Variable Flow Pumps
Flow and Pressure Testing (Cont’d)
Pump Flow
It is not possible to test full pump flow at system pressure
whilst the pump is installed on the machine. This is because
the pump swashplate angle will return to minimum angle
(zero flow) when the system reaches full pressure (see
descriptions).
However, it is possible to test the pump flow whilst ‘blowing
off’ an auxiliary relief valve which is set lower than system
pressure. In the example below, the shovel head side A.R.V.
is used. The readings taken in this test give a ‘snapshot’ of
pump performance and can be used to establish if major
pump maintenance is required.
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
Connect a flowmeter to the pump pressure out line as
shown at
C
.
5
Start the engine and run at 2200 rev/min.
6
Raise the loader arms and fully dump the loader shovel.
7
Hold the shovel in the dump position (to blow off the
A.R.V.) and c hec k t he f lo w and p ressure g aug e
readings, which should be as specified in
Technical
Data
.
8
If the pump flow is not as indicated, do not make any
adjustments at this stage. Complete the other checks
detailed in this section.
9
Refer to
Regulator Valve Adjustment
.
Load Sense Line Flow
The load sense line c ommunic at es t he load p ressure
required at a service to the pump. If there is a blockage or
leak in the line, the hydraulic system will not operate
effectively.
Load sensing is a ‘dynamic flow’ type. That is, there is a
constant flow of oil from the pump to the shuttle valves.
When a pressure signal is felt at the service port, the flow is
interrupted and the pump immediately responds to the
demand. (Unlike a ‘static’ system where the pressure signal
must move from the valve block, back up the load sense
line to the pump).
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 flowmeter into the load sense line, a good
access point is where the LS line enters the backhoe
valve as shown at
D
.
5
Start the engine and run at 2200 rev/min. Check the
flow which should be as specified in
Technical Data
.
6
If a service is selected, the flow should drop to zero
(but the pressure will increase).
7
If there is no flow in the system, then check the load
sense lines for being trapped or kinked, also move the
service control levers and the steering wheel.
If there is still no flow, then there is the possibility of a
shuttle valve being stuck. Do not dismantle valves at
this stage but complete all other tests listed in this
section.
22 - 4
Section E
9803/3280
Section E
22 - 4
Issue 1
Service Procedures
