Variable Flow Pumps
Flow and Pressure Testing (Cont’d)
Maximum Hydraulic Stall
With variable flow hydraulics the pump swashplate angle will
increase or decrease according to pressure demand.
However in situations of maximum hydraulic stall, i.e. ram full
travel, the pressure in the circuit will achieve the setting of
the pressure regulator spool. To check the setting:
Note: Machines with a load sense relief valve, disconnect
and blank the load sense relief valve E at F.
1 Warm the hydraulic oil to working temperature, i.e. 50°C
(122°F):
a Set the engine speed to 2200 rev/min.
b Operate the loader shovel dump service to blow off
the auxiliary relief valve.
2 Lower the backhoe bucket and loader shovel to rest on
the ground; stop the engine; operate the control levers
to vent residual hydraulic pressure.
3 Connect a 0 - 400 bar (0 - 6000 lbf/in
2
) pressure gauge
to pressure test connector B located on the pump
pressure out line.
4 Start the engine and run at 2200 rev/min.
5 Raise the loader arms to achieve full travel, hold the
arms in this position and note the gauge reading, which
should be as specified in Technical Data.
6 If the pressure is higher than specified, the pressure
compensator spool may be set incorrectly or the
swashplate may not be moving.
If the pump pressure is lower than specified, the flow
spool may be set incorrectly, or there may be a leak in
the load sense line.
Do not make any adjustments at this stage. Complete
the other checks detailed in this section.
7 Refer to Regulator Valve Adjustment.
22 - 3
Section E
Hydraulics
9803/3280
Section E
22 - 3
Issue 1
Service Procedures
E
S315770
F
B
C
D
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