Attachments
Section A Section A
7 - 2 7 - 2
9803/8500 Issue 1
Circuit Description
Neutral Circuit
Oil from the Skid Steer Robot's hydraulic circuit enters the
backhoe circuit at X. If all the control levers are at their
central 'neutral' positions the oil passes directly through the
neutral gallery of valve block 1 and returns to the Robot via
Y.
Boom, Dipper and Bucket Operation
The boom ram 2, dipper ram 3 and bucket ram 4 are
controlled by valve sections F, A and B respectively.
Operation of the appropriate lever diverts oil from the neutral
gallery to one end of the ram and at the same time connects
the other end of the ram to tank via the exhaust gallery.
Stabiliser Operation
The stabiliser rams 5 and 6 are controlled by valve sections
D and C. These circuits operate in the same way as the
boom, dipper and bucket.
Slew Operation
The slew rams 7 and 8 are controlled by valve section E.
Operation of the slew control lever connects system
pressure to opposite ends of the two rams to create a 'push-
pull' effect which swings the boom. As the ram pistons move
along their bores, exhaust oil is directed to tank via the
exhaust gallery.
Relief Valves and Non-return Valves
Main relief valve G dumps excess oil to tank via the exhaust
gallery if system pressure rises above a preset maximum.
The dipper, boom, slew and bucket crowd circuits are
protected by auxiliary relief valves (ARV's) located in the
appropriate valve sections. The 'dipper lower' and 'boom
lower' ARV's incorporate anti-cavitation valves.
Each valve section also incorporates a check valve to
prevent oil being forced backwards through the valve block.
Carriage Clamp Operation
The carriage clamps 9 are operated by control valve 10,
which either connects them to system pressure or tank,
depending on the position of the valve lever.
Auxiliary Circuit Operation
On earlier backhoes fitted with an auxiliary circuit there is a
separate valve block to control auxiliary attachments such as
a breaker. On later backhoes this circuit is controlled by a
seventh section on the main valve block.
Backhoe
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