loader hydraulic training courseware

Loader Hydraulic Training Courseware

2011

Main Content

� Suitable Group

� Contents

� Training Objectives

19/05/2015

� Evaluation Topics

� Contents

Suitable Group

This course is suitable for domestic and foreign intermediate and above technical service personnel

It also applies to…

19/05/2015

Main Content

� Suitable Group

� Contents

� Training Objectives

19/05/2015

� Evaluation Topics

� Contents

Training Objectives

1. This training course is expected to have 12 hours.

2. After training of this course, students should master the following main knowledge points:

（1）Basic knowledge of hydraulic system

（2）Structure and principle of LG hydraulic system

19/05/2015

（2）Structure and principle of LG hydraulic system

（3）Common failure and troubleshooting of systems and components

1

Basic Knowledge of Hydraulic Transmission

1

Contents

19/05/20152015/5/19

Hydraulic System Introduction of LG Loader

2

1

Basic Principle of Hydraulic Transmission

Composition of Hydraulic Transmission System

1

2

Part 1 Basic Knowledge of Hydraulic

Transmission

3

4

Advantages of Hydraulic Transmission System

Disadvantages of Hydraulic Transmission

System

19/05/20152015/5/19

5

6

7

8

System

Hydraulic Medium

Hydraulic Power Components

Hydraulic Control Components

Hydraulic Actuating Components

●●●● A machine is basically made up of four parts, including prime motor,

transmission device, working mechanism, and assistant mechanism.

The purpose of prime motor is to change various forms of energy into

mechanical energy, which is power supply of the machine. Working

mechanism works outside with mechanical energy. Transmission device

ⅠⅠⅠⅠ. Basic Principle of Hydraulic Transmission

19/05/2015

mechanism works outside with mechanical energy. Transmission device

between prime motor and working mechanism transfers power and

controls.

There are many transmission types. Transmission can be divided into

mechanical transmission, power transmission, pneumatic transmission and

liquid transmission by parts or working medium.

●●●● Transferring and controlling energy with liquid as working medium is

called liquid transmission.

It can be divided into hydraulic pressure transmission and hydraulic

transmission by principle. Hydraulic pressure transmission mainly


19/05/2015

transmission by principle. Hydraulic pressure transmission mainly

delivers power with liquid pressure. Hydraulic transmission mainly

transfers power with kinetic energy of liquid.

●●●● Take hydraulic jack for example to

illustrate principle and features of

hydraulic transmission.

1. Force transmission follows Pascal's

Principle

1））））Thrust on piston equals oil pressure times


19/05/2015

piston area.

2））））P, oil pressure, depends on external load.

2. Loading speed transfers according to the

principle of equal liquid volume after

changes. Its speed depends on quantity

of flow. Ignoring loss, hydraulic

transmission force is irrelevant with

speed.

Pressure：：：：P=F1/A1=F2/A2；；；；(Pascal's Principle)

Quantity of flow：：：：Q=A1V1=A2V2; (V=S/t)

(the Principle of Continuity )；；；；

Power：：：：P＝＝＝＝V1F1=V2F2=PQ ；；；；

Figure 1-1 Working Principle of Oil Jack

1-oil tank 2-control valve 3,6-cylinder 4,7-plunger 5-lever

8,9-one-way valve 10,11-pipelines

1. Hydraulic Power Supply

Components converting mechanical energy into liquid pressure. Typical

component is hydraulic pump.

2. Control Components

Control force, movement speed and direction actuating components by

controlling pressure, flow quantity and direction of fluid. Pressure, flow

ⅡⅡⅡⅡ. Composition of Hydraulic Transmission System

19/05/2015

controlling pressure, flow quantity and direction of fluid. Pressure, flow

quantity and direction usually control hydraulic valve.

3. Actuating Components

Components converting liquid pressure into mechanical energy,

including hydraulic cylinder moving in a straight line and hydraulic

motor with rotation movement.

4. Assistant Components

Other devices besides the above three components to guarantee

normal operation of the system in the system have delivering, storage,

heating, cooling, filtration, measurement and other functions, such as

pipeline, connector, fuel tank, radiator, filter, etc.

ⅡⅡⅡⅡ. Composition of Hydraulic Transmission System

19/05/2015

pipeline, connector, fuel tank, radiator, filter, etc.

5. Working Medium

Deliver energy and signal with it.

1. Unit power is light in weight, which means large force and torque can be obtained with

lighter equipment weight.

2. Small inertia, fast starting and braking due to its small volume and light weight.

3. Stepless speed regulation is easy during operating process with a large speed regulation

range.

4. Linear reciprocating motion can be easily achieved with the help of hydraulic cylinder with

simple structure.

ⅢⅢⅢⅢ. Advantages of Hydraulic Transmission System

19/05/2015

5. Easy to realize automation

6. Easy to achieve overload protection. Work is safe and reliable.

7. Hydraulic transmission can layout transmission mechanism flexibly.

8. Liquid working medium with elasticity and vibration absorbing ability makes hydraulic

transmission smooth and reliable.

It can be lubricated by itself during operation. Easy heat dissipation and long service life.

9. Easy to realize standardization, serialization and universalization. Easy to design,

manufacture and market.

1. Low transmission efficiency (75% ~ 80%). Leakage and environmental pollution.

2. Largely influenced by temperature change during operation.

3. Reliability of hydraulic system is still not as good as that of power transmission and

mechanical transmission.

4. Hydraulic components have high requirements to manufacturing accuracy and high

manufacturing cost. Use and maintenance require a certain professional knowledge and

a higher level of skill.

ⅣⅣⅣⅣ. Disadvantages of Hydraulic Transmission System

19/05/2015

a higher level of skill.

5. Acquisition and transfer of hydraulic energy is not as convenient as that of electricity.

Due to pressure loss and other reasons, hydraulic energy should not be transmitted

over a long distance.

6. Components, accessories and working medium in the hydraulic system work in a

closed system. Failures are difficult to discover in time. Failure causes are difficult to

determine.

7. Hydraulic transmission is sensitive to pollution of hydraulic oil and easy to have

failures.

• Energy and signal transmission;

• Lubricate hydraulic components, and reduce friction and wear;

• Heat dissipation;

• Corrosion prevention;

ⅤⅤⅤⅤ. Hydraulic Transmission Medium

1. Functions of Hydraulic Medium

19/05/2015

• Corrosion prevention;

• Sealing of clearance in hydraulic components to prevent dual friction;

• Transmission, separation and precipitation of non-soluble

contaminants; and

• Provide diagnosis information for component and system failure.

• One is flammable hydrocarbon hydraulic oil (mineral oil type and

synthetic hydrocarbon type);

• Another is nonflammable (or fire resistant) hydraulic fluid.


2. Types of Hydraulic Medium

19/05/2015

• Another is nonflammable (or fire resistant) hydraulic fluid.

• Nonflammable fluid includes aqueous (such as HFA, HFB and HFC)

and non-aqueous synthetic fluid（（（（HFD））））.

1））））Viscosity

2））））Abrasion resistance

3））））Oxidation stability and thermal stability

4））））Demulsibility and hydrolytic stability


3. Main Performance of Hydraulic Medium

19/05/2015

4））））Demulsibility and hydrolytic stability

5））））Defoaming

6））））Anti-corrosion

7）））） Shear stability

8）））） Material compatibility

9）））） Filtering property

10）））） Other performance requirements


3. Main Performance of Hydraulic Medium （（（（Continued））））

19/05/2015

10）））） Other performance requirements

Other requirements include flame resistance, resistance to low temperature,

radiation resistance (radioresistant) stability, nonpoisonous and tasteless,

harmless to human body, easy processing of waste fluid and other

performance.

• HH Hydraulic Oil. HH Oil is refined mineral oil without any additives.

• HL Hydraulic Oil. HL Oil is made from neutral base oil with high refined depth,

and antioxidant and anti-rust . It is anti-corrosive and anti-oxidative type.

• HM Hydraulic Oil. HM Oil is developed from HL anti-corrosive and anti-oxidative

oil.


4. Classification and Features of Hydraulic Oil of Mineral Oil Type

19/05/2015

oil.

• HR Hydraulic Oil. HR Oil is HL Oil added with viscosity index additive, which

makes oil viscosity decrease with temperature change.

• HG Hydraulic Oil. HG Oil is HM Oil added with anti-sticking agent (oiliness

solvent or antifriction agent)

• HV and HS Oil. HV and HS Oil are both low-temperature hydraulic oil used over

wide range of temperature variation according to ISO Standard. HV Oil is mainly

used in cold area. HS Oil is mainly used in freezing area.

●●●● Key Points of Reasonable Use

1））））Identify variety and mark of oil;

2））））Hydraulic system should be thoroughly cleaned before

liquid filling;

3））））New oil must be filtered before use;


5. Reasonable Use and Maintenance of Hydraulic Medium

19/05/2015

3））））New oil must be filtered before use;

4））））Oil cannot be mixed optionally;

5））））Pollution should be strictly controlled to prevent moisture,

air and solid impurities from entering hydraulic system.

●●●● Monitoring of hydraulic oil of mineral oil type

Due to mechanical, chemical and physical effect, additive in oil will be

gradually consumed during use and oil will decay. Its performance will

gradually deteriorate, which is characterized by:

1））））Changes of oil state, such as odor, color and appearance;



19/05/2015

1））））Changes of oil state, such as odor, color and appearance;

2））））Point of flammability decreases. other oil may be mixed;

3））））Mechanical impurities increase;

4））））Viscosity changes；；；；

5））））Acid value increases;

6））））Demulsibility becomes bad; and

7））））Defoaming becomes bad.

●●●● Replacing of hydraulic oil of mineral oil type

• For some main performance parameters of oil should be monitored periodically

and frequently. When deterioration reaches a certain degree, oil must be

replaced. At present, there are generally 3 methods to determine the oil

replacing period.

1) Specify fixed oil replacing period



19/05/2015

1) Specify fixed oil replacing period

Specify fixed oil replacing period according to equipment, condition and type of

oil and oil injection quantity, such as half a year, one year or operation of 1000

to 2000h;

2））））Determine whether to replace oil according to experience and observation of oil

sample; and

3））））Specify oil drainage index. Determine whether to replace oil according to test

result of oil sample;

●●●● Pollution of hydraulic oil is mainly caused by the following reasons.

1））））If sand, scraps, abrasive materials, welding slag, rust slice, dust and other dirt in

pipelines of hydraulic system and hydraulic components are not removed in

washing before use, these dirt will enter hydraulic oil when hydraulic system

works.


6. Pollution and Protection of Hydraulic Oil

19/05/2015

2））））External dust and sand, and oil lead flowing back into the tank pass the

repeatedly stretching piston rod during operation of hydraulic system and enter

hydraulic oil. In addition, dust, cotton lint and other things may enter hydraulic oil

during maintenance due to carelessness.

3））））Hydraulic system itself also constantly produces dirt, which will directly enter

hydraulic oil, such as wear particles of metal and seal materials, particles

dropping form filter materials, jelly generated due to oxidative deterioration of

fiber and oil caused by oil temperature increase, etc.

●●●● Harms of oil pollution

Serious hydraulic oil pollution will directly influence work performance of

hydraulic system, cause frequent failure of hydraulic system , and shorten

service life of hydraulic components. Main reason causing these risks are

particles in dirt. For hydraulic components, if these solid particles enter



19/05/2015

particles in dirt. For hydraulic components, if these solid particles enter

components, wear of sliding parts of components will be intensified, orifice and

damping hole in hydraulic components may be blocked, or spool will be stuck,

causing hydraulic system failure. Water and air mixing will reduce lubrication

capacity of hydraulic oil reduction, accelerate oxidative deterioration, cause

corrosion, accelerate corrosion of hydraulic components, and make hydraulic

system vibrate or craw.

●●●● Pollution prevention measures

1））））Keep hydraulic oil clean before use;

2））））Keep hydraulic system clean after assembling and before operation;

3））））Keep hydraulic oil clean during operation;



19/05/2015

3））））Keep hydraulic oil clean during operation;

4））））Use appropriate oil filter;

5））））Regularly replace hydraulic oil; and

6））））Control working temperature of hydraulic oil.

Hydraulic pump works on the principle of

Hydraulic power components provide power supply for the system. They are

indispensable core components of the system. Hydraulic pump is the power

component providing the system with certain flow quantity and pressure.

ⅥⅥⅥⅥ. Hydraulic Transmission Components

1. Working Principle of Hydraulic Pump

19/05/2015

Hydraulic pump works on the principle of

seal volume change, so it is generally

called volumetric hydraulic pump.

The operation principle is explained with

Figure and gear pump.

Figure

1））））With several seals and can periodically change space;

2））））Absolute pressure of liquid in the tank must be identical to or greater than

the atmospheric pressure, which is the external condition for volumetric

hydraulic pump to absorb oil.

3））））Have corresponding assignment mechanism to separate oil absorption


2. Features of Hydraulic Pump

19/05/2015

3））））Have corresponding assignment mechanism to separate oil absorption

cavity from liquid discharge cavity.

Ensure regular and continuous absorption and discharge of liquid of

hydraulic pump . Hydraulic pumps with different structure principle have

different assignment mechanism.

1））））Pressure

Working pressure, rated pressure and maximum permissible pressure.

2））））Discharge and flow

Theoretical flow, rated flow, and actual flow


3. Main Performance Parameters of Hydraulic Pump

19/05/2015

3））））Power and efficiency

●●●● Power loss of hydraulic pump includes volume loss and mechanical

loss.

●●●● Power of hydraulic pump: input power and output power

1））））By structure: Gear pump, vane pump, plunger pump, screw pump, etc.

①①①① Gear pump: Inner gearing gear pump and outer gearing gear pump;

②②②② Vane pump: Single acting vane pump and double acting vane pump;

③③③③ Plunger pump: Axial plunger pump, radial plunger pump and valve oil

distributing valve plunger pump;


4. Type of Hydraulic Pump

19/05/2015

distributing valve plunger pump;

2））））By function: Constant delivery pump and variable pump

gear pump axial plunger pump radial plunger pump

Hydraulic transmission control and regulating components are also

called control valve, valve for short. They are used to control

direction of flow and adjust pressure and flow of fluid of, in order to

satisfy start, stop, redirection, speed regulation, voltage

ⅦⅦⅦⅦ. Control Components (Hydraulic Valve)

1. Concept

19/05/2015

satisfy start, stop, redirection, speed regulation, voltage

stabilization, unloading, pressurization, decompression and other

operational needs of actuating components.

1）））） In structure, all valves consist of valve body, valve spool (turn valve or

slide valve) and components of driven valve spool movements (such as

spring and electromagnet).

2）））） In working principle, relationship among opening size, pressure

difference between inlet and outlet of valve and flow through valve of all


2. Common Features

19/05/2015

difference between inlet and outlet of valve and flow through valve of all

valves comforts to orifice flow formula, but different valves have

different control parameters.

●●●● Performance Parameters

①①①① Nominal pressure Maximum working pressure allowed by long-term reliable

work of hydraulic control valve , which is limited by intensity of valve. Actual

permissible maximum working pressure is also related to other factors, such


3. Performance Parameters and Basic Requirements of Hydraulic Control Valve

19/05/2015

as reversing reliability of reversing valve and pressure regulating scope of

pressure valve.

②②②② Nominal diameter Unit of nominal diameter of hydraulic control valve is mm. A

certain nominal diameter represents a certain of flow capacity, which is

permissible maximum flow (nominal flow). It should be pointed out that, valves

with the same nominal diameter may have different nominal flow because of

their different functions.

●●●● Performance requirements

a. High action sensitivity. Reliable to use. Small impact and vibration during

operation. Low noise.

b. When valve port is closed, sealing should be good. When valve port is opened,


3. Performance Parameters and Basic Requirements of Hydraulic Control Valve

19/05/2015

direction valve should have small fluid flow pressure loss, direction valve

should have good core stability.

c. Controlled parameters (pressure or flow) should have high precision and

small fluctuation when influenced by outside interference.

d. Compact structure. Convenient to install, debug and maintain. High

universality.

There are many varieties of control valves used in hydraulic transmission, which can

be classified by characteristics. It is the most common to classify by purpose of

control valves.

（（（（1））））Directional control valve (such as one-way valve and reversing valve);

（（（（2））））Pressure control valve (such as overflow valve, pressure reducing valve and


4. Classification of Hydraulic Control Valve

19/05/2015

（（（（2））））Pressure control valve (such as overflow valve, pressure reducing valve and

sequence valve);

（（（（3））））Flow control valve（（（（such as throttling valve, flow speed control valve and flow

distributing and collecting valve );

They can also be classified by structure, operation mode, connection mode, control

mode, adjustability of output parameters, etc. Different combination valves can be

composed according to needs.

• Concept：：：：Valve used to control fluid flow pressure in the hydraulic system

or control.

• Common Points：：：：Work in the principle of balanced liquid pressure and

spring force on valve core.

• Classification：：：：


5. Pressure Control Valve

19/05/2015

• Classification：：：：

Overflow valve－－－－safety valve and constant pressure valve;

Pressure reducing valve－－－－fixed pressure reducing valve, fixed

differential reducing valve and proportional pressure reducing valve;

Sequence valve－－－－ sequence valve, unloading valve, back pressure

valve, balanced valve, hydraulic switch, etc.

●●●● Main purpose of overflow valve is pressure leveling (constant pressure valve) or

security protection (safety valve) of hydraulic system.

Almost all the hydraulic systems need to use it. Its performance has very big effect on

normal operation of the whole hydraulic system.

●●●● System figure illustrates the role of overflow valve. Overflow Valve 2 in the left figure


1）））） Overflow valve

19/05/2015

●●●● System figure illustrates the role of overflow valve. Overflow Valve 2 in the left figure

is constant pressure valve. Overflow Valve 2 in the right figure is safety valve.

constant pressure valve

safety valve

●●●● Structure type: can be divided into directly

operated type and pilot operated type by form

of structure and basic action mode.

①①①① Directly operated overflow valve（（（（see figure））））


1）））） Overflow valve（（（（Continued））））

19/05/2015

Directly operated overflow valve controls on-off

movement with pressure oil in the system directly

acting on valve core which is balanced with spring

force.

Limited by structure and control precision, directly

operated overflow valve is commonly used in little

traffic system with low pressure (less than 2.5 MPa).

Function Symbol Map

Figure of Low-pressure Directly Operated Overflow Valve

1-nut 2-pressure adjusting spring 3-top cover 4-valve core 5-valve body

②②②② Pilot operated overflow valve （（（（see figure

for operating principle））））

● Consist of main valve and pilot valve;

●●●● Damping hole has small diameter (0.6-1.2);

Easy to block. Will not operate normally.


1) Overflow valve（（（（Continued））））

Remote Control

19/05/2015

Easy to block. Will not operate normally.

● Advantages in performance (pressure

adjusting range, on-off characteristic,

dynamic performance, remote control, etc.).

Suitable for system with high pressure and

big flow.

Function Symbol Map

Principle Demo

Pilot Overflow Valve

1-spring of main valve 2-main valve core 3-damper hole

4-valve core of pilot valve 5-sping of pilot valve

Pressure reducing valve is a pressure control valve

which makes outlet pressure (secondary pressure)

below inlet pressure (primary pressure). Its function

is to provide two or several different pressure

output with one oil source.


2））））Pressure reducing valve

19/05/2015

output with one oil source.

In addition, when oil pressure is unstable, a stable

low pressure can be obtained by putting a pressure

reducing valve in the return circuit.

It can be divided into fixed pressure reducing valve,

fixed differential reducing valve and proportional

pressure reducing valve by pressure controlled by

pressure reducing valve.Function Symbol Map

Pressure Reducing Valve

1-main valve core 2-damper hole 3-vavle core of pilot valve V-flow speed of valve port

L-outside leakage port

As in the picture above, working principle of fixed pressure reducing valve can be considered according to

that of pilot operated overflow valve .

Compare pilot operated pressure reducing value and pilot operated overflow valve. They have the

following differences.

a. Pressure reducing valve keeps outlet pressure basically unchanged, and overflow valve keeps inlet

pressure basically unchanged.


2) Pressure reducing valve

19/05/2015

b. When not working, inlet opening and outlet opening of pressure reducing valve are connected. Inlet

opening and outlet opening of overflow are not connected.

c. To ensure pressure setting value of outlet of pressure reducing valve is constant, its spring cavity of

pilot valve needs to be connected to external oil tank separately through drain port. Outlet of overflow

valve is connected to oil tank, so its spring cavity and oil leakage of pilot valve can be connected to

outlet through pass on the valve. It doesn’t need to be connected to external oil tank separately.

★★★★ Other types of pressure reducing valves will not be described.

●●●● Sequence valve is a pressure valve which allows

actuating components to act successively with

pressure. See figure for working principle.

●●●● Sequence valve includes directly operated type

and pilot operated type. The former is generally


3））））Sequence valveRemote Control

19/05/2015

and pilot operated type. The former is generally

used in low pressure system. The latter is used in

middle or high pressure system.

●●●● Sequence valve and overflow valve have similar

structure. Compare pilot operated sequence valve

and pilot operated overflow valve. They have the

following differences.

Fu

nc

tion

Sym

bo

l M

ap

directly operated external control sequence valve

pilot operated sequence valve

Pilot Sequence Valve

①①①① Inlet pressure of overflow valve is basically unchanged

under through-flow condition. Inlet pressure of

sequence valve is determined by outlet pressure under

through-flow condition. If outlet pressure p2 is much

lower than inlet pressure p1, p1 will be basically


3））））Sequence valveRemote Control

19/05/2015

unchanged. When p2 increases to a certain degree, p1

will also increase. p1 = p2 + ∆ p. ∆ p is pressure loss

on sequence valve.

②②②② Overflow valve has internal leakage and sequence

valve needs to separately draw out leakage path,

which is external leakage.

③③③③ Outlet of overflow valve has to return to the oil tank.

Outlet of sequence valve can be connected to load.

Fu

nctio

n S

ym

bo

l Mapdirectly operated external

control sequence valve

pilot operated

sequence valve

Pilot Sequence Valve

Pressure switch is a electrohydraulic control

component converting oil pressure signal into

electrical signal. When oil pressure reaches setting

pressure of pressure switch, electrical signal will


4) Pressure switch（（（（hydraulic switch））））

19/05/2015

pressure of pressure switch, electrical signal will

be sent out to control movements of electromagnet,

electromagnetic clutch, relay and other

components, so as to realize sequential actions of

oil-way pressure relief, reversing and actuating

components, or close electromotor to stop

operation of system for safe protection, etc.

1—Plunger 2—Lever 3—Spring 4—Switch

Structure Chart

Concept: Function of directional control valve is to control flow direction of fluid. It

realizes connection or disconnection of pathways with relative motion between valve

core and valve body, to meet requirements of the system.

Type: Directional control valve includes one-way valve and reversing valve.


6. Directional control valve

19/05/2015

One-wayReversing Valve（（（（2-position

figure））））

Rig

ht p

ositio

n o

f thre

e-p

ositio

n

fou

r-join

t rev

ers

ing

valv

e

Left p

ositio

n o

f thre

e-p

ositio

n

fou

r-join

t rev

ers

ing

valv

e

●●●● Classification of one-way valve

①①①① By function: Common one-way valve and hydraulic controlled one-way valve.

②②②② By structure: Tubular (direct connection) and plate (right angle)

1））））One-way valve

19/05/2015

Tubular Plate

Oil Inlet P1

Oil Outlet P2

Oil Inlet P1 Oil Outlet P2

①①①① Common One-way Valve

●●●● Principle and performance: One-way valve only allows fluid flow to flow in one direction, but not reverse

flow. It can be used for outlet of hydraulic pump, to prevent system oil from flowing back; it can be used

to separate the connection between oil channels, to prevent oil from mutual interference; it also can be

used as the bypass valve to connect parallelly with sequence valve, pressure reducing valve, throttling

valve and speed control valve, so as to assemble into one-way sequence valve, one-way pressure

reducing valve, one-way throttling valve one-way speed control valve, etc.

19/05/2015

●●●● Structural form and

function symbol:

●●●● Opening pressure:

Generally 0.04～～～～0.1MPa;

opening pressure of back

pressure valve is 0.2～～～～

0.6 MPa

Oil Inlet P1Oil Outlet P2



(d) Symbol

Mode

Mode

Mode

●●●● Application:

①①①①Reverse protection of hydraulic pump

On one hand, prevent system pressure from influencing normal operation of pump. On the other hand, prevent the liquid from flowing back to oil tank through pump when stopped.

②②②②Separate oil channels prevent interference

19/05/2015

③③③③Comprise combination valve

One-way valve can comprise one-way combination valve with other valves

④④④④Installed in outlet oil line to produce back pressure

②②②②Hydraulic Controlled One-way Valve

●●●● Principle and performance: When the hydraulic controlled port K doesn’t connect pressure oil,

its function is same to common one-way valve. When the hydraulic controlled mouth

connects oil, valve can flow freely in two ways. The figure explains the working principle.

●●●● Structure: Hydraulic controlled piston, plunger, valve, spring etc.

●●●● Application：：：：Hydraulic controlled one-way valve has characteristics of common one-way

valve. It can also allow forward and reverse fluid flow to go through freely under certain

conditions. Therefore, it is commonly used in pressure maintaining, locking and balanced

circuit of hydraulic system.

19/05/2015

P1 P2

K

Function Symbol

Structure

Chart

symbol

Change flow direction and connect or cut off oil channels by relative motion of valve core in

valve body, so as to control reversing, start or stop of actuating components.

●●●● Classification of reversing valve

①①①① By motion mode of valve core relative to valve body:

Steering valve type, sliding valve type, ball valve type, etc.

②②②② By control method:

2））））Reversing Valve

Man

ual

Rev

ers

ing

Valv

e

19/05/2015

Manual, engine driven, electromagnetic, hydraulic, electric hydraulic, etc;

③③③③ By working position of valve core on valve body:

Two-position valve and three-position valve

④④④④ By number of main oil port on valve body:

Two-port valve, three-port valve, four-port valve and five-port valve.

Man

ual

Rev

ers

ing

Ele

ctro

mag

netic

Rev

ers

ing

Valv

e

●●●●Control mode symbols of commonly used sliding

reversing valve

Electric SpringManualEngine Drive (Roller

Type)

19/05/2015

HydraulicHydraulic Pilot

ControlElectromagnetic-Hydraulic Pilot

Control

●●●●Working principle of sliding reversing valve

Valve CoreValve Body

19/05/2015

Position of Valve Core Valve Port State Piston State

Middle Port A and Port B don’t connect oil Stop

Left P A Right

Right P B Left

Big Box Valve bodySmall Box

Station

Crossover point of arrow line in the small box or┴ symbol and bounding

Oil port

Oil channels connected （（（（not always flow direction））））

●●●●Station and pathway symbols of main structure of reversing valve（（（（see figure））））

19/05/2015

always flow direction））））

┴ Oil channels disconnected

Functional chart of three-position four-port

reversing valve

Head of symbol

Normal position（（（（valve core without force);

A, B Oil ports connected to the oil tank；；；；

P, O Oil inlet and return opening

●●●● Principle and type symbols of main structure of reversing valve

Name Structure and Principle Chart Symbol

Two-position

two-port

A

P

A B

19/05/2015

Two-position

three-port

Two-position

four-port

A B

P O

A

P

B

Name Structure and Principle Chart Symbol

Two-position five-

port O1 O2

A B

P

A B

●●●● Principle and type symbols of main structure of reversing valve （（（（continued））））

19/05/2015

Three-position

four-port

Three-position five-

port

P O

A B

PO1 O2

A B

●●●● The most commonly used six median functions of

three-position reversing valve

Function

Model

Median Symbols State, Features and Application of Median

Symbols

O

Port P, A, B and O are all closed；；；； Hydraulic

cylinder is locked. Hydraulic pump doesn’t

unload.

19/05/2015

H

Port P, A, B and O are Hydraulic pump ; Piston

of hydraulic cylinder is floating. Hydraulic

pump unloads.

Y

Port P is closed. Port A, B and O are

connected. Piston of hydraulic cylinder is

floating. Hydraulic pump doesn’t unload.

Function

ModelMedian Symbols

State, Features and Application of Median

Symbols

P

Port P, A and B are connected. Port O is

closed. Pump and hydraulic cylinder are

connected, which can comprise differential

motion and connect inlet.

●●●● The most commonly used six median functions of three-

position reversing valve（（（（continued））））

19/05/2015

motion and connect inlet.

M

Port P and Port O are connected. Port A and

Port B are closed. Piston of hydraulic cylinder

is locked. Hydraulic pump unloads.

K

Port P, A and B are connected. Port O is

closed. Piston of is locked. Hydraulic pump

unloads.

●●●● Several Commonly Used Reversing Valves

Armature

Coil

①①①① Electromagnetic reversing valve

Valve Body

19/05/2015

Valve Core

Function Symbol

Three-position four-port electromagnetic reversing valve

Two-position four-port electromagnetic reversing valve

★★★★ Performance of electromagnetic reversing valve

◆◆◆◆ AC power type: Convenient to use. Big starting force. Big reversing

impact. Noisy. Low frequency (about 30 times/min). Coil is easy to burn

out when valve is locked or voltage is low.

19/05/2015

◆◆◆◆ DC power type: Small reversing impact. High tolerance level of

reversing frequency. Due to constant current, coil is not easy to burn out.

Working reliability is high, but structure is complicated.

②②②② Hydraulic reversing valve

Hydraulic controlled pressure

port

Hydraulic controlled pressure port

19/05/2015

Hydraulic three-position four-port reversing valve

Function Symbol

★★★★ Performance of hydraulic reversing valve

Hydraulic reversing valve changes position of valve core with oil pressure. It has

big starting force. When flow of hydraulic controlled oil is big, reversing impact is

big. To control movement speed of valve core and reduce impact, one-way

throttling device (called damper regulator) is usually installed in front of

hydraulic controlled pressure port.

19/05/2015

Damper Regulator

③③③③ Electro-hydraulic reversing valve

Pilot valve

（（（（electromagnetic valve））））

Main valve

（（（（electromagnetic

valve））））

19/05/2015

Control oil channel

Main oil channel

★★★★ Principle drawing of electro-hydraulic reversing valve

19/05/2015

channel

Simplified Function Symbol

★★★★ Performance of electro-hydraulic reversing

valve

Electro-hydraulic reversing valve is combination of electromagnetic reversing

valve (pilot valve) and hydraulic reversing valve (main valve). Therefore, it can

control the high-power main valve with small-power electromagnet. Oil source and

return oil of pilot electromagnetic reversing valve can be established separately. It

can also be shared with main oil channel.

19/05/2015

④④④④ Engine driven reversing valve（（（（motion valve））））

Oil Inlet

19/05/2015

Lift type, two-port, normally closed

Lift type, two-port, normally opened

Roller type, three-port

Oil OutletBack-moving SpringValve Core

Roller Push Rod

Purpose of engine driven reversing valve is to move valve core with cam-action

strokedog installed on actuating mechanism, in order to control on-off of oil

channels and control stroke.

Appropriate reversing speed is obtained and reversing impact is reduced by

★★★★ Performance of electro-hydraulic engine driven

reversing valve

19/05/2015

changing appearance of cam.

⑤⑤⑤⑤ Manual reversing valve

19/05/2015

Self-restoring Type

Mechanical Positioning Type

Manual reversing valve is convenient to use. It is applicable to

occasion with small flow and longer interval.

★★★★ Performance of manual reversing valve

19/05/2015

◆◆◆◆ 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

19/05/2015

3. Three-position four-port hydraulic with damper reversing valve（（（（Median function：：：：P）；）；）；）；

Figure 3Figure 2Figure 1

●●●● Overview: Movement speed of actuating components in the hydraulic

system is determined by oil flow entering actuating components. Flow

control valve is a hydraulic valve controlling the flow by changing flow

area of port (local resistance of throttling port) or length of channels.


7. Flow Control Valve

19/05/2015

area of port (local resistance of throttling port) or length of channels.

●●●● Classification: Common throttling valve, pressure compensation speed control valve,

overflow throttling valve, temperature compensation speed control valve, flow

distributing and collecting valve, etc. Functional chart of all kinds of valves is shown

as below. Working principle of each flow control valve will not be described. See


7. Flow Control Valve (Continued)

19/05/2015

teaching material.

• Function：：：：Convert pressure of liquid into mechanical energy. Make linear,

swinging and rotating with motion drive working mechanism.

• Type: Hydraulic cylinder and motor.

1. Hydraulic Cylinder

ⅧⅧⅧⅧ. Hydraulic Actuating Components

19/05/2015

1））））Type of Hydraulic Cylinder

Hydraulic cylinder has the following types by structure and function.

●●●● Single-acting hydraulic cylinder ●●●● Double-acting hydraulic cylinder

●●●● Swinging hydraulic cylinder ●●●● Combination hydraulic cylinder

2））））Single-rod Piston Cylinder

The piston only has piston rod at one end.

There are cylinder fixed type and piston

rod fixed type. Single-rod piston cylinder

is a commonly used oil cylinder type.

2. Motor1））））Features of Motor

Sketch Map of Single-rod Piston Cylinder


19/05/2015

1））））Features of Motor

Hydraulic motor is a device converting fluid pressure into mechanical energy. In

principle, hydraulic pump can be used as hydraulic motor, and hydraulic motor

can be also used as hydraulic pump. In fact the same type of hydraulic pump

and hydraulic motor have similar structure, but by the two have different work

situation, which makes the two different in structure. Main differences are as

follows:

• Hydraulic motor generally needs forward and reversing rotating, so it should

have symmetry in the inside structure. Hydraulic pump usually rotates in single

direction. It doesn’t have this requirement.

• In order to reduce oil absorption resistance and radial force, inlet port of

hydraulic pump is generally larger than outlet port. Pressure in low-pressure


1））））Features of Motor

19/05/2015

hydraulic pump is generally larger than outlet port. Pressure in low-pressure

cavity of hydraulic motor is slightly above atmospheric pressure, so it doesn’t

have the above requirement.

• Hydraulic motor is required to operate normally at a wide speed range. Therefore,

we should adopt hydraulic bearing or hydrostatic bearing. Because when motor

is at low speed, if hydraulic bearing is used, it is not easy to formed lubrication

film.

• Vane pump rotates at high speed with blades to generate centrifugal force, so that

blades always adhere to the inner surface of stator to seal the oil and form working

volume. If it is used as motor, spring must be installed on root of blades of hydraulic

motor, in order to ensure that blades always adhere to the inner surface of stator and

motor can normally start.

• Hydraulic pump should have self-priming capacity in structure , and hydraulic motor


1））））Features of Motor (Continued)

19/05/2015

• Hydraulic pump should have self-priming capacity in structure , and hydraulic motor

doesn’t have this requirement.

• Hydraulic motor must have large starting torque. Starting torque is the torque that

can be output by motor axle when motor starts from static state. The torque is

generally larger than that under operation condition under the same operating

differential pressure. Therefore, in order to make the starting torque near to torque

under operation condition, it is required that motor torque has small pulsation and

small internal friction.

Hydraulic motor can also be divided into gear type, vane type, piston

type and other types by structure types.


2））））Type of Motor

19/05/2015

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


3））））Axial Piston Motor

19/05/2015

Working Principle of Swash-plate Axial Piston Motor

piston motor and bent axial piston motor. See

figure for working principle (see textbook for

content).

F1=p*A*tanγ

T1=F*r=F*R*conφ=p*A*R*tanγ*conφ

T=ηm*∆p*V/2π

Torque of cylinder generated by piston

Total torque actually output by motor

Torque force of cylinder generated by piston

1Basic Knowledge of Hydraulic Transmission

1

Contents of Training Courseware

19/05/20152015/5/19

Hydraulic System Introduction of LG Loader

2

1

Working Device Hydraulic System

Steering Hydraulic

1

2

Part 2 LG Hydraulic

System Introduction

19/05/20152015/5/19

Steering Hydraulic

System 2

3 Case Analysis

ⅠⅠⅠⅠ. Working Hydraulic System

1. Type

Loader working device hydraulic system has two types by control method of

multiple unit valve .

1) Manual (Flexible Axle) Control Working Hydraulic System;

918, 933, 936, 40F, 952, 953, 956 and other types of our company

19/05/2015

use this type.

2) Hydraulic Pilot Control Working Hydraulic System;

Exported 918, 936, 938, 958, 959, 968, 969, 979 and other types of our

company use this type.

2. Principle of Working Hydraulic System

Manual manipulation of flexible axel makes swing

arm slide valve and rotating bucket slide valve of

multiple unit valve do reciprocating movement,

connects ports of oil inlet and slide valve of multiple

unit valve, changes flow direction of hydraulic oil,

Working and Steering Hydraulic System Demo


19/05/2015

unit valve, changes flow direction of hydraulic oil,

and realizes different actions of working device.

①①①①When flexible axel and rotating bucket reversing

valve of multiple unit valve are in the middle position,

flexible axel and bucket remain in the original

position. At this time, hydraulic oil in working oil

pump directly returns to oil tank through middle

channel of multiple unit valve.

Principle Drawing of Working Hydraulic System

②②②② Swing arm can lift, descent or float by controlling reversing slide valve on

swing arm.

③③③③ Bucket can turn forward and backward back controlling rotating bucket


2. Principle of Working Hydraulic System (Continued)

19/05/2015

reversing valve. Double-acting safety valves are installed on oil channels in

front and back cavity of rotating bucket oil cylinder to protect from

overloading of big and small cavity of rotating bucket cylinder caused by

rotating bucket link mechanism.

3. Composition of Working Hydraulic System

●●●● Gear pump（（（（working

pump））））

●●●● Multiple unit valve

●●●● Oil cylinder (swing arm cylinder and rotating


19/05/2015

cylinder and rotating

bucket cylinder））））

●●●● Oil tank（（（（shared with

steering system））））

●●●● Pipe, filter and other accessories

Describe the components according to system principle drawing

System Principle Drawing

Gear Pump（（（（Working Pump））））

●●●● Main parameters（（（（take LG953 and CBGj3166 for example））））

1））））Rated pressure （（（（18MPa））））

2））））Rated rotate speed（（（（2200r/min））））

3））））Displacement（（（（166ml/r））））

★★★★ Liquid volume discharged per round of hydraulic pump

19/05/2015

Liquid volume discharged per round of hydraulic pump

4））））Flow（（（（265 l/min)

★★★★ Flow= Displacement××××Rotate speed

★★★★ Module of transfer gear with 42 gear teeth, working pump spindle

with 42 gear teeth and steering pump gear with 48 gear teeth are all 4.

●●●● Working Principle of Gear Pump

Gear pump is a hydraulic pump widely used in hydraulic system. It is generally made into quantitative

pump. By structure, gear pump can be divided into outer gearing gear pump and inner gearing gear pump.

Outer gearing gear pump is most widely used. working principle of outer gearing gear pump will be

explained with outer gearing gear pump.

It generally has separate three-piece structure. Three-piece

means front and back pump cover and pump body. A pair of gear

are installed in the pump body. They have the same number of

19/05/2015

are installed in the pump body. They have the same number of

gear teeth and gear into each other. Their width are close to that

of pump body. This pair of gear form a seal chamber with covers

at two ends and pump body. Tooth point of gear and gearing line

divide the seal chamber into two parts, which are oil absorption

cavity and oil pressure chamber. Two gears are respectively

fixed on driving axle and driven axle supported by needle roller

bearing with keys. Driving axle is driven by power machine.

Figure of Outer Gearing Gear

Demo Map

When driving gear of the pump rotates according to direction of arrow as shown in the figure,

teeth on the right of gear (oil absorption cavity) will throw out of gear and gear teeth will exit

tooth space, so that sealing volume will increase and partial vacuum will be formed. Under

the action of external atmospheres, oil in the oil tank will enter tooth space through oil

absorption channels and oil absorption cavity. With gear rotating, inhaled tooth between oil

was brought to the other side, into the pressure oil chamber. Then rotation of gear, oil

absorbed into tooth space will be brought to the other side and enter oil pressure cavity. At

this time, gear teeth are engaged each other, so that sealing volume will decrease and some

●●●● Working Principle of Gear Pump (Continued)

19/05/2015

this time, gear teeth are engaged each other, so that sealing volume will decrease and some

oil in the gear will be squeezed out, which forms oil pressure process of gear pump. During

gear engagement, tooth contact line will separate oil absorption cavity and oil pressure

cavity for oil distributing. When driving gear of gear pump is driven by power machine, the

gear meshing side, withdraw because sealing capacity greaten is constantly from tank in oil

absorption, gear meshing side, the side of teeth throwing out of gear will continually absorb

oil from oil tank because sealing volume increases. The side with gear engagement will

continually discharge oil because sealing volume decreases. This is the working principle of

gear pump.

●●●● Common fault analysis of loader gear pumpNo. Failure Reason Troubleshooting Method

1Hydraulic oil decreases. Transmission oil increases.

Oil seal is brokenTest pressure. Change working pump (or steering pump)

2Hydraulic oil increases. Transmission oil decreases.

Oil seal is brokenTest pressure. Change working pump (or steering pump)

3Oil leakage on joint surface of pump body

O ring or bolt is loose Change O ring or fasten bolt

4 Oil leakage of pump body Pump body cracks Test pressure. Change pump

Overwear of spline shaft Change spline shaft or pump

19/05/2015

5 Abnormal sound of pump

Overwear of spline shaft Change spline shaft or pump

Overwear of side plate Change side plate or pump

Poor size of spline shaft. Push the shaft.

Change spline shaft or pump

Bearing is brokenChange bearing or pump

6Insufficient flow of pump causes weak and slow lifting

Internal leakage caused by overwear of gear or side plate

Change pump (or broken parts)

Multiple Unit Valve

1））））Type

●●●● Double-joint multiple unit valve-used in loader with common

functions

●●●● Multiple unit valve-used in loader of multifunctional working device

19/05/2015

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

19/05/2015

standing, lifting, dropping and floating of swing arm.

●●●● Reversing action of slide valve is realized by manual control of flexible axle (or

pilot oil pressure). Rotating bucket slide valve returns to the middle position with

spring. Swing arm slide valve returns to the middle position by manual control

and ball locking.

Piping Map of Working Device Hydraulic System

19/05/2015

Profile Map of Double-joint Multiple Unit Valve（（（（DF32））））

Action Demo

1 Swing arm slide valve

Tu

rn b

elo

w

Se

al o

ff

su

pra

ve

rge

nc

e

19/05/2015

2 Turning slide valve

3 Turn cylinder small cavityoverload valve

4 Turn cylinder big cavity overload valve

5 Safety valve

6 Valve body

Liftin

g

Se

al o

ff

De

sc

en

d

Flo

at

Safety Valve

1））））Safety valve of multiple unit reversing valve is between oil inlet cavity and returning

cavity. When system pressure is greater than setting pressure, safety valve will open

and overflow, so that working pressure of the system will be within the scope limited

by the setting pressure for safeguard of system. See structure chart for working

principle of safety valve.

2））））Pressure control: realized by adjusting pressure adjusting screw to change spring

preload.

3））））Setting pressure of safety valve

19/05/2015

3））））Setting pressure of safety valve

of different types of LG Loader

★★★★ LG956 and LG953 Loader

System setting pressure is 18MPa;

★★★★ LG952 Loader

System setting pressure is 16MPa；；；；

★★★★ LG933 and LG936 Loader

System setting pressure is 16MPa.Structure Chart of Safety Valve

Demo Map of Safety Valve

Overload Supplemental Valve

Overload supplemental valve (also called safety valve) is the combination of pilot type

overflow valve and on-way valve. It is installed on multiple unit reversing valve through

bolt. Two ports are respectively connected to oil channels in big and small cavity of turn

cylinder in multiple unit reversing valve . The other two ports are connected to oil-

returning circuit.

19/05/2015

Profile Map of Overload Supplemental Valve

Overload Supplemental Valve (Continued)

●●●● When turn reversing valve is in the middle position, front and back

cavity of turn cylinder are closed. At this time, if the bucket is affected by

external impact load, sharp rise of partial pressure can be effectively

1））））Functions of Overload Supplemental Valve

19/05/2015

external impact load, sharp rise of partial pressure can be effectively

prevented.

●●●● When swing arm lifts or drops, oil drainage and oil supplementation will be automatically

completed. If swing arm lifts to a certain position, piston rod of turn cylinder will be pulled

out, which will cause pressure rise in front cavity of turn oil cylinder. When the pressure

increases to a certain degree, hydraulic oil cylinder or hydraulic pipelines may be

destroyed. Due to double-acting safety valve, oil trapped in front cavity of hydraulic oil

cylinder can return to hydraulic oil tank through safety valve. When volume of front cavity

of oil cylinder reduces, volume of back cavity will increase, forming partial vacuum.

Supplemental valve of double-acting safety valve will be opened to supplement hydraulic


19/05/2015

oil for back cavity of turn oil cylinder and eliminate partial vacuum.

●●●● During unloading of loader, the bucket can quickly turn down by its weight. When the

bucket quickly turns down, after gravity center of the bucket goes over lower hinge point,

the bucket will turn faster by gravity, but movement speed of turn oil cylinder will be limited

by insufficient oil supple of oil pump. Because supplemental valve of double-acting safety

valve supplements oil timely for front cavity of turn oil cylinder, bucket can quickly turn

down, hit stop block, and realize unloading.

• Setting pressure of overload valve in big cavity of turn cylinder of LG953, LG956

and LG958 Loader is 21MPa. Setting pressure of small cavity is 12MPa.

• Setting pressure of overload valve in big cavity of turn cylinder of LG952, LG936

2））））Setting Pressure of Overload Supplemental Valve


19/05/2015

and LG933 Loader is 19 MPa. Setting pressure of small cavity is 12MPa.

• Setting pressure of overload valve in big cavity of turn cylinder of LG918 Loader

is 20 MPa. Setting pressure of small cavity is 12.5MPa.

Basic Failure and Troubleshooting of Multiple Unit Valve (DF)

No. Reason Failure Troubleshooting Method

1

Insufficient working pressure

Pressure setting of safety valve is low

Adjust pressure of safety valve

Slide valve of safety valve is locked Take apart, clean and reassemble

Pressure adjusting spring is broken

Change new spring

Pressure loss in system pipelines is too large

Change pipelines or adjust pressure of overflow valve within permissible pressure scope

19/05/2015

permissible pressure scope

2Insufficient working flow

Oil supply of system is not enough Check oil source

Port opening is not enough Adjust control mechanism

Oil temperature is too high. Viscosity drops

Take measures to reduce oil temperature

Improper selection of oil Change oil

Fit clearance between slide valve and valve body is too big

Change slide valve or assembly according to proper clearance

Basic Failure and Troubleshooting of Multiple Unit Valve (DF) (Continued)

No. Reason Failure Troubleshooting Method

3 Reset failureRestoring spring is broken or deforms Change spring or assembly

Restoring parts are not in the same axle, pulled, etc.

Change broken parts or assembly

4 Outside leakage

Seal ring is broken Change to new parts

Oil temperature is too high. Viscosity drops

Take measures to reduce oil temperature

19/05/2015

4 Outside leakagedrops temperature

Flange face installed on port is not well sealed.

Check fastening and sealing of corresponding parts

Fastening screws on joint surfaces are blocked or cap of pressure adjusting screw is loose

Fasten corresponding parts

5 Big deflection of swing arm

Clearance between valve body and valve rod of multiple unit valve increases

Change valve rod or assembly

Basic Failure and Troubleshooting of Multiple Unit Valve (DF) (Continued)

No. Reason Reason Troubleshooting Method

6 Bucket dropsInner leakage of overload supplemental valve in big cavity of turn cylinder (dirt blocked and broken)

Disassemble, clean, reassemble or replace

Wear and clearance between valve body and valve rod of multiple unit valve increases

Change valve rod or assembly

7 Bucket is put away Inner leakage of overload supplemental Change supplemental valve.

19/05/2015

7 Bucket is put away Inner leakage of overload supplemental valve in small cavity of turn cylinder (dirt blocked and broken)

Change supplemental valve. Low pressure

8

Front tire cannot support

Setting pressure of overload valve in small cavity of rotating bucketis low

Increase pressure of overload valve in small cavity

Large amount of leakage in small cavity of rotating bucket

Change slide valve according to proper clearance

Oil Cylinder• Type：：：：Hydraulic cylinder used in loader is single-rod piston double-acting oil cylinder.

• Classification: Swing arm oil cylinder, turn oil cylinder and steering oil cylinder.

• Composition：：：：Piston double-acting hydro-cylinder generally consists of oil cylinder

body, piston, piston rod guide sleeve, etc.

• Comments：：：：In order to analyze the problem, oil cylinder is usually divided into cavity

with rod (or small cavity, the side with piston rod) and cavity without rod (or big cavity).

Pressure oil enters left cavity of hydraulic cylinder from Port A and pushes piston to the

right. Hydraulic oil in the right cavity is discharged through Port B.

19/05/2015

right. Hydraulic oil in the right cavity is discharged through Port B.

Structure of Oil Cylinder1. Back cylinder cover2. Stop collar 3. Lantern ring 4. Snap ring5. Piston 6. O Ring 7. Back-up ring 8. Stop dog 9. Ax seal ring10. Oil cylinder body11. Port stand 12. Guide sleeve 13. Cylinder end 14. Dust ring 15. Piton rod16. 16. Screw Buffer Plunger

Hydraulic Pilot Control Working Hydraulic System

Working hydraulic system of LG918, LG933, LG936, LG956L, LG958L and other loaders, which

are export products of our company, uses pilot control working hydraulic system. main oil

channels with high pressure and big flow are controlled by pilot oil channels with low pressure

and small flow. Compared with mechanical control hydraulic system, this working hydraulic

system has the following features:

1））））Features of the System

●●●● Pilot control is light, flexible and efficient. Finger control can be realized.

19/05/2015

●●●● Pilot control is light, flexible and efficient. Finger control can be realized.

●●●● By pressure-relief type proportional pilot valve control, stroke of valve rod of main valve is in

proportion to control angle of pilot value handle, which means proportional pilot control to

work of main valve is realized.

●●●● Safety valve, overload valve, supplemental valve and one-way valve use insert type structure.

With good generality, it is convenient to maintain.

●●●● Pilot valve uses overall structure. With a small volume it is convenient to arrange.

●●●● When engine shuts down, drop of swing arm and forward tilting of bucket can be realized

by pressure selecting valve and pilot valve.

●●●● Pilot valve has orientation with electromagnetic iron at lifting position of swing arm and

backward tilting position of bucket. Vertical limit of lifting height of swing arm and automatic

leveling control of bucket at any position can be realized, which simplifies operating

procedures, reduces labor intensity, and avoids energy loss and pressure shock caused by

frequent movement of safety valve.

1））））Features of the System (Continued)

19/05/2015

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.

19/05/2015

Principe of Hydraulic Pilot Control System

Pilot Valve

Pilot valve is equipped with control rod. Rotating bucket control has

forward tilting, middle standing and backward titling positions. Swing

arm control has lifting, neutral, middle standing, dropping and floating

positions. Pilot valve has orientation with electromagnetic iron at lifting,

floating and backward titling position. See figure.

19/05/2015

Structure of Pilot Valve

When pulling the control rod to dropping position, pressure pin will push down pressure

lever. Measurement spring will push down measurement valve core, cut off the channel

between control cavity and oil returning chamber, connect oil inlet cavity to control oil cavity,

guide pressure oil to the end of multiple unit valve, push multiple unit valve to move, and

corresponding reversing action. Meanwhile, oil pressure of control cavity will act on lower

end of measurement valve core, and balance with the force of measurement spring. When

●●●● Working principle of pilot valve（（（（proportional pilot

control and automatic control of electromagnet)

19/05/2015

end of measurement valve core, and balance with the force of measurement spring. When

control rod remains in one position, the spring force and control cavity pressure will be fixed,

which is similar to action process of fixed pressure reducing valve. Spring force will change

with pivot angle of control rod. The bigger pivot angle is, the bigger spring force will be and

the higher control cavity pressure will be. Thrust on valve core of multiple unit valve will

increase accordingly, which means stroke of main valve core is in proportion to pivot angle

of control rod of pilot valve, so as to achieve proportional pilot control.

When control rod is pulled from dropping position to floating position, because this

position has electromagnet positioning, pilot valve will be locked. At this time, oil pressure

at control port will increase. Sequence valve in pilot valve will open. Hydraulic oil in Drain

Hole K of multiple unit valve will enter oil tank through Drain Hole 2C in pilot valve.

Supplemental valve in small cavity of swing arm oil cylinder will open. Port P, A2, B2 and T

will be connected. Swing arm floating will be realized. When pilot valve is pulled out of

●●●● Working principle of pilot valve（（（（proportional pilot

control and automatic control of electromagnet)

19/05/2015

will be connected. Swing arm floating will be realized. When pilot valve is pulled out of

floating position and loosen, restoring spring will push up pressure lever. Control rod will

return to the middle position.

When control rod of pilot valve is pulled from whole lifting or bucket collecting position,

control rod will be locked and positioned. When swing arm or bucket reaches limited lifting

height or limited bucket angle, which is close to switch action, magnetic coil will shut off

and lose its magnetism. Control rod will automatically go back to the middle position under

the action of restoring spring.

Multiple Unit Valve (D32)

• The function of multiple unit valve is changing flow direction of working oil,

realizing different movement direction of turn oil cylinder and swing arm oil

cylinder, and completing corresponding different action of working device,

by different open direction of slide valve under the action of pilot control oil.

19/05/2015

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

19/05/2015

swing arm reversing valve, overload valve, supplemental valve and one-way

valve.


• 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

19/05/2015

connected to oil channels by series-parallel connection. They are at a certain

position under the pressure of pilot hydraulic oil and action of spring.

●●●● Automatic control of lifting height of swing arm

When swing arm automatically controls lifting

position, work position of slide valve of

multiple unit valve is exactly the same to lifting

position of swing arm. Because control rod of

pilot valve is pulled to whole lifting position,

control rod is locked and positioned at this

time. When swing arm reaches lifting height


19/05/2015

time. When swing arm reaches lifting height

limit, and stator fixed on swing arm is close to

switch action, magnetic coil will disconnect

and lose magnetic force. Control rod will move

to the middle position under the action of

restoring spring. Multiple unit valve will lose

control of pilot oil. Lifting of swing arm will

automatically end.

Structure of Multiple Unit Valve

●●●●Floating of swing arm

When swing arm is at floating position, work position of slide valve of multiple

unit valve is exactly the same to dropping position of swing arm. Because

control rod of pilot valve is at floating position and this position doesn’t have

electromagnet, sequence valve in pilot valve will open. Hydraulic oil in Drain

Hole K of multiple unit valve will enter oil tank through Drain Hole 2C in pilot


19/05/2015

Hole K of multiple unit valve will enter oil tank through Drain Hole 2C in pilot

valve. Supplemental valve in small cavity of swing arm oil cylinder will open.

Port P, A2, B2 and T will be connected. At this time, piston rod of swing arm oil

cylinder will freely float under the action of external force. When control rod of

pilot valve is pulled out of floating position and returns to the middle position,

floating of swing arm will end.

●●●● Automatic leveling of bucket

When bucket is at automatic leveling position, work position of multiple unit

valve is exactly the same to backward titling position of bucket. Because

control rod of pilot valve is pulled to whole bucket collecting position, control

rod is locked and positioned at this time. When bucket reaches limited bucket

collecting angle, and stator fixed on turn oil cylinder is close to switch action,


19/05/2015

collecting angle, and stator fixed on turn oil cylinder is close to switch action,

magnetic coil will disconnect and lose magnetic force. Control rod will move to

the middle position under the action of restoring spring. Multiple unit valve will

lose control of pilot oil. Backward titling of swing arm will automatically end.

With this function, at any unloading height, when swing arm drops to ground

shoveling position of bucket, undersurface of bucket will be parallel with

ground.

Pressure Selecting Valve

●●●● Function: Purpose of pressure selecting valve

is to provide a certain pressure of control oil to

pilot valve, and ensure swing arm on the ground

position when diesel engine shuts off.

●●●● Structure: Pressure selecting valve is installed

in pilot oil channel. Control valve of pressure

One-way valve

19/05/2015

Structure and Principle of

Pressure Selecting Valve

in pilot oil channel. Control valve of pressure

selecting valve mainly consists of valve body,

valve core, spring, etc. Port P1 is connected to

pilot pump. Port Pr is connected to big cavity of

swing arm oil cylinder. Port P2 is oil outlet,

which is connected to pilot valve. L is oil

returning port. See structure chart.

One-way valve

●●●● Working PrincipleDuring operation, oil in pilot pump enters Port P1, and flows to pilot valve through valve

centre hole and oil outlet P2. When pressure of oil outlet P2 is greater than 1.5 MPa, valve

core will move left. Port P1 and Port Pr mouth will stagger to close the oil in lower cavity of

swing arm oil cylinder. Port Pr is equipped with one-way valve, in order to prevent reverse

flow of oil.

When diesel engine shuts off, Port P1 doesn’t have oil supple of pilot pump. Pressure will

drop. Under the action of control spring, valve core will return to the connection position of

Port Pr and Port P2. If swing arm in at lifting condition and control rod is at the middle

position at this time , hydraulic oil in big cavity of swing arm oil cylinder will be sealed. At

19/05/2015

position at this time , hydraulic oil in big cavity of swing arm oil cylinder will be sealed. At

this time as long as control rod is pulled to dropping position of swing arm, under the

gravity hydraulic oil in big cavity of swing arm oil cylinder will enter pilot valve through Port

Pr and Port P2. Pilot valve controls multiple unit reversing valve, so that valve core of swing

arm is at dropping position. Swing arm can be put down. In this process, valve core of

pressure selecting valve also controls pressure from Port Pr to pilot valve of about 1.5 MPa.

If pressure of oil outlet P2 rises, valve core will move left, throttling damping will be

increased, flow of Port Pr will be reduced, and pressure of oil outlet P2 will be reduced,

which will realize pilot pressure control.

ⅡⅡⅡⅡ. Steering System

• Function: Wheel loader steering system is used to control driving direction of

loader. It can make loader run straight steadily and change driving direction

flexibly according to requirements.

• Classification: By steering method, wheel loader can be divided into deflection

wheel steering, skid steering and articulated steering.

19/05/2015

• Advantages of articulated steering: Work device is installed on front frame.

When the frame deflects relatively, direction of work device will be always same

to that of front frame, which can help work device to quickly aim at working

plane, reduce distance and time of work cycle, and improve working efficiency

of the loader. Therefore, articulated steering becomes the most widely used

steering method of modern loader.

Steering system has many varieties. Different types of steering system

respectively represent development level of different hydraulic technique.

At present wheel loader uses the following types of steering system.

●●●●Type of Steering System

①①①① Whole hydraulic steering system consisting of single stable valve and

open center non-reaction steering gear;

②②②② Load sensing whole hydraulic steering system consisting of priority valve

19/05/2015

②②②② Load sensing whole hydraulic steering system consisting of priority valve

and load sensing steering gear;

③③③③ Load sensing whole hydraulic steering system consisting of priority valve

and coaxial flow amplifying steering gear;

④④④④ Flow amplifying steering system

1. Whole Hydraulic Steering System Controlled by Solenoid Valve

1)1) Composition of System

Whole hydraulic steering system controlled by solenoid valve

mainly consists of hydraulic pump, one-way steady flow

divider valve, BZZ1 (open center non-reaction) whole hydraulic

steering gear, steering oil cylinder, pipelines, etc. See principle

chart of the system.

2)Steering Gear

19/05/2015

System Principle

2)Steering Gear

BZZ Whole Hydraulic Steering Gear is a cycloid

rotary valve whole hydraulic steering gear consisting of servo

valve and pin wheel gear pair. It is current widely used steering

component at home and aboard. It is flexible to operate, energy

saving, compact in structure, reliable, and convenient to install.

Manual steering can be realized after engine shuts off.

There are the following major types of

BZZ Whole Hydraulic Steering Gear.

Open center non-reaction （（（（BZZ1）；）；）；）；

Open center reaction （（（（BZZ2）；）；）；）；

Closed center non-reaction（（（（BZZ3）；）；）；）；

Load sensing （（（（BZZ5）；）；）；）；

Coaxial flow-amplifying（（（（BZZ6）；）；）；）；

●●●●Type of Whole Hydraulic Steering Gear

19/05/2015

Coaxial flow-amplifying（（（（BZZ6）；）；）；）；

and other structural styles

Function symbols are shown in the

figure.

Type Symbol of BZZ

It is mainly consists of valve body, valve core,

valve pocket, universal driving shaft, guide

spring, pin, rotor, stator, rear cover, etc.

Working principle of steering gear

Structure of BZZ Whole Hydraulic Steering Gear

19/05/2015

Structure of Whole Hydraulic Steering GearMiddle position Steering position

Correspondence of valve core, valve pocket , stator and rotor

19/05/2015

High Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil TrapHigh Pressure Low Pressure Oil Trap

3) Combined Valve Block

Combined valve block is a combined hydraulic component. Connected between

steering oil pump and steering gear, it forms a complete set with whole hydraulic

steering gear. It is generally installed directly on flange of valve body, and makes a

whole with steering gear.

FunctionsFunctions：：：：：：：：On one hand, ensure that steering gear and the whole steering system

works normally and smoothly under pressure rated; On the other hand, ensure that

19/05/2015

works normally and smoothly under pressure rated; On the other hand, ensure that

steering cylinder and connected pipelines will not be damaged during sudden

overload, and protect steering pump. So valve block is an indispensable hydraulic

component in hydraulic steering system.

Composition of Combined Valve Block：：：：

According to different requirements of

steering system, combined types of valve

block are different. Valve block generally

consists of one-way valve, overflow valve

(safety valve), two-way buffer overload

valve, supplementary valve, etc. (but some

valve blocks are only equipped with two-

3) Combined Valve Block

19/05/2015

way buffer valve and one-way valve, and

some only have overflow valve and one-way

valve). Structure of valve block is shown in

figure.

Composition of existing steering gear valve

block: one-way valve, overflow valve (safety

valve), and two-way buffer overload valve.

Structure Chart of Valve Block

Functional Chart of Valve Block

4) Single stable ValveSingle-channel stable flow divider valve (single stable valve for short) mainly works with BZZ

series of whole hydraulic steering gear. It is used in whole hydraulic steering system. When oil

supply of steering oil pump and system load change, stable flow required by steering gear is

ensured by single stable valve, to satisfy hydraulic steering requirement of loader.

Single-channel stable flow divider valve mainly consists of valve body, valve core, spring,

safety valve, damping plug and other parts. It has shunt type and constant-current type. See

figure.

Single stable valve is used in

19/05/2015

independent system. Oil from steering is

supplied to the system. The rest oil and

oil overflowing when safety valve opens

unloading will flow back to the oil tank

through Port T.

Structure and

Principle Chart

★★★★ Safety valve is on the valve block now！！！！

2. Load Sensing Whole Hydraulic Steering System

1））））Composition of System

Mainly consisting of priority valve, BZZ5 load sensing

steering gear (or BZZ6 coaxial flow amplifying steering

gear), steering oil cylinder, pipelines, radiator, oil tank,

etc.

19/05/2015

Priority valve can realize combination and distributing

with working hydraulic steering system, improve

efficiency, and reduce loss. This type is widely used at

present. LG933, LG936, LG953, LG956 and other types

of our company all use this type.

System Principle

Chart

2. Load Sensing Whole Hydraulic Steering System

1））））Composition of System（（（（Continued））））

If LG953 steering hydraulic system is independent load

sensing hydraulic system steering, this system will

preferentially supply oil to steering hydraulic system.

The residual oil will return to oil tank after combining

with returning oil of steering system through radiator.

19/05/2015

with returning oil of steering system through radiator.

Safety valve is on priority valve. The system setting

pressure is 16MPa. See system principle chart.

System Principle

Chart

Load Dynamic Sensor System

19/05/2015

2））））Pipeline Direction of Load Sensing Whole Hydraulic Steering System

19/05/2015

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.

19/05/2015

Ports of SteeringGear3D Profile of Structure

Following Rotary Valve

Measurement Motor

T：：：：oil return

P：：：：oil inlet

R：：：：right steering

L：：：：left steering

TLLS

19/05/2015

L

PR

LS

Position of ports on steering gear

Main Components of Steering Gear

19/05/2015

Core components of whole hydraulic steering gear:

• Metering mechanism---stator and rotor

• Servo proportional control valve ---valve core/valve pocket pair

●●●● Working Principle（（（（BZZ5））））

When following rotary valve is at the middle

position (steering wheel doesn’t move), valve

package and valve core are in the middle

under the action of positioning spring, and

channels connected to tooth cavity of rotor

and stator and two cavity of steering cylinder

are closed, only a small amount of pressure

oil pumped from steering pass through

Combin

es or

returns

to oil

tank

19/05/2015

System Sketch Map

oil pumped from steering pass through

inside of steering gear, and most oil will be

distributed by Port EF of priority valve

(combined to working hydraulic system or

flows back to oil tank). Oil in two cavity of

steering cylinder will be closed, piston

cannot move, and loader will run in original

direction.

PumpDiesel

Engine

Hydraul

ic oil

tank

When steering wheel turns, priority valve will preferentially satisfy steering needs.

Oil in steering pump will go to measurement motor through priority valve and

following rotary valve, and turn in the direction of steering wheel with rotor.

Working oil will be delivered to a cavity of steering cylinder and realize steering.

Oil in the other cavity of steering cylinder will return to oil tank with following

●●●● Working Principle（（（（BZZ5 Continued））））

19/05/2015

Oil in the other cavity of steering cylinder will return to oil tank with following

rotary valve. When steering wheel turns fast, a large amount of oil will reach

steering cylinder through measurement motor. Steering will be fast.

4) Priority Valve

This valve works together with BZZ5 Steering

Gear (or BZZ6 Steering Gear) and forms load

sensing steering system. When rotate speed of

steering wheel changes, flow required by

steering gear can be ensured preferentially.

The red oil will enter working device hydraulic

system or flow back to oil tank.

19/05/2015

Structure and Principle Chart of

Priority Valve

4) Priority Valve (Continued)●●●● When steering wheel doesn’t move, pressure oil from steering pump will enter working

device hydraulic system or directly flow back to oil tank through Port P, valve core and

Port EF.

●●●● When steering wheel turns, valve core will move right under the action of spring force and

LS pressure. Port P will be connected to Port CF. Pressure oil will enter steering gear and

push oil cylinder to realize loader steering. The rest oil will be distributed by Port EF, enter

working device hydraulic system or flow back to oil tank. Therefore, when priority valve

preferentially satisfies steering, the rest power oil will be distributed by Port EF and

applied to other working hydraulic system, which will reduce system power loss and save

19/05/2015

energy.

5））））Coaxial Flow Amplifying Steering Gear

Coaxial Flow Amplifying Steering Gear (BZZ6 and TLF) and BZZ5 type are all load

sensing steering gear. With the same displacement, two steering gears can replace

each other. But displacement of coaxial flow amplifying steering gear changes with

input turning speed of steering wheel.

19/05/2015

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

19/05/2015

stage. When input turning speed of steering wheel is above 40rpm, effective displacement of

steering gear will be its calibrated equivalent displacement.

Coaxial Flow Amplifying Steering Gear has good relative performance. It has high pressure

loss (about 0.5MPa higher than the first two kinds), good sealing and small leakage.) At

present, LG953 Loader uses BZZ6 (or TLF) Coaxial Flow Amplifying Whole Hydraulic Steering

Gear to replace BZZ5 Load Sensing Steering Gear.

• Flow amplifying system mainly consists of hydraulic pump, flow

amplifying valve, limit valve, steering gear (BZZ3) , steering cylinder, etc.

Oil channels are divided into pilot oil channel and main oil channel. oil

amount change of pilot oil channel is in proportion to flow change of

steering cylinder in main oil channels. High pressure and big flow is

3. Flow Amplifying Steering System (Flow Amplifying Valve)

19/05/2015

controlled by low pressure and small flow, so that steering control is

convenient and flexible. Because flow amplifying valve has pressure

compensation device, flow doesn’t change with load, which improves

performance and has certain energy-saving effect. Therefore, it has small

power consumption, reduces system heating, and improves flow

adjusting property.

• Besides functions of common flow amplifying valve, priority flow

amplifying valve can combine with working hydraulic system by priority

valve. It has characteristics of load sensing steering system.

• For example, LG958 Flow Amplifying Steering System mainly consists of

3. Flow Amplifying Steering System（（（（Continued））））

19/05/2015

double pump, steering gear, flow amplifying valve, unloading valve,

steering cylinder, hydraulic oil tank, pipeline accessories, etc. See the

following figure for system principle.

1－－－－Oil returning filter

2－－－－Radiator

3－－－－Hydraulic oil tank

4－－－－Working pump

5－－－－Pressure selecting

valve

6－－－－Steering gear

7－－－－Steering cylinder

19/05/2015

8－－－－Flow amplifying valve

9－－－－Air change filter

10－－－－Steering pump

11－－－－Unloading valve

12－－－－Oil absorption filter

core

Principle Chart of Flow Amplifying System

Structure and working principle of priority flow amplifying valve:1））））Flow Amplifying Valve

19/05/2015

1 front door 2 amplifying valve core 3 valve body 4 adjusting washer 5 steering valve spring

6 back door 7 pressure adjusting screw 8 pilot valve spring 9 cone valve 10 flow divider valve spring 11 adjusting shim 12 flow divider valve core 13 shuttle valve

1））））Flow Amplifying Valve（（（（Continued））））

When steering wheel stops turning or turns to extreme position, pilot oil will be

●●●● Middle Position

19/05/2015

cut off. Steering valve spring (5) will make amplify valve spool (2) keep in

middle position. Oil in steering pump will push distributing valve core (12) right.

Flowing into working system from Port PF, oil in steering pump is fully utilized,

so as to reduce displacement of working pump. Because amplifying valve core (2)

is at the middle position, hydraulic oil in p cavity will not be connected to

hydraulic oil in A and B cavity of left and right steering cylinder, so that loader

will run in the direction when steering wheel loader stops turning. Hydraulic oil

1））））Flow Amplifying Valve（（（（Continued））））

19/05/2015

will run in the direction when steering wheel loader stops turning. Hydraulic oil

sealed in A and B cavity of left and right steering port will act on cone valve (9) of

safety valve through internal channel. When steering wheel carries external

resistance, pressure in A (or B) cavity will increase, until cone valve (9) is opened,

in order to protect steering cylinder and other hydraulic components from

damage.

When steering wheel turns right, pilot oil will flow into spring chamber from pilot oil port

along direction b. As pressure in spring cavity of steering valve spring (5) increases,

amplifying valve core (2) will be pushed left. Then P cavity will be connected to right

steering port (B). Left steering port (A) will be connected to oil returning port (T1).

Hydraulic oil will enter oil cylinder of right turning port and realize right turning. When

right turning is preferentially met, the rest oil will be distributed to working system

● Right Steering Position

19/05/2015

through Port PF.

Movement amount of valve core is controlled by turning speed of steering wheel. The

faster steering wheel turns, the larger pilot oil flow is, the greater valve core displacement

is, and the higher steering speed is. Conversely, if steering wheel turns slow, valve core

displacement will be small and steering speed will be low (Note: Two ends of valve core

are connected to orifice on the oil channels. The hydraulic damping realizes this function).

When pressure oil flows into right turning port (B), because of load feedback effect,

pressure difference of two ends of distributing valve (12) remain unchanged, so as to

ensure that flow in steering cylinder only relates to displacement of valve core , and

doesn’t related to load pressure. Oil pressure acts on core valve (9) and distributing

valve core (12) through shuttle valve (13) , which automatically controls flow. If

pressure continues to rise and goes beyond the setting pressure of safety valve,

● Right Steering Position (Continued)

19/05/2015

cone valve (9) will open, distributing valve core (12) will move right, and flow will go

to working system. Oil returning in oil channels at middle position will have

protection function. When load is eliminated, pressure will reduce, distributing valve

core (12) will go back to its normal position, and cone valve (9)will be closed.

Left steering is similar to right steering.

ⅢⅢⅢⅢ. Failure Case Analysis

1. Failure Case Analysis of Working Hydraulic System

1））））Weak lifting of swing arm

2））））Slow and weak bucket

3））））Bucket turns over or shakes during lifting operation

4））））Hydraulic oil temperature is too high

19/05/2015

4））））Hydraulic oil temperature is too high

ⅢⅢⅢⅢ. Failure Case Analysis

1））））Heavy steering

2））））No terminal point for steering

3））））Reason for vehicle deflection

2. Failure Case Analysis of Steering Hydraulic System

19/05/2015

4））））Inaccurate steering

5））））Steering wheel rotates freely. Steering doesn’t move or slow.

6））））Blanking stroke of steering wheel

7））））Steering wheel shakes or rotates

8））））Steering wheel rebounds

1））））Weak lifting of swing arm （（（（analysis and judgment process））））

1. Failure Case Analysis of Working Hydraulic System

Reason Measures

1. Valve rod is blocked

2. Positioning steel ball of

valve rod becomes invalid

due to wear. Positioning

spring becomes invalid

3. Control mechanism

doesn’t control well

Hydraulic oil amount is not

enough

Dirt or rubber dropping of

tubes makes pump unable to

absorb oil

Pump axle is broken or

drops. Working pump cannot

absorb oil

Setting pressure of main

1. Check valve rod,

steel ball, positioning

spring of valve rod or

change valve

2. Check control

mechanism

Add hydraulic oil to

specified mark

Remove dirt or change

rubber tubes

Change pump axle

Set to system pressure

value

Wash or change spring

Check whether

stroke of multiple

unit valve rod is in

place

No

Yes

No

Check whether

hydraulic oil

amount meets

standard Check whether oil

absorption tube of

working pump is

blocked

Measure when

pressure is zero or

low

Test pressure is

below requirement

Pressure changes

after adjustment

Pressure doesn’t

change after

adjustment

Check whether

pump driving axle

is broken or fallsAction stroke of 918 swing

arm valve is 7mm. Action

stroke of rotating bucket

valve is 8.1mm. Action

stroke of the two valve

rods of other types are all

16mm.

When bucket is flat on the

ground, oil position is

between 6 and 10 on mark

of hydraulic oil tank

Yes No

Yes

Yes

YesYes No

Yes

19/05/2015

Setting pressure of main

safety valve is low

Spring in main safety valve

is broken or valve core is

blocked

Working gear pump wears or

is broken

Internal leakage of swing

arm cylinder

1. Leakage of swing arm

slide valve

2. Internal leakage of main

safety valve

Accelerator pedal or cable

cause low rotating speed

Oil absorption channels are

blocked

Wash or change spring

Change gear pump or

repair

Repair of change oil

cylinder

Repair or change

multiple unit valve

Check pedal and cable.

Adjust rotating speed

to specified value

Change filter screen

adjustment

Check whether

multiple valve leaks

Check whether

working device

hydraulic system is

normal

Check whether

swing arm cylinder

has internal leakage

Pressure increases

with engine throttle,

but doesn’t reach

setting pressure

Meets setting

requirement of

working system

pressure

When stroke of valve rod is in

place and hydraulic oil amount

meets standard, check whether

rotating speed of engine meets

standard

Measure with tachymeter

to check whether rated

rotating speed of engine

reaches 2200r/min

When big arm lifts to extreme

position and control rod of swing

arm is at lifting position, rotating

of engine will gradually increase

to not less than 2200r/min. And

than measure

Adjust pressure of main safety valve. 933, 936 and 952 are 16MPa. 918 is 17.5MPa.

953, 956 and 958 are 18MPa.Yes

Yes

Yes

Yes

No Yes

Yes

No

2））））Slow and weak bucket （（（（analysis and judgment process））））

Reason Measures

Broken seal ring causes

internal leakage and bucket

dropping

Scratching or wear on valve

rod or valve hole of rotating

bucket makes leakage of

hydraulic oil large

1. Main valve core of

overload valve has dust

particles, which makes

overload valve open

Change seal ring

Repair or change

1. Wash main valve

core and remove

impurities

Check whether broken rotating bucket slide valve causes internal

leakage

Check whether overload valve has

internal leakage

Check whether rotating bucket

cylinder has internal leakage

Check whether setting pressure of two

overload valves in rotating bucket

cylinder is normal

Pressure in big cavity of 933, 936, 938 and 952 is from 18 to 18.5MPa. Pressure in big cavity of 918, 953 and 956 is from 20 to 20.5MPa. Pressure in big cavity of 958 and 968 is 21.5MPa. Pressure in big cavity of 40F is

Yes

YesNo

Yes

Yes

No

19/05/2015

overload valve open

2. Aging of seal ring

3. Improper clearance

between valve core and

valve body

1. Low pressure of overload

valve causes bucket

dropping or floating

2. Spring of overload valve

is broken or invalid

impurities

2. Change seal ring

3. Change overload

valve

1. Adjust pressure to

specified value

2. Repair or change

internal leakage

Check whether pressure of overload

valve is low

Pressure in big cavity of 40F is 15.5MPa. Pressure in small cavity of all types is from 12 to 12.5MPa.

No

Yes

3））））Bucket turns over or shakes during lifting operation（（（（analysis and judgment process））））

Reason Measures

Oil amount is not

enough

Working gear pump

wears or is broken

Unstable starting

pressure of safety

valve changes

pressure of hydraulic

oil

Caused by aging and

foaming of inlayer of

rubber tubes, or

Add hydraulic oil to

specified mark

Change or repair

Check setting

pressure of valve, and

whether spring

deforms. Adjust

starting pressure

Repair or change

Check whether oil amount

meets standard

Test pressure of working device

hydraulic system

Check whether starting pressure of

safety valve is stable

Check whether oil channels are

Check pressure increases with increase of engine throttle

Check whether indicator of

pressure gage swings

intensively

Oil position is between 6 and 10 on mark of hydraulic oil tank

When big arm rises to extreme position and control rod of swing arm is at lifting position, rotating speed of engine will gradually increase to not less than 2200r/min. And then measure. 933, 936 and 952 are 16MPa.

Yes

Yes

No

Yes

No

Yes

No

19/05/2015

rubber tubes, or

blocking of transiting

valve block and joint

Air entering system

makes working

pressure unstable

Different leakage

amount causes flow

fluctuation and

shaking

Loosen piston makes

piston rod move in

hydraulic cylinder

Repair or change

Repair or change

Repair or change

When system pressure and hydraulic oil amount are normal, check whether leakage amount of rotating bucket cylinder and swing arm cylinder are same

When system pressure and hydraulic oil amount are normal, check whether pistons in rotating bucket cylinder and swing arm cylinder are loosen

channels are blocked or flat

Check whether oil absorption rubber

tubes are well sealed

936 and 952 are 16MPa. 918 is 17.5MPa. 953, 956 and 958 are 18MPa.

No

Yes

No

YesNo

Yes

4））））Hydraulic oil temperature is too high（（（（analysis and judgment process ））））

Reason Measures

Insufficient hydraulic oil

makes working pump absorb

air

Hydraulic components are

blocked, causing throttling

and temperature rise of

Too much grease causes poor

heat dissipation

Blocking in radiator or other

reasons cause poor heat

dissipation

When system pressure is set

too high, overflow valve

cannot overflow and reduce

pressure normally, internal

Add hydraulic oil to specified mark

Change or filter hydraulic oil

Clean with high pressure gun

Repair or change

Repair or change

Check whether position of hydraulic oil is too low

Check whether hydraulic oil is too dirty or goes bad

Check whether there is too much grease between blades of cooling fin in water box

Check whether hydraulic radiator has problem

No

Yes

Yes

Yes

Yes

No

No

No

19/05/2015

leakage will increase, oil

temperature of system will

rise. When oil returning filter

core is blocked or oil

returning channels become

old and delaminate, back

pressure will be high and oil

temperature will rise.

Serious internal leakage of

hydraulic components will

cause temperature rise of

system

Low volumetric efficiency will

cause temperature rise of

hydraulic oil

Repair or change

Repair or change

Check whether improper pressure setting causes high temperature of hydraulic oil

Check whether cylinder, pump and valve have leakage

Check whether gear pump, gear pair, side plate or pump body have wear

No

Yes

Yes

Yes

No

No

1））））Heavy steering（（（（analysis and judgment process））））

2. Failure Case Analysis of Steering Hydraulic System

Decid

e a

cco

rdin

g to

fau

lt p

hen

om

en

on

Cylinder crawls. Foam in oil. Regular sound

Heavy steering. Steering cylinder doesn’t move.

Check whether steering pillar is

flexible

Whether system pressure meets

Check whether feedback oil

Reason Measures

Air in system

-One-way valve

failure of manual

steering

-Leakage of FK

overload valve

-Internal leakage of

oil cylinder

Steering pillar is

broken

Remove air in system.

Check whether oil inlet of

oil pump leaks.

-Check whether steel ball

exists and whether it is

blocked

-Change FK combination

valve

-Check whether oil cylinder

has internal leakage

Repair or change

Clean or change

Yes

Yes

YesNo

Yes

No

No

19/05/2015

Is fast steering heavy and slow steering light?

pressure meets the needs

feedback oil channels are unblocked

Adjust system press. Does the

pressure change?

Is surface of hydraulic oil low?

Is oil sucking pipe blocked?

broken

Pipelines are

blocked

Low system

pressure

Spring of priority

valve is broken.

Shuttle valve is

blocked

Lack oil

Pipelines are

blocked

Wear and internal

leakage of steering

pump

Clean or change

Repair or change

Adjust system pressure

Supplement hydraulic oil

Clean or change

Repair or change

Yes

Yes

Yes

Yes

Yes

No

No

No

No

Yes

No

2））））No terminal point for steering or limit position cannot be reached （（（（analysis and judgment process)

No terminal point Failure Reason Troubleshooting

Method

Low overload

valve pressure

Increase overload

valve pressure

properly

After steering cylinder turns to extreme position, turning the steering wheel, steering wheel can turn lightly, which means no sense of terminal point.

19/05/2015

Steering cylinder cannot turn to extreme position

Failure Reason Troubleshooting Method

Low safety valve

pressure

Increase safety valve

pressure properlySteering cylinder cannot turn to extreme position. Steering response is heavy.

①①①① Leakage at cylinder port when closed center steering gear is at middle

position. It is normal for closed center steering gear system to have

slight deflection.

②②②② Check whether connecting rod of oil cylinder is loosen.

③③③③ Leakage in oil cylinder

④④④④ Pressure of two tires has big difference.

⑤⑤⑤⑤ Leakage on two-way overload valve or two-way supplemental valve.

3））））Reason for Vehicle Deflection

19/05/2015

⑤⑤⑤⑤ Leakage on two-way overload valve or two-way supplemental valve.

⑥⑥⑥⑥ Air in oil

①①①① Air in system;

②②②② Pin of oil cylinder is loosen;

③③③③ Priority valve or main valve of

flow divider valve is blocked;

L

T

R

P

4））））Inaccurate Steering

19/05/2015

flow divider valve is blocked;

④④④④ Oil cylinder has leakage;

⑤⑤⑤⑤ Low efficiency of pump causes unstable pressure.

EngineFixed Pump

Reservoir

Filter

p

①①①① Serious leakage in two-way overload valve

5））））Steering wheel rotates freely. Steering doesn’t move or slow.

19/05/2015

②②②② Serious leakage in piston of oil cylinder

②②②② Nut on steering wheel moves

①①①① Connection of steering pillar and steering gear wears or is broken

L

T

R

PP

6））））Blanking Stroke of Steering Wheel

19/05/2015

③③③③ Air in oil

④④④④ Leakage in two-way overload valve

⑤⑤⑤⑤ Leakage in steering cylinder

EngineFixed Pump

Reservoir

Filter

p

EngineFixed Pump

①①①① Assembly relation mistake. During overhaul

and reassemble, it is required that spine gear

corresponding to pin groove of universal

driving shaft engages with internal spine

gear corresponding to gear groove of rotor

②②②② When oil in pump is connected to Port R or

7））））Steering wheel shakes or rotates

19/05/2015

②②②② When oil in pump is connected to Port R or

L, steering gear will rotate like motor.

Reason：：：：One-way valve at oil inlet of

steering gear is broken.

Function of one-way valve:

Prevent backflow of oil when pressure of

8））））Steering wheel rebounds

19/05/2015

steering oil cylinder under external force is

higher than that of oil inlet. If one-way valve

is damaged and oil backflows, steering

wheel will rebound.

19/05/2015

Reliability bears great

trust!

loader hydraulic training courseware

Documents

hydraulic transmission

power transmission

liquid transmission

hydraulic jack

mechanical transmission

transmission device

force transmission

pneumatic transmission