Manitowoc 18000, Service Maintenance Manual, Page: 69 / 316

Reference
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Manitowoc
Published 12-05-17, Control # 035-23
1-57
18000 SERIVCE/MAINTENANCE MANUAL INTRODUCTION
1
Main hoist 2/5 pump EDC tilts swashplate in the up direction
to satisfy pressure memory. Node-1 controller compares
drum holding pressure to value in pressure memory. When
system pressure is high enough, node-6 controller sends a
24 volt output to drum brake solenoid valve HS-11. The drum
brake solenoid shifts to block drain port and opens charge
pressure port from pump 2/5 to release brake.
When brake is released, node-3 controller sends a 24 volt
output voltage to pump EDC to tilt swashplate to stroke
pump in the lower direction. In the lower direction, hydraulic
fluid flow is from port B of pump to port A of motor. Return
fluid is from port B of motor to port A of pump. As mast raises
from transport position, mast hoist drum pays out wire rope
between mast drum and gantry sheaves.
Node-4 controller sends a 24 volt output to enable mast
raising cylinders solenoid valve HS-33 in extend (mast
raising) direction. Solenoid valve shifts to block tank port and
open port to system pressure controlled by node-1 controller.
The accessory system pressure builds with the actual
pressure between a minimum of 500-psi (34 bar) at the
beginning and 4,000 psi (276 bar) after the mast starts
moving.
From the accessory valve, the fluid pressure enters free-flow
check valve sections on side “A” of load equalizing valve.
From equalizing valve, fluid enters counterbalance valves
and piston end of mast cylinders, extending cylinder rods to
raise the mast assembly. Node-4 controller monitors
accessory system pressure to control mast cylinder raising
speed rate.
Fluid flow from rod end of mast raising cylinders is blocked
b y f r e e - f l o w c h e c k v a l v e s e c t i o n s o n s i d e “ B ” o f
counterbalance valves and flows through valve flow restrain
sections preset for a relief pressure of 3,500 psi (240 bar).
Counterbalance valves operate with a 5:1 pilot ratio of the
relief valve pressure, permitting valve to open when pressure
in rod end of the cylinders is approximately 700 psi (48 bar).
Hydraulic fluid from side “B” sections of both counterbalance
valves combines, and the free-flow check valve section on
side “B” of load equalizing valve blocks the flow.
The fluid then passes through the valve flow restrain section
that is preset at 4,000 psi (276 bar). Load equalizing valve
operates with a 1.5:1 pilot ratio of the relief valve pressure,
permitting valve to open when the hydraulic pressure on side
“A” of the load-equalizing valve is approximately 2,670 psi
(185 bar). Restraining section on side “B” of load equalizing
valve opens, controlling flow of fluid out of the cylinders to
ensure cylinder operation is balanced.
When the mast cylinders are extending, node-3 controller
monitors mast hoist drum speed sensor. Node-1 controller
maintains a speed that is proportional to accessory system
hydraulic pressure applied to the mast raising cylinders.
Node-4 controller monitors the mast angle sensor when
mast is moving. When mast is raised to 115°, node-3
controller sends a zero output voltage to pump EDC. Node-4
controller sends a zero output voltage to shift spool of mast
raising cylinder solenoid valve HS-33 to center position.
Node-3 controller output voltage to pump EDC is relative to
control handle movement. The system pump varies flow to
keep drum at handle command setting. As control handle is
moved forward, an output voltage increases the pump
swashplate angle.
The live mast continues to lower until the mast hoist control
handle is moved to neutral position. Node-3 controller sends
a zero output voltage to main hoist pump 2/5 EDC that
moves swashplate to center position.
After control handle center switch opens, node-6 controller
sends a zero output voltage is sent to disable mast hoist
brake solenoid valve HS-11 to apply brake before pump de-
strokes.