JLG Lull 1044C-54 II Series Service Manual page 284

Frame Tilt and Oscillation
Control Centered
Control to Right
Control to Left
Frame Tilt Disabled
7-2
The frame tilt system works in combination with the rear oscillation lock
system. The frame tilt system is explained here. See "Rear Oscillation
Lock System" on page 7-17 for detailed information concerning that
system.
With the engine on and the boom below 40° elevation, the frame tilt system
is enabled. The frame tilt control valve (see page 7-3) is normally centered
and no pilot pressure is supplied to ports A6 or B6 of the frame tilt section
of the multi-spool control valve. In this condition, the spool in the frame tilt
section remains centered and no pressure is supplied to the frame tilt
cylinder.
Two (2) counterbalance valves on the frame tilt cylinder prevent fluid
escaping from the cylinder. This mechanically locks the cylinder in position
and prevents the frame from rotating on the front axle.
Moving the frame tilt control handle to the right allows pilot pressure to flow
from port #2 of the control valve. This pilot pressure is routed to port A6 of
the frame tilt section of the multi-spool control valve. The spool is shifted
away from port A6, allowing pump flow to be routed through port A to the
rod end of the frame tilt cylinder. Pressure is sufficient to pilot the
counterbalance valves open, allowing fluid to enter and leave the cylinder.
As the cylinder retracts, the frame tilts to the right and fluid from the base
end of the cylinder is routed through port B of the frame tilt section and on
to the filtered tank return.
Moving the frame tilt control handle to the left allows pilot pressure to flow
from port #1 of the control valve. This pilot flow is routed to port B6 of the
frame tilt section of the multi-spool control valve. The spool is shifted away
from port B6, allowing pump flow to be routed through port B to the base
end of the frame tilt cylinder. Pressure is sufficient to pilot the
counterbalance valves open, allowing fluid to enter and leave the cylinder.
As the cylinder extends, the frame tilts to the left and fluid from the rod end
of the cylinder is routed through port A of the frame tilt section and on to
the filtered tank return.
Under certain conditions the frame tilt system is disabled by the frame tilt
lockout valve. The lockout valve prevents or allows pilot flow to be routed to
ports A6 and B6 on the frame tilt section of the multi-spool valve. The
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