Manitowoc 18000, Service Maintenance Manual, Page: 57 / 316

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Manitowoc
Published 12-05-17, Control # 035-23
1-45
18000 SERIVCE/MAINTENANCE MANUAL INTRODUCTION
1
Main Hoist 1 Lowering
The following drum lowering operation is for main hoist 1
while operating in Standard mode.
When main hoist 1 control handle is moved forward for
lowering load, an input voltage of 2.6 volts or more is sent to
node-1 controller. Node-3 controller sends a variable zero to
24 volt output that is divided by a resistor and applied to each
pump EDC in the hoist direction. Node-8 controller sends a
variable zero to 24 volt output that is divided by a resistor and
applied to each motor PCP. The controller checks that drum
block-up limit switches are closed and no system faults are
present.
Each pump EDC tilts swashplate in the up direction to satisfy
pressure memory. Node-1 controller compares holding
pressure to value in pressure memory. When system
pressure is high enough, node-8 controller sends a 24 volt
output to enable drum brake solenoid valve HS-7. The brake
solenoid shifts to block drain port and opens port to low-
pressure side of drum system to release drum brake.
When brake is released, node controllers output voltage to
each pump EDC and to each motor PCP tilts pump
swashplate to stroke pump in the lowering direction.
Hydraulic fluid flow is from port A of each pump to port B of
left side motor and port A of right side motor. Return fluid is
from motor ports A and B to return ports B of each pump.
Controller output voltage to each pump EDC and each motor
PCP is relative to control handle movement. As drum control
handle is pushed forward, an output voltage increases the
pump swashplate angle. When system pressure exceeds
the PCOR 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.
Node controllers are continuously balancing the system
pressure and the motor displacement angle so the motor
displacement goes to minimum when control handle is all the
way forward, if the motor torque requirement is not too high.
Node-1 controller monitors motor displacement and controls
motor speed by regulating the hydraulic fluid flow through the
pump.
The load weight 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 motor over speed.
Pressure builds on fluid return side of closed-loop, acting as
a hydraulic brake to control lowering speed.
When drum control handle is moved to neutral position,
node-1 controller compensates for hydraulic system leakage
or changing engine speed. Node-3 controller sends a zero
output voltage to each 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. Node-1 controller stores the load holding pressure
in pressure memory. After control handle center switch
opens, node-8 controller sends a zero output voltage is sent
to disable drum brake solenoid valve HS-7 and to apply
brake before pump de-strokes.
The diverting valve lines to main hoist 1/3 drum motor remain
open until whip line hoist control handle is selected for
operating whip line hoist in any mode.