INTRODUCTION 2250 SERVICE/MAINTENANCE MANUAL
1-62
Published 11-06-15, Control # 040-13
Gantry Cylinders
See Figure 1-36 and Figure 1-37 for the following procedure.
The gantry cylinders partially raise and lower the gantry.
Boom hoist rigging continues raising or lowering the gantry
from or back to this position. See Crane Assembly and
Rigging Guide topic in the Operator Manual for gantry raising
and lowering procedure.
Power is available to jacking remote control when the cable
is connected at auxiliary valve junction box on right side of
rotating bed and engine is running.
Gantry Cylinders Extend
When power button is pressed and gantry cylinders switch is
held in the up extend position, an input voltage is sent to the
PC. The PC sends a 12 volt output signal to auxiliary system
disable relief valve HS-12 that adjust system pressure to
3,500 psi (241 bar).
The PC also sends a 12 volt output signal to enable gantry
cylinders extend solenoid HS-4. Hydraulic pilot pressure at
350 psi (24 bar) or 300 psi (21 bar) shifts the valve in the
selected direction. Fluid from auxiliary pump flows past
auxiliary system disable relief valve HS-12 and enters upper
accessory valve.
Hydraulic fluid leaves upper accessory valve and flows
through free-flow check valve sections of counterbalance
valves, entering piston end of the gantry cylinders and
extends the cylinders to raise the gantry.
Fluid from rod end of cylinders is blocked by free-flow check
valve sections of counterbalance valves and flows through
the flow restraining section that has a relief setting of 3,500
psi (241 bar). Counterbalance valves serve as a deceleration
control, with a 3:1 pilot ratio of the relief pressure. Hydraulic
fluid then exits counterbalance valves and passes through
upper accessory valve before returning to tank.
If more power is needed to raise gantry cylinders, engine
speed can be increased with remote engine speed switch in
remote start junction box on right side of rotating bed.
When power button or gantry cylinder switch is released,
fluid to the gantry cylinders is stopped. Free-flow check valve
sections trap the fluid in the rod and piston ends of cylinders
to lock the gantry in position.
When power button or gantry switch is moved to off position,
the PC sends a 0 volt output to shift spool of solenoid HS-4 to
center position.
Gantry Cylinders Retract
When power button is pressed and gantry cylinders switch is
held in the down retract position, an input voltage is sent to
the PC. The PC sends a 12 volt output signal to auxiliary
system disable relief valve HS-12 that adjust system
pressure to 3,500 psi (241 bar).
The PC also sends a 12 volt output signal to enable gantry
cylinders retract solenoid HS-5. Hydraulic pilot pressure at
350 psi (24 bar) or 300 psi (21 bar) shifts the valve in the
selected direction. Fluid from auxiliary pump flows past
auxiliary system disable relief valve HS-12 and enters upper
accessory valve.
Gantry cylinder valve shifts to direct fluid through free-flow
check valve sections to rod end of gantry cylinder. Gantry
lower weight increases pressure in the piston end of
cylinders. Exit of fluid out of cylinders is blocked by free-flow
check valve sections and flows through the flow restraining
section that has a relief setting of 3,500 psi (241 bar),
allowing valves to open and controlling the flow out of
cylinders. Maintaining a back pressure on piston end of
cylinders prevents the gantry from falling or lowering faster
than supply of fluid. Hydraulic fluid returns to tank through
the gantry cylinder solenoid valve as gantry lowers.
When power button or gantry cylinder switch is released, the
PC sends a 0 volt output to shift spool of solenoid valve HS-5
to center position. Fluid to the gantry cylinders is stopped.
Free-flow check valve sections trap the fluid in the rod and
piston ends of cylinders to lock the gantry in position.
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