Hoist Circuit
The hoist circuit controls boom raise and lower. Pilot fluid from the left hand joy stick (controller) is directed to the
selected end cap of the main control valve shifting the spool. Whenever the spool shifts, fluid is directed to the two
hoist cylinders, raising or lowering the boom.
A 10 cu. in. dry nitrogen accumulator is installed in the hoist up circuit to dampen boom bounce. Refer to
SUPPLEMENTAL PRESSURE SETTING MANUAL
if service to the accumulator becomes necessary.
Do not
use anything
other than dry nitrogen gas to fill the accumulator. Serious injury could occur if accumulator is improperly filled. It is
best to contact your GRADALL Distributor for accumulator service.
FIGURE 57
HOIST CIRCUIT
Hoist Cylinders
There are two (2) cylinders used in the GRADALL Hoist circuit. They are attached to the main frame and boom
cradle. Whenever the cylinder rods retract, the boom lowers. Whenever the cylinder rods extend the boom raises.
Main pump fluid is directed to both cylinders simultaneously through large hydraulic fluid tubes located at the rear
of the cylinders. These tubes are fed from port A or B of the control valve. Return fluid flows through the opposite
unpressurized port.
XV. Hoist Circuit
Hoist Up
Accumulator
Hoist Cylinders
Hoist Down
Hoist
C.V.
Main Pump
Joystick
Pilot Pressure
Tank
Form No. 29704
NOTE!
Fluid Path Simplified for Clarity
P - Pilot Pressure
T - Return Fluid To Tank
A/B - Main Control Valve Ports
50
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