INTRODUCTION 2250 SERVICE/MAINTENANCE MANUAL
1-56
Published 11-06-15, Control # 040-13
Upper Accessory System Components
General
Upper accessory system components include four jacking
cylinders, front and rear adapter frame pin cylinders, and
gantry raising cylinders. During normal operation the upper
accessory solenoid valves are “motor spooled” where both
cylinder ports and tank port of valve spool section are
connected in center position and open to tank.
Setup mode must be selected for operating the accessory
system components. In Setup mode, the PC supplies power
to equalizer limit switch, turns off boom hoist up/down limits,
and prevents travel/swing from being operated faster than
one-third speed.
The auxiliary pump is the hydraulic pressure source to
operate accessory system components. Hydraulic fluid from
auxiliary pump flows through auxiliary system disable relief
valve HS-12. Hydraulic fluid enters upper accessory valve
and flows through to the lower accessory valve.
Auxiliary system disable relief valve HS-12 is controlled by
the PC. During normal operation the relief valve is open and
excess supply flow from auxiliary pump is dumped through
valve to tank. When a component of either accessory system
is enabled, an input signal is sent to the PC. The PC sends a
12 volt output signal to auxiliary system enable relief that
adjust system pressure to 3,500 psi (241 bar).
Hydraulic pilot pressure to shift upper accessory valves is
from boom hoist charge pump at 350 psi (24 bar) with
Cummins engine or from fan pump circuit at 300 psi (21 bar)
with Caterpillar engine.
Jacking Cylinders
See Figure 1-33 and Figure 1-34 for the following procedure.
Jacking cylinders are mounted on each corner of rotating
bed. Jacking cylinder operation is controlled with switches on
jacking remote control and PC programming. Operation of all
four jacking cylinders is the same. All cylinders can be
operated at the same time if the crane is level.
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. Pressing the power
button and jacking remote switch(es) supplies power to
operate the jacking cylinders.
The rotating bed level sensor monitors rotating bed level
when the all switch is used. The sensor controls fluid to each
cylinder by opening/closing control valves.
Each jacking cylinder has a counterbalance valve at the
cylinder ports. Counterbalance valves ensure smooth control
when raising or lowering the crane. Counterbalance valves
lock the jacking cylinders in place if there is a hydraulic line
breakage or accidental operation of control valve when the
crane's power is shut down. Also, counterbalance valves
provide relief protection for the cylinders and shields them
from mechanical overloading.
When a jacking cylinder control valve is not enabled, it shifts
to the neutral position where both valve section cylinder
ports are connected to tank. This prevents inline pressure
from opening counterbalance valve, holding rotating bed
load in position by the counterbalance valve.
Jacking Cylinders Extend
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 up extend position, an input
voltage is sent through a diode to the PC. The PC sends a 12
volt output signal to the 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-25 and HS-27 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 piston end of front jacking cylinders,
extending the cylinders to lift the front of rotating bed.
Fluid returning to tank from rod end of jacking cylinders is
blocked by free-flow check valve sections of counterbalance
valves and goes through flow restraining relief valve set at
3,000 psi (207 bar). Counterbalance valves provide
deceleration control with 3:1 pilot ratio of relief pressure. This
allows valves to open when pressure in rod end of cylinders
is approximately 1,000 psi (69 bar).
WARNING
Collapsing Hazard!
Keep rotating bed as level as possible while jacking.
Operating jacking cylinder with rotating bed more than 3°
out of level can cause structural damage to jacking
cylinders and possible collapse of rotating bed.
When rotating bed is 3° out of level, a red level warning
light and beeper comes on.
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