Loader Hydraulic Training Courseware
Main Content
Suitable Group
Contents
Training Objectives
Evaluation Topics
Contents
Suitable Group
This course is suitable for domestic and foreign intermediate and
above technical service personnel
Main Content
Suitable Group
Contents
Training Objectives
Evaluation Topics
Contents
Training Objectives
1. This training course is expected to have 12 hours.
2. After training of this course, students should master the following main
knowledge points:
（
1
）
Basic knowledge of hydraulic system
（
2
）
Structure and principle of LG hydraulic system
（
2
）
Structure and principle of LG hydraulic system
1
Basic Knowledge of
Hydraulic
Transmission
1
Contents
Hydraulic
System Introduction of LG
Loader
2
1
Basic Principle of Hydraulic Transmission
Composition of Hydraulic Transmission System
1
2
Part 1 Basic Knowledge of Hydraulic
Transmission
3
4
Advantages of Hydraulic Transmission System
Disadvantages of Hydraulic Transmission
System
5
6
7
8
System
Hydraulic Medium
Hydraulic Power Components
Hydraulic Control Components
Hydraulic Actuating Components
●
●
●
●
A machine is basically made up of four parts, including prime motor,
transmission device, working mechanism, and assistant mechanism.
The purpose of prime motor is to change various forms of energy into
mechanical energy, which is power supply of the machine. Working
mechanism works outside with mechanical energy. Transmission device
Ⅰ
Ⅰ
Ⅰ
Ⅰ
. Basic Principle of Hydraulic Transmission
mechanism works outside with mechanical energy. Transmission device
between prime motor and working mechanism transfers power and
controls.
There are many transmission types. Transmission can be divided into
mechanical transmission, power transmission, pneumatic transmission and
liquid transmission by parts or working medium.
●
●
●
●
Transferring and controlling energy with liquid as working medium is
called liquid transmission.
It can be divided into hydraulic pressure transmission and hydraulic
transmission by principle. Hydraulic pressure transmission mainly
Ⅰ
Ⅰ
Ⅰ
Ⅰ
. Basic Principle of Hydraulic Transmission
transmission by principle. Hydraulic pressure transmission mainly
delivers power with liquid pressure. Hydraulic transmission mainly
transfers power with kinetic energy of liquid.
● ●●
● Take hydraulic jack for example to
illustrate principle and features of hydraulic transmission.
1. Force transmission follows Pascal's Principle
1））））Thrust on piston equals oil pressure times
Ⅰ
Ⅰ
Ⅰ
Ⅰ
. Basic Principle of
Hydraulic Transmission
piston area.2））））P, oil pressure, depends on external load. 2. Loading speed transfers according to the
principle of equal liquid volume after changes. Its speed depends on quantity of flow. Ignoring loss, hydraulic
transmission force is irrelevant with speed.
Pressure：：：：P=F1/A1=F2/A2；；；；(Pascal's Principle) Quantity of flow：：：：Q=A1V1=A2V2; (V=S/t)
(the Principle of Continuity )；；；； Power：：：：P＝＝＝＝V1F1=V2F2=PQ
；
；
；
；
Figure 1-1 Working Principle of Oil Jack 1-oil tank 2-control valve 3,6-cylinder 4,7-plunger 5-lever 8,9-one-way valve 10,11-pipelines
1. Hydraulic Power Supply
Components converting mechanical energy into liquid pressure. Typical
component is hydraulic pump.
2. Control Components
Control force, movement speed and direction actuating components by
controlling pressure, flow quantity and direction of fluid. Pressure, flow
Ⅱ
Ⅱ
Ⅱ
Ⅱ
. Composition of Hydraulic Transmission System
controlling pressure, flow quantity and direction of fluid. Pressure, flow
quantity and direction usually control hydraulic valve.
3. Actuating Components
Components converting liquid pressure into mechanical energy,
including hydraulic cylinder moving in a straight line and hydraulic
motor with rotation movement.
4. Assistant Components
Other devices besides the above three components to guarantee
normal operation of the system in the system have delivering, storage,
heating, cooling, filtration, measurement and other functions, such as
pipeline, connector, fuel tank, radiator, filter, etc.
Ⅱ
Ⅱ
Ⅱ
Ⅱ
. Composition of Hydraulic Transmission System
pipeline, connector, fuel tank, radiator, filter, etc.
5. Working Medium
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.
Ⅲ
Ⅲ
Ⅲ
Ⅲ
. Advantages of Hydraulic Transmission System
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,
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.
Ⅳ
Ⅳ
Ⅳ
Ⅳ
. Disadvantages of Hydraulic Transmission System
a higher level of skill.
5. Acquisition and transfer of hydraulic energy is not as convenient as that of electricity. Due to pressure loss and other reasons, hydraulic energy should not be transmitted over a long distance.
6. Components, accessories and working medium in the hydraulic system work in a
closed system. Failures are difficult to discover in time. Failure causes are difficult to determine.
7. Hydraulic transmission is sensitive to pollution of hydraulic oil and easy to have failures.
•
Energy and signal transmission;
•
Lubricate hydraulic components, and reduce friction and wear;
•
Heat dissipation;
•
Corrosion prevention;
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
1. Functions of Hydraulic Medium
•
Corrosion prevention;
•
Sealing of clearance in hydraulic components to prevent dual friction;
•
Transmission, separation and precipitation of non-soluble
contaminants; and
•
One is flammable hydrocarbon hydraulic oil (mineral oil type and
synthetic hydrocarbon type);
•
Another is nonflammable (or fire resistant) hydraulic fluid.
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
2. Types of Hydraulic Medium
•
Another is nonflammable (or fire resistant) hydraulic fluid.
•
Nonflammable fluid includes aqueous (such as HFA, HFB and HFC)
and non-aqueous synthetic fluid
（
（
（
（
HFD
）
）
）
）
.
1
）
）
）
）
Viscosity
2
）
）
）
）
Abrasion resistance
3
）
）
）
）
Oxidation stability and thermal stability
4
）
）
）
）
Demulsibility and hydrolytic stability
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
3. Main Performance of Hydraulic Medium
4
）
）
）
）
Demulsibility and hydrolytic stability
5
）
）
）
）
Defoaming
7
）
）
）
）
Shear stability
8
）
）
）
）
Material compatibility
9
）
）
）
）
Filtering property
10
）
）
）
）
Other performance requirements
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
3. Main Performance of Hydraulic Medium
（
（
（
（
Continued
）
）
）
）
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
•
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.
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
4. Classification and Features of Hydraulic Oil of Mineral Oil Type
oil.
•
HR Hydraulic Oil.
HR Oil is HL Oil added with viscosity index additive, which
makes oil viscosity decrease with temperature change.
•
HG Hydraulic Oil.
HG Oil is HM Oil added with anti-sticking agent (oiliness
solvent or antifriction agent)
•
HV and HS Oil.
HV and HS Oil are both low-temperature hydraulic oil used over
wide range of temperature variation according to ISO Standard. HV Oil is mainly
used in cold area. HS Oil is mainly used in freezing area.
●
●
●
●
Key Points of Reasonable Use
1
）
）
）
）
Identify variety and mark of oil;
2
）
）
）
）
Hydraulic system should be thoroughly cleaned before
liquid filling;
3
）
）
）
）
New oil must be filtered before use;
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
5. Reasonable Use and Maintenance of Hydraulic Medium
3
）
）
）
）
New oil must be filtered before use;
4
）
）
）
）
Oil cannot be mixed optionally;
5
）
）
）
）
Pollution should be strictly controlled to prevent moisture,
●
●
●
●
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;
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
5. Reasonable Use and Maintenance of Hydraulic Medium
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
●
●
●
●
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
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
5. Reasonable Use and Maintenance of Hydraulic Medium
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
●
●
●
●
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.
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
6. Pollution and Protection of Hydraulic Oil
2
）
）
）
）
External dust and sand, and oil lead flowing back into the tank pass the
repeatedly stretching piston rod during operation of hydraulic system and enter
hydraulic oil. In addition, dust, cotton lint and other things may enter hydraulic oil
during maintenance due to carelessness.
3
）
）
）
）
Hydraulic system itself also constantly produces dirt, which will directly enter
hydraulic oil, such as wear particles of metal and seal materials, particles
dropping form filter materials, jelly generated due to oxidative deterioration of
fiber and oil caused by oil temperature increase, etc.
●
●
●
●
Harms of oil pollution
Serious hydraulic oil pollution will directly influence work performance of
hydraulic system, cause frequent failure of hydraulic system , and shorten
service life of hydraulic components. Main reason causing these risks are
particles in dirt. For hydraulic components, if these solid particles enter
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
6. Pollution and Protection of Hydraulic Oil
particles in dirt. For hydraulic components, if these solid particles enter
components, wear of sliding parts of components will be intensified, orifice and
damping hole in hydraulic components may be blocked, or spool will be stuck,
causing hydraulic system failure. Water and air mixing will reduce lubrication
capacity of hydraulic oil reduction, accelerate oxidative deterioration, cause
corrosion, accelerate corrosion of hydraulic components, and make hydraulic
system vibrate or craw.
●
●
●
●
Pollution prevention measures
1
）
）
）
）
Keep hydraulic oil clean before use;
2
）
）
）
）
Keep hydraulic system clean after assembling and before operation;
3
）
）
）
）
Keep hydraulic oil clean during operation;
Ⅴ
Ⅴ
Ⅴ
Ⅴ
. Hydraulic Transmission Medium
6. Pollution and Protection of Hydraulic Oil
3
）
）
）
）
Keep hydraulic oil clean during operation;
4
）
）
）
）
Use appropriate oil filter;
5
）
）
）
）
Regularly replace hydraulic oil; and
Hydraulic pump works on the principle of
Hydraulic power components provide power supply for the system. They are
indispensable core components of the system. Hydraulic pump is the power
component providing the system with certain flow quantity and pressure.
Ⅵ
Ⅵ
Ⅵ
Ⅵ
. Hydraulic Transmission Components
1. Working Principle of Hydraulic Pump
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.
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
Ⅵ
Ⅵ
Ⅵ
Ⅵ
. Hydraulic Transmission Components
2. Features of Hydraulic Pump
3
）
）
）
）
Have corresponding assignment mechanism to separate oil absorption
cavity from liquid discharge cavity.
Ensure regular and continuous absorption and discharge of liquid of
hydraulic pump . Hydraulic pumps with different structure principle have
different assignment mechanism.
1
）
）
）
）
Pressure
Working pressure, rated pressure and maximum permissible pressure.
2
）
）
）
）
Discharge and flow
Theoretical flow, rated flow, and actual flow
Ⅵ
Ⅵ
Ⅵ
Ⅵ
. Hydraulic Transmission Components
3. Main Performance Parameters of Hydraulic Pump
3
）
）
）
）
Power and efficiency
●
●
●
●
Power loss of hydraulic pump includes volume loss and mechanical
loss.
●
●
●
1
）
）
）
）
By structure: Gear pump, vane pump, plunger pump, screw pump, etc.
①
①
①
①
Gear pump: Inner gearing gear pump and outer gearing gear pump;
②
②
②
②
Vane pump: Single acting vane pump and double acting vane pump;
③
③
③
③
Plunger pump: Axial plunger pump, radial plunger pump and valve oil
distributing valve plunger pump;
Ⅵ
Ⅵ
Ⅵ
Ⅵ
. Hydraulic Transmission Components
4. Type of Hydraulic Pump
distributing valve plunger pump;
2
）
）
）
）
By function: Constant delivery pump and variable 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
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
1. Concept
satisfy start, stop, redirection, speed regulation, voltage
stabilization, unloading, pressurization, decompression and other
operational needs of actuating components.
1
）
）
）
）
In structure, all valves consist of valve body, valve spool (turn valve or
slide valve) and components of driven valve spool movements (such as
spring and electromagnet).
2
）
）
）
）
In working principle, relationship among opening size, pressure
difference between inlet and outlet of valve and flow through valve of all
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
2. Common Features
difference between inlet and outlet of valve and flow through valve of all
valves comforts to orifice flow formula, but different valves have
●
●
●
●
Performance Parameters
①
①
①
①
Nominal pressure
Maximum working pressure allowed by long-term reliable
work of hydraulic control valve , which is limited by intensity of valve. Actual
permissible maximum working pressure is also related to other factors, such
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
3. Performance Parameters and Basic Requirements of
Hydraulic Control Valve
as reversing reliability of reversing valve and pressure regulating scope of
pressure valve.
②
②
②
②
Nominal diameter
Unit of nominal diameter of hydraulic control valve is mm. A
certain nominal diameter represents a certain of flow capacity, which is
permissible maximum flow (nominal flow). It should be pointed out that, valves
with the same nominal diameter may have different nominal flow because of
their different functions.
●
●
●
●
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,
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
3. Performance Parameters and Basic Requirements of
Hydraulic Control Valve
direction valve should have small fluid flow pressure loss, direction valve
should have good core stability.
c. Controlled parameters (pressure or flow) should have high precision and
small fluctuation when influenced by outside interference.
d. Compact structure. Convenient to install, debug and maintain. High
universality.
There are many varieties of control valves used in hydraulic transmission, which can
be classified by characteristics. It is the most common to classify by purpose of
control valves.
（
（
（
（
1
）
）
）
）
Directional control valve
(such as one-way valve and reversing valve);
（
（
（
（
2
）
）
）
）
Pressure control valve
(such as overflow valve, pressure reducing valve and
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
4. Classification of Hydraulic Control 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.
•
Concept
：
：
：
：
Valve used to control fluid flow pressure in the hydraulic system
or control.
•
Common Points
：
：
：
：
Work in the principle of balanced liquid pressure and
spring force on valve core.
•
Classification
：
：
：
：
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
5. Pressure Control Valve
•
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
●
●
●
●
Main purpose of overflow valve is pressure leveling (constant pressure valve) orsecurity 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 figureⅦ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
1
）
）
）
）
Overflow valve
●
●
●
●
System figure illustrates the role of overflow valve. Overflow Valve 2 in the left figureis constant pressure valve. Overflow Valve 2 in the right figure is safety valve.
constant pressure
valve
●
●
●
●
Structure type: can be divided into directly
operated type and pilot operated type by form
of structure and basic action mode.
① ① ①
① Directly operated overflow valve（（（（see figure））））
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
1
）
）
）
）
Overflow valve
（
（
（
（
Continued
）
）
）
）
Directly operated overflow valve controls on-off movement with pressure oil in the system directly acting on valve core which is balanced with spring force.
Limited by structure and control precision, directly operated overflow valve is commonly used in little traffic system with low pressure (less than 2.5 MPa).
Function Symbol
Map
Figure of Low-pressure Directly Operated Overflow Valve 1-nut 2-pressure adjusting spring 3-top cover 4-valve core 5-valve body
② ②②
② Pilot operated overflow valve （（（（see figure
for operating principle））））
● Consist of main valve and pilot valve;
● ●●
● Damping hole has small diameter (0.6-1.2);
Easy to block. Will not operate normally.
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components
(Hydraulic Valve)
1) Overflow valve
（
（
（
（
Continued
）
）
）
）
Remote Control
Easy to block. Will not operate normally.
● Advantages in performance (pressure
adjusting range, on-off characteristic,
dynamic performance, remote control, etc.). Suitable for system with high pressure and big flow.
Function
Symbol Map
Principle
Demo
Pilot Overflow Valve
1-spring of main valve 2-main valve core 3-damper hole 4-valve core of pilot valve 5-sping of pilot valve
Pressure reducing valve is a pressure control valve which makes outlet pressure (secondary pressure) below inlet pressure (primary pressure). Its function is to provide two or several different pressure
output with one oil source.
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
2
）
）
）
）
Pressure reducing valve
output with one oil source.
In addition, when oil pressure is unstable, a stable low pressure can be obtained by putting a pressure reducing valve in the return circuit.
It can be divided into fixed pressure reducing valve, fixed differential reducing valve and proportional pressure reducing valve by pressure controlled by
pressure reducing valve. Function Symbol Map
Pressure Reducing Valve
1-main valve core 2-damper hole 3-vavle core of pilot valve V-flow speed of valve port
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.
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
2) Pressure reducing valve
b. When not working, inlet opening and outlet opening of pressure reducing valve are connected. Inlet opening and outlet opening of overflow are not connected.
c. To ensure pressure setting value of outlet of pressure reducing valve is constant, its spring cavity of pilot valve needs to be connected to external oil tank separately through drain port. Outlet of overflow valve is connected to oil tank, so its spring cavity and oil leakage of pilot valve can be connected to outlet through pass on the valve. It doesn’t need to be connected to external oil tank separately.
★ ★ ★
● ●●
● 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
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
3
）
）
）
）
Sequence valve
Remote Control
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. F u n c tio n S y m b o l M a p
directly operated external
control sequence valve pilot operated sequence valve
① ① ①
① Inlet pressure of overflow valve is basically unchanged under through-flow condition. Inlet pressure of
sequence valve is determined by outlet pressure under through-flow condition. If outlet pressure p2 is much lower than inlet pressure p1, p1 will be basically
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
3
）
）
）
）
Sequence valve
Remote Control
unchanged. When p2 increases to a certain degree, p1 will also increase. p1 = p2 + ∆ p. ∆ p is pressure loss on sequence valve.
② ② ②
② Overflow valve has internal leakage and sequence valve needs to separately draw out leakage path, which is external leakage.
③ ③ ③
③ Outlet of overflow valve has to return to the oil tank. Outlet of sequence valve can be connected to load.
F u n c tio n S y m b o l M a p
directly operated external control sequence valve
pilot operated 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
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
4) Pressure switch
（
（
（
（
hydraulic switch
）
）
）
）
pressure of pressure switch, electrical signal will be sent out to control movements of electromagnet, electromagnetic clutch, relay and other
components, so as to realize sequential actions of oil-way pressure relief, reversing and actuating components, or close electromotor to stop operation of system for safe protection, etc.
1—Plunger 2—Lever
3—Spring 4—Switch
Structure Chart
Concept:
Function of directional control valve is to control flow direction of fluid. It
realizes connection or disconnection of pathways with relative motion between valve
core and valve body, to meet requirements of the system.
Type:
Directional control valve includes one-way valve and reversing valve.
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
6. Directional control valve
One-way Reversing Valve（（（（2-position
figure）））） R ig h t p o s iti o n o f t h re e -p o s iti o n fo u r-jo in t r e v e rs in g v a lv e L e ft p o s iti o n o f t h re e -p o s iti o n fo u r-jo in t r e v e rs in g v a lv e
●
●
●
●
Classification of one-way valve
①
①
①
①
By function:
Common one-way valve and hydraulic controlled one-way valve.
②
②
②
②
By structure:
Tubular (direct connection) and plate (right angle)
1
）
）
）
）
One-way valve
Tubular
Plate
Oil Inlet P1 Oil Outlet P2①
①
①
①
Common One-way Valve
● ● ●
● Principle and performance: One-way valve only allows fluid flow to flow in one direction, but not reverse
flow. It can be used for outlet of hydraulic pump, to prevent system oil from flowing back; it can be used to separate the connection between oil channels, to prevent oil from mutual interference; it also can be used as the bypass valve to connect parallelly with sequence valve, pressure reducing valve, throttling valve and speed control valve, so as to assemble into one-way sequence valve, one-way pressure
reducing valve, one-way throttling valve one-way speed control valve, etc.
●
●
●
●
Structural form and
function symbol:
●
●
●
●
Opening pressure:
Generally 0.04
～
～
～
～
0.1MPa;
opening pressure of back
pressure valve is 0.2
～
～
～
～
0.6 MPa
Oil Inlet P1 Oil Outlet P2
Oil Inlet P1 Oil Outlet P2
Oil Inlet P1 Oil Outlet P2
(d) Symbol Mode
Mode
●
●
●
●
Application:
①
①
①
①
Reverse protection of
hydraulic pump
On one hand, prevent system pressure from influencing normal operation of pump. On the other hand, prevent the liquid from flowing back to oil tank through pump when stopped.
②
②
②
②
Separate oil channels prevent
interference
③
③
③
③
Comprise combination
valve
One-way valve can comprise one-way combination valve with other valves④
④
④
④
Installed in outlet oil line to
②
②
②
②
Hydraulic Controlled One-way Valve
●
●
●
●
Principle and performance: When the hydraulic controlled port K doesn’t connect pressure oil,its function is same to common one-way valve. When the hydraulic controlled mouth connects oil, valve can flow freely in two ways. The figure explains the working principle.
● ●●
● Structure: Hydraulic controlled piston, plunger, valve, spring etc. ●
●●
● Application：：：：Hydraulic controlled one-way valve has characteristics of common one-way
valve. It can also allow forward and reverse fluid flow to go through freely under certain conditions. Therefore, it is commonly used in pressure maintaining, locking and balanced circuit of hydraulic system.
P
1P
2K
Function Symbol Structure Chart symbolChange flow direction and connect or cut off oil channels by relative motion of valve core in valve body, so as to control reversing, start or stop of actuating components.
● ● ●
● Classification of reversing valve
① ① ①
① By motion mode of valve core relative to valve body:
Steering valve type, sliding valve type, ball valve type, etc.
② ② ② ② By control method:
2
）
）
）
）
Reversing Valve
M a n u a l R e v e rs in g V a lv eManual, engine driven, electromagnetic, hydraulic, electric hydraulic, etc;
③ ③ ③
③ By working position of valve core on valve body:
Two-position valve and three-position valve
④ ④ ④
④ By number of main oil port on valve body:
Two-port valve, three-port valve, four-port valve and five-port valve. M a n u a l R e v e rs in g E le c tr o m a g n e tic R e v e rs in g V a lv e
●
●
●
●
Control mode symbols of commonly used sliding
reversing valve
Electric Spring
Manual
Engine Drive (Roller Type) Hydraulic Hydraulic Pilot Control Electromagnetic-Hydraulic Pilot Control
●
●
●
●
Working principle of
sliding reversing valve
Valve Core Valve Body
Position of Valve Core Valve Port State Piston State
Middle Port A and Port B don’t connect oil Stop
Left P A Right
Big Box
Valve body
SmallBox
Station
Crossover point of arrow line in the small box or┴
symbol and bounding
Oil port
Oil channels connected
（
（
（
（
not
always flow direction
）
）
）
）
●
●
●
●
Station and pathway symbols of main structure of reversing
valve
（
（
（
（
see figure
）
）
）
）
always flow direction
）
）
）
）
┴
Oil channels
disconnected
Functional chart of
three-position four-port
reversing valve
Head of symbol
Normal position
（
（
（
（
valve core without
force);
A, B
Oil ports connected to the oil tank
；
；
；
；
●
●
●
●
Principle and type symbols of main structure of reversing valve
Name
Structure and Principle Chart
Symbol
Two-position two-port
A
P
A
B
Two-position three-port Two-position four-portA B
P O
A
P
B
Name
Structure and Principle Chart
Symbol
Two-position five-portO
1O
2A
B
P
A B
●
●
●
●
Principle and type symbols of main structure of reversing valve
（
（
（
（
continued
）
）
）
）
Three-position four-port Three-position five-port
P O
A B
P
O
1O
2A B
●
●
●
●
The most commonly used six median functions of
three-position reversing valve
Function Model
Median Symbols State, Features and Application of Median
Symbols
O
Port P, A, B and O are all closed；；；； Hydraulic cylinder is locked. Hydraulic pump doesn’t unload.
H
Port P, A, B and O are Hydraulic pump ; Piston of hydraulic cylinder is floating. Hydraulic
pump unloads.
Y
Port P is closed. Port A, B and O are
connected. Piston of hydraulic cylinder is floating. Hydraulic pump doesn’t unload.
Function
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.
●
●
●
●
The most commonly used six median functions of
three-position reversing valve
（
（
（
（
continued
）
）
）
）
motion and connect inlet.
M
Port P and Port O are connected. Port A and Port B are closed. Piston of hydraulic cylinder is locked. Hydraulic pump unloads.
K
Port P, A and B are connected. Port O is closed. Piston of is locked. Hydraulic pump unloads.
●
●
●
●
Several Commonly Used Reversing Valves
Armature Coil
①
①
①
①
Electromagnetic reversing valve
Valve Body Valve Core Function Symbol Three-position four-port
electromagnetic reversing valve
Two-position four-port
★
★
★
★
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.
②
②
②
②
Hydraulic reversing valve
Hydraulic controlled pressure port Hydraulic controlled pressure port
Hydraulic three-position four-port
reversing valve
Function
Symbol
★
★
★
★
Performance of hydraulic reversing valve
Hydraulic reversing valve changes position of valve core with oil pressure. It has
big starting force. When flow of hydraulic controlled oil is big, reversing impact is
big. To control movement speed of valve core and reduce impact, one-way
throttling device (called damper regulator) is usually installed in front of
hydraulic controlled pressure port.
③
③
③
③
Electro-hydraulic reversing valve
Pilot valve （ （ （ （electromagn etic valve）））） Main valve （ （（ （electromagnetic valve））））
Control oil
channel
Main oil
channel
★
★
★
★
Principle drawing of electro-hydraulic reversing valve
channel
Simplified Function Symbol
★
★
★
★
Performance of electro-hydraulic reversing
valve
Electro-hydraulic reversing valve is combination of electromagnetic reversing
valve (pilot valve) and hydraulic reversing valve (main valve). Therefore, it can
control the high-power main valve with small-power electromagnet. Oil source and
return oil of pilot electromagnetic reversing valve can be established separately. It
can also be shared with main oil channel.
④
④
④
④
Engine driven reversing valve
（
（
（
（
motion valve
）
）
）
）
Oil Inlet
Lift type, two-port, normally closed
Lift type, two-port,
normally opened Roller type,
three-port
Oil Outlet Back-moving Spring Valve Core
Roller Push Rod
Purpose of engine driven reversing valve is to move valve core with cam-action
strokedog installed on actuating mechanism, in order to control on-off of oil
channels and control stroke.
Appropriate reversing speed is obtained and reversing impact is reduced by
★
★
★
★
Performance of electro-hydraulic engine driven
reversing valve
⑤
⑤
⑤
⑤
Manual reversing valve
Self-restoring Type
Mechanical Positioning Type
Manual reversing valve is convenient to use. It is applicable to
occasion with
small flow and
longer
interval.
★
★
★
◆
◆
◆
◆
Student practice: draw out symbols of
the following reversing valves
1. Two-position two-port electromagnetic reversing valve (normally
closed);
2. Three-position four-port manual reversing valve
（
（
（
（
Median function
：
：
：
：
H);
3. Three-position four-port hydraulic
（
（
（
（
with damper
）
）
）
）
reversing valve
3. Three-position four-port hydraulic
with damper
reversing valve
（
（
（
（
Median function
：
：
：
：
P
）；
）；
）；
）；
Figure 3
Figure 2
Figure 1
●
●
●
●
Overview:
Movement speed of actuating components in the hydraulic
system is determined by oil flow entering actuating components. Flow
control valve is a hydraulic valve controlling the flow by changing flow
area of port (local resistance of throttling port) or length of channels.
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
7. Flow Control Valve
●
●
●
●
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
Ⅶ
Ⅶ
Ⅶ
Ⅶ
. Control Components (Hydraulic Valve)
7. Flow Control Valve (Continued)
•
Function
：
：
：
：
Convert pressure of liquid into mechanical energy. Make linear,
swinging and rotating with motion drive working mechanism.
•
Type: Hydraulic cylinder and motor.
1. Hydraulic Cylinder
Ⅷ
Ⅷ
Ⅷ
Ⅷ
. Hydraulic Actuating Components
1
）
）
）
）
Type of Hydraulic Cylinder
Hydraulic cylinder has the following types by structure and function.
●
●
●
●
Single-acting hydraulic cylinder
●
●
●
●
Double-acting hydraulic cylinder
●
●
●
2
）
）
）
）
Single-rod Piston Cylinder
The piston only has piston rod at one end.
There are cylinder fixed type and piston
rod fixed type. Single-rod piston cylinder
is a commonly used oil cylinder type.
2. Motor
1
）
）
）
）
Features of Motor
Sketch Map of Single-rod
Piston Cylinder
Ⅷ
Ⅷ
Ⅷ
Ⅷ
. Hydraulic Actuating Components
1
）
）
）
）
Features of Motor
Hydraulic motor is a device converting fluid pressure into mechanical energy. In
principle, hydraulic pump can be used as hydraulic motor, and hydraulic motor
can be also used as hydraulic pump. In fact the same type of hydraulic pump
and hydraulic motor have similar structure, but by the two have different work
situation, which makes the two different in structure. Main differences are as
follows:
•
Hydraulic motor generally needs forward and reversing rotating, so it should
have symmetry in the inside structure. Hydraulic pump usually rotates in single
direction. It doesn’t have this requirement.
•
In order to reduce oil absorption resistance and radial force, inlet port of
hydraulic pump is generally larger than outlet port. Pressure in low-pressure
Ⅷ
Ⅷ
Ⅷ
Ⅷ
. Hydraulic Actuating Components
1
）
）
）
）
Features of Motor
hydraulic pump is generally larger than outlet port. Pressure in low-pressure
cavity of hydraulic motor is slightly above atmospheric pressure, so it doesn’t
have the above requirement.
•
Hydraulic motor is required to operate normally at a wide speed range. Therefore,
we should adopt hydraulic bearing or hydrostatic bearing. Because when motor
is at low speed, if hydraulic bearing is used, it is not easy to formed lubrication
film.
• Vane pump rotates at high speed with blades to generate centrifugal force, so that blades always adhere to the inner surface of stator to seal the oil and form working volume. If it is used as motor, spring must be installed on root of blades of hydraulic motor, in order to ensure that blades always adhere to the inner surface of stator and motor can normally start.
• Hydraulic pump should have self-priming capacity in structure , and hydraulic motor
Ⅷ
Ⅷ
Ⅷ
Ⅷ
. Hydraulic Actuating Components
1
）
）
）
）
Features of Motor (Continued)
• Hydraulic pump should have self-priming capacity in structure , and hydraulic motor
doesn’t have this requirement.
• Hydraulic motor must have large starting torque. Starting torque is the torque that
can be output by motor axle when motor starts from static state. The torque is generally larger than that under operation condition under the same operating
differential pressure. Therefore, in order to make the starting torque near to torque under operation condition, it is required that motor torque has small pulsation and small internal friction.
Hydraulic motor can also be divided into gear type, vane type, piston
type and other types by structure types.
Ⅷ
Ⅷ
Ⅷ
Ⅷ
. Hydraulic Actuating Components
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
Ⅷ
Ⅷ
Ⅷ
Ⅷ
. Hydraulic Actuating Components
3
）
）
）
）
Axial Piston Motor
Working Principle of
Swash-plate Axial Piston Motor
piston motor and bent axial piston motor. See
figure for working principle (see textbook for
content).
F
1=p
*A
*tanγ
T
1=F
*r=F
*R
*conφ
=p
*A
*R
*tanγ
*conφ
T=η
m*∆p
*V/2π
Torque of cylinder generated by pistonTotal torque actually output by motor
Torque force of cylinder generated by piston