jcb 1CX, Service Manual

Page: 125 / 242

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 V
alve - Pilot-Operated
A.R.V
. Pr
essur
e 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
P
ilot 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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