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Loader Hydraulic Training Courseware 2011

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Title: Loader Hydraulic Training Courseware 2011


1
Loader Hydraulic Training Courseware 2011
2
Main Content
  • Suitable Group
  • Training Objectives
  • Contents
  • Evaluation Topics

3
Suitable Group
This course is suitable for domestic and foreign
intermediate and above technical service
personnel It also applies to
4
Main Content
  • Suitable Group
  • Training Objectives
  • Contents
  • Evaluation Topics

5
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
6
Contents
Basic Knowledge of Hydraulic Transmission
1
1
Hydraulic System Introduction of LG Loader
2
2016/10/7
7
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
Disadvantages of Hydraulic Transmission System
4
Hydraulic Medium
5
Hydraulic Power Components
6
7
Hydraulic Control Components
8
Hydraulic Actuating Components
2016/10/7
8
?. 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.

9
?. 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.

10
?. 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 principle of equal
liquid volume after changes. Its speed depends on
quantity of flow. Ignoring loss, hydraulic
transmission force is irrelevant with speed.
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
  • PressurePF1/A1F2/A2(Pascal's Principle)
  • Quantity of flowQA1V1A2V2 (VS/t)
  • (the Principle of
    Continuity )
  • PowerPV1F1V2F2PQ

11
?. 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.

12
?. 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.

13
?. 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.

14
?. 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.

15
?. 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.

16
?. 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).

17
?. 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

18
  • 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.

19
?. 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.

20
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.

21
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.

22
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

23
  • ? 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.

24
  • ? 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.

25
  • ? 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.

26
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
27
  • 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.

28
  • 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

29
  • 1)By 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
  • 2)By function Constant delivery pump and
    variable pump

gear pump
axial plunger pump
radial plunger pump
30
  • 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.

31
  • 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.

32
  • ? 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.

33
  • ? 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.

34
  • 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.

35
  • 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 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.

36
? 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
safety valve
37
? Structure type can be divided into directly
operated type and pilot operated type by form of
structure and basic action mode.
? 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. 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).
Figure of Low-pressure Directly Operated Overflow
Valve 1-nut 2-pressure adjusting spring 3-top
cover 4-valve core 5-valve body
Function Symbol Map
38
?. Control Components (Hydraulic Valve)
Remote Control
1) Overflow valve(Continued)
  • ? 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, dynamic
    performance, remote control, etc.). Suitable for
    system with high pressure and big flow.

Pilot Overflow
Valve 1-spring of main valve 2-main valve core
3-damper hole 4-valve core of pilot valve 5-sping
of pilot valve
Principle Demo
Function Symbol Map
39
  • 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.

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
Function Symbol Map
40
  • 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.

41
?. 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.
  • ? Sequence valve and overflow valve have similar
    structure. Compare pilot operated sequence valve
    and pilot operated overflow valve. They have the
    following differences.

Pilot Sequence
Valve
Function Symbol Map
directly operated external control sequence valve
pilot operated sequence valve
42
Remote 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.

Pilot Sequence
Valve
Function Symbol Map
pilot operated sequence valve
directly operated external control sequence valve
43
  • 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 4Switch
Structure Chart
44
  • 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 four-joint
reversing valve
Right position of three-position four-joint
reversing valve
Reversing Valve(2-position figure)
One-way
45
? Classification of one-way valve
1)One-way valve
? By function Common one-way valve and hydraulic
controlled one-way valve. ? By structure Tubular
(direct connection) and plate (right angle)
Oil Inlet P1
Oil Outlet P2
Oil Inlet P1
Oil Outlet P2
Tubular
Plate
46
? 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 Generally 0.040.1MPa
opening pressure of back pressure valve is
0.20.6 MPa
Oil Outlet P2
Oil Inlet P1
Mode
Oil Inlet P1
Oil Outlet P2
Mode
? Structural form and function symbol
Oil Inlet P1
Oil Outlet P2
(d) Symbol
Mode
47
? Application
?Reverse protection of hydraulic pump
?Separate oil channels prevent interference
?Comprise combination valve
?Installed in outlet oil line to produce back
pressure
48
?Hydraulic Controlled One-way Valve
  • ? Principle 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.

symbol
Structure Chart
Function Symbol
49
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
? 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.
Manual Reversing Valve
Electromagnetic Reversing Valve
50
? Control mode symbols of commonly used sliding
reversing valve
Engine Drive (Roller Type)
Electric
Spring
Manual
Hydraulic Pilot Control
Electromagnetic-Hydraulic Pilot Control
Hydraulic
51
?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 dont connect oil Stop
Left P A Right
Right P B Left
52
?Station and pathway symbols of main structure
of reversing valve(see figure)
Big Box
Valve body
Small Box
Station
Crossover point of arrow line in the small box
or- symbol and bounding
Oil port
Oil channels connected (not always flow direction)
-
Oil channels disconnected
Head of symbol
Normal position(valve core without force)
A, B
Oil ports connected to the oil tank
Functional chart of three-position four-port
reversing valve
P, O
Oil inlet and return opening
53
? Principle and type symbols of main structure of
reversing valve
Name Structure and Principle Chart Symbol
Two-position two-port
Two-position three-port
Two-position four-port
54
? Principle and type symbols of main structure of
reversing valve (continued)
Name Structure and Principle Chart Symbol
Two-position five-port
Three-position four-port
Three-position five-port
55
? The most commonly used six median functions of
three-position reversing valve
Function Model Median Symbols State, Features and Application of Median Symbols
O Port P, A, B and O are all closed Hydraulic cylinder is locked. Hydraulic pump doesnt unload.
H Port P, A, B and O are Hydraulic pump Piston of hydraulic cylinder is floating. Hydraulic pump unloads.
Y Port P is closed. Port A, B and O are connected. Piston of hydraulic cylinder is floating. Hydraulic pump doesnt unload.
56
? The most commonly used six median functions of
three-position reversing valve(continued)
Function Model Median Symbols State, Features and Application of Median Symbols
P Port P, A and B are connected. Port O is closed. Pump and hydraulic cylinder are connected, which can comprise differential motion and connect inlet.
M Port P and Port O are connected. Port A and Port B are closed. Piston of hydraulic cylinder is locked. Hydraulic pump unloads.
K Port P, A and B are connected. Port O is closed. Piston of is locked. Hydraulic pump unloads.
57
? Several Commonly Used Reversing Valves
? 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
58
? 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.
59
? Hydraulic reversing valve
Hydraulic controlled pressure port
Hydraulic controlled pressure port
Hydraulic three-position four-port reversing valve
Function Symbol
60
? 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
61
? Electro-hydraulic reversing valve
Main valve (electromagnetic valve)
Pilot valve (electromagnetic valve)
62
? Principle drawing of electro-hydraulic
reversing valve
Control oil channel
Main oil channel
Simplified Function Symbol
63
? 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.
64
? Engine driven reversing valve(motion valve)
Oil Inlet
Back-moving Spring
Roller Push Rod
Oil Outlet
Valve Core
Lift type, two-port, normally opened
65
? 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.
66
? Manual reversing valve
Self-restoring Type
Mechanical Positioning Type
67
? Performance of manual reversing valve
Manual reversing valve is convenient to use. It
is applicable to occasion with small flow and
longer interval.
68
? 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 functionH) 3. Three-position
four-port hydraulic(with damper) reversing
valve(Median functionP)
69
  • ? 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.

70
  • ? 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.

71
  • FunctionConvert 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
72
  • 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.

Sketch Map of Single-rod Piston Cylinder
2. Motor
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
73
  • 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.

74
  • 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.

75
  • Hydraulic motor can also be divided into gear
    type, vane type, piston type and other types by
    structure types.

76
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).
Working Principle of Swash-plate Axial Piston
Motor
Torque force of cylinder generated by piston
F1pAtan?
T1FrFRconf pARtan?conf
Torque of cylinder generated by piston
T?m?pV/2p
Total torque actually output by motor
77
Contents of Training Courseware
Basic Knowledge of Hydraulic Transmission
1
1
Hydraulic System Introduction of LG Loader
2
2016/10/7
78
Part 2 LG Hydraulic System Introduction
Working Device Hydraulic System
1
1
Steering Hydraulic System
2
Case Analysis
3
2016/10/7
79
?. Working Hydraulic System
1. Type
Loader 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.

80
2. Principle of Working Hydraulic System
?. 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. ?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 System
81
?. Working Hydraulic System
2. Principle of Working Hydraulic System
(Continued)
? 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.
82
3. Composition of Working Hydraulic System
?. 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
83
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
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.
84
? 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
bearing with keys. Driving axle is driven by
power machine.
Demo Map
Figure of Outer Gearing Gear
85
? 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.

86
? 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
5 Abnormal sound of pump Overwear of spline shaft Change spline shaft or pump
5 Abnormal sound of pump Overwear of side plate Change side plate or pump
5 Abnormal sound of pump Poor size of spline shaft. Push the shaft. Change spline shaft or pump
5 Abnormal sound of pump Bearing is broken Change bearing or pump
6 Insufficient flow of pump causes weak and slow lifting Internal leakage caused by overwear of gear or side plate Change pump (or broken parts)
87
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
88
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.
89
Piping Map of Working Device Hydraulic System
90
Profile Map of Double-joint Multiple Unit
Valve(DF32)
Action Demo
supravergence
Turn below
Seal off
1 Swing arm slide valve 2 Turning slide valve 3
Turn cylinder small cavity overload valve 4 Turn
cylinder big cavity overload valve 5 Safety
valve 6 Valve body
Lifting
Seal off
Descend
Float
91
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.

Demo Map of Safety Valve
Structure Chart of Safety Valve
92
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
93
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.
94
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.
95
2)Setting Pressure of Overload Supplemental Valve
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.

96
Basic Failure and Troubleshooting of Multiple
Unit Valve (DF)
No. Reason Failure Troubleshooting Method
1 Insufficient working pressure Pressure setting of safety valve is low Adjust pressure of safety valve
1 Insufficient working pressure Slide valve of safety valve is locked Take apart, clean and reassemble
1 Insufficient working pressure Pressure adjusting spring is broken Change new spring
1 Insufficient working pressure Pressure loss in system pipelines is too large Change pipelines or adjust pressure of overflow valve within permissible pressure scope
2 Insufficient working flow Oil supply of system is not enough Check oil source
2 Insufficient working flow Port opening is not enough Adjust control mechanism
2 Insufficient working flow Oil temperature is too high. Viscosity drops Take measures to reduce oil temperature
2 Insufficient working flow Improper selection of oil Change oil
2 Insufficient working flow Fit clearance between slide valve and valve body is too big Change slide valve or assembly according to proper clearance
97
Basic Failure and Troubleshooting of Multiple
Unit Valve (DF) (Continued)
No. Reason Failure Troubleshooting Method
3 Reset failure Restoring spring is broken or deforms Change spring or assembly
3 Reset failure Restoring parts are not in the same axle, pulled, etc. Change broken parts or assembly
4 Outside leakage Seal ring is broken Change to new parts
4 Outside leakage Oil temperature is too high. Viscosity drops Take measures to reduce oil temperature
4 Outside leakage Flange face installed on port is not well sealed. Check fastening and sealing of corresponding parts
4 Outside leakage Fastening screws on joint surfaces are blocked or cap of pressure adjusting screw is loose Fasten corresponding parts
5 Big deflection of swing arm Clearance between valve body and valve rod of multiple unit valve increases Change valve rod or assembly
98
Basic Failure and Troubleshooting of Multiple
Unit Valve (DF) (Continued)
No. Reason Reason Troubleshooting Method
6 Bucket drops Inner leakage of overload supplemental valve in big cavity of turn cylinder (dirt blocked and broken) Disassemble, clean, reassemble or replace
6 Bucket drops 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
8 Front tire cannot support Large amount of leakage in small cavity of rotating bucket Change slide valve according to proper clearance
99
Oil Cylinder
  • TypeHydraulic 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 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
  • Piton rod
  • 16. Screw

Buffer Plunger
100
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.
101
? Pilot valve uses overall structure. With a
small volume it is convenient to arrange. ?
When engine shuts down, drop of swing arm and
forward tilting of bucket can be realized by
pressure selecting valve and pilot valve. ?
Pilot valve has orientation with electromagnetic
iron at lifting position of swing arm and
backward tilting position of bucket. Vertical
limit of lifting height of swing arm and
automatic leveling control of bucket at any
position can be realized, which simplifies
operating procedures, reduces labor intensity,
and avoids energy loss and pressure shock caused
by frequent movement of safety valve.
1)Features of the System (Continued)
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.
102
  • Principe of Hydraulic Pilot Control System

103
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
104
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 valve(proportional
pilot control and automatic control of
electromagnet)
105
? 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.

106
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.

107
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.

108
Multiple Unit Valve (D32 Continued)
  • Rotating bucket reversing valve is three-position
    valve. It can control middle standing, forward
    titling and backward titling action of bucket.
    Swing arm reversing valve is four-position valve.
    It can control middle standing, lifting, dropping
    and floating action of swing arm. Movement of
    slide valve relies on action of pilot control
    oil. It restores by spring. Two reversing valves
    are connected to oil channels by series-parallel
    connection. They are at a certain
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