Loader Hydraulic Training Courseware
2011
Main Content
 Suitable Group
 Training Objectives
 Contents
 Evaluation Topics
14/03/2016
Suitable Group
This course is suitable for domestic and foreign intermediate and
above technical service personnel
It also applies to…
14/03/2016
Main Content
 Suitable Group
 Training Objectives
 Contents
 Evaluation Topics
14/03/2016
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
（3）Common failure and troubleshooting of systems and components
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Contents
1
2016/3/14
1
Basic Knowledge of
Hydraulic
Transmission
2
Hydraulic
System Introduction of LG
Loader
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Part 1 Basic Knowledge of Hydraulic
Transmission
Basic Principle of Hydraulic Transmission
1
Composition of Hydraulic Transmission System
2
1
Advantages of Hydraulic Transmission System
3
4
5
6
7
Disadvantages of Hydraulic Transmission
System
Hydraulic Medium
Hydraulic Power Components
Hydraulic Control Components
8
Hydraulic Actuating Components
2016/3/14
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Ⅰ. Basic Principle of Hydraulic Transmission
● 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
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.
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Ⅰ. Basic Principle of Hydraulic Transmission
●
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
delivers power with liquid pressure. Hydraulic transmission mainly
transfers power with kinetic energy of liquid.
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Ⅰ. Basic Principle of
Hydraulic Transmission
● 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
piston area.
2）P, oil pressure, depends on external load.
2. Loading speed transfers according to the
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
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
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；
Ⅱ. Composition of Hydraulic Transmission System
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
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.
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Ⅱ. Composition of Hydraulic Transmission System
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.
5. Working Medium
Deliver energy and signal with it.
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Ⅲ. Advantages of Hydraulic Transmission System
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.
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.
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Ⅳ. Disadvantages of Hydraulic Transmission System
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.
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.
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Ⅴ. Hydraulic Transmission Medium
1. Functions of Hydraulic Medium
•
Energy and signal transmission;
•
Lubricate hydraulic components, and reduce friction and wear;
•
Heat dissipation;
•
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.
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Ⅴ. Hydraulic Transmission Medium
2. Types of Hydraulic Medium
•
One is flammable hydrocarbon hydraulic oil (mineral oil type and
synthetic hydrocarbon type);
•
Another is nonflammable (or fire resistant) hydraulic fluid.
•
Nonflammable fluid includes aqueous (such as HFA, HFB and HFC)
and non-aqueous synthetic fluid（HFD）.
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Ⅴ. Hydraulic Transmission Medium
3. Main Performance of Hydraulic Medium
1）Viscosity
2）Abrasion resistance
3）Oxidation stability and thermal stability
4）Demulsibility and hydrolytic stability
5）Defoaming
6）Anti-corrosion
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Ⅴ. Hydraulic Transmission Medium
3. Main Performance of Hydraulic Medium （Continued）
7） Shear stability
8） Material compatibility
9） Filtering property
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.
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Ⅴ. Hydraulic Transmission Medium
4. Classification and Features of Hydraulic Oil of Mineral Oil Type
•
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.
•
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.
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Ⅴ. Hydraulic Transmission Medium
5. Reasonable Use and Maintenance of Hydraulic Medium
● 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;
4）Oil cannot be mixed optionally;
5）Pollution should be strictly controlled to prevent moisture,
air and solid impurities from entering hydraulic system.
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Ⅴ. Hydraulic Transmission Medium
5. Reasonable Use and Maintenance of Hydraulic Medium
● 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;
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.
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Ⅴ. Hydraulic Transmission Medium
5. Reasonable Use and Maintenance of Hydraulic Medium
● 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
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;
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Ⅴ. Hydraulic Transmission Medium
6. Pollution and Protection of Hydraulic Oil
● 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.
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.
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Ⅴ. Hydraulic Transmission Medium
6. Pollution and Protection of Hydraulic Oil
● 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
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.
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Ⅴ. Hydraulic Transmission Medium
6. Pollution and Protection of Hydraulic Oil
● 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;
4）Use appropriate oil filter;
5）Regularly replace hydraulic oil; and
6）Control working temperature of hydraulic oil.
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Ⅵ. Hydraulic Transmission Components
1. Working Principle of Hydraulic Pump
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.
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
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Ⅵ. Hydraulic Transmission Components
2. Features of Hydraulic Pump
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
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.
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Ⅵ. Hydraulic Transmission Components
3. Main Performance Parameters of Hydraulic Pump
1）Pressure
Working pressure, rated pressure and maximum permissible pressure.
2）Discharge and flow
Theoretical flow, rated flow, and actual flow
3）Power and efficiency
●
Power loss of hydraulic pump includes volume loss and mechanical
loss.
●
Power of hydraulic pump: input power and output power
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Ⅵ. Hydraulic Transmission Components
4. Type of Hydraulic Pump
1）By structure: Gear pump, vane pump, plunger pump, screw pump, etc.
① Gear pump: Inner gearing gear pump and outer gearing gear pump;
② Vane pump: Single acting vane pump and double acting vane pump;
③ Plunger pump: Axial plunger pump, radial plunger pump and valve oil
distributing valve plunger pump;
2）By function: Constant delivery pump and variable pump
gear pump
axial plunger pump
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radial plunger pump
Ⅶ. Control Components (Hydraulic Valve)
1. Concept
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
stabilization, unloading, pressurization, decompression and other
operational needs of actuating components.
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Ⅶ. Control Components (Hydraulic Valve)
2. Common Features
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
valves comforts to orifice flow formula, but different valves have
different control parameters.
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Ⅶ. Control Components (Hydraulic Valve)
3. Performance Parameters and Basic Requirements of
Hydraulic Control Valve
● Performance Parameters
① 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
as reversing reliability of reversing valve and pressure regulating scope of
pressure valve.
② 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.
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Ⅶ. Control Components (Hydraulic Valve)
3. Performance Parameters and Basic Requirements of
Hydraulic Control Valve
● 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,
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.
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Ⅶ. Control Components (Hydraulic Valve)
4. Classification of Hydraulic Control Valve
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
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.
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Ⅶ. Control Components (Hydraulic Valve)
5. Pressure Control Valve
•
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：
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.
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Ⅶ. Control Components (Hydraulic Valve)
1） Overflow valve
● 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
is constant pressure valve. Overflow Valve 2 in the right figure is safety valve.
constant pressure
valve
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safety valve
Ⅶ. Control Components (Hydraulic Valve)
1） Overflow valve（Continued）
● Structure type: can be divided into directly
operated type and pilot operated type by form
of structure and basic action mode.
① Directly operated overflow valve（see figure）
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.
Figure of Low-pressure Directly Operated Overflow Valve
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).
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1-nut 2-pressure adjusting spring 3-top cover 4-valve core 5valve body
Function Symbol
Map
Ⅶ. Control Components
(Hydraulic Valve)
Remote
Control
1) Overflow valve（Continued）
② 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.
● Advantages in performance (pressure
adjusting range, on-off characteristic,
Pilot Overflow Valve
1-spring of main valve 2-main valve core 3-damper hole
dynamic performance, remote control, etc.).
Suitable for system with high pressure and
big flow.
4-valve core of pilot valve 5-sping of pilot valve
Principle
Demo
Function
Symbol Map
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Ⅶ. Control Components (Hydraulic Valve)
2）Pressure reducing 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.
In addition, when oil pressure is unstable, a stable
low pressure can be obtained by putting a pressure
Pressure Reducing Valve
reducing valve in the return circuit.
It can be divided into fixed 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
fixed differential reducing valve and proportional
pressure reducing valve by pressure controlled by
pressure reducing valve.
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Function
Symbol Map
Ⅶ. Control Components (Hydraulic Valve)
2) Pressure reducing valve
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.
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.
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Ⅶ. Control Components (Hydraulic Valve)
Remote
Control
3）Sequence valve
● 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
used in low pressure system. The latter is used in
middle or high pressure system.
Pilot Sequence Valve
● Sequence valve and overflow valve have similar
structure. Compare pilot operated sequence valve
following differences.
directly operated external
control sequence valve
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pilot operated
sequence valve
Function Symbol
Map
and pilot operated overflow valve. They have the
Ⅶ. Control Components (Hydraulic Valve)
Remote
Control
3）Sequence valve
① 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
unchanged. When p2 increases to a certain degree, p1
will also increase. p1 = p2 + Δ p. Δ p is pressure loss
Pilot Sequence Valve
on sequence valve.
② Overflow valve has internal leakage and sequence
which is external leakage.
③ Outlet of overflow valve has to return to the oil tank.
Outlet of sequence valve can be connected to load.
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directly operated external
control sequence valve
pilot operated
sequence valve
Function Symbol Map
valve needs to separately draw out leakage path,
Ⅶ. Control Components (Hydraulic Valve)
4) Pressure switch（hydraulic switch）
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
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
1—Plunger 2—Lever
3—Spring 4—Switch
operation of system for safe protection, etc.
Structure
Chart
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Ⅶ. Control Components (Hydraulic Valve)
6. Directional control valve
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.
Left position of three-position
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four-joint reversing valve
Right position of three-position
four-joint reversing valve
Reversing Valve（2-position
figure）
One-way
1）One-way valve
● Classification of one-way valve
① By function: Common one-way valve and hydraulic controlled one-way valve.
② By structure: Tubular (direct connection) and plate (right angle)
Oil Inlet
P1
Oil Outlet
P2
Oil Inlet P1
Tubular
Oil Outlet P2
Plate
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①
●
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.
● Opening pressure:
Oil Outlet
P2
Oil Inlet P1
Generally 0.04～0.1MPa;
opening pressure of back
pressure valve is 0.2～
0.6 MPa
● Structural form and
Mode
Oil Inlet P1
Oil Outlet P2
Mode
Oil Inlet P1
Oil Outlet P2
(d) Symbol
function symbol:
Mode
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● Application:
①Reverse protection of
hydraulic pump
②Separate oil channels prevent
interference
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.
③Comprise combination
valve
④Installed in outlet oil line to
produce back pressure
One-way valve
can comprise
one-way
combination
valve with
other valves
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②Hydraulic 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.
P1
K
symbol
P2
Structure
Chart
Function Symbol
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2）Reversing Valve
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
① By motion mode of valve core relative to valve body:
② By control method:
Manual
Reversing
Valve
Steering valve type, sliding valve type, ball valve type, etc.
Manual, engine driven, electromagnetic, hydraulic, electric
hydraulic, etc;
③ By working position of valve core on valve body:
Two-position valve and three-position valve
Two-port valve, three-port valve, four-port valve and five-port
valve.
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Electromagnetic
Reversing
Valve
④ By number of main oil port on valve body:
● Control mode symbols of commonly used sliding
reversing valve
Manual
Hydraulic
Engine Drive (Roller
Type)
Hydraulic Pilot
Control
Electric
Spring
Electromagnetic-Hydraulic Pilot
Control
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●Working principle of sliding reversing valve
Valve Body
Valve Core
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
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●Station and pathway symbols of main structure of reversing
valve（see figure）
Big Box
Small
Box
Valve body
Station
Crossover point of arrow line in the small box or┴
symbol and bounding
Oil port
Oil channels connected （not
always flow direction）
┴
Head of
symbol
Oil channels
disconnected
Normal position（valve core without
force);
A, B
Oil ports connected to the oil tank；
P, O
Oil inlet and return opening
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Functional chart of threeposition four-port
reversing valve
●
Principle and type symbols of main structure of reversing valve
Name
Structure and Principle Chart
Symbol
A
Two-position
two-port
P
A
B
Two-position
three-port
P
A B
Two-position
four-port
P O
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●
Principle and type symbols of main structure of reversing valve （continued）
Name
Structure and Principle Chart
Symbol
A
B
Two-position fiveport
O1 P O2
A B
Three-position
four-port
PO
AB
Three-position five-
O1 P O2
port
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●
The most commonly used six median functions of
three-position reversing valve
Function
Median Symbols
State, Features and Application of Median
Model
Symbols
Port P, A, B and O are all closed；
O
Hydraulic
cylinder is locked. Hydraulic pump doesn’t
unload.
Port P, A, B and O are Hydraulic pump ; Piston
H
of hydraulic cylinder is floating. Hydraulic
pump unloads.
Port P is closed. Port A, B and O are
Y
connected. Piston of hydraulic cylinder is
floating. Hydraulic pump doesn’t unload.
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● The most commonly used six median functions of threeposition reversing valve（continued）
Function
Model
Median Symbols
State, Features and Application of Median
Symbols
Port P, A and B are connected. Port O is
P
closed. Pump and hydraulic cylinder are
connected, which can comprise differential
motion and connect inlet.
Port P and Port O are connected. Port A and
M
Port B are closed. Piston of hydraulic cylinder
is locked. Hydraulic pump unloads.
Port P, A and B are connected. Port O is
K
closed. Piston of is locked. Hydraulic pump
unloads.
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● Several Commonly Used Reversing Valves
① Electromagnetic reversing valve
Valve
Body
Coil
Armature
Valve
Core
Function
Symbol
Three-position four-port
electromagnetic reversing valve
Two-position four-port
electromagnetic reversing valve
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★ 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.
◆
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.
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② Hydraulic reversing valve
Hydraulic
controlled
pressure
port
Hydraulic
controlled
pressure
port
Hydraulic three-position four-port
reversing valve
Function
Symbol
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★ 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.
Damper Regulator
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③ Electro-hydraulic reversing valve
Pilot valve
（electromagn
etic valve）
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Main valve
（electromagnetic
valve）
★
Principle drawing of electro-hydraulic reversing valve
Control oil
channel
Main oil
channel
Simplified Function
Symbol
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★ 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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④ Engine driven reversing valve（motion valve）
Oil Inlet
Roller Push
Rod
Lift type, two-port,
normally closed
Valve Core
Oil Outlet
Back-moving
Spring
Lift type, two-port,
normally opened
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Roller type, threeport
★ Performance of electro-hydraulic engine driven
reversing valve
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
changing appearance of cam.
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⑤ Manual reversing valve
Mechanical
Positioning Type
Self-restoring
Type
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★ Performance of manual reversing valve
Manual reversing valve is convenient to use. It is applicable to
occasion with small flow and longer interval.
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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
（Median function：P）；
Figure 1
Figure 2
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Figure 3
Ⅶ. Control Components (Hydraulic Valve)
7. Flow Control Valve
● 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.
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Ⅶ. Control Components (Hydraulic Valve)
7. Flow Control Valve (Continued)
● 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
teaching material.
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Ⅷ. Hydraulic Actuating Components
•
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
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
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Ⅷ. Hydraulic Actuating Components
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. Motor
Sketch Map of Single-rod
Piston Cylinder
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:
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Ⅷ. Hydraulic Actuating Components
1）Features of Motor
•
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
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.
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Ⅷ. Hydraulic Actuating Components
1）Features of Motor (Continued)
•
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
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.
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Ⅷ. Hydraulic Actuating Components
2）Type of Motor
Hydraulic motor can also be divided into gear type, vane type, piston
type and other types by structure types.
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Ⅷ. Hydraulic Actuating Components
3）Axial Piston Motor
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
figure for working principle (see textbook for
content).
F1=p*A*tanγ
Torque force of cylinder
generated by piston
T1=F*r=F*R*conφ
=p*A*R*tanγ*conφ
Torque of cylinder
generated by piston
T=ηm*Δp*V/2π
Total torque actually output
by motor
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Working Principle of
Swash-plate Axial Piston
Motor
Contents of Training
Courseware
1
2016/3/14
1
Basic Knowledge of Hydraulic
Transmission
2
Hydraulic
System Introduction of LG
Loader
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Part 2 LG Hydraulic
System Introduction
Working Device Hydraulic
System
1
1
2
3
2016/3/14
Steering Hydraulic
System
Case Analysis
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Ⅰ. 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
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.
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Ⅰ. Working Hydraulic System
2. Principle of Working Hydraulic
System
Working and Steering
Hydraulic System Demo
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,
and realizes different actions of working device.
①When 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.
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Principle Drawing of Working
Hydraulic System
Ⅰ. Working Hydraulic System
2. Principle of Working Hydraulic System
(Continued)
② Swing arm can lift, descent or float by controlling reversing slide valve on
swing arm.
③ Bucket can turn forward and backward back controlling rotating bucket
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.
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Ⅰ. Working Hydraulic System
3. Composition of
Working Hydraulic
System
● Gear pump（working
pump）
● Multiple unit valve
● Oil cylinder (swing arm
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
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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
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.
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● 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
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
Demo
Map
bearing with keys. Driving axle is driven by power machine.
Figure of Outer Gearing Gear
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● Working Principle of Gear Pump (Continued)
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
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.
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● Common fault analysis of loader gear pump
No.
Failure
Reason
Troubleshooting Method
1
Hydraulic oil decreases. Transmission
oil increases.
Oil seal is broken
Test pressure. Change working
pump (or steering pump)
2
Hydraulic oil increases. Transmission
oil decreases.
Oil seal is broken
Test pressure. Change working
pump (or steering pump)
3
Oil 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
Overwear of side plate
Change side plate or pump
Poor size of spline shaft.
Push the shaft.
Change spline shaft or pump
5
Abnormal sound of pump
Bearing is broken
6
Insufficient flow of pump causes weak
and slow lifting
Internal leakage caused
by overwear of gear or
side plate
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Change bearing or pump
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
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.
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Piping Map of Working Device Hydraulic System
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Profile Map of Double-joint Multiple Unit Valve（DF32）
Action
Demo
supravergence
Seal off
Turn below
1 Swing arm slide
valve
Lifting
Seal off
Descend
Float
2 Turning slide
valve
3 Turn cylinder
small cavity
overload valve
4 Turn cylinder big
cavity overload
valve
5 Safety valve
6 Valve body
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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
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
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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 oilreturning circuit.
Profile Map of Overload
Supplemental Valve
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Overload Supplemental Valve (Continued)
1）Functions of Overload Supplemental Valve
● 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
prevented.
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Overload Supplemental Valve
● 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
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.
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Overload Supplemental Valve
2）Setting Pressure of Overload Supplemental Valve
•
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
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.
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Basic Failure and Troubleshooting of Multiple Unit Valve (DF)
No.
Reason
1
Insufficient
working pressure
2
Insufficient
working flow
Failure
Troubleshooting Method
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
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
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Basic Failure and Troubleshooting of Multiple Unit Valve (DF)
(Continued)
No.
Reason
Failure
Restoring spring is broken or deforms
3
Troubleshooting Method
Change spring or assembly
Reset failure
Restoring parts are not in the same axle, Change broken parts or
pulled, etc.
assembly
4
5
Outside leakage
Big deflection of
swing arm
Seal ring is broken
Change to new parts
Oil temperature is too high. Viscosity
drops
Take measures to reduce oil
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
Clearance between valve body and
valve rod of multiple unit valve
increases
Change valve rod or
assembly
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Basic Failure and Troubleshooting of Multiple Unit Valve (DF)
(Continued)
No.
6
Reason
Bucket drops
Reason
Troubleshooting Method
Inner 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
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
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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.
Structure of Oil Cylinder
1. Back cylinder cover
2. Stop collar
3. Lantern ring
4. Snap ring
5. Piston
6. O Ring
7. Back-up ring 8. Stop dog
9. Ax seal ring
10. Oil cylinder body
11. Port stand
12. Guide sleeve
13. Cylinder end
14. Dust ring
15. Piton rod
16. 16. Screw
Buffer Plunger
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Hydraulic Pilot Control Working Hydraulic System
1）Features of the 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:
● 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.
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1）Features of the System (Continued)
● 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.
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
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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.
Structure of Pilot Valve
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● Working principle of pilot valve（proportional
pilot
control and automatic control of electromagnet)
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
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.
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● Working principle of pilot valve（proportional pilot
control and automatic control of electromagnet)
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
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.
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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
valve.
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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
position under the pressure of pilot hydraulic oil and action of spring.
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Multiple Unit Valve (D32 Continued)
● 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
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
Structure of Multiple
Unit Valve
control of pilot oil. Lifting of swing arm will
automatically end.
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Multiple Unit Valve (D32 Continued)
● 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
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.
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Multiple Unit Valve (D32 Continued)
● 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,
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.
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Pressure Selecting Valve
● Function: Purpose of pressure selecting valve
is to provide a certain pressure of control oil to
One-way
valve
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
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
One-way
valve
swing arm oil cylinder. Port P2 is oil outlet,
which is connected to pilot valve. L is oil
returning port. See structure chart.
Structure and Principle of
Pressure Selecting Valve
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● Working Principle
During 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
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.
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Ⅱ. 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.
•
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.
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●Type of Steering System
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.
① Whole hydraulic steering system consisting of single stable valve and
open center non-reaction steering gear;
② Load sensing whole hydraulic steering system consisting of priority valve
and load sensing steering gear;
③ Load sensing whole hydraulic steering system consisting of priority valve
and coaxial flow amplifying steering gear;
④ Flow amplifying steering system
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1. Whole Hydraulic Steering System Controlled by
Solenoid Valve
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
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.
System Principle
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●Type of Whole Hydraulic Steering Gear
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）；
and other structural styles
Function symbols are shown in the
figure.
Type Symbol of BZZ
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Structure of BZZ Whole Hydraulic Steering Gear
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
Middle position
Steering position
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Structure of Whole Hydraulic
Steering Gear
Correspondence of valve core, valve
pocket , stator and rotor
High
High
HighPressure
Pressure
Pressure
Pressure
Pressure
Low
Low
Low
Low
LowPressure
Pressure
Pressure
Pressure
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Oil
Oil
Oil
Oil
Oil
Trap
Trap
Trap
Trap
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.
Functions：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
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.
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3) Combined Valve Block
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 twoway 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
Structure Chart
of Valve Block
valve), and two-way buffer overload valve.
Functional Chart
of Valve Block
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4) Single stable Valve
Single-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
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
★ Safety valve is on the valve
block now！
Principle Chart
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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.
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
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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.
Safety valve is on priority valve. The system setting
pressure is 16MPa. See system principle chart.
System Principle
Chart
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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.
Following
Rotary Valve
Measurement
Motor
Ports of Steering
Gear
3D Profile of Structure
14/03/2016
T：oil return
P：oil inlet
R：right
steering
L：left steering
LS
T
L
P
R
Position of ports on
steering gear
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Main Components
of Steering Gear
Core components of whole hydraulic
steering gear:
• Metering mechanism---stator and rotor
• Servo proportional control valve ---valve
core/valve pocket pair
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● Working Principle（BZZ5）
When following rotary valve is at the middle
position (steering wheel doesn’t move), valve
Combin
es or
returns
to oil
tank
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
Pump
inside of steering gear, and most oil will be
Diesel
Engine
Hydraul
ic oil
tank
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.
System Sketch Map
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● Working Principle（BZZ5 Continued）
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
rotary valve. When steering wheel turns fast, a large amount of oil will reach
steering cylinder through measurement motor. Steering will be fast.
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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.
Structure and
Principle Chart of
Priority Valve
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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
energy.
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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
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.
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3. Flow Amplifying Steering System (Flow
Amplifying Valve)
•
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
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.
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3. Flow Amplifying Steering System（Continued）
•
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
double pump, steering gear, flow amplifying valve, unloading valve,
steering cylinder, hydraulic oil tank, pipeline accessories, etc. See the
following figure for system principle.
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1－Oil returning filter
2－Radiator
3－Hydraulic oil tank
4－Working pump
5－Pressure selecting
valve
6－Steering gear
7－Steering cylinder
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
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1）Flow Amplifying Valve
Structure and working principle of priority flow amplifying valve:
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
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1）Flow Amplifying Valve（Continued）
● Middle Position
When steering wheel stops turning or turns to extreme position, pilot oil will be
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.
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1）Flow Amplifying Valve（Continued）
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
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.
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● Right Steering Position
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
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).
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● Right Steering Position (Continued)
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,
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.
14/03/2016
Ⅲ. 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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Ⅲ. Failure Case Analysis
2. Failure Case Analysis of Steering Hydraulic System
1）Heavy steering
2）No terminal point for steering
3）Reason for vehicle deflection
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
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1. Failure Case Analysis of Working Hydraulic System
1）Weak lifting of swing arm （analysis and
judgment process）
起因
Reason
1.1.阀杆卡滞
Valve rod is blocked
1. Check valve rod,
1.检修阀杆、钢
2.阀杆定位钢球
因磨损失效，定 簧或换阀
valve rod becomes invalid
spring of valve rod or
位弹簧失效
due to wear. Positioning 2.检修操纵机构
change valve
3.操纵机构控制
spring becomes invalid
2. Check control
不到位
加液压油至规定
3. Control mechanism
mechanism
液压油量不足
刻度
doesn’t control well
Add hydraulic oil to
球、阀杆定位弹
2. Positioning steel ball of
steel ball, positioning
是
Yes
否
No
Check whether
检查多路阀阀
stroke of multiple
杆行程是否到
unit valve rod is in
位
place
918动臂阀杆一个
Action
stroke of 918 swing
arm动作行程7mm、转
valve is 7mm. Action
斗阀杆一个动作行
stroke
of rotating bucket
程8.1mm，其余机
valve
is 8.1mm. Action
型两个阀杆均为
stroke
of the two valve
16mm
rods of other types are all
16mm.
否
No
Check whether
检查液压油量
hydraulic oil
amount meets
是否符合标准
standard
清除污物或更换
Hydraulic
oil amount is not
specified mark
有污物或胶管
是
Yes
Measure when
测量压力为零
pressure is zero or Yes
是
或很低时
low
When铲斗平放到地面，
bucket is flat on the
ground,
oil position is
油位在液压油箱油
标刻度6～10之间
between
6 and 10 on mark
of hydraulic oil tank
Check whether oil
检查工作泵吸
absorption tube of
working pump is
油管是否堵塞
blocked
检查泵驱动轴
pump driving axle
是否断裂、脱
is broken or falls
落
胶管
泵无法吸油
Remove dirt or change
泵轴断裂、脱
Dirt
or rubber dropping of更换泵轴
rubber tubes
落，工作泵无
tubes makes pump unable to Change pump axle
法吸油
胶层脱落造成
enough
Check whether
否
No
措施
Measures
是
Yes
absorb oil
主安全阀调定
压力偏低
是
Yes
Test pressure is
测量压力低于
below requirement Yes
是
要求
是
Yes
Check whether
检测工作装置
working device
液压系统压力
hydraulic system is
是否正常
normal
When big arm
lifts to extreme
大臂上升到极限位
置，动臂操纵杆处在
position and
control rod of swing
arm is at 上升位置，发动机的
lifting position, rotating
of engine转速逐渐加至不低于
will gradually increase
2200r/min后进行测量
to not less
than 2200r/min. And
than measure
否
No
change after
调整后压力无
adjustment
变化
absorb oil
是
Yes
需调整主安全阀压力，933、936、952为16MPa，918为
Adjust
pressure of main safety valve. 933, 936 and 952 are 16MPa. 918 is 17.5MPa.
17.5MPa，953、956、958为18MPa
953,
956 and 958 are 18MPa.
Pressure increases
压力随着发动
with engine throttle,
机油门的增大
but doesn’t reach
Yes
是
而增大，但达
setting pressure
是
Yes
When stroke of valve rod is in
阀杆行程到位、液压油
place and hydraulic oil amount
量符合标准的情况下检
meets standard, check whether
查发动机转速是否符合
rotating
speed of engine meets
标准
standard
Measure
with tachymeter
用测速仪测定发动
机额定转速是否达
to check
whether rated
到2200r/min
rotating
speed of engine
reaches 2200r/min
14/03/2016
Check whether
检查动臂油缸
swing
arm cylinder
是否内泄
has
internal leakage
否
No
Check whether
检查多路阀是
multiple valve leaks
否内泄
清洗或更换弹簧
Wash or change spring
Spring in main safety valve
Change gear pump or
is broken or valve core is
repair
工作齿轮泵磨
损或损坏
Repair of change oil
更换齿轮泵或维
修
Working gear pump wears or cylinder
is broken
是
Yes
Meets setting
主安全阀中的
弹簧折断或阀
safety valve is low
芯卡死
Setting pressure of main
blocked
不到设定压力
达到工作系统
requirement of
的压力设定要
working system
求 pressure
调至系统压力值
Set to system pressure
drops. Working pump cannot value
Pressure doesn’t
Pressure changes
调整后压力有
after adjustment
变化
Pump axle is broken or
Repair or change
Internal
leakage of swing 维修或更换油缸
multiple unit valve
动臂油缸内漏
是
Yes
arm cylinder
Check pedal and cable.
1. Leakage of swing arm
Adjust rotating speed
1.动臂滑阀泄
slide valve
to specified value
漏
维修或更换多路
2.2.主安全阀内
Internal leakage of main Change filter screen
阀
safety
漏 valve
Accelerator pedal or cable
因油门踏板、
cause
low rotating speed
否
No
是
Yes
油门拉线等原
因导致转速过
blocked
低
检查踏板、油
门拉线等，调
整转速至规定
值
Oil absorption channels are
吸油管路堵塞
更换滤网
2）Slow and weak bucket （analysis and judgment
process）
Reason
起因
Broken
seal ring causes
因密封圈损坏
是
Yes
Check whether
检查转斗油缸
rotating bucket
cylinder has internal
是否内漏
leakage
No
否
Check whether setting
pressure of two
检查转斗油缸
overload
valves in
两过载阀调定
rotating bucket
压力是否正常
cylinder is normal
933、936、938、952大腔
Pressure in big cavity of 933, 936,
压力18～18.5MPa，918、
938 and 952 is from 18 to
953、956大腔压力20～
18.5MPa. Pressure in big cavity
of 918, 953 and 956 is from 20 to
20.5MPa，958、968大腔
20.5MPa. Pressure in big cavity
压力21.5MPa，40F大腔压
of 958 and 968 is 21.5MPa.
力15.5MPa，所有机型小
Pressure in big cavity of 40F is
腔压力12～12.5MPa。
15.5MPa. Pressure in small
cavity of all types is from 12 to
12.5MPa.
internal
leakage and bucket
造成内漏，铲
Measures
措施
Change seal ring
更换密封圈
斗掉斗
dropping
Yes
是
Check whether broken
检查转斗滑阀
rotating bucket slide
是否损坏导致
valve causes internal
内漏 leakage
Scratching
or wear on valve
转斗阀杆和阀
Yes
是
rod孔出现拉沟﹑
or valve hole of rotating
维修或更换
Repair or change
划伤或磨损而
bucket
makes leakage of
使液压油泄漏
hydraulic
oil large
大
1. Main valve core of
No
否
Check whether
检查过载阀是
overload valve has
internal leakage
否内漏
1.清洗主阀芯，
1. Wash main valve
去除杂质
芯有杂质颗
particles, which makes
core and remove
粒，将主阀芯
2.更换密封圈
overload
valve open
impurities
卡死，使过载
3.更换过载阀
2. Aging of seal ring
2. Change seal ring
阀处于常开状
3. Improper clearance
3. Change overload
态
between valve core and
valve
2.密封圈老化
valve
body
3.阀芯与阀体
1. 的配合间隙不
Low pressure of overload
合适
valve
causes bucket
1. Adjust pressure to
overload
valve has dust
1.过载阀主阀
Yes
是
No
否
dropping or floating
Check whether
检查过载阀压
pressure of overload
valve is low
力是否偏低
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Yes
是
1.过载阀压力
2. Spring of overload valve
偏低导致掉斗
is broken or invalid
或发飘
2.过载阀弹簧
折断或失效
specified value
1.调整压力至规
2. Repair or change
定值
2.维修或更换
3）Bucket turns over or shakes during lifting operation
（analysis and judgment process）
No
Reason
Measures
Oil amount is not
Add hydraulic oil to
enough
specified mark
Change or repair
Check whether
oil amount
meets standard
Oil position is
between 6 and 10
on mark of
hydraulic oil tank
Yes
Test pressure of
working device
hydraulic system
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.
918 is 17.5MPa. 953, 956
and 958 are 18MPa.
Check pressure
increases with
increase of engine
throttle
No
Check whether
indicator of
pressure gage
swings
intensively
No
Working gear pump
Yes
Check whether
starting pressure of
safety valve is
stable
Yes
No
wears or is broken
Check setting
Unstable starting
pressure of valve, and
pressure of safety
whether spring
valve changes
deforms. Adjust
pressure of hydraulic
starting pressure
oil
Repair or change
Caused by aging and
Check whether oil
channels are
blocked or flat
foaming of inlayer of
Yes
rubber tubes, or
blocking of transiting
valve block and joint
When system pressure and
hydraulic oil amount are
normal, check whether leakage
amount of rotating bucket
cylinder and swing arm
cylinder are same
Check whether oil
absorption rubber
tubes are well
sealed
Yes
makes working
Repair or change
pressure unstable
Different leakage
No
amount causes flow
fluctuation and
shaking
Yes
Loosen piston makes
When system pressure and
hydraulic oil amount are
normal, check whether pistons
in rotating bucket cylinder and
swing arm cylinder are loosen
Repair or change
Air entering system
piston rod move in
No
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hydraulic cylinder
Repair or change
4）Hydraulic oil temperature is too high
（analysis and judgment process ）
Reason
起因
Check whether position of hydraulic oil is too
检查液压油油位是否过低
low
Insufficient
hydraulic oil
液压油量不足
Yes
是
No
否
Check
whether hydraulic oil is too dirty or goes
检查液压油是否过脏或变质
bad
规定的要求
air
Change or filter hydraulic oil
件，造成节流
blocked,
causing throttling
增温
and
temperature rise of
否
No
Add
hydraulic oil to specified mark
添加液压油到
makes
working pump absorb
使工作泵吸空
卡滞液压元
Hydraulic
components are
是
Yes
Measures
措施
更换或过滤液
压油
Clean with high pressure gun
Too much grease causes poor
检查水箱散热片叶片之间油
Check whether there is too much grease
between blades of cooling fin in water box
泥过多
Yes
是
用高压水枪进
Repair
or change
散热不良
Blocking
in radiator or other
行清洗
reasons cause poor heat
No
否
Check whether hydraulic radiator has
检查液压散热器是否出现问
problem
题
油泥过多导致
heat
dissipation
dissipation
Repair or change
When
system pressure is set
因散热器内堵
Yes
是
too
high, overflow valve
塞等原因导致
维修或更换
cannot
overflow and reduce
散热性变差
pressure normally, internal
当系统压力调整
leakage will increase, oil
过高时，溢流阀
temperature of system will
不能正常溢流降
rise. When oil returning filter
压造成内泄漏增
core is blocked or oil
加，致使系统油
returning channels become
温升高。当回油
old and delaminate, back
滤芯堵塞或回油
pressure will be high and oil
管老化脱层时造
temperature will rise.
成背压偏高，也
Serious internal leakage of
会造成油温升高
No
否
Check whether improper pressure setting
检查是否因压力调整不当造
causes high temperature of hydraulic oil
成液压油高温
Yes
是
No
否
维修或更换
Repair or change
hydraulic components will
Check whether cylinder, pump and valve have
检查缸、泵、阀等是否内漏
cause
temperature rise of
液压元件内漏
Yes
是
严重可造成系
system
leakage
Repair or change
维修或更换
统温度升高
Low
volumetric efficiency will
No
否
cause temperature rise of
Check
whether gear pump, gear pair, side plate
检查齿轮泵齿轮副、侧板或
or pump body have wear
泵体是否存在磨损
hydraulic
oil
容积效率过低
是
Yes
导致液压油温
上升
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维修或更换
2. Failure Case Analysis of Steering Hydraulic System
1）Heavy steering（analysis and judgment process）
Reason
Air in system
Decide according to fault
phenomenon
oil pump leaks.
Yes
Heavy steering. Steering cylinder
doesn’t move.
Check whether
steering pillar is
flexible
No
Is fast steering
heavy and slow
steering light?
Remove air in system.
Check whether oil inlet of
Yes
Cylinder crawls. Foam in oil. Regular
sound
Measures
Yes
-One-way valve
-Check whether steel ball
failure of manual
exists and whether it is
steering
blocked
-Leakage of FK
-Change FK combination
overload valve
valve
-Internal leakage of
-Check whether oil cylinder
oil cylinder
has internal leakage
Repair or change
No
Whether system
pressure meets
the needs
No
Check whether
feedback oil
channels are
unblocked
Steering pillar is
Yes
broken
Clean or change
Pipelines are
No
Yes
Adjust system
Yes
press. Does the
pressure change?
blocked
Repair or change
Low system
pressure
Adjust system pressure
Spring of priority
No
valve is broken.
Yes
Shuttle valve is
Is surface of
hydraulic oil low?
Yes
blocked
Supplement hydraulic oil
Lack oil
Clean or change
Pipelines are
No
Is oil sucking pipe
blocked?
Yes
blocked
Wear and internal
No
leakage of steering
pump
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Repair or change
2）No terminal point for steering or limit position
cannot be reached （analysis and judgment process)
No terminal
point
Failure Reason
Troubleshooting
Method
After steering cylinder turns to extreme
position, turning the steering wheel,
steering wheel can turn lightly, which
means no sense of terminal point.
Low overload
Increase overload
valve pressure
valve pressure
properly
Steering cylinder cannot
turn to extreme position
Steering cylinder cannot turn to
extreme position. Steering
response is heavy.
Failure Reason
Troubleshooting Method
Low safety valve
Increase safety valve
pressure
pressure properly
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3）Reason for Vehicle Deflection
① 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.
② Check whether connecting rod of oil cylinder is loosen.
③ Leakage in oil cylinder
④ Pressure of two tires has big difference.
⑤ Leakage on two-way overload valve or two-way supplemental valve.
⑥ Air in oil
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4）Inaccurate Steering
① Air in system;
② Pin of oil cylinder is loosen;
③ Priority valve or main valve of
flow divider valve is blocked;
L
R
T
P
④ Oil cylinder has leakage;
⑤ Low efficiency of pump causes
unstable pressure.
p
Fixed
Pump
Filter
Reservoir
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Engine
5）Steering wheel rotates freely. Steering doesn’t
move or slow.
① Serious leakage in two-way
overload valve
② Serious leakage in piston of oil
cylinder
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6）Blanking Stroke of Steering Wheel
① Connection of steering pillar and steering gear
wears or is broken
② Nut on steering wheel
moves
L
R
T
P
③ Air in oil
p
④ Leakage in two-way
overload valve
Fixed
Fixed
Pump
Pump
Filter
⑤ Leakage in steering
cylinder
Reservoir
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Engine
Engine
7）Steering wheel shakes or rotates
① 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
② When oil in pump is connected to Port R or
L, steering gear will rotate like motor.
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8）Steering wheel rebounds
Reason：One-way valve at oil inlet of
steering gear is broken.
Function of one-way valve:
Prevent backflow of oil when pressure of
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.
14/03/2016
Reliability
bears great
trust!
14/03/2016