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 p ump out p ut p ressure w ill c ont inue t o inc rease,
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
eq uivalent t o 20 b ar (290 lb f/ in
2
), t herefore t he p ump
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
9803/3280
Section E
5 - 7
Issue 1
Circuit Descriptions
1
2
7
3
4
5
P
A
T
6
A275770
