Variable Flow Pumps
Flow and Pressure Testing
Load Sensing Pressure
With no services operating, there should be no pressure in
the load sense line, this is because hydraulic oil flows
through the load sense circuit back to the hydraulic tank. If a
shuttle valve is ‘stuck’, or a hose kinked, then a pressure
could be induced in the load sense lines, this will have an
effec t on t he hyd raulic syst em. To c hec k load sense
pressure:
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
A
located on the load sense
line from the loader valve.
4
Start the engine and run at 2200 rev/min.
5
Do not move the steering wheel and make sure that all
control levers remain in ‘neutral’ position.
6
Check the pressure gauge reading, which should be as
specified in
Technical Data
.
7
If the pressure is higher than specified, first move the
steering wheel and then any of the service levers. If this
does not reduce the pressure, physically check the load
sense lines for trapping or kinking. As a last resort, the
service valves may have to be removed and checked for
sticking shuttle valves. However, this should not be
done until all other checks have been completed.
8
Machines with the load sense pressure relief valve
adjust the load sense pressure relief valve
E
. Machines
without a load sense pressure relief valve adjust the
regulator valve.
Stand-by Pressure
With the engine switched off, the pump swashplate is spring
loaded to the full flow position. On engine start up standby
pressure moves the swash plate to minimum flow position
(see descriptions). To check stand-by pressure:
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
Do not move the steering wheel and make sure that all
control levers remain in ‘neutral’ position.
6
Check the pressure gauge reading, which should be as
specified in
Technical Data
.
7
If the pressure is not as specified, do not make any
adjustments at this stage. Complete the other checks
detailed in this section.
8
Refer to
Regulator Valve Adjustment
.
22 - 2
Section E
9803/3280
Section E
22 - 2
Issue 1
Service Procedures
E
S315770
