Manitowoc Published 07-19-16, Control # 249-01 1-45
2250 SERVICE/MAINTENANCE MANUAL INTRODUCTION
solenoid AS-10 air pressure is exhausted so the clutch
remains spring-applied to the drum shaft.
The pump’s EDC tilts the swashplates in the UP direction to
satisfy pressure memory. The PC compares the load-holding
pressure to pressure memory. When system pressure is high
enough, the PC sends a 12 V output to the right rear brake
solenoid AS-9. The valve is enabled and shifts to allow
manifold air pressure to release the spring-applied brake.
The pump’s EDC continues to tilt the swashplate in the UP
direction as hydraulic fluid flow is from the pump’s outlet port
to the motor’s inlet port. Fluid then flows from pump ports A
to motor port A. Fluid from the motor port B returns to the
load drum pump ports B.
The PC output voltage to the pump’s EDC and the motor’s
PCP is relative to the control handle’s movement. As the
control handle is moved back, the pump’s swashplate angle
is increased. When system pressure exceeds the pressure-
compensating override (PCOR) valve setting of 340 bar
(4,930 psi), the valve shifts to direct the flow from the shuttle
valve into the maximum displacement side of the servo
cylinder. The PCOR valve overrides the command from the
servo PC valve, increasing motor displacement, output
torque, and reducing output speed. When the PCOR valve
closes, control of the motor returns to the servo PC valve.
The PC is continuously balancing the system pressure and
the motor displacement angle so the motor displacement
goes to minimum when the control handle is fully back, 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 pumps.
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