8 - 8
Section E Hydraulics
9803/8550
Section E
8 - 8
Issue 1
Descriptions
3 Main Poppet Opens
As service pressure continues to rise and oil
escapes from cavity L, the pressure differential
between the upper and lower surfaces of piston C
causes this piston to rise and seat on the point of
pilot poppet E.
Oil continues to escape from cavity L but the
incoming flow to the cavity has been cut off. This
produces a pressure drop above poppet B, causing
the poppet to lift and release service pressure into
exhaust gallery K.
Excavator Valve - Pilot-Operated
A.R.V. Pressure Relief Operation
1 Valve at Rest
A.R.V's are positioned in the excavator valve block
in order to relieve excessive pressure in the
services as shown on page E/8 - 6.
When the service is in neutral and there are no
excessive forces acting on the equipment, service
pressure at A will be acting on the lower face of
poppet B and will also be felt inside the valve via
hollow piston C.
The force of springs D and F, combined with the
service pressure acting on the upper faces of
poppet B and piston C, keeps poppets B and E
tightly seated.
The force of spring F is adjustable to suit the
relevant service by means of adjuster screw and
locknut G.
2 Pilot Valve Opens
As service pressure reaches the pilot setting of the
valve, pilot poppet E lifts, allowing oil to escape into
cavity H and pass down the sides of sleeve J into
the exhaust gallery K.
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