control can be realized.
●●●● By pressure-relief type proportional pilot valve control, stroke of valve rod of main valve is in
proportion to control angle of pilot value handle, which means proportional pilot control to
work of main valve is realized.
●●●● Safety valve, overload valve, supplemental valve and one-way valve use insert type structure.
With good generality, it is convenient to maintain.
●●●● Pilot valve uses overall structure. With a small volume it is convenient to arrange.
●●●● When engine shuts down, drop of swing arm and forward tilting of bucket can be realized
by pressure selecting valve and pilot valve.
●●●● Pilot valve has orientation with electromagnetic iron at lifting position of swing arm and
backward tilting position of bucket. Vertical limit of lifting height of swing arm and automatic
leveling control of bucket at any position can be realized, which simplifies operating
procedures, reduces labor intensity, and avoids energy loss and pressure shock caused by
frequent movement of safety valve.
1))))Features of the System (Continued)
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frequent movement of safety valve.
2))))System Composition
Composition of pilot control working hydraulic system:
Consists of Working pump, pilot pump. Pilot valve, multiple unit valve, pressure selecting
valve, swing arm cylinder, rotating bucket cylinder, oil tank, pipelines filter and other
accessories. See principle chart of hydraulic system.
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Principe of Hydraulic Pilot Control System
Pilot Valve
Pilot valve is equipped with control rod. Rotating bucket control has
forward tilting, middle standing and backward titling positions. Swing
arm control has lifting, neutral, middle standing, dropping and floating
positions. Pilot valve has orientation with electromagnetic iron at lifting,
floating and backward titling position. See figure.
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Structure of Pilot Valve
When pulling the control rod to dropping position, pressure pin will push down pressure
lever. Measurement spring will push down measurement valve core, cut off the channel
between control cavity and oil returning chamber, connect oil inlet cavity to control oil cavity,
guide pressure oil to the end of multiple unit valve, push multiple unit valve to move, and
corresponding reversing action. Meanwhile, oil pressure of control cavity will act on lower
end of measurement valve core, and balance with the force of measurement spring. When
●●●● Working principle of pilot valve((((proportional pilot
control and automatic control of electromagnet)
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end of measurement valve core, and balance with the force of measurement spring. When
control rod remains in one position, the spring force and control cavity pressure will be fixed,
which is similar to action process of fixed pressure reducing valve. Spring force will change
with pivot angle of control rod. The bigger pivot angle is, the bigger spring force will be and
the higher control cavity pressure will be. Thrust on valve core of multiple unit valve will
increase accordingly, which means stroke of main valve core is in proportion to pivot angle
of control rod of pilot valve, so as to achieve proportional pilot control.
When control rod is pulled from dropping position to floating position, because this
position has electromagnet positioning, pilot valve will be locked. At this time, oil pressure
at control port will increase. Sequence valve in pilot valve will open. Hydraulic oil in Drain
Hole K of multiple unit valve will enter oil tank through Drain Hole 2C in pilot valve.
Supplemental valve in small cavity of swing arm oil cylinder will open. Port P, A2, B2 and T
will be connected. Swing arm floating will be realized. When pilot valve is pulled out of
●●●● Working principle of pilot valve((((proportional pilot
control and automatic control of electromagnet)
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will be connected. Swing arm floating will be realized. When pilot valve is pulled out of
floating position and loosen, restoring spring will push up pressure lever. Control rod will
return to the middle position.
When control rod of pilot valve is pulled from whole lifting or bucket collecting position,
control rod will be locked and positioned. When swing arm or bucket reaches limited lifting
height or limited bucket angle, which is close to switch action, magnetic coil will shut off
and lose its magnetism. Control rod will automatically go back to the middle position under
the action of restoring spring.
Multiple Unit Valve (D32)
• The function of multiple unit valve is changing flow direction of working oil,
realizing different movement direction of turn oil cylinder and swing arm oil
cylinder, and completing corresponding different action of working device,
by different open direction of slide valve under the action of pilot control oil.
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Multiple Unit Valve (D32 Continued)
• There are two-joint multiple unit valve and three-joint multiple unit valve.
Two-joint valve is used for common loader. Three-joint valve is used for
multifunctional work device of loader. As shown in the following profile
structure chart, two-joint multiple unit valve is hydraulic multiple unit valve
with overall structure. It is mainly consists of rotating bucket reversing valve,
swing arm reversing valve, overload valve, supplemental valve and one-way
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swing arm reversing valve, overload valve, supplemental valve and one-way
valve.
Multiple Unit Valve (D32 Continued)
• Rotating bucket reversing valve is three-position valve. It can control middle
standing, forward titling and backward titling action of bucket. Swing arm
reversing valve is four-position valve. It can control middle standing, lifting,
dropping and floating action of swing arm. Movement of slide valve relies on
action of pilot control oil. It restores by spring. Two reversing valves are
connected to oil channels by series-parallel connection. They are at a certain
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connected to oil channels by series-parallel connection. They are at a certain
position under the pressure of pilot hydraulic oil and action of spring.
●●●● Automatic control of lifting height of swing arm
When swing arm automatically controls lifting
position, work position of slide valve of
multiple unit valve is exactly the same to lifting
position of swing arm. Because control rod of
pilot valve is pulled to whole lifting position,
control rod is locked and positioned at this
time. When swing arm reaches lifting height
Multiple Unit Valve (D32 Continued)
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time. When swing arm reaches lifting height
limit, and stator fixed on swing arm is close to
switch action, magnetic coil will disconnect
and lose magnetic force. Control rod will move
to the middle position under the action of
restoring spring. Multiple unit valve will lose
control of pilot oil. Lifting of swing arm will
automatically end.
Structure of Multiple Unit Valve
●●●●Floating of swing arm
When swing arm is at floating position, work position of slide valve of multiple
unit valve is exactly the same to dropping position of swing arm. Because
control rod of pilot valve is at floating position and this position doesn’t have
electromagnet, sequence valve in pilot valve will open. Hydraulic oil in Drain
Hole K of multiple unit valve will enter oil tank through Drain Hole 2C in pilot
Multiple Unit Valve (D32 Continued)
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Hole K of multiple unit valve will enter oil tank through Drain Hole 2C in pilot
valve. Supplemental valve in small cavity of swing arm oil cylinder will open.
Port P, A2, B2 and T will be connected. At this time, piston rod of swing arm oil
cylinder will freely float under the action of external force. When control rod of
pilot valve is pulled out of floating position and returns to the middle position,
floating of swing arm will end.
●●●● Automatic leveling of bucket
When bucket is at automatic leveling position, work position of multiple unit
valve is exactly the same to backward titling position of bucket. Because
control rod of pilot valve is pulled to whole bucket collecting position, control
rod is locked and positioned at this time. When bucket reaches limited bucket
collecting angle, and stator fixed on turn oil cylinder is close to switch action,
Multiple Unit Valve (D32 Continued)
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collecting angle, and stator fixed on turn oil cylinder is close to switch action,
magnetic coil will disconnect and lose magnetic force. Control rod will move to
the middle position under the action of restoring spring. Multiple unit valve will
lose control of pilot oil. Backward titling of swing arm will automatically end.
With this function, at any unloading height, when swing arm drops to ground
shoveling position of bucket, undersurface of bucket will be parallel with
ground.
Pressure Selecting Valve
●●●● Function: Purpose of pressure selecting valve
is to provide a certain pressure of control oil to
pilot valve, and ensure swing arm on the ground
position when diesel engine shuts off.
●●●● Structure: Pressure selecting valve is installed
in pilot oil channel. Control valve of pressure
One-way valve
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Structure and Principle of
Pressure Selecting Valve
in pilot oil channel. Control valve of pressure
selecting valve mainly consists of valve body,
valve core, spring, etc. Port P1 is connected to
pilot pump. Port Pr is connected to big cavity of
swing arm oil cylinder. Port P2 is oil outlet,
which is connected to pilot valve. L is oil
returning port. See structure chart.
One-way valve
●●●● Working PrincipleDuring operation, oil in pilot pump enters Port P1, and flows to pilot valve through valve
centre hole and oil outlet P2. When pressure of oil outlet P2 is greater than 1.5 MPa, valve
core will move left. Port P1 and Port Pr mouth will stagger to close the oil in lower cavity of
swing arm oil cylinder. Port Pr is equipped with one-way valve, in order to prevent reverse
flow of oil.
When diesel engine shuts off, Port P1 doesn’t have oil supple of pilot pump. Pressure will
drop. Under the action of control spring, valve core will return to the connection position of
Port Pr and Port P2. If swing arm in at lifting condition and control rod is at the middle
position at this time , hydraulic oil in big cavity of swing arm oil cylinder will be sealed. At
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position at this time , hydraulic oil in big cavity of swing arm oil cylinder will be sealed. At
this time as long as control rod is pulled to dropping position of swing arm, under the
gravity hydraulic oil in big cavity of swing arm oil cylinder will enter pilot valve through Port
Pr and Port P2. Pilot valve controls multiple unit reversing valve, so that valve core of swing
arm is at dropping position. Swing arm can be put down. In this process, valve core of
pressure selecting valve also controls pressure from Port Pr to pilot valve of about 1.5 MPa.
If pressure of oil outlet P2 rises, valve core will move left, throttling damping will be
increased, flow of Port Pr will be reduced, and pressure of oil outlet P2 will be reduced,
which will realize pilot pressure control.
ⅡⅡⅡⅡ. Steering System
• Function: Wheel loader steering system is used to control driving direction of
loader. It can make loader run straight steadily and change driving direction
flexibly according to requirements.
• Classification: By steering method, wheel loader can be divided into deflection
wheel steering, skid steering and articulated steering.
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• Advantages of articulated steering: Work device is installed on front frame.
When the frame deflects relatively, direction of work device will be always same
to that of front frame, which can help work device to quickly aim at working
plane, reduce distance and time of work cycle, and improve working efficiency
of the loader. Therefore, articulated steering becomes the most widely used
steering method of modern loader.
Steering system has many varieties. Different types of steering system
respectively represent development level of different hydraulic technique.
At present wheel loader uses the following types of steering system.
●●●●Type of Steering System
①①①① Whole hydraulic steering system consisting of single stable valve and
open center non-reaction steering gear;
②②②② Load sensing whole hydraulic steering system consisting of priority valve
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②②②② Load sensing whole hydraulic steering system consisting of priority valve
and load sensing steering gear;
③③③③ Load sensing whole hydraulic steering system consisting of priority valve
and coaxial flow amplifying steering gear;
④④④④ Flow amplifying steering system
1. Whole Hydraulic Steering System Controlled by Solenoid Valve
1)1) Composition of System
Whole hydraulic steering system controlled by solenoid valve
mainly consists of hydraulic pump, one-way steady flow
divider valve, BZZ1 (open center non-reaction) whole hydraulic
steering gear, steering oil cylinder, pipelines, etc. See principle
chart of the system.
2)Steering Gear
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System Principle
2)Steering Gear
BZZ Whole Hydraulic Steering Gear is a cycloid
rotary valve whole hydraulic steering gear consisting of servo
valve and pin wheel gear pair. It is current widely used steering
component at home and aboard. It is flexible to operate, energy
saving, compact in structure, reliable, and convenient to install.
Manual steering can be realized after engine shuts off.
There are the following major types of
BZZ Whole Hydraulic Steering Gear.
Open center non-reaction ((((BZZ1););););
Open center reaction ((((BZZ2););););
Closed center non-reaction((((BZZ3););););
Load sensing ((((BZZ5););););
Coaxial flow-amplifying((((BZZ6););););
●●●●Type of Whole Hydraulic Steering Gear
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Coaxial flow-amplifying((((BZZ6););););
and other structural styles
Function symbols are shown in the
figure.
Type Symbol of BZZ
It is mainly consists of valve body, valve core,
valve pocket, universal driving shaft, guide
spring, pin, rotor, stator, rear cover, etc.
Working principle of steering gear
Structure of BZZ Whole Hydraulic Steering Gear
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Structure of Whole Hydraulic Steering GearMiddle position Steering position
Correspondence of valve core, valve pocket , stator and rotor
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High Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil Trap
3) Combined Valve Block
Combined valve block is a combined hydraulic component. Connected between
steering oil pump and steering gear, it forms a complete set with whole hydraulic
steering gear. It is generally installed directly on flange of valve body, and makes a
whole with steering gear.
FunctionsFunctions::::::::On one hand, ensure that steering gear and the whole steering system
works normally and smoothly under pressure rated; On the other hand, ensure that
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works normally and smoothly under pressure rated; On the other hand, ensure that
steering cylinder and connected pipelines will not be damaged during sudden
overload, and protect steering pump. So valve block is an indispensable hydraulic
component in hydraulic steering system.
Composition of Combined Valve Block::::
According to different requirements of
steering system, combined types of valve
block are different. Valve block generally
consists of one-way valve, overflow valve
(safety valve), two-way buffer overload
valve, supplementary valve, etc. (but some
valve blocks are only equipped with two-
3) Combined Valve Block
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way buffer valve and one-way valve, and
some only have overflow valve and one-way
valve). Structure of valve block is shown in
figure.
Composition of existing steering gear valve
block: one-way valve, overflow valve (safety
valve), and two-way buffer overload valve.
Structure Chart of Valve Block
Functional Chart of Valve Block
4) Single stable ValveSingle-channel stable flow divider valve (single stable valve for short) mainly works with BZZ
series of whole hydraulic steering gear. It is used in whole hydraulic steering system. When oil
supply of steering oil pump and system load change, stable flow required by steering gear is
ensured by single stable valve, to satisfy hydraulic steering requirement of loader.
Single-channel stable flow divider valve mainly consists of valve body, valve core, spring,
safety valve, damping plug and other parts. It has shunt type and constant-current type. See
figure.
Single stable valve is used in
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independent system. Oil from steering is
supplied to the system. The rest oil and
oil overflowing when safety valve opens
unloading will flow back to the oil tank
through Port T.
Structure and
Principle Chart
★★★★ Safety valve is on the valve block now!!!!
2. Load Sensing Whole Hydraulic Steering System
1))))Composition of System
Mainly consisting of priority valve, BZZ5 load sensing
steering gear (or BZZ6 coaxial flow amplifying steering
gear), steering oil cylinder, pipelines, radiator, oil tank,
etc.
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Priority valve can realize combination and distributing
with working hydraulic steering system, improve
efficiency, and reduce loss. This type is widely used at
present. LG933, LG936, LG953, LG956 and other types
of our company all use this type.
System Principle
Chart
2. Load Sensing Whole Hydraulic Steering System
1))))Composition of System((((Continued))))
If LG953 steering hydraulic system is independent load
sensing hydraulic system steering, this system will
preferentially supply oil to steering hydraulic system.
The residual oil will return to oil tank after combining
with returning oil of steering system through radiator.
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with returning oil of steering system through radiator.
Safety valve is on priority valve. The system setting
pressure is 16MPa. See system principle chart.
System Principle
Chart
Load Dynamic Sensor System
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2))))Pipeline Direction of Load Sensing Whole Hydraulic Steering System
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3) BZZ5 Load Sensing Whole Hydraulic Steering Gear
Structure of BZZ5 Load Sensing Whole Hydraulic Steering Gear is similar to that of BZZ1
Whole Hydraulic Steering Gear. It is mainly consists of rotary valve and measurement motor.
The valve body has 4 ports, respectively connected to oil inlet, oil outlet and two cavities of oil
cylinder. Load Feedback Port Ls is connected to priority valve. See the following photo for
position of ports of steering gear.
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Ports of SteeringGear3D Profile of Structure
Following Rotary Valve
Measurement Motor
T::::oil return
P::::oil inlet
R::::right steering
L::::left steering
TLLS
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L
PR
LS
Position of ports on steering gear
Main Components of Steering Gear
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Core components of whole hydraulic steering gear:
• Metering mechanism---stator and rotor
• Servo proportional control valve ---valve core/valve pocket pair
●●●● Working Principle((((BZZ5))))
When following rotary valve is at the middle
position (steering wheel doesn’t move), valve
package and valve core are in the middle
under the action of positioning spring, and
channels connected to tooth cavity of rotor
and stator and two cavity of steering cylinder
are closed, only a small amount of pressure
oil pumped from steering pass through
Combin
es or
returns
to oil
tank
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System Sketch Map
oil pumped from steering pass through
inside of steering gear, and most oil will be
distributed by Port EF of priority valve
(combined to working hydraulic system or
flows back to oil tank). Oil in two cavity of
steering cylinder will be closed, piston
cannot move, and loader will run in original
direction.
PumpDiesel
Engine
Hydraul
ic oil
tank
When steering wheel turns, priority valve will preferentially satisfy steering needs.
Oil in steering pump will go to measurement motor through priority valve and
following rotary valve, and turn in the direction of steering wheel with rotor.
Working oil will be delivered to a cavity of steering cylinder and realize steering.
Oil in the other cavity of steering cylinder will return to oil tank with following
●●●● Working Principle((((BZZ5 Continued))))
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Oil in the other cavity of steering cylinder will return to oil tank with following
rotary valve. When steering wheel turns fast, a large amount of oil will reach
steering cylinder through measurement motor. Steering will be fast.
4) Priority Valve
This valve works together with BZZ5 Steering
Gear (or BZZ6 Steering Gear) and forms load
sensing steering system. When rotate speed of
steering wheel changes, flow required by
steering gear can be ensured preferentially.
The red oil will enter working device hydraulic
system or flow back to oil tank.
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Structure and Principle Chart of
Priority Valve
4) Priority Valve (Continued)●●●● When steering wheel doesn’t move, pressure oil from steering pump will enter working
device hydraulic system or directly flow back to oil tank through Port P, valve core and
Port EF.
●●●● When steering wheel turns, valve core will move right under the action of spring force and
LS pressure. Port P will be connected to Port CF. Pressure oil will enter steering gear and
push oil cylinder to realize loader steering. The rest oil will be distributed by Port EF, enter
working device hydraulic system or flow back to oil tank. Therefore, when priority valve
preferentially satisfies steering, the rest power oil will be distributed by Port EF and
applied to other working hydraulic system, which will reduce system power loss and save
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energy.
5))))Coaxial Flow Amplifying Steering Gear
Coaxial Flow Amplifying Steering Gear (BZZ6 and TLF) and BZZ5 type are all load
sensing steering gear. With the same displacement, two steering gears can replace
each other. But displacement of coaxial flow amplifying steering gear changes with
input turning speed of steering wheel.
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5))))Coaxial Flow Amplifying Steering Gear (Continued)
In low-speed steering (turning speed of steering wheel is under 10 rpm), effective
displacement and measurement displacement of steering gear are identical; When input
turning speed of steering wheel increases (turning speed of steering wheel is 10 ~ 40 rpm),
the effective displacement is in proportion to turning speed of steering wheel. At this time
only part of oil in oil inlet P will enter stator and rotor pair for measurement. The rest oil will
directly enter oil cylinder through Port A or Port B, so it has flow amplifying function at this
stage. When input turning speed of steering wheel is above 40rpm, effective displacement of
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stage. When input turning speed of steering wheel is above 40rpm, effective displacement of
steering gear will be its calibrated equivalent displacement.
Coaxial Flow Amplifying Steering Gear has good relative performance. It has high pressure
loss (about 0.5MPa higher than the first two kinds), good sealing and small leakage.) At
present, LG953 Loader uses BZZ6 (or TLF) Coaxial Flow Amplifying Whole Hydraulic Steering
Gear to replace BZZ5 Load Sensing Steering Gear.
• Flow amplifying system mainly consists of hydraulic pump, flow
amplifying valve, limit valve, steering gear (BZZ3) , steering cylinder, etc.
Oil channels are divided into pilot oil channel and main oil channel. oil
amount change of pilot oil channel is in proportion to flow change of
steering cylinder in main oil channels. High pressure and big flow is
3. Flow Amplifying Steering System (Flow Amplifying Valve)
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controlled by low pressure and small flow, so that steering control is
convenient and flexible. Because flow amplifying valve has pressure
compensation device, flow doesn’t change with load, which improves
performance and has certain energy-saving effect. Therefore, it has small
power consumption, reduces system heating, and improves flow
adjusting property.
• Besides functions of common flow amplifying valve, priority flow
amplifying valve can combine with working hydraulic system by priority
valve. It has characteristics of load sensing steering system.
• For example, LG958 Flow Amplifying Steering System mainly consists of
3. Flow Amplifying Steering System((((Continued))))
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double pump, steering gear, flow amplifying valve, unloading valve,
steering cylinder, hydraulic oil tank, pipeline accessories, etc. See the
following figure for system principle.
1----Oil returning filter
2----Radiator
3----Hydraulic oil tank
4----Working pump
5----Pressure selecting
valve
6----Steering gear
7----Steering cylinder
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8----Flow amplifying valve
9----Air change filter
10----Steering pump
11----Unloading valve
12----Oil absorption filter
core
Principle Chart of Flow Amplifying System
Structure and working principle of priority flow amplifying valve:1))))Flow Amplifying Valve
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1 front door 2 amplifying valve core 3 valve body 4 adjusting washer 5 steering valve spring
6 back door 7 pressure adjusting screw 8 pilot valve spring 9 cone valve 10 flow divider valve spring 11 adjusting shim 12 flow divider valve core 13 shuttle valve
1))))Flow Amplifying Valve((((Continued))))
When steering wheel stops turning or turns to extreme position, pilot oil will be
●●●● Middle Position
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cut off. Steering valve spring (5) will make amplify valve spool (2) keep in
middle position. Oil in steering pump will push distributing valve core (12) right.
Flowing into working system from Port PF, oil in steering pump is fully utilized,
so as to reduce displacement of working pump. Because amplifying valve core (2)
is at the middle position, hydraulic oil in p cavity will not be connected to
hydraulic oil in A and B cavity of left and right steering cylinder, so that loader
will run in the direction when steering wheel loader stops turning. Hydraulic oil
1))))Flow Amplifying Valve((((Continued))))
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will run in the direction when steering wheel loader stops turning. Hydraulic oil
sealed in A and B cavity of left and right steering port will act on cone valve (9) of
safety valve through internal channel. When steering wheel carries external
resistance, pressure in A (or B) cavity will increase, until cone valve (9) is opened,
in order to protect steering cylinder and other hydraulic components from
damage.
When steering wheel turns right, pilot oil will flow into spring chamber from pilot oil port
along direction b. As pressure in spring cavity of steering valve spring (5) increases,
amplifying valve core (2) will be pushed left. Then P cavity will be connected to right
steering port (B). Left steering port (A) will be connected to oil returning port (T1).
Hydraulic oil will enter oil cylinder of right turning port and realize right turning. When
right turning is preferentially met, the rest oil will be distributed to working system
● Right Steering Position
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through Port PF.
Movement amount of valve core is controlled by turning speed of steering wheel. The
faster steering wheel turns, the larger pilot oil flow is, the greater valve core displacement
is, and the higher steering speed is. Conversely, if steering wheel turns slow, valve core
displacement will be small and steering speed will be low (Note: Two ends of valve core
are connected to orifice on the oil channels. The hydraulic damping realizes this function).
When pressure oil flows into right turning port (B), because of load feedback effect,
pressure difference of two ends of distributing valve (12) remain unchanged, so as to
ensure that flow in steering cylinder only relates to displacement of valve core , and
doesn’t related to load pressure. Oil pressure acts on core valve (9) and distributing
valve core (12) through shuttle valve (13) , which automatically controls flow. If
pressure continues to rise and goes beyond the setting pressure of safety valve,
● Right Steering Position (Continued)
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cone valve (9) will open, distributing valve core (12) will move right, and flow will go
to working system. Oil returning in oil channels at middle position will have
protection function. When load is eliminated, pressure will reduce, distributing valve
core (12) will go back to its normal position, and cone valve (9)will be closed.
Left steering is similar to right steering.
ⅢⅢⅢⅢ. Failure Case Analysis
1. Failure Case Analysis of Working Hydraulic System
1))))Weak lifting of swing arm
2))))Slow and weak bucket
3))))Bucket turns over or shakes during lifting operation
4))))Hydraulic oil temperature is too high
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4))))Hydraulic oil temperature is too high
ⅢⅢⅢⅢ. Failure Case Analysis
1))))Heavy steering
2))))No terminal point for steering
3))))Reason for vehicle deflection
2. Failure Case Analysis of Steering Hydraulic System
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4))))Inaccurate steering
5))))Steering wheel rotates freely. Steering doesn’t move or slow.
6))))Blanking stroke of steering wheel
7))))Steering wheel shakes or rotates
8))))Steering wheel rebounds
1))))Weak lifting of swing arm ((((analysis and judgment process))))
1. Failure Case Analysis of Working Hydraulic System
Reason Measures
1. Valve rod is blocked
2. Positioning steel ball of
valve rod becomes invalid
due to wear. Positioning
spring becomes invalid
3. Control mechanism
doesn’t control well
Hydraulic oil amount is not
enough
Dirt or rubber dropping of
tubes makes pump unable to
absorb oil
Pump axle is broken or
drops. Working pump cannot
absorb oil
Setting pressure of main
1. Check valve rod,
steel ball, positioning
spring of valve rod or
change valve
2. Check control
mechanism
Add hydraulic oil to
specified mark
Remove dirt or change
rubber tubes
Change pump axle
Set to system pressure
value
Wash or change spring
Check whether
stroke of multiple
unit valve rod is in
place
No
Yes
No
Check whether
hydraulic oil
amount meets
standard Check whether oil
absorption tube of
working pump is
blocked
Measure when
pressure is zero or
low
Test pressure is
below requirement
Pressure changes
after adjustment
Pressure doesn’t
change after
adjustment
Check whether
pump driving axle
is broken or fallsAction stroke of 918 swing
arm valve is 7mm. Action
stroke of rotating bucket
valve is 8.1mm. Action
stroke of the two valve
rods of other types are all
16mm.
When bucket is flat on the
ground, oil position is
between 6 and 10 on mark
of hydraulic oil tank
Yes No
Yes
Yes
YesYes No
Yes
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Setting pressure of main
safety valve is low
Spring in main safety valve
is broken or valve core is
blocked
Working gear pump wears or
is broken
Internal leakage of swing
arm cylinder
1. Leakage of swing arm
slide valve
2. Internal leakage of main
safety valve
Accelerator pedal or cable
cause low rotating speed
Oil absorption channels are
blocked
Wash or change spring
Change gear pump or
repair
Repair of change oil
cylinder
Repair or change
multiple unit valve
Check pedal and cable.
Adjust rotating speed
to specified value
Change filter screen
adjustment
Check whether
multiple valve leaks
Check whether
working device
hydraulic system is
normal
Check whether
swing arm cylinder
has internal leakage
Pressure increases
with engine throttle,
but doesn’t reach
setting pressure
Meets setting
requirement of
working system
pressure
When stroke of valve rod is in
place and hydraulic oil amount
meets standard, check whether
rotating speed of engine meets
standard
Measure with tachymeter
to check whether rated
rotating speed of engine
reaches 2200r/min
When big arm lifts to extreme
position and control rod of swing
arm is at lifting position, rotating
of engine will gradually increase
to not less than 2200r/min. And
than measure
Adjust pressure of main safety valve. 933, 936 and 952 are 16MPa. 918 is 17.5MPa.
953, 956 and 958 are 18MPa.Yes
Yes
Yes
Yes
No Yes
Yes
No
2))))Slow and weak bucket ((((analysis and judgment process))))
Reason Measures
Broken seal ring causes
internal leakage and bucket
dropping
Scratching or wear on valve
rod or valve hole of rotating
bucket makes leakage of
hydraulic oil large
1. Main valve core of
overload valve has dust
particles, which makes
overload valve open
Change seal ring
Repair or change
1. Wash main valve
core and remove
impurities
Check whether broken rotating bucket slide valve causes internal
leakage
Check whether overload valve has
internal leakage
Check whether rotating bucket
cylinder has internal leakage
Check whether setting pressure of two
overload valves in rotating bucket
cylinder is normal
Pressure in big cavity of 933, 936, 938 and 952 is from 18 to 18.5MPa. Pressure in big cavity of 918, 953 and 956 is from 20 to 20.5MPa. Pressure in big cavity of 958 and 968 is 21.5MPa. Pressure in big cavity of 40F is
Yes
YesNo
Yes
Yes
No
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overload valve open
2. Aging of seal ring
3. Improper clearance
between valve core and
valve body
1. Low pressure of overload
valve causes bucket
dropping or floating
2. Spring of overload valve
is broken or invalid
impurities
2. Change seal ring
3. Change overload
valve
1. Adjust pressure to
specified value
2. Repair or change
internal leakage
Check whether pressure of overload
valve is low
Pressure in big cavity of 40F is 15.5MPa. Pressure in small cavity of all types is from 12 to 12.5MPa.
No
Yes
3))))Bucket turns over or shakes during lifting operation((((analysis and judgment process))))
Reason Measures
Oil amount is not
enough
Working gear pump
wears or is broken
Unstable starting
pressure of safety
valve changes
pressure of hydraulic
oil
Caused by aging and
foaming of inlayer of
rubber tubes, or
Add hydraulic oil to
specified mark
Change or repair
Check setting
pressure of valve, and
whether spring
deforms. Adjust
starting pressure
Repair or change
Check whether oil amount
meets standard
Test pressure of working device
hydraulic system
Check whether starting pressure of
safety valve is stable
Check whether oil channels are
Check pressure increases with increase of engine throttle
Check whether indicator of
pressure gage swings
intensively
Oil position is between 6 and 10 on mark of hydraulic oil tank
When big arm rises to extreme position and control rod of swing arm is at lifting position, rotating speed of engine will gradually increase to not less than 2200r/min. And then measure. 933, 936 and 952 are 16MPa.
Yes
Yes
No
Yes
No
Yes
No
19/05/2015
rubber tubes, or
blocking of transiting
valve block and joint
Air entering system
makes working
pressure unstable
Different leakage
amount causes flow
fluctuation and
shaking
Loosen piston makes
piston rod move in
hydraulic cylinder
Repair or change
Repair or change
Repair or change
When system pressure and hydraulic oil amount are normal, check whether leakage amount of rotating bucket cylinder and swing arm cylinder are same
When system pressure and hydraulic oil amount are normal, check whether pistons in rotating bucket cylinder and swing arm cylinder are loosen
channels are blocked or flat
Check whether oil absorption rubber
tubes are well sealed
936 and 952 are 16MPa. 918 is 17.5MPa. 953, 956 and 958 are 18MPa.
No
Yes
No
YesNo
Yes
4))))Hydraulic oil temperature is too high((((analysis and judgment process ))))
Reason Measures
Insufficient hydraulic oil
makes working pump absorb
air
Hydraulic components are
blocked, causing throttling
and temperature rise of
Too much grease causes poor
heat dissipation
Blocking in radiator or other
reasons cause poor heat
dissipation
When system pressure is set
too high, overflow valve
cannot overflow and reduce
pressure normally, internal
Add hydraulic oil to specified mark
Change or filter hydraulic oil
Clean with high pressure gun
Repair or change
Repair or change
Check whether position of hydraulic oil is too low
Check whether hydraulic oil is too dirty or goes bad
Check whether there is too much grease between blades of cooling fin in water box
Check whether hydraulic radiator has problem
No
Yes
Yes
Yes
Yes
No
No
No
19/05/2015
leakage will increase, oil
temperature of system will
rise. When oil returning filter
core is blocked or oil
returning channels become
old and delaminate, back
pressure will be high and oil
temperature will rise.
Serious internal leakage of
hydraulic components will
cause temperature rise of
system
Low volumetric efficiency will
cause temperature rise of
hydraulic oil
Repair or change
Repair or change
Check whether improper pressure setting causes high temperature of hydraulic oil
Check whether cylinder, pump and valve have leakage
Check whether gear pump, gear pair, side plate or pump body have wear
No
Yes
Yes
Yes
No
No
1))))Heavy steering((((analysis and judgment process))))
2. Failure Case Analysis of Steering Hydraulic System
Decid
e a
cco
rdin
g to
fau
lt p
hen
om
en
on
Cylinder crawls. Foam in oil. Regular sound
Heavy steering. Steering cylinder doesn’t move.
Check whether steering pillar is
flexible
Whether system pressure meets
Check whether feedback oil
Reason Measures
Air in system
-One-way valve
failure of manual
steering
-Leakage of FK
overload valve
-Internal leakage of
oil cylinder
Steering pillar is
broken
Remove air in system.
Check whether oil inlet of
oil pump leaks.
-Check whether steel ball
exists and whether it is
blocked
-Change FK combination
valve
-Check whether oil cylinder
has internal leakage
Repair or change
Clean or change
Yes
Yes
YesNo
Yes
No
No
19/05/2015
Is fast steering heavy and slow steering light?
pressure meets the needs
feedback oil channels are unblocked
Adjust system press. Does the
pressure change?
Is surface of hydraulic oil low?
Is oil sucking pipe blocked?
broken
Pipelines are
blocked
Low system
pressure
Spring of priority
valve is broken.
Shuttle valve is
blocked
Lack oil
Pipelines are
blocked
Wear and internal
leakage of steering
pump
Clean or change
Repair or change
Adjust system pressure
Supplement hydraulic oil
Clean or change
Repair or change
Yes
Yes
Yes
Yes
Yes
No
No
No
No
Yes
No
2))))No terminal point for steering or limit position cannot be reached ((((analysis and judgment process)
No terminal point Failure Reason Troubleshooting
Method
Low overload
valve pressure
Increase overload
valve pressure
properly
After steering cylinder turns to extreme position, turning the steering wheel, steering wheel can turn lightly, which means no sense of terminal point.
19/05/2015
Steering cylinder cannot turn to extreme position
Failure Reason Troubleshooting Method
Low safety valve
pressure
Increase safety valve
pressure properlySteering cylinder cannot turn to extreme position. Steering response is heavy.
①①①① Leakage at cylinder port when closed center steering gear is at middle
position. It is normal for closed center steering gear system to have
slight deflection.
②②②② Check whether connecting rod of oil cylinder is loosen.
③③③③ Leakage in oil cylinder
④④④④ Pressure of two tires has big difference.
⑤⑤⑤⑤ Leakage on two-way overload valve or two-way supplemental valve.
3))))Reason for Vehicle Deflection
19/05/2015
⑤⑤⑤⑤ Leakage on two-way overload valve or two-way supplemental valve.
⑥⑥⑥⑥ Air in oil
①①①① Air in system;
②②②② Pin of oil cylinder is loosen;
③③③③ Priority valve or main valve of
flow divider valve is blocked;
L
T
R
P
4))))Inaccurate Steering
19/05/2015
flow divider valve is blocked;
④④④④ Oil cylinder has leakage;
⑤⑤⑤⑤ Low efficiency of pump causes unstable pressure.
EngineFixed Pump
Reservoir
Filter
p
①①①① Serious leakage in two-way overload valve
5))))Steering wheel rotates freely. Steering doesn’t move or slow.
19/05/2015
②②②② Serious leakage in piston of oil cylinder
②②②② Nut on steering wheel moves
①①①① Connection of steering pillar and steering gear wears or is broken
L
T
R
PP
6))))Blanking Stroke of Steering Wheel
19/05/2015
③③③③ Air in oil
④④④④ Leakage in two-way overload valve
⑤⑤⑤⑤ Leakage in steering cylinder
EngineFixed Pump
Reservoir
Filter
p
EngineFixed Pump
①①①① Assembly relation mistake. During overhaul
and reassemble, it is required that spine gear
corresponding to pin groove of universal
driving shaft engages with internal spine
gear corresponding to gear groove of rotor
②②②② When oil in pump is connected to Port R or
7))))Steering wheel shakes or rotates
19/05/2015
②②②② When oil in pump is connected to Port R or
L, steering gear will rotate like motor.
Reason::::One-way valve at oil inlet of
steering gear is broken.
Function of one-way valve:
Prevent backflow of oil when pressure of
8))))Steering wheel rebounds
19/05/2015
steering oil cylinder under external force is
higher than that of oil inlet. If one-way valve
is damaged and oil backflows, steering
wheel will rebound.
19/05/2015
Reliability bears great
trust!