Gradall G-550C Operation And Maintenance Manual page 12

G-660C & G-880C GRADALL (Crawler)
Pilot Control Oil: Oil from the 6 gpm pilot pump (1)
feeds the pilot circuit control manifold (2). Oil from
the manifold feeds the travel/steer joystick (3) and
the two-speed crawler selector valve (4) located on
the left front floor of the operator's cab.
Joystick Pilot Circuits: Movement of the travel
joystick (3) in any direction feeds the pilot control
pressure to the various end caps of the two track
control valves located in the hoist boom and travel
control valve bank (5). Moving the joystick forward
makes the crawler move forward. Pulling back on
the joystick makes the crawler move in reverse.
Pushing the joystick to the right or to the left causes
if to turn in either direction. See the operating
instructions for details.
CRAWLER TRAVEL PILOT CIRCUITS
The function of the crawler travel circuit is to propel
the machine forward and backward and to steer
right or left as necessary. For clarity the drive
sprocket end is the rear and the idler end is the front
of the machine.
When the travel joystick (3) is moved in any
direction pilot pressure is routed thru the brake valve
(6) and thru the center pin (7) to release the brakes in
the drive transmission (9).
When the right hand two speed pedal is depressed
pilot oil is routed from the two speed valve (4), thru
the center pin (7) and to the two drive motors (8). A
piston in each motor shifts the swash plate for
maximum speed. When the left hand pedal is
depressed for the lower speed the circuit is open to
dump and the swash plate positions itself for
maximum power.
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OPERATION & MAINTENANCE