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Section E
8 - 22
Excavator Valve
Precision Control (Servo)
(Machines from January 2003)
Load Sense - Pressure Compensator Valves
Operation
Operating an individual service
It must be noted that the load sense gallery LS is connected
to all the pressure compensator valves PC (one for each
service) as shown. The pressure in the load sense gallery LS
will always be equal to the highest load from any of the
backhoe services.
The pressure compensator valves are fitted between each
service spool and service ram and sense the pressure acting
on either side of the particular service spool. The pressure
compensator valve will move in response to the pressure
drop (pressure differential) created across the spool.
When one service only is operated the pressure
compensator valve PC is FULLY opened as shown,
connecting the gallery P1 to gallery P2 and to the ram
service port without any pressure drop.
Operating multiple services
a)
Normal Condition
When another service with a higher load is operated
simultaneously, a typical example is the lifting of the boom
and simultaneous operation of the bucket as shown.
The higher load pressure in the boom service causes the
pressure compensator valve PC in the bucket service to
partially close, reducing the size of the opening through
which the oil must flow, and in this way maintains a pressure
drop across the pressure compensator equal to the pressure
drop across the bucket service spool.
In this example, because of the action of the pressure
compensator valve the bucket service is always kept
independant of the other services, the bucket ram speed
remains constant (as controlled by the bucket service spool)
and is not affected by the greater operating pressure in the
boom service.
9803/3280
Hydraulics
Circuit Descriptions
(continued)
Purchased from www.WorkshopManuals.co.uk
b)
With insufficient flow from pump
Should the oil flow demanded by the sum of the combined
services operating ever exceed that of the pump, all the
pressure compensator valves will partially close accordingly,
effectively dividing the available flow between all the services
proportionally.
In this condition the service ram with the highest load will
NOT stop, because the speed of the other service rams
operating will have been reduced proportionaly by the action
of the pressure compensator valves to compensate.
When one of the service spools is returned to neutral, the
speed of the other service rams still operating will all
increase proportionally.
Section E
8 - 22
Issue 1
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