Manitowoc Published 07-19-16, Control # 249-01 1-43
2250 SERVICE/MAINTENANCE MANUAL INTRODUCTION
(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 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 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 boom attempts to drive the motor faster
than return fluid can return to the low-pressure side of the
pump. The system charge pump maintains fluid supply at a
positive pressure to the motor. The pump’s swashplate
position restricts the returning fluid flow. Pressure builds on
the fluid return side of the closed-loop system, acting as a
hydraulic brake to control the lowering speed.
When the boom hoist control handle is moved toward the
neutral position, the PC compensates for hydraulic system
leakage or changing engine speed. The PC sends a 0 V
output to the pump’s EDC that moves the swashplate to the
center position. This shifts the motors back to maximum
displacement for slower output speed to slow the drum’s
rotation.
The PC stores the boom-holding pressure in pressure
memory. After the control handle center switch opens, the
PC sends a 0 V output to disable the brake solenoid valve
HS-6. The drum brake solenoid valve shifts to block the
boom hoist charge pump pilot pressure to the brakes and
opens a line to the tank. The brake applies before the drum
pump de-strokes.
HS-6
RF-18
Drum
Suction
Manifold
DOWN
UP
(340 psi)
23 bar
A
B
Boom Hoist/Luffing Jib Pump
.060
Pilot
Boom Hoist
Brake
A
(275 psi)
19 bar
B
Air Pawl
Cylinder
Pressure
Sender
HS-19
Drum
Brake
A
(277 psi)
19 bar
B
Servo
Luffing
Jib
Air Pawl
Cylinder
Pressure
Luffing Jib Motor
Boom Hoist Motor
DOWN
UP
Pressure
Sender
Servo
FIGURE 1-25
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