INTRODUCTION 2250 SERVICE/MAINTENANCE MANUAL
1-50
Published 11-06-15, Control # 040-13
When control handle is moved toward neutral position, the
PC compensates for hydraulic system leakage or changing
engine speed. The PC sends a 0 volt output to pump EDC
that moves swashplate to center position. This shifts the
motor back to maximum displacement for slower output
speed to slow the drum rotation.
The PC stores the load holding pressure in pressure
memory. After control handle center switch opens, the PC
sends a 0 volt output signal to right-rear brake solenoid AS-
9. The valve is disabled and shifts to block manifold air
pressure to brake cylinder and apply brake. The brake
applies before drum pump de-strokes.
Load Drum Lowering
When right load drum control handle is moved forward for
lowering, an input voltage of 5 volts or less is sent to the PC.
The PC sends a variable plus 0 to 2.8 volt output that is
applied to both load drum pump EDC’s. The PC sends a
variable 0 to 2.19 volt output that is applied to load drum
motor PCP. The PC checks that right-rear maximum bail and
block-up limit switches are closed and that there are no faults
in the air or hydraulic system.
The PC sends a 12 volt output signal to enable front drum
clutch solenoid AS-8 and left-rear drum clutch solenoid AS-
12. The valves shift to allow manifold air pressure flow to
clutch cylinders and compress the springs to release the
clutches from drum shaft. The right-rear drum clutch solenoid
AS-10 air pressure is exhausted so clutch remains spring-
applied to drum shaft.
The pump EDC’s tilt swashplates in the up direction to satisfy
pressure memory. The PC compares load holding pressure
to value in pressure memory. When system pressure is high
enough, the PC sends a 12 volt output to release right-rear
brake solenoid AS-9. The valve is enabled and shifts to allow
manifold air pressure to release spring applied brake.
The pump EDC’s tilt swashplate to stroke pump in the down
direction. In the down direction, fluid flow is from low-
pressure side from pump ports B to port B of motor. Fluid
from motor port A returns to pump ports A.
The PC output voltage to pump EDC’s and the PC output
voltage to motor PCP is relative to control handle movement.
As control handle is moved forward, pump swashplate angle
is increased. When system pressure exceeds the PCOR
(Pressure Compensating Over-Ride) valve setting of 4,930
psi (340 bar), the valve shifts to direct flow from shuttle valve
into maximum displacement side of servo cylinder.
The PCOR valve over-rides the command from servo PC
valve, increasing motor displacement and output torque and
reducing output speed. When PCOR valve closes, control of
the motor returns to servo PC valve.
The PC is continuously balancing the system pressure and
the motor displacement angle so the motor displacement
goes to minimum when control handle is fully forward, if the
motor torque is not too high. The PC monitors motor
displacement and controls motor speed by regulating the
hydraulic fluid flow through the pump.
The weight of the load attempts to drive motor faster than
return fluid can return to low-pressure side of pump. System
charge pump maintains fluid supply at a positive pressure to
motor. Pump swashplate position restricts the returning fluid
flow. Pressure builds on fluid return side of closed-loop,
acting as a hydraulic brake to control lowering speed.
The PC controls the lowering speed by varying voltage to
EDC's in relation to control handle movement to program
requirements. Each pump swashplate angle is increased as
control handle is moved forward. As more fluid is returned to
pumps, more fluid is pumped to motor, and the drum lowers
the load faster.
When control handle is moved toward neutral position, the
PC compensates for hydraulic system leakage or changing
engine speed. The PC sends a 0 volt output to each pump
EDC that moves swashplate to center position. This shifts
the motors back to maximum displacement for slower output
speed to slow the drum rotation.
The PC stores the load holding pressure in pressure
memory. After control handle center switch opens, the PC
sends an output signal to apply right-rear brake solenoid AS-
9. The valve is disabled and shifts to block manifold air
pressure flow to brake cylinder and apply brake. The brake
applies before drum pump de-strokes.
Dual Load Drum Motor Operation
See Figure 1-28, Figure 1-29, and Figure 1-30 for the
following procedure.
The optional dual load drum motors are usually equipped on
cranes configured for duty cycle. The operation of the dual
load drum motors is similar to what is described for Load
Drum System — Full Power. Operation of brakes and
clutches is the same. The operation that is different includes:
• The sequence/flow valve for each motor opens when
system pressure exceeds 365 psi (25 bar). The variable
speed motor removes 2.6 gallons per minute (10 l/m)
while the fixed speed motor removes 1.32 gallons per
minute (5 l/m) of hot fluid from system by dumping the
fluid in the motor case where fluid returns to tank
through tank cooler.
• The motor electrical control is with a proportional
solenoid that is proportional to the electrical control
current applied (400 – 1200 mA).
• The motor PCP (Pressure Control Pilot) is replaced with
the proportional solenoid.
There is no hydraulic servo system to motors. The servo PC
valve and the PCOR (Pressure Compensating Over-Ride)
valve is replaced with the proportional solenoid.
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