Hydraulics
9803/7130 Issue 1
6 - 2 6 - 2
Circuit Descriptions
Section E Section E
Main Relief Valve - Operation
Component Key:
A Pilot Poppet
B Cavity
C Sleeve
D Exhaust Gallery
E Cavity
F Piston
T Tank Port
G Poppet
1A Pump Inlet
1B High Pressure Carry Over Port
3D Main Relief Valve
3B Lift Ram Spool
The main relief valve (M.R.V.) 3D, situated in the loader valve
block, provides control of both loader and excavator
pressures.
The illustration shows a loader service selected by spool 3B
causing pressure to rise in the service line. In the main view
the service is operating under light load and the pressure is
not sufficient to cause any response in the M.R.V.
View X.
As service pressure reaches the pilot setting of the valve,
pilot poppet A lifts, allowing oil to escape into cavity B and
pass down the sides of sleeve C into the exhaust gallery D.
View Y.
As service pressure continues to rise and oil escapes from
cavity E, the pressure differential between the upper and
lower surfaces of piston F causes this piston to rise and seat
on the point of pilot poppet A.
Oil continues to escape from cavity E but the incoming flow
to the cavity has been cut off. This produces a pressure
drop above poppet G, causing the poppet to lift and release
service pressure into exhaust gallery D.
For a further detailed description, refer also to Pilot
Operated Pressure Relief Valve Operation.
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