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Section E
8 - 17
Excavator Valve
Precision Control (Servo)
(Machines up to serial no. 931159)
*
Hydraclamp Valve Operation
When the backhoe is being used for excavating duties, the
kingpost assembly must be 'clamped' to the sideshift
rearframe.
The hydraclamp control valve assembly (items G, D and C) is
positioned in the front face of the excavator valve block and
is connected directly to the parallel gallery B. The valve
operates in conjunction with solenoid valve E located in the
bottom of the excavator valve block.
1 - Clamps Pressurised
When the hydraclamp switch A is in the OFF position (not
pressed), the solenoid valve E is de-energised. The solenoid
valve in this de-energised state blocks the exhaust path from
the galleries B and F to the drain port T (tank).
When an excavator service is operated, pressure is
generated in parallel gallery B, this pressurised oil moves
piston C which pushes ball D off its seat against the force of
spring G. The oil flows through restrictor H, past the ball and
out to the hydra-clamps 62.
A
9803/3280
Hydraulics
Circuit Descriptions
G
C
F
62
E
Purchased from www.WorkshopManuals.co.uk
2 - Clamps Released - Precision Control Machines Only
To enable clamps release, the hydraclamp switch A must be
in the ON position and an excavator service must be
operated.
With the hydraclamp switch A in the ON position (pressed
down), the solenoid valve E is energised. Pressure resulting
from the operation of an excavator service moves piston C
which pushes ball D off its seat.
With ball D lifted and the solenoid valve in its energised
state, oil from the hydra-clamps is vented through the clamp
valve and gallery F to the drain port T (tank).
Also, pressure resulting from the operation of an excavator
service passes through restrictor H. The oil takes the path of
least resistance and is vented via gallery F to the drain port T
(tank).
Restrictor H ensures that only a small amount of oil from
gallery B is dumped back to tank.
3 - Clamps Locked Up
If no service is being operated, pressure in the parallel gallery
falls to that of the neutral circuit and the force of spring G is
sufficient to keep the ball D seated. Pressure is therefore
trapped in the line to the clamps, maintaining the excavator
end in a securely clamped condition.
D
H
C B
P
T
T
Section E
8 - 17
62
G
E
P
A402930
Issue 2*
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