Hydraulic Pump - Variable Flow
Pressure/Flow Regulator Valve
Load Sensing - Maximum Flow
When a service is operated, the signal pressure from the
loader (or backhoe) valve 13 increases. The increase in signal
pressure combined with the force of spring 6 moves spool 4
down. Oil in control piston 7 is allowed to drain back to the
tank via restrictor 9 and passage 10.
The force of spring 1 is now sufficient to increase the angle
of swashplate 2. The increased angle of the swashplate
increase the output of the pump.
The pump output pressure will continue to increase,
eventually the pressure will move flow regulating spool 4
against the force of spring 6 and the signal pressure in cavity
11. Pump output pressure is now sent to control piston 7 via
port A. Control piston 7 will overcome the force of spring 1.
The pump swashplate angle decreases and therefore the
pump outlet decreases. Eventually the pressure in the load
sense line and the force of spring 6 will move spool 4 down
and the ‘metering’ cycle starts again.
The up and down movement of the spool 4 keeps the
pressure on both ends of the spool equal. Spring 6 is
equivalent to 20 bar (290 lbf/in
2
), therefore the pump
pressure should be this amount greater than the signal
pressure (except when at maximum pressure - see Load
Sensing - Maximum Pressure (no flow).
5 - 7
Section E
Hydraulics
9803/3280
Section E
5 - 7
Issue 1
Circuit Descriptions
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