Loader Hydraulic Training Courseware

2011

*Main Content Evaluation Topics Suitable Group Contents Training Objectives

*Suitable Group This course is suitable for domestic and foreign intermediate and above technical service personnelIt also applies to

*Main Content Evaluation Topics Suitable Group Contents Training Objectives

*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:1Basic knowledge of hydraulic system2Structure and principle of LG hydraulic system3Common failure and troubleshooting of systems and components

**1Basic Knowledge of Hydraulic TransmissionHydraulic System Introduction of LG Loader12Contents

**1Basic Principle of Hydraulic TransmissionComposition of Hydraulic Transmission System12Part 1 Basic Knowledge of Hydraulic Transmission345678Advantages of Hydraulic Transmission SystemDisadvantages of Hydraulic Transmission SystemHydraulic Medium Hydraulic Power Components Hydraulic Control Components Hydraulic Actuating Components

* A machine is basically made up of four parts, including prime motor, transmission device, working mechanism, and assistant mechanism. The purpose of prime motor is to change various forms of energy into mechanical energy, which is power supply of the machine. Working mechanism works outside with mechanical energy. Transmission device 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.. 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.. 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 1Thrust on piston equals oil pressure times piston area. 2P, oil pressure, depends on external load. 2. Loading speed transfers according to the principle of equal liquid volume after changes. Its speed depends on quantity of flow. Ignoring loss, hydraulic transmission force is irrelevant with speed.PressureP=F1/A1=F2/A2(Pascal's Principle)Quantity of flowQ=A1V1=A2V2; (V=S/t) (the Principle of Continuity )PowerPV1F1=V2F2=PQ . Basic Principle of Hydraulic Transmission Figure 1-1 Working Principle of Oil Jack1-oil tank 2-control valve 3,6-cylinder 4,7-plunger 5-lever8,9-one-way valve 10,11-pipelines

*1. Hydraulic Power Supply Components converting mechanical energy into liquid pressure. Typical component is hydraulic pump.

2. Control Components Control force, movement speed and direction actuating components by controlling pressure, flow quantity and direction of fluid. Pressure, flow 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.. Composition of Hydraulic Transmission System

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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.. Composition 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 automation6. 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.. Advantages 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.. Disadvantages of Hydraulic Transmission System

*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; andProvide diagnosis information for component and system failure.. Hydraulic Transmission Medium 1. Functions 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 fluidHFD. . Hydraulic Transmission Medium 2. Types of Hydraulic Medium

*1Viscosity2Abrasion resistance3Oxidation stability and thermal stability4Demulsibility and hydrolytic stability5Defoaming6Anti-corrosion. Hydraulic Transmission Medium 3. Main Performance of Hydraulic Medium

*7Shear stability8Material compatibility9Filtering property10Other performance requirements Other requirements include flame resistance, resistance to low temperature, radiation resistance (radioresistant) stability, nonpoisonous and tasteless, harmless to human body, easy processing of waste fluid and other performance.

*HH Hydraulic Oil. HH Oil is refined mineral oil without any additives. HL Hydraulic Oil. HL Oil is made from neutral base oil with high refined depth, and antioxidant and anti-rust . It is anti-corrosive and anti-oxidative type.HM Hydraulic Oil. HM Oil is developed from HL anti-corrosive and anti-oxidative oil.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.. Hydraulic Transmission Medium 4. Classification and Features of Hydraulic Oil of Mineral Oil Type

*Key Points of Reasonable Use1Identify variety and mark of oil; 2Hydraulic system should be thoroughly cleaned before liquid filling;3New oil must be filtered before use;4Oil cannot be mixed optionally;5Pollution should be strictly controlled to prevent moisture, air and solid impurities from entering hydraulic system. 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:1Changes of oil state, such as odor, color and appearance;2Point of flammability decreases. other oil may be mixed;3Mechanical impurities increase; 4Viscosity changes5Acid value increases;6Demulsibility becomes bad; and7Defoaming becomes bad.5. Reasonable Use and Maintenance of Hydraulic Medium

*Replacing of hydraulic oil of mineral oil typeFor 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;2Determine whether to replace oil according to experience and observation of oil sample; and3Specify oil drainage index. Determine whether to replace oil according to test result of oil sample; 5. Reasonable Use and Maintenance of Hydraulic Medium

*Pollution of hydraulic oil is mainly caused by the following reasons.1If 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. 2External 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.3Hydraulic system itself also constantly produces dirt, which will directly enter hydraulic oil, such as wear particles of metal and seal materials, particles dropping form filter materials, jelly generated due to oxidative deterioration of fiber and oil caused by oil temperature increase, etc.

*Harms of oil pollution Serious hydraulic oil pollution will directly influence work performance of hydraulic system, cause frequent failure of hydraulic system , and shorten service life of hydraulic components. Main reason causing these risks are particles in dirt. For hydraulic components, if these solid particles enter components, wear of sliding parts of components will be intensified, orifice and damping hole in hydraulic components may be blocked, or spool will be stuck, causing hydraulic system failure. Water and air mixing will reduce lubrication capacity of hydraulic oil reduction, accelerate oxidative deterioration, cause corrosion, accelerate corrosion of hydraulic components, and make hydraulic system vibrate or craw.

*Pollution prevention measures1Keep hydraulic oil clean before use;2Keep hydraulic system clean after assembling and before operation; 3Keep hydraulic oil clean during operation;4Use appropriate oil filter;5Regularly replace hydraulic oil; and6Control working temperature of hydraulic oil.

* 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 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.

*1With several seals and can periodically change space;2Absolute 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.3Have 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.

*1Pressure Working pressure, rated pressure and maximum permissible pressure.2Discharge and flow Theoretical flow, rated flow, and actual flow3Power and efficiency Power loss of hydraulic pump includes volume loss and mechanical loss. Power of hydraulic pump: input power and output power

*1By structure: Gear pump, vane pump, plunger pump, screw pump, etc. Gear pump: Inner gearing gear pump and outer gearing gear pump; Vane pump: Single acting vane pump and double acting vane pump; Plunger pump: Axial plunger pump, radial plunger pump and valve oil distributing valve plunger pump;2By function: Constant delivery pump and variable pumpgear pumpaxial plunger pumpradial plunger pump

* Hydraulic transmission control and regulating components are also called control valve, valve for short. They are used to control direction of flow and adjust pressure and flow of fluid of, in order to satisfy start, stop, redirection, speed regulation, voltage stabilization, unloading, pressurization, decompression and other operational needs of actuating components.

* 1In 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). 2In 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.

* Performance Parameters 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. Nominal diameter Unit of nominal diameter of hydraulic control valve is mm. A certain nominal diameter represents a certain of flow capacity, which is permissible maximum flow (nominal flow). It should be pointed out that, valves with the same nominal diameter may have different nominal flow because of their different functions.

*Performance requirements a. High action sensitivity. Reliable to use. Small impact and vibration during operation. Low noise. b. When valve port is closed, sealing should be good. When valve port is opened, direction valve should have small fluid flow pressure loss, direction valve should have good core stability. c. Controlled parameters (pressure or flow) should have high precision and small fluctuation when influenced by outside interference. d.Compact structure. Convenient to install, debug and maintain. High universality.

* There are many varieties of control valves used in hydraulic transmission, which can be classified by characteristics. It is the most common to classify by purpose of control valves.1Directional control valve (such as one-way valve and reversing valve);2Pressure control valve (such as overflow valve, pressure reducing valve and sequence valve);3Flow control valvesuch 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.

*ConceptValve used to control fluid flow pressure in the hydraulic system or control.Common PointsWork in the principle of balanced liquid pressure and spring force on valve core.Classification Overflow valvesafety valve and constant pressure valve; Pressure reducing valvefixed pressure reducing valve, fixed differential reducing valve and proportional pressure reducing valve; Sequence valve sequence valve, unloading valve, back pressure valve, balanced valve, hydraulic switch, etc.

*Main purpose of overflow valve is pressure leveling (constant pressure valve) or security protection (safety valve) of hydraulic system. Almost all the hydraulic systems need to use it. Its performance has very big effect on normal operation of the whole hydraulic system.System figure illustrates the role of overflow valve. Overflow Valve 2 in the left figure is constant pressure valve. Overflow Valve 2 in the right figure is safety valve.constant pressure valvesafety valve

*Structure type: can be divided into directly operated type and pilot operated type by form of structure and basic action mode. Directly operated overflow valvesee figureDirectly operated overflow valve controls on-off movement with pressure oil in the system directly acting on valve core which is balanced with spring force.Limited by structure and control precision, directly operated overflow valve is commonly used in little traffic system with low pressure (less than 2.5 MPa).Function Symbol MapFigure of Low-pressure Directly Operated Overflow Valve 1-nut 2-pressure adjusting spring 3-top cover 4-valve core 5-valve body

*Pilot operated overflow valve see figure for operating principleConsist 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, dynamic performance, remote control, etc.). Suitable for system with high pressure and big flow.Function Symbol MapPrinciple Demo. Control Components (Hydraulic Valve)1) Overflow valveContinued Pilot Overflow Valve 1-spring of main valve 2-main valve core 3-damper hole4-valve core of pilot valve 5-sping of pilot valveRemote Control

* 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 reducing valve in the return circuit. It can be divided into fixed pressure reducing valve, fixed differential reducing valve and proportional pressure reducing valve by pressure controlled by pressure reducing valve.Function Symbol Map Pressure Reducing Valve 1-main valve core 2-damper hole 3-vavle core of pilot valve V-flow speed of valve portL-outside leakage port

*As in the picture above, working principle of fixed pressure reducing valve can be considered according to that of pilot operated overflow valve .Compare pilot operated pressure reducing value and pilot operated overflow valve. They have the following differences.a. Pressure reducing valve keeps outlet pressure basically unchanged, and overflow valve keeps inlet pressure basically unchanged.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 doesnt need to be connected to external oil tank separately. Other types of pressure reducing valves will not be described.

*Sequence valve is a pressure valve which allows actuating components to act successively with pressure. See figure for working principle.Sequence valve includes directly operated type and pilot operated type. The former is generally used in low pressure system. The latter is used in middle or high pressure system.Sequence valve and overflow valve have similar structure. Compare pilot operated sequence valve and pilot operated overflow valve. They have the following differences.Function Symbol Mapdirectly operated external control sequence valve pilot operated sequence valve . Control Components (Hydraulic Valve)3Sequence valve Pilot Sequence ValveRemote Control

* 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 on sequence valve. Overflow valve has internal leakage and sequence valve needs to separately draw out leakage path, which is external leakage. Outlet of overflow valve has to return to the oil tank. Outlet of sequence valve can be connected to load.Function Symbol Mapdirectly operated external control sequence valve pilot operated sequence valve Remote Control Pilot Sequence Valve

* Pressure switch is a electrohydraulic control component converting oil pressure signal into electrical signal. When oil pressure reaches setting pressure of pressure switch, electrical signal will be sent out to control movements of electromagnet, electromagnetic clutch, relay and other components, so as to realize sequential actions of oil-way pressure relief, reversing and actuating components, or close electromotor to stop operation of system for safe protection, etc.1Plunger 2Lever 3Spring 4SwitchStructure Chart

*Concept: Function of directional control valve is to control flow direction of fluid. It realizes connection or disconnection of pathways with relative motion between valve core and valve body, to meet requirements of the system.Type: Directional control valve includes one-way valve and reversing valve.One-wayReversing Valve2-position figureRight position of three-position four-joint reversing valveLeft position of three-position four-joint reversing valve

*Classification of one-way valveBy function: Common one-way valve and hydraulic controlled one-way valve.By structure: Tubular (direct connection) and plate (right angle) Tubular Plate1One-way valveOil Inlet P1Oil Outlet P2Oil Inlet P1Oil Outlet P2

*Common One-way Valve Structural form and function symbol: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:Generally 0.040.1MPa; opening pressure of back pressure valve is 0.20.6 MPaOil Inlet P1Oil Outlet P2Oil Inlet P1Oil Outlet P2Oil Inlet P1Oil Outlet P2(d) SymbolModeModeMode

* Application:Reverse protection of hydraulic pumpSeparate oil channels prevent interferenceComprise combination valveInstalled in outlet oil line to produce back pressure

*Hydraulic Controlled One-way ValvePrinciple and performance: When the hydraulic controlled port K doesnt 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.ApplicationHydraulic 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.Function SymbolStructure Chart symbol

*Change flow direction and connect or cut off oil channels by relative motion of valve core in valve body, so as to control reversing, start or stop of actuating components.Classification of reversing valve By motion mode of valve core relative to valve body: Steering valve type, sliding valve type, ball valve type, etc. By control method: Manual, engine driven, electromagnetic, hydraulic, electric hydraulic, etc; By working position of valve core on valve body: Two-position valve and three-position valve By number of main oil port on valve body: Two-port valve, three-port valve, four-port valve and five-port valve.2Reversing ValveManual Reversing ValveElectromagnetic Reversing Valve

*Control mode symbols of commonly used sliding reversing valveElectricSpringManualHydraulicHydraulic Pilot ControlEngine Drive (Roller Type)Electromagnetic-Hydraulic Pilot Control

*Working principle of sliding reversing valveValve CoreValve Body

Position of Valve CoreValve Port StatePiston StateMiddle Port A and Port B dont connect oilStopLeft P ARightRight P B Left

*Big BoxValve bodySmall BoxStationCrossover point of arrow line in the small box or symbol and boundingOil portOil channels connected not always flow directionOil channels disconnected Functional chart of three-position four-port reversing valveHead of symbolNormal positionvalve core without force);A, BOil ports connected to the oil tankP, OOil inlet and return openingStation and pathway symbols of main structure of reversing valvesee figure

*Principle and type symbols of main structure of reversing valve

NameStructure and Principle ChartSymbolTwo-position two-port Two-position three-port Two-position four-port

*Principle and type symbols of main structure of reversing valve continued

NameStructure and Principle ChartSymbol Two-position five-port Three-position four-port Three-position five-port

*The most commonly used six median functions of three-position reversing valve

Function ModelMedian SymbolsState, Features and Application of Median SymbolsOPort P, A, B and O are all closed Hydraulic cylinder is locked. Hydraulic pump doesnt unload.HPort P, A, B and O are Hydraulic pump ; Piston of hydraulic cylinder is floating. Hydraulic pump unloads.YPort P is closed. Port A, B and O are connected. Piston of hydraulic cylinder is floating. Hydraulic pump doesnt unload.

* The most commonly used six median functions of three-position reversing valvecontinued

Function ModelMedian SymbolsState, Features and Application of Median SymbolsPPort P, A and B are connected. Port O is closed. Pump and hydraulic cylinder are connected, which can comprise differential motion and connect inlet.MPort P and Port O are connected. Port A and Port B are closed. Piston of hydraulic cylinder is locked. Hydraulic pump unloads.KPort P, A and B are connected. Port O is closed. Piston of is locked. Hydraulic pump unloads.

*Several Commonly Used Reversing ValvesArmatureCoilValve CoreElectromagnetic reversing valve Valve BodyFunction SymbolThree-position four-port electromagnetic reversing valveTwo-position four-port electromagnetic reversing valve

*Performance of electromagnetic reversing valveAC 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.

*Hydraulic reversing valveHydraulic controlled pressure portHydraulic controlled pressure portHydraulic three-position four-port reversing valveFunction Symbol

*Performance of hydraulic reversing valveHydraulic 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

*Electro-hydraulic reversing valvePilot valve electromagnetic valveMain valve electromagnetic valve

*Control oil channelMain oil channelPrinciple drawing of electro-hydraulic reversing valveSimplified Function Symbol

*Performance of electro-hydraulic reversing valveElectro-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.

*Engine driven reversing valvemotion valveLift type, two-port, normally openedOil InletOil OutletBack-moving SpringValve CoreRoller Push Rod

*Purpose of engine driven reversing valve is to move valve core with cam-action strokedog installed on actuating mechanism, in order to control on-off of oil channels and control stroke.

Appropriate reversing speed is obtained and reversing impact is reduced by changing appearance of cam.Performance of electro-hydraulic engine driven reversing valve

*Manual reversing valveSelf-restoring TypeMechanical Positioning Type

*Manual reversing valve is convenient to use. It is applicable to occasion with small flow and longer interval.Performance of manual reversing valve

*Student practice: draw out symbols of the following reversing valves1. Two-position two-port electromagnetic reversing valve (normally closed);2. Three-position four-port manual reversing valveMedian functionH);3. Three-position four-port hydraulicwith damper reversing valveMedian functionP

*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.

*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.

*FunctionConvert pressure of liquid into mechanical energy. Make linear, swinging and rotating with motion drive working mechanism.Type: Hydraulic cylinder and motor.1. Hydraulic Cylinder1Type of Hydraulic CylinderHydraulic cylinder has the following types by structure and function. Single-acting hydraulic cylinder Double-acting hydraulic cylinder Swinging hydraulic cylinder Combination hydraulic cylinder

*2Single-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. Motor1Features of MotorHydraulic 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:Sketch Map of Single-rod Piston Cylinder

*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 doesnt 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 doesnt have the above requirement.Hydraulic motor is required to operate normally at a wide speed range. Therefore, we should adopt hydraulic bearing or hydrostatic bearing. Because when motor is at low speed, if hydraulic bearing is used, it is not easy to formed lubrication film.

*Vane pump rotates at high speed with blades to generate centrifugal force, so that blades always adhere to the inner surface of stator to seal the oil and form working volume. If it is used as motor, spring must be installed on root of blades of hydraulic motor, in order to ensure that blades always adhere to the inner surface of stator and motor can normally start.Hydraulic pump should have self-priming capacity in structure , and hydraulic motor doesnt have this requirement.Hydraulic motor must have large starting torque. Starting torque is the torque that can be output by motor axle when motor starts from static state. The torque is generally larger than that under operation condition under the same operating differential pressure. Therefore, in order to make the starting torque near to torque under operation condition, it is required that motor torque has small pulsation and small internal friction.

*Hydraulic motor can also be divided into gear type, vane type, piston type and other types by structure types.

*Working Principle of Swash-plate Axial Piston MotorStructure 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*tan T1=F*r=F*R*con =p*A*R*tan*con T=m*p*V/2 Torque of cylinder generated by pistonTotal torque actually output by motor Torque force of cylinder generated by piston

**1Basic Knowledge of Hydraulic TransmissionHydraulic System Introduction of LG Loader12Contents of Training Courseware

**1Working Device Hydraulic System Steering Hydraulic System 12Part 2 LG Hydraulic System Introduction3Case Analysis

*. Working Hydraulic System 1. TypeLoader working device hydraulic system has two types by control method of multiple unit valve .Manual (Flexible Axle) Control Working Hydraulic System; 918, 933, 936, 40F, 952, 953, 956 and other types of our company use this type.Hydraulic Pilot Control Working Hydraulic System; Exported 918, 936, 938, 958, 959, 968, 969, 979 and other types of our company use this type.

*2. Principle of Working Hydraulic System Manual manipulation of flexible axel makes swing arm slide valve and rotating bucket slide valve of multiple unit valve do reciprocating movement, connects ports of oil inlet and slide valve of multiple unit valve, changes flow direction of hydraulic oil, and realizes different actions of working device.When flexible axel and rotating bucket reversing valve of multiple unit valve are in the middle position, flexible axel and bucket remain in the original position. At this time, hydraulic oil in working oil pump directly returns to oil tank through middle channel of multiple unit valve.Principle Drawing of Working Hydraulic SystemWorking and Steering Hydraulic System Demo . Working Hydraulic System

*Swing arm can lift, descent or float by controlling reversing slide valve on swing arm.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.. Working Hydraulic System 2. Principle of Working Hydraulic System (Continued)

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3. Composition of Working Hydraulic SystemGear pumpworking pumpMultiple unit valve Oil cylinder (swing arm cylinder and rotating bucket cylinderOil tankshared with steering systemPipe, filter and other accessoriesDescribe the components according to system principle drawingSystem Principle Drawing. Working Hydraulic System

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Gear PumpWorking PumpMain parameterstake LG953 and CBGj3166 for example1Rated pressure 18MPa2Rated rotate speed2200r/min3Displacement166ml/r Liquid volume discharged per round of hydraulic pump4Flow265 l/min) Flow= DisplacementRotate speed

Module of transfer gear with 42 gear teeth, working pump spindle with 42 gear teeth and steering pump gear with 48 gear teeth are all 4.

*

Working Principle of Gear PumpGear 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 bearing with keys. Driving axle is driven by power machine.Figure of Outer Gearing GearDemo Map

* When driving gear of the pump rotates according to direction of arrow as shown in the figure, teeth on the right of gear (oil absorption cavity) will throw out of gear and gear teeth will exit tooth space, so that sealing volume will increase and partial vacuum will be formed. Under the action of external atmospheres, oil in the oil tank will enter tooth space through oil absorption channels and oil absorption cavity. With gear rotating, inhaled tooth between oil was brought to the other side, into the pressure oil chamber. Then rotation of gear, oil absorbed into tooth space will be brought to the other side and enter oil pressure cavity. At this time, gear teeth are engaged each other, so that sealing volume will decrease and some 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. Working Principle of Gear Pump (Continued)

* Common fault analysis of loader gear pump

No.FailureReasonTroubleshooting Method1Hydraulic oil decreases. Transmission oil increases.Oil seal is brokenTest pressure. Change working pump (or steering pump)2Hydraulic oil increases. Transmission oil decreases.Oil seal is brokenTest pressure. Change working pump (or steering pump)3Oil leakage on joint surface of pump bodyO ring or bolt is looseChange O ring or fasten bolt4Oil leakage of pump bodyPump body cracksTest pressure. Change pump5Abnormal sound of pumpOverwear of spline shaftChange spline shaft or pumpOverwear of side plateChange side plate or pumpPoor size of spline shaft. Push the shaft.Change spline shaft or pump

Bearing is brokenChange bearing or pump

6Insufficient flow of pump causes weak and slow lifting Internal leakage caused by overwear of gear or side plateChange pump (or broken parts)

*Multiple Unit Valve1Type Double-joint multiple unit valve-used in loader with common functions Multiple unit valve-used in loader of multifunctional working device

*Multiple Unit Valve2Composition 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.

*Piping Map of Working Device Hydraulic System

*Profile Map of Double-joint Multiple Unit ValveDF32Action Demo1 Swing arm slide valve2 Turning slide valve3 Turn cylinder small cavity overload valve 4 Turn cylinder big cavity overload valve 5 Safety valve6 Valve bodyTurn belowSeal off supravergenceLiftingSeal offDescendFloat

*Safety Valve1Safety 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.2Pressure control: realized by adjusting pressure adjusting screw to change spring preload.3Setting 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 ValveDemo Map of Safety Valve

*Overload Supplemental Valve Overload supplemental valve (also called safety valve) is the combination of pilot type overflow valve and on-way valve. It is installed on multiple unit reversing valve through bolt. Two ports are respectively connected to oil channels in big and small cavity of turn cylinder in multiple unit reversing valve . The other two ports are connected to oil-returning circuit.Profile Map of Overload Supplemental Valve

*Overload Supplemental Valve (Continued) When turn reversing valve is in the middle position, front and back cavity of turn cylinder are closed. At this time, if the bucket is affected by external impact load, sharp rise of partial pressure can be effectively prevented.1Functions of 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.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.2Setting Pressure of Overload Supplemental Valve Overload Supplemental Valve

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

No.ReasonFailureTroubleshooting Method

1Insufficient working pressurePressure setting of safety valve is low Adjust pressure of safety valve Slide valve of safety valve is lockedTake apart, clean and reassemblePressure adjusting spring is brokenChange new springPressure loss in system pipelines is too largeChange pipelines or adjust pressure of overflow valve within permissible pressure scope

2Insufficient working flowOil supply of system is not enough Check oil sourcePort opening is not enoughAdjust control mechanismOil temperature is too high. Viscosity dropsTake measures to reduce oil temperatureImproper selection of oil Change oilFit clearance between slide valve and valve body is too bigChange slide valve or assembly according to proper clearance

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

No.ReasonFailureTroubleshooting Method3Reset failureRestoring spring is broken or deformsChange spring or assemblyRestoring parts are not in the same axle, pulled, etc.Change broken parts or assembly

4

Outside leakageSeal ring is brokenChange to new partsOil temperature is too high. Viscosity dropsTake measures to reduce oil temperatureFlange face installed on port is not well sealed.Check fastening and sealing of corresponding partsFastening screws on joint surfaces are blocked or cap of pressure adjusting screw is looseFasten corresponding parts5Big deflection of swing armClearance between valve body and valve rod of multiple unit valve increasesChange valve rod or assembly

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

No.ReasonReasonTroubleshooting Method6Bucket dropsInner leakage of overload supplemental valve in big cavity of turn cylinder (dirt blocked and broken)Disassemble, clean, reassemble or replaceWear and clearance between valve body and valve rod of multiple unit valve increasesChange valve rod or assembly

7Bucket is put awayInner leakage of overload supplemental valve in small cavity of turn cylinder (dirt blocked and broken)Change supplemental valve. Low pressure8Front tire cannot supportSetting pressure of overload valve in small cavity of rotating bucketis lowIncrease pressure of overload valve in small cavity Large amount of leakage in small cavity of rotating bucketChange slide valve according to proper clearance

*Oil CylinderTypeHydraulic cylinder used in loader is single-rod piston double-acting oil cylinder.Classification: Swing arm oil cylinder, turn oil cylinder and steering oil cylinder. CompositionPiston double-acting hydro-cylinder generally consists of oil cylinder body, piston, piston rod guide sleeve, etc.CommentsIn 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 Cylinder1. Back cylinder cover 2. Stop collar 3. Lantern ring 4. Snap ring5. Piston 6. O Ring 7. Back-up ring 8. Stop dog 9. Ax seal ring10. Oil cylinder body 11. Port stand 12. Guide sleeve 13. Cylinder end 14. Dust ring Piton rod 16. Screw Buffer Plunger

*Hydraulic Pilot Control Working Hydraulic System Working hydraulic system of LG918, LG933, LG936, LG956L, LG958L and other loaders, which are export products of our company, uses pilot control working hydraulic system. main oil channels with high pressure and big flow are controlled by pilot oil channels with low pressure and small flow. Compared with mechanical control hydraulic system, this working hydraulic system has the following features:1Features of the SystemPilot control is light, flexible and efficient. Finger control can be realized. By pressure-relief type proportional pilot valve control, stroke of valve rod of main valve is in proportion to control angle of pilot value handle, which means proportional pilot control to work of main valve is realized.Safety valve, overload valve, supplemental valve and one-way valve use insert type structure. With good generality, it is convenient to maintain.

* Pilot valve uses overall structure. With a small volume it is convenient to arrange. When engine shuts down, drop of swing arm and forward tilting of bucket can be realized by pressure selecting valve and pilot valve. Pilot valve has orientation with electromagnetic iron at lifting position of swing arm and backward tilting position of bucket. Vertical limit of lifting height of swing arm and automatic leveling control of bucket at any position can be realized, which simplifies operating procedures, reduces labor intensity, and avoids energy loss and pressure shock caused by frequent movement of safety valve.2System CompositionComposition 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.1Features of the System (Continued)

*Principe of Hydraulic Pilot Control System

*Pilot Valve Pilot valve is equipped with control rod. Rotating bucket control has forward tilting, middle standing and backward titling positions. Swing arm control has lifting, neutral, middle standing, dropping and floating positions. Pilot valve has orientation with electromagnetic iron at lifting, floating and backward titling position. See figure.Structure of Pilot Valve

*When pulling the control rod to dropping position, pressure pin will push down pressure lever. Measurement spring will push down measurement valve core, cut off the channel between control cavity and oil returning chamber, connect oil inlet cavity to control oil cavity, guide pressure oil to the end of multiple unit valve, push multiple unit valve to move, and corresponding reversing action. Meanwhile, oil pressure of control cavity will act on lower end of measurement valve core, and balance with the force of measurement spring. When 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.Working principle of pilot valveproportional 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.Working principle of pilot valveproportional pilot control and automatic control of electromagnet)

*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.

*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.

*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.

*Automatic control of lifting height of swing armWhen 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 control of pilot oil. Lifting of swing arm will automatically end.

Structure of Multiple Unit ValveMultiple Unit Valve (D32 Continued)

*Floating of swing armWhen 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 doesnt 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.

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.Multiple Unit Valve (D32 Continued)

*Pressure Selecting ValveStructure and Principle of Pressure Selecting Valve Function: Purpose of pressure selecting valve is to provide a certain pressure of control oil to pilot valve, and ensure swing arm on the ground position when diesel engine shuts off.Structure: Pressure selecting valve is installed in pilot oil channel. Control valve of pressure selecting valve mainly consists of valve body, valve core, spring, etc. Port P1 is connected to pilot pump. Port Pr is connected to big cavity of swing arm oil cylinder. Port P2 is oil outlet, which is connected to pilot valve. L is oil returning port. See structure chart.

One-way valveOne-way valve

*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 doesnt 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.

*. Steering SystemFunction: 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.

*Steering system has many varieties. Different types of steering system respectively represent development level of different hydraulic technique. At present wheel loader uses the following types of steering system.Type of Steering SystemWhole hydraulic steering system consisting of single stable valve and open center non-reaction steering gear;Load sensing whole hydraulic steering system consisting of priority valve and load sensing steering gear; Load sensing whole hydraulic steering system consisting of priority valve and coaxial flow amplifying steering gear;Flow amplifying steering system

*1. Whole Hydraulic Steering System Controlled by Solenoid Valve1) 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.System Principle 2)Steering Gear BZZ Whole Hydraulic Steering Gear is a cycloid rotaryvalve whole hydraulic steering gear consisting of servo valve and pin wheel gear pair. It is current widely used steering component at home and aboard. It is flexible to operate, energy saving, compact in structure, reliable, and convenient to install. Manual steering can be realized after engine shuts off.

*There are the following major types of BZZ Whole Hydraulic Steering Gear.Open center non-reaction BZZ1Open center reaction BZZ2Closed center non-reactionBZZ3Load sensing BZZ5Coaxial flow-amplifyingBZZ6and other structural stylesFunction symbols are shown in the figure.

Type Symbol of BZZType of 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.Structure of Whole Hydraulic Steering GearMiddle position Steering position Working principle of steering gearStructure of BZZ Whole Hydraulic Steering Gear

*Correspondence of valve core, valve pocket , stator and rotor

*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.

FunctionsOn one hand, ensure that steering gear and the whole steering system works normally and smoothly under pressure rated; On the other hand, ensure that steering cylinder and connected pipelines will not be damaged during sudden overload, and protect steering pump. So valve block is an indispensable hydraulic component in hydraulic steering system.

*Composition of Combined Valve BlockAccording to different requirements of steering system, combined types of valve block are different. Valve block generally consists of one-way valve, overflow valve (safety valve), two-way buffer overload valve, supplementary valve, etc. (but some valve blocks are only equipped with two-way buffer valve and one-way valve, and some only have overflow valve and one-way valve). Structure of valve block is shown in figure.Composition of existing steering gear valve block: one-way valve, overflow valve (safety valve), and two-way buffer overload valve.Structure Chart of Valve BlockFunctional Chart of Valve Block3) Combined Valve Block

*4) Single stable ValveSingle-channel stable flow divider valve (single stable valve for short) mainly works with BZZ series of whole hydraulic steering gear. It is used in whole hydraulic steering system. When oil supply of steering oil pump and system load change, stable flow required by steering gear is ensured by single stable valve, to satisfy hydraulic steering requirement of loader.Single-channel stable flow divider valve mainly consists of valve body, valve core, spring, safety valve, damping plug and other parts. It has shunt type and constant-current type. See figure.Single stable valve is used in independent system. Oil from steering is supplied to the system. The rest oil and oil overflowing when safety valve opens unloading will flow back to the oil tank through Port T.Structure and Principle Chart Safety valve is on the valve block now

*2. Load Sensing Whole Hydraulic Steering System 1Composition 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

*2. Load Sensing Whole Hydraulic Steering System 1Composition of SystemContinued 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

*Load Dynamic Sensor System

*2Pipeline Direction of Load Sensing Whole Hydraulic Steering System

*3) BZZ5 Load Sensing Whole Hydraulic Steering GearStructure 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.Ports of Steering Gear3D Profile of StructureFollowing Rotary ValveMeasurement Motor

*Toil returnPoil inletRright steeringLleft steeringTLPRLSPosition of ports on steering gear

*Main Components of Steering GearCore components of whole hydraulic steering gear: Metering mechanism---stator and rotor Servo proportional control valve ---valve core/valve pocket pair

* Working PrincipleBZZ5System Sketch MapWhen following rotary valve is at the middle position (steering wheel doesnt move), valve package and valve core are in the middle under the action of positioning spring, and channels connected to tooth cavity of rotor and stator and two cavity of steering cylinder are closed, only a small amount of pressure oil pumped from steering pass through inside of steering gear, and most oil will be distributed by Port EF of priority valve (combined to working hydraulic system or flows back to oil tank). Oil in two cavity of steering cylinder will be closed, piston cannot move, and loader will run in original direction.PumpDiesel EngineHydraulic oil tankCombines or returns to oil tank

*When steering wheel turns, priority valve will preferentially satisfy steering needs. Oil in steering pump will go to measurement motor through priority valve and following rotary valve, and turn in the direction of steering wheel with rotor. Working oil will be delivered to a cavity of steering cylinder and realize steering. Oil in the other cavity of steering cylinder will return to oil tank with following rotary valve. When steering wheel turns fast, a large amount of oil will reach steering cylinder through measurement motor. Steering will be fast. Working PrincipleBZZ5 Continued

*4) Priority ValveStructure and Principle Chart of Priority ValveThis 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.

*4) Priority Valve (Continued) When steering wheel doesnt 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.

*5Coaxial Flow Amplifying Steering GearCoaxial 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.

*5Coaxial 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.

*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 doesnt 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.3. Flow Amplifying Steering System (Flow Amplifying Valve)

*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.3. Flow Amplifying Steering SystemContinued

*1Oil returning filter 2Radiator 3Hydraulic oil tank 4Working pump 5Pressure selecting valve 6Steering gear 7Steering cylinder 8Flow amplifying valve 9Air change filter 10Steering pump 11Unloading valve 12Oil absorption filter core Principle Chart of Flow Amplifying System

* Structure and working principle of priority flow amplifying valve:1Flow Amplifying Valve1 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

*1Flow Amplifying ValveContinuedWhen 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.Middle Position

*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.1Flow Amplifying ValveContinued

* 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). Right Steering Position

*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 doesnt 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.Right Steering Position (Continued)

*. Failure Case Analysis1. Failure Case Analysis of Working Hydraulic System1Weak lifting of swing arm2Slow and weak bucket 3Bucket turns over or shakes during lifting operation4Hydraulic oil temperature is too high

*. Failure Case Analysis1Heavy steering2No terminal point for steering3Reason for vehicle deflection4Inaccurate steering5Steering wheel rotates freely. Steering doesnt move or slow.6Blanking stroke of steering wheel7Steering wheel shakes or rotates 8Steering wheel rebounds 2. Failure Case Analysis of Steering Hydraulic System

*1Weak lifting of swing arm analysis and judgment process1. Failure Case Analysis of Working Hydraulic SystemCheck whether stroke of multiple unit valve rod is in placeNoYesNoCheck whether hydraulic oil amount meets standardCheck whether oil absorption tube of working pump is blockedMeasure when pressure is zero or lowTest pressure is below requirementPressure changes after adjustmentPressure doesnt change after adjustmentCheck whether pump driving axle is broken or fallsCheck whether multiple valve leaksCheck whether working device hydraulic system is normalCheck whether swing arm cylinder has internal leakagePressure increases with engine throttle, but doesnt reach setting pressureMeets setting requirement of working system pressureWhen stroke of valve rod is in place and hydraulic oil amount meets standard, check whether rotating speed of engine meets standardAction stroke of 918 swing arm valve is 7mm. Action stroke of rotating bucket valve is 8.1mm. Action stroke of the two valve rods of other types are all 16mm.When bucket is flat on the ground, oil position is between 6 and 10 on mark of hydraulic oil tankMeasure with tachymeter to check whether rated rotating speed of engine reaches 2200r/minWhen 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 measureAdjust pressure of main safety valve. 933, 936 and 952 are 16MPa. 918 is 17.5MPa. 953, 956 and 958 are 18MPa.YesYesNoYesYesYesYesYesYesYesNoNoYesYesNoYes

ReasonMeasures1. Valve rod is blocked2. Positioning steel ball of valve rod becomes invalid due to wear. Positioning spring becomes invalid3. Control mechanism doesnt control wellHydraulic oil amount is not enough

Dirt or rubber dropping of tubes makes pump unable to absorb oilPump axle is broken or drops. Working pump cannot absorb oilSetting pressure of main safety valve is lowSpring in main safety valve is broken or valve core is blockedWorking gear pump wears or is brokenInternal leakage of swing arm cylinder1. Leakage of swing arm slide valve2. Internal leakage of main safety valveAccelerator pedal or cable cause low rotating speedOil absorption channels are blocked1. Check valve rod, steel ball, positioning spring of valve rod or change valve2. Check control mechanismAdd hydraulic oil to specified mark

Remove dirt or change rubber tubesChange pump axle

Set to system pressure value

Wash or change spring

Change gear pump or repairRepair of change oil cylinderRepair or change multiple unit valveCheck pedal and cable. Adjust rotating speed to specified valueChange filter screen

610

2200r/min

9187mm8.1mm16mm

1

1.2.

93393695216MPa91817.5MPa95395695818MPa

1.2.

2200r/min

*2Slow and weak bucket analysis and judgment processCheck whether broken rotating bucket slide valve causes internal leakageCheck whether overload valve has internal leakageCheck whether pressure of overload valve is lowCheck whether rotating bucket cylinder has internal leakageCheck whether setting pressure of two overload valves in rotating bucket cylinder is normalPressure 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.NoYesYesYesNoYesYesNo

ReasonMeasuresBroken seal ring causes internal leakage and bucket droppingScratching or wear on valve rod or valve hole of rotating bucket makes leakage of hydraulic oil large1. Main valve core of overload valve has dust particles, which makes overload valve open2. Aging of seal ring3. Improper clearance between valve core and valve body1. Low pressure of overload valve causes bucket dropping or floating2. Spring of overload valve is broken or invalidChange seal ring

Repair or change

1. Wash main valve core and remove impurities2. Change seal ring3. Change overload valve

1. Adjust pressure to specified value2. Repair or change

9339369389521818.5MPa9189539562020.5MPa95896821.5MPa40F15.5MPa1212.5MPa

1.2.3

1.2.3.

1.2.

1.2.

*3Bucket turns over or shakes during lifting operation analysis and judgment processCheck whether oil amount meets standardTest pressure of working device hydraulic systemWhen system pressure and hydraulic oil amount are normal, check whether leakage amount of rotating bucket cylinder and swing arm cylinder are sameWhen system pressure and hydraulic oil amount are normal, check whether pistons in rotating bucket cylinder and swing arm cylinder are loosenCheck whether starting pressure of safety valve is stableCheck whether oil channels are blocked or flatCheck pressure increases with increase of engine throttleCheck whether indicator of pressure gage swings intensivelyCheck whether oil absorption rubber tubes are well sealedOil position is between 6 and 10 on mark of hydraulic oil tankWhen 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.NoYesNoYesYesNoYesNoNoYesYesNo

ReasonMeasuresOil amount is not enough

Working gear pump wears or is broken Unstable starting pressure of safety valve changes pressure of hydraulic oilCaused by aging and foaming of inlayer of rubber tubes, or blocking of transiting valve block and joint Air entering system makes working pressure unstableDifferent leakage amount causes flow fluctuation and shakingLoosen piston makes piston rod move in hydraulic cylinderAdd hydraulic oil to specified markChange or repair

Check setting pressure of valve, and whether spring deforms. Adjust starting pressureRepair or change

Repair or change

Repair or change

Repair or change

2200r/min93393695216MPa91817.5MPa95395695818MPa

610

*4Hydraulic oil temperature is too high analysis and judgment process Check whether position of hydraulic oil is too lowCheck whether hydraulic oil is too dirty or goes badCheck whether there is too much grease between blades of cooling fin in water boxCheck whether hydraulic radiator has problemCheck whether improper pressure setting causes high temperature of hydraulic oil Check whether cylinder, pump and valve have leakage Check whether gear pump, gear pair, side plate or pump body have wearNoYesYesYesYesYesYesYesNoNoNoNoNo

ReasonMeasuresInsufficient hydraulic oil makes working pump absorb airHydraulic components are blocked, causing throttling and temperature rise of Too much grease causes poor heat dissipationBlocking in radiator or other reasons cause poor heat dissipationWhen system pressure is set too high, overflow valve cannot overflow and reduce pressure normally, internal leakage will increase, oil temperature of system will rise. When oil returning filter core is blocked or oil returning channels become old and delaminate, back pressure will be high and oil temperature will rise.Serious internal leakage of hydraulic components will cause temperature rise of systemLow volumetric efficiency will cause temperature rise of hydraulic oilAdd hydraulic oil to specified mark

Change or filter hydraulic oil

Clean with high pressure gun

Repair or change

Repair or change

Repair or change

Repair or change

* 1Heavy steeringanalysis and judgment process2. Failure Case Analysis of Steering Hydraulic SystemDecide according to fault phenomenonCylinder crawls. Foam in oil. Regular soundHeavy steering. Steering cylinder doesnt move.Is fast steering heavy and slow steering light?Check whether steering pillar is flexibleWhether system pressure meets the needsCheck whether feedback oil channels are unblockedAdjust system press. Does the pressure change?Is surface of hydraulic oil low?Is oil sucking pipe blocked?YesYesYesYesYesYesYesNoNoNoNoYesYesNoNoNo

ReasonMeasuresAir in system

-One-way valve failure of manual steering -Leakage of FK overload valve-Internal leakage of oil cylinder

Steering pillar is brokenPipelines are blockedLow system pressureSpring of priority valve is broken. Shuttle valve is blockedLack oil

Pipelines are blockedWear and internal leakage of steering pumpRemove air in system. Check whether oil inlet of oil pump leaks.-Check whether steel ball exists and whether it is blocked-Change FK combination valve-Check whether oil cylinder has internal leakageRepair or change

Clean or change

Repair or change

Adjust system pressure

Supplement hydraulic oilClean or change

Repair or change

*2No terminal point for steering or limit position cannot be reached analysis and judgment process)No terminal pointSteering cylinder cannot turn to extreme positionAfter steering cylinder turns to extreme position, turning the steering wheel, steering wheel can turn lightly, which means no sense of terminal point.Steering cylinder cannot turn to extreme position. Steering response is heavy.

Failure ReasonTroubleshooting MethodLow overload valve pressureIncrease overload valve pressure properly

Failure ReasonTroubleshooting MethodLow safety valve pressureIncrease safety valve pressure properly

*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.Check whether connecting rod of oil cylinder is loosen.Leakage in oil cylinderPressure of two tires has big difference.Leakage on two-way overload valve or two-way supplemental valve.Air in oil3Reason for Vehicle Deflection

*Air in system;Pin of oil cylinder is loosen;Priority valve or main valve of flow divider valve is blocked;Oil cylinder has leakage;Low efficiency of pump causes unstable pressure. 4Inaccurate Steering

* Serious leakage in two-way overload valve Serious leakage in piston of oil cylinder5Steering wheel rotates freely. Steering doesnt move or slow.

*Nut on steering wheel movesConnection of steering pillar and steering gear wears or is brokenAir in oil

Leakage in two-way overload valve

Leakage in steering cylinder

6Blanking Stroke of Steering Wheel

*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 rotorWhen oil in pump is connected to Port R or L, steering gear will rotate like motor.

7Steering wheel shakes or rotates

*ReasonOne-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.

8Steering wheel rebounds

*Reliability bears great trust!