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