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Chapter 9 Typical Hydraulic Systems
Objectives
After completing this chapter, you should be able to
1. Interpret the hydraulic operation principle.
2. Identify power transmission and flow path through the
system.
3. Describe the function of each element in the hydraulic
system.
4. Identify safety considerations for working with the
hydraulic system.
5. Understand the conditions necessary for proper operation
of the hydraulic system
6. Explain performance characteristics of the system.
1
Chapter 9 Typical Hydraulic Systems and Some examples
How to read a hydraulic system diagram ?
(1)Identify the function and operation of an objective oriented
machine and the machine’s requirements to its hydraulic system.
(2)Browse the overall system, recognize hydraulic symbols and
separate the system into several subsystems .
(3)Analyze each subsystem, clarify which circuits constitute the
subsystem, and comprehend the subsystem.
(4)Analyze the interrelationship among subsystems.
(5)Explain the operation of the system and the function of each
control element.
(6)Summarize the systematic characteristics.
2
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
1 Introduction
YT4543 power sliding feed unit is a general component
of modular machine tool which is used to accomplish feed
motion.
Mounted different spindle boxes the unit can carry out
many machining jobs such as drilling, reaming, boring, milling,
scraping end surface, chamfering, tapping and so on.
3
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
The common work cycle is that first the cylinder has a rapid
advance motion, second moves with the feeding motion at a slow
rate, third moves further with another feeding motion at a slower
rate, next stays for a predetermined time at the end of the stroke,
after that returns rapidly, finally stops at the original position.
rapid advance
first feed
second feed
stops at
the original
position
rapid return
stays for a
preditermined
time
4
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
Requirements for its hydraulic system
The feed speed ranges from 6.6 to 600 mm/min , the
maximum feed force is 45×103N. Additionally, the feed
speed should be stable, the re-direction operation smooth,
the power utilization reasonable, the systematic efficiency as
high as possible and the heat amount generated as low as
possible.
5
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
15
2 Identify elements
13
14
12
11
0. tank 1.filter 2.pressure
3YA
compensated variable
9
pump 3,7,9.check valve 10
4. pressure relief valve
5.back pressure valve 6.sequence
valve 8,12.pressure compensated flow
control valve 10.mechanically
operated sequence valve 12.solenoid
operated directional valve 13.pressure
switch 14.cylinder 15.solenoidcontrolled, pilot-operated, directional
control valve
1YA
2YA
8
7
6
4
3
2
5
1
6
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
Qp
A
B
p
C
7
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
2
5
1
The main directional
control valve is a 5-way 3position pressure operated
spring centered valve
which is actuated by a
solenoid operated valve.
To make the cylinder
move in two different
speeds during
feed
movement besides rapid
approach and
rapid
return
stroke,
two
pressure regulating valves
are arranged in series.
8
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
15
13
14
12
11
1YA
2YA
3YA
10
9
A two-way two-position
solenoid operated direction
control valve is used for the
redirection from first feed
motion to second.
8
7
6
4
3
2
5
A mechanically operated
2-way 2-position direction
control vale is used for the
redirection
from
rapid
motion to first feed.
1
0
A dead iron block is used
to limit the position of the
platform as to ensure
dimensional accuracy of the
9
feed motion.
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
2 Schematics
14
(1)Rapid movement
When the start
button is pressed, it
energizes the solenoid
10
1YA, causing the 4/3
solenoid operated
directional control valve
to its left position.
As a result, the main
directional control valve
shifts to its left position.
15
13
12
11
1YA
2YA
3YA
9
8
7
6
4
3
2
5
1
0
10
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
Now flow path is
The supply line:
15
13
14
12
11
1YA
2YA
3YA
10
9
8
0→1→2→3→main
valve(its left position)
→10(its down position)
→13(its blank end)
The return line:
7
6
4
3
2
5
1
0
13(its rod end)→main
valve(its left position)
→10 (its down position)
→13 (its blank end )
A differential circuit is
11
used for rapid advance
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
Please note:
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
2
5
1
The cylinder moves
at a rather high speed.
The cylinder is
connected
in
a
differential circuit, on
the other hand, the
pressure compensated
variable displacement
pump delivers the
highest flow rate to
the cylinder.
12
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
2
5
1
0
(2)First feed movement
As soon as the cylinder
actuates valve 10, it closes
stopping flow through it
and allowing fluid to move
to the cylinder only
through valve 8, thus
reducing its speed.
Because of both load
and throttle action, the
systematic pressure rises,
valve 6 opening and valve
7 closing. The fluid from
the rod end of the cylinder
returns to the reservoir
through valve 6 and back
pressure valve 5.
13
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
Now flow path is as
following:
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
2
5
The supply line:
0→1→2→3→main
directional valve
(its left position)→8
→11(its right position)
→13(its the blank end )
The return line：
13(its rod end )→main
directional valve (its left
position)→6→ 5→0.
1
14
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
Please note:
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
2
5
Because of both
load action and throttle
action,
the
pump
reduces delivery flow
rate so as to meet the
needs of feed motion.
The feed speed can be
adjusted by pressure
compensated
flow
control valve 8.
1
15
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
2
5
(3)Second feed movement
As soon as the cylinder
comes in contact with the
limit switch L2 which
energizes the solenoid
3YA, valve 11 closes
stopping oil through it
and allowing oil to move
to the cylinder only
through valve 12, thus
further reducing cylinder
speed because the flow
area of valve 12 is smaller
than that of valve 8.
1
16
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
Now flow path is as follows:
The supply line:
0→1→ 2→3→
main directional valve
(its left position)→
8→12→13(it blank end)
The return line：
13(its rod end)→
main directional valve
(its left position)
→6→5→0.
2
5
1
17
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
Please note:
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
2
5
The cylinder extends
with a slower rate
because the flow area of
the pressure compensated
flow control valve 12 is
smaller than that of the
valve 8.
The second feed speed
can be adjusted by valve
12.
1
18
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
2
5
1
0
(4) Halts at the dead iron
At the end of the stroke
the platform is blocked by
a dead iron block and
halts here, thus the system
pressure further rises.
When
the
system
pressure
reaches
the
preset
level
of
the
pressure
switch,
the
pressure switch sends an
electric signal to the timer.
After receiving the signal
the timer starts timing.
The setting of the timer
can be adjusted within
definite range.
19
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
15
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
2
5
1
(5) Return rapidly
Having reaching the
setting the timer sends a
signal which energizes
2YA, simultaneously deenergizes 1YA and 3YA.
Thus the 4/3 directional
control vale is shifted to its
right position, then the
main valve is shift to its
right position.
The oil from the pump
flows to the rod end of the
cylinder and the oil pushed
by the piston returns to
the reservoir.
20
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
15
Please note:
13
14
12
11
1YA
2YA
3YA
10
9
8
7
6
4
3
The pump delivers
highest flow rate to the
cylinder
and
the
annular area of cylinder
is substantially small.
Therefore, the cylinder
returns
rapidly
to
original position.
2
5
1
21
0
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
(6) Stop at the original position
After the platform returning to the original position the limit
switch sends a signal. All direction control valves are de-actuated
and the pump is unloaded.
The action sequence of solenoids and the mechanically operated
directional control valve is tabulated in Tab. 9--1
Tab. 9—1 The action sequence of solenoids and mechanically operated
directional control valve
elements
cylinder action
advances rapidly
moves at the first feed speed
moves at the second feed speed
halts at the dead iron block
returns rapidly
stops at the original position
1YA 2YA 3YA
＋
＋
＋
＋
－
－
－
－
－
－
＋
－
－
－
＋
＋
±
－
pressure mechanically operated
switch directional control valve
open
－
close
－
close
－
close
＋
－
close→open
22
open
－
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
The system has several unique operational features:
(1) Use of the solenoid valve, pilot operated directional control
valve, pressure switch, timer, limit switch and dead iron block
ensures the automatic accomplishment of the work cycle.
(2) The speed at rapid advance is much higher than the feed speed.
A differential circuit and a pressure compensated variable
displacement pump meets the needs of rapid advance.
(3) The return speed is much higher than the feed speed too. The
smaller annular piston area and the pressure compensated variable
displacement pump meets the needs of the rapid return.
(4) The solenoid-controlled, pilot-operated, directional control
valve with bi-directional dampers can ensure the redirection
smoothness.
23
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
(5) A mechanically operated directional vale, a 5/3 directional
control vave and a sequence valve as the redirection from rapid
advance to first feed not only ensures the position accuracy but also
higher reliability and smoothness.
(6) Use of a solenoid directional control valve as the redirection
from first feed to second can meet the systematic needs since the
two feed speeds are low.
(7) Flow regulating valves in the meter-in circuit not only ensures
to adjust the feed speed conveniently but also ensures the stability of
the feed speed (characteristic of the valve itself).
24
9.1 Power Sliding Feed Unit System
of Modular Machine Tool
(8) The back pressure valve not only ensures that the cylinder may
endure a certain overrunning load but also prevents air from
entering to the system. That is, the back pressure valve may ensure
the stability of the feed speed.
(9) Use of the pressure compensated variable displacement pump
as well as the direction control neutral position unloading ensures
the system to utilize power reasonably and to run efficiently,
accordingly to generate less amount of heat.
25
9.3 Hydraulic system of 8 ton hydraulic truck crane
6
5
7
4
3
1
2
A truck crane is a kind of general
mobile hoisting machinery which is a
crane mounted on a truck chassis.
An 8 ton hydraulic crane primarily
consists of a hoisting mechanism, a
slewing mechanism, a derricking or
luffing
mechanism,
a
boom
telescoping mechanism as well as an
outrigger operating mechanism.
The operations of all these
mechanisms
are
accomplished
hydraulically except travel propelling.
Fig. 9-4 The external view of an 8-ton truck crane
1. truck chassis 2. slewing mechanism 3. outrigger
4. derricking cylinder
5. boom telescoping section
6. hoisting mechanism 7. basic section
26
9.3 The hydraulic system of 8 ton hydraulic truck cranes
The system requirements of a truck crane are as followings:
(1) Outriggers should be locked reliably whether during a work
cycle or during traveling.
(2) The hoisting mechanism should work within a wide speed
range and with a finer speed control feature. On the other hand,
the hoisting mechanism circuit should function to limit the
lowering speed so as not to drop by the action of a load。
(3) The derricking mechanism and telescoping mechanism
should function to be locked and to limit the lowering speed.
(4) The work safety and operating reliability are very important.
27
9.3 The hydraulic system of 8 ton hydraulic truck cranes
21
8
25
7
9
7
15
18
23
20
24
6
A
14
17
13
16
5
4
10
19
3
22
B
12
2
1
Fig. 9-4 hydraulic
system diagram of an
8-ton truck crane
1. pump 2.filter 3. 3-way, 2-position manually operated directional control valve
4,12.pressure relief valve 10.front outrigger cylinder 5,6,13,16,17,18. 4-way 3-position
directional valve 7,11.dual pilot operated check valve 9. locking cylinder 8.aft outrigger
cylinder 14,17,19. counterbalance valve 20.brake cylinder 21.flow control valve
28
9.3 The hydraulic system of 8 ton hydraulic truck cranes
21
8
25
7
9
7
15
18
23
20
24
6
A
14
17
13
16
5
4
10
19
3
22
B
12
2
1
A gear pump(pmax=21MPa,V=40mL/r,n=1500r/min) is attached to the engine through
the gear box. The pump draws hydraulic oil form the reservoir through a centrally
mounted rotating junction, then high-pressure oil is directed to actuators by directional
control valve group A and B. Valve 12 is used to prevent the hydraulic system from
overloading. The preset level of the valve is 19MPa. an actual pressure can be read via
29
a pressure gage. The system is an open-center system.
9.3 The hydraulic system of 8 ton hydraulic truck cranes
Outriggers are used to stabilize the
(1) The outrigger operating subsystem truck during lifting operations. All tyres
must be suspended. outriggers should be
9
7
7
retracted during the truck traveling.
Two front outrigger cylinders are
controlled by valve 6, while two aft
6
outrigger cylinders are controlled by
valve 5. The two directional valves
5
arranged in series.
A
8
4
3
2
10
1
A double pilot operated check valve
is arranged on each outrigger cylinder
to ensure the outrigger cylinder to be
locked reliably to prevent the outrigger
cylinders from retracting during lifting
operations and from extending during
30
traveling due to leakage.
9.3 The hydraulic system of 8 ton hydraulic truck cranes
(2) Hoisting subsystem
25
21
23
24
22
A weight should not only be
raised/lowered within a wider speed
range but also be suspended in the air.
A ZMD40 axle piston motor is used
to drive the winch. The speedadjusting
and
redirecting
are
accomplished by varying the flow area
of valve 22.
A counterbalance valve is used to
limit lowering speed to prevent a
weight from overrunning.
The brake is used to mechanically
lock the hoisting motor.
A flow control valve is used to
ensure to take off brake slowly and to
31
put on brake quickly.
9.3 The hydraulic system of 8 ton hydraulic truck cranes
25
21
23
24
22
When the brake taken off, highpressure oil first enters the motor and
makes the motor create torque then
take off the brake, which prevents a
weight from dropping.
When the hoisting motor put on
brake the hydraulic oil in the brake
cylinder returns immediately to the
reservoir, which ensures the hoisting
motor is braked quickly.
32
9.3 The hydraulic system of 8 ton hydraulic truck cranes
(3) Main boom telescoping subsystem
15
14
13
12
The telescoping section is driven by a long
single-class cylinder.
The telescoping section extends to a desired
length before lifting duties and retracts before
traveling.
A special counterbalance valve is arranged
in the return line to ensure the telescoping
section to be locked to a desired position, and
to prevent the telescoping section from
retracting at an overrunning speed, that is, to
ensure the telescoping mechanism to work
safely.
33
9.3 The hydraulic system of 8 ton hydraulic truck cranes
(4) The derricking mechanism subsystem
18
17
The derricking mechanism , via changing boom
angle in a vertical plane, is used to change the
working radius to suit the demands of various
duties.
The derricking mechanism should change
boom angle steadily under a load.
Like the telescoping device circuit, a special
counterbalance valve is used to ensure the boom
to be locked to a desired angle, and to prevent
the boom from lowering at an overrunning speed.
16
34
9.3 The hydraulic system of 8 ton hydraulic truck cranes
(5) The slewing mechanism subsystem
A slewing mechanism make a crane enable to
perform hoisting duties in any direction.
The slewing mechanism of an 8-ton hydraulic
truck crane is driven by a ZMD40 hydraulic
motor. The rotational speed of the crane
superstructure is 1-3r/min.
No buffer elements are arranged in the system
since the crane is a small-size crane and the
rotating inertia is not very large.
19
35
9.3 The hydraulic system of 8 ton hydraulic truck cranes
To summarize, the system have the following features:
(1) When either a weight lowering, or the telescoping section
retracting or the derricking mechanism increasing working
radius, the mechanisms are all exerted the overrunning loads,
therefore, special counterbalance valves must be arrange in the
return lines of these mechanisms.
(2) As working situations vary substantially and all
mechanisms are operated frequently, in general, the springreturn directional valves are used to control various actuators.
When each directional valve is located in its neutral position all
actuators stop moving and the pump is unloaded.
36