8. 8
Direct Acting Relief Valve
• These valves are used mainly where volume
is low, and for less frequent operations.
• They have fast response, making them ideal
for relieving shock pressure.
• They are often used as safety valves to
prevent damage to components.
9. 9
Pilot Operated Relief Valve
• Because these valves don’t start to open until
almost full-flow pressure, the efficiency of the
system is protected-less oil is released.
• These valves are best for high-pressure, high
volume systems.
• Although slower to operate than direct acting
valves, the pilot operated relief valve keeps
system oil at a more constant pressure while
releasing oil
11. 11
Constant Reduced Pressure Valves
• They supply a fixed pressure regardless of main
circuit pressure. (So long as it is higher)
12. 12
Constant Reduced Pressure Valve
VALVE OPEN,
NOT OPERATING
VALVE PARTLY CLOSES
TO REDUCE PRESSURE
FROM
MAIN
CIRCUIT TO
SECONDARY
CIRCUIT
13. 13
Fixed Amount Reduction Valves
• They supply a fixed amount of pressure
reduction, which means that it varies with the
main circuit pressure.
• For example,the valve might be set to give a
reduction of 500 PSI. If system pressure was
2000 PSI, the valve would reduce pressure to
________ PSI.
15. 15
Pressure Sequence Valves
• They are used to control the sequence of flow
to various branches of a circuit.
• Usually the valves allow flow to a second
function only after a first has been fully
satisfied.
17. 17
Unloading Valve
• This valve directs pump output oil back
to the reservoir at low pressure after
system pressure has been reached.
• They may be installed in the pump outlet
line with a tee connection.
19. 19
Directional Control Valves
• Direct the flow of oil in the system
• Types of valves
- Check valves
- Rotary valves
- Spool valves
- Pilot controlled poppet valves
- Electro-hydraulic valves
20. 20
Check Valves
• One way valves, only allow fluid to flow in one
direction
• The valve is open by system pressure
• The valve closes when inlet pressure drops
• Usually installed in oil line
21. 21
Rotary Valve
• This valve allows
pressurized oil from the
pump to enter one
port, flow through the
valve, and out another
port to the work
To Reservoir From Work
From Pump To Work
22. 22
Rotary Valve
• This valve also allows
oil from another
working port to flow
through the valve
and return to the
reservoir.
To Reservoir From Work
From Pump To Work
23. 23
Rotary Valves
• Used as pilot valves to direct flow to other
valves
• Can be modified to operate as two, three, or
four way valves
• Done by relocating parts, altering
passageways, or adding and removing oil
routes
24. 24
Spool Valves
• Most common is open center and closed
center
• Directs oil to start, operate, and stop actuating
units
• Dirt can cause these valves to stick or work
erratically
25. 25
Spool Valves
• open center allows fluid to flow thru the
center when in neutral and return to tank
• Closed center stops the flow of oil in neutral
• Used as a control valves
28. 28
Pilot Controlled Poppet Valves
• May be mounted close to the function it
controls
• Eliminates the need for routing hydraulic pipes
and hoses over long distances for every
control function
• Reduces valve leakage (i.e. cylinder drift)
• Adjustable to vary amount of oil flow
29. 29
Electro-Hydraulic Valves
• Actuated by an electric solenoid
+ BATTERY
ROCKER
SWITCH
SOLENOID SOLENOID
TO
RESERVOIR FROM
PUMP
+ BATTERY
ROCKER
SWITCH
SOLENOID SOLENOID
TO
RESERVOIR FROM
PUMP
32. 32
Flow Control Valves
• Restricts flow in or out
of the component
whose speed is being
regulated.
• These valves are
noncompensated.
33. 33
Bypass Flow Regulator
• This valve works by
diverting flow away from
the component whose
speed is being regulated.
• These valve are usually
compensated.
BYPASS OUTLET
FULL FLOW TO BYPASS
35. 35
Priority Flow Divider
• Allows oil to feed two
different circuit.
• Example,steering
circuit and loader
circuit.
• Pump output 10 gpm.
• Steering 2 gpm.
• Loader 8 gpm.
PRIORITY
OUTLET
SECONDARY
OUTLET
FIXED ORIFICE
INLET
FROM
PUMP
36. 36
Proportional Flow Divider
OUTLET #1 OUTLET #2
INLET
• Divides a single flow
of oil to two
circuits.
• Can divided oil flow
in ratios from 50-50
to 90-10.
37. 37
Hydraulic Pumps
The pump is the heart of the hydraulic system.
The pump is the generating force of the hydraulic system, it creates the
flow of fluid which supplies the whole circuit.
Pumps convert mechanical energy to hydraulic power
40. 40
Variable Displacement Pumps
• Changing Displacement- this is accomplished by
changing the angle of the swashplate.
• Swash Plate Positioning - The position is
controlled by one of two ways.
- A small hydraulic cylinder called a “servo”
- A spring loaded cylinder called a “pressure
compensator”
43. 43
Gear Pumps
• Simple Design.
• Economical.
• Fixed Displacement.
• Used as charging pumps for larger
system pumps.
44. 44
Gear Pump Side Plates
• Some gear pumps are equipped with
pressurized plates on both side of the gears.
These plates are used to prevent cavitation.
The plates seal tightly when the pump is under
a load and relax when there is no load.
45. 45
Internal Gear Pumps
Pump Housing
Inlet
Outlet
Separator
(fixed)
Outer Ring
Gear
Internal Gear
• The internal gear is
the drive gear, which
is meshed with the
outer ring gear and
traps fluid between
the gear teeth on both
gears and the
separator, which is
fixed.
46. 46
External Gear Pump
• Oil is trapped
between the gear
teeth and flows
around the outer
perimeter of the
pump housing, not
through the middle
of the meshing
gears.
Inlet
Outlet
Pump Housing
Drive Gear
Idle Gear
47. 47
Gear Pump
Advantages
• Most widely used.
• Easiest to manufacture.
• Produces a large volume of oil for its size.
• Tolerant to dirt.
• Inexpensive to manufacture.
49. 49
Vane Pumps
• Balanced Vane Pump
- Fixed Displacement only.
- Equalized force increases bearing life.
• Unbalanced Vane Pump
- Either Fixed or Variable Displacement.
- Frequent bearing failure.
50. 50
Balanced Vane Pump
PRESSURE
HERE
• Balanced pumps are
preferred because
they allow an even
load of oil around
the circumference of
the pump shaft, this
reduces the wear on
the pump.
INLET
ROTOR
OUTLET
PRESSURE
HERE
DRIVE
SHAFT
VANE
PUMP
HOUSING
51. 51
Unbalanced Vane Pump
• As the name implies
only one side of the
pump forces oil
through, causing the
oil load to shift to
one side of the
pump.
INLET
PRESSURE
UNBALANCED
HERE
OUTLET
VANE
55. 55
Radial Piston Pump
(Rotating Cam)
CAM
PISTON • Pistons are driven
outward to discharge
oil by the shaft cam,
they move inward to
take in oil by the
force of their springs.
• Normally designed as
a 4 or 8 piston
model.
SPRINGS
56. 56
Radial Piston Pump
(Rotating Piston)
• As the cylinder
rotates pistons are
thrown out against
the housing by
centrifugal force. A
partial vacuum is
created in the piston
bores and oil flows
into the inlet ports to
fill the bores.
ROTATING
CYLINDER
FIXED
SHAFT
INLET PORTS
OUTLET PORTS
PISTON
PISTON BORE
57. 57
Radial Piston Pump
(Rotating Piston)
As the cylinder keeps turning,
the pistons are pushed back
into the bores and force the oil
out the ports on the outlet
side.
OUTLET PORTS
ROTATING
CYLINDER
FIXED
SHAFT
INLET PORTS
PISTON
PISTON BORE
58. 58
Axial Piston Pumps
• The axial flow of fluid provides a more compact
design and is the second most widely used
pump in the industry next to the gear pump.
• Inline axial piston pump.
• Bent-axis axial piston pump
59. 59
Axial Piston Pumps
(Inline)
• Pump can be variable
displacement.
• Swashplate directs the
intake and discharge of
flow.
• Piston, draws and
discharges the fluid.
• Cylinder block, holds the
piston and rotates them
from inlet to outlet ports.
OUTLET
SWASH
PLATE
PISTON
DRIVE
SHAFT
INLET
ROTATING
CYLINDER
BLOCK
60.
61. 61
Axial Piston Pumps
(Bent-axis)
• Fixed displacement.
• Rotating drive member
directs the intake and
discharge of flow.
• Piston, draws and
discharges the fluid.
• Cylinder block, holds the
pistons and rotates them
from inlet to outlet
ports.
DRIVE
SHAFT
INLET
OUTLET
PISTON
ROTATING DRIVE
MEMBER
ROTATING
CYLINDER
BLOCK
65. 65
Questions
• What are the three types of pumps?
- Gear, Piston and Vane
• What will change the displacement of the
piston pump?
- Angle of the swashplate
• What is the purpose of the side plates in the
gear type pump ?
- These plates are used to prevent cavitation
67. 67
Inlet
Outlet
Pump Housing
Drive Gear
Idle Gear
Hydraulic Pump and Motor
Drive Gear
Motor Housing
Inlet
Outlet
Idle Gear
• A pump drives its fluid, while the motor is driven by its
fluid.
68.
69. 69
Hydraulic Motors
• A motor is a rotary actuator that rotates in a
full circle.
• The work output of a motor is called torque.
• They convert hydraulic energy to mechanical
energy.
70. 70
Hydraulic Motors
• Fixed displacement motors- have variable
speed but fixed torque
• Variable displacement motors- have variable
speeds and torques
