INTRODUCTION 2250 SERVICE/MAINTENANCE MANUAL
1-58
Published 11-06-15, Control # 040-13
Jacking Cylinders Retract
The following operating description is for front jacks.
Operation of rear jacks is the same, except different switches
are used.
When power button is pressed and both left and right front
jack switches are 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 jacking
solenoids HS-26 and HS-28 to extend left and right front
jacks. Hydraulic pilot pressure at 350 psi (24 bar) or 300 psi
(21 bar) shifts the valve(s) in the selected direction.
Hydraulic fluid from auxiliary pump flows through auxiliary
system disable relief valve HS-12 and enters accessory
valve. Fluid exits valve sections of accessory valve and flows
through free-flow check valve sections of counterbalance
valves. Fluid then enters rod end of front jacking cylinders,
retracting the cylinders to lower the front of rotating bed.
Fluid exhausting from piston end of jacking cylinders is
blocked by free-flow check valve sections of counterbalance
valves. From counterbalance valve flow is through flow
restraining section that has a relief setting of 2,500 psi (172
bar). Counterbalance valve acts as a deceleration control
and functions with a 3:1 pilot ratio of the relief pressure. This
permits the valve to open when the pressure in piston end of
the cylinder is approximately 833 psi (57 bar).
Restraining section of counterbalance valves open to control
fluid out of jacking cylinders while maintaining back pressure
on piston end of cylinders to prevent rotating bed from falling
or lowering. Hydraulic fluid then flows through free-flow
check valve section of flow control valve before entering
upper accessory valve and returns to tank.
When power button or jacking switch is moved to off position,
the PC sends a 0 volt output to shift spool of solenoid valves
HS-26 and HS-28 to center position.
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