Manitowoc Published 11-06-15, Control # 040-13 1-45
2250 SERVICE/MAINTENANCE MANUAL INTRODUCTION
Boom Hoist/Luffing Jib System Operation
General
See Figure 1-25, Figure 1-26, and Figure 1-27 for the
following procedure.
The boom hoist system and luffing jib system (optional)
share the same hydraulic pump. Only one system can be
operated at a time. In Standard mode the boom hoist (Drum
4) is controlled with control handle on left side console and
luffing jib is inoperable. In Luffing Jib mode boom hoist is
inoperable while the luffing jib hoist (Drum 5) is controlled
with control handle on left side console. Each motor drives a
gearbox on the end of a drum shaft.
Hydraulic pilot pressure from boom hoist charge pump
operates boom hoist and luffing jib motor servos. A pressure
sender in the high-pressure side of each system provides
pressure information to the PC. A fixed orifice between motor
ports A and B allows for smoother drum operation.
When boom hoist or luffing jib drum rotates, a speed sensor
mounted at end of boom hoist drum shaft or luffing jib drum
flange sends an input voltage to the PC. The PC sends a
variable 0 to 12 volt output to rotation indicator in control
handle. As selected drum rotates faster, the rotation indicator
on top of control handle pulsates to indicate drum rotational
speed. The drum speed is shown on the display.
Continuous changing of system fluid occurs through leakage
in pump, motor, and external sequence/flow valve.
Sequence/flow valve opens at 275 psi (19 bar) and removes
4 gallons per minute (15 l/m) of hot fluid from system by
dumping into the motor case where fluid returns to tank.
Brake and Pawl
Hydraulic pilot pressure from boom hoist charge pump
operates boom hoist or luffing jib brake. Air pressure
operates the boom hoist or luffing jib drum pawl.
When selected brake switch is in on position, boom hoist
brake solenoid valve HS-6 or luffing jib brake solenoid valve
HS-19 is disabled to apply brake to drum. Boom hoist drum
pawl in air solenoid valve AS-14 or luffing jib pawl in air
solenoid valve AS-16 is enabled to keep pawl applied to
drum flange. Boom hoist/luffing jib pump does not stroke in
response to control handle movement.
When selected brake switch is placed in off position, boom
hoist or luffing jib brake remains applied, waiting for a control
handle command. The PC sends a 0 volt output to disable
boom hoist pawl in air solenoid AS-14 or luffing jib pawl in air
solenoid AS-16. The PC sends a 12 volt output to enable
boom hoist pawl out air solenoid AS-13 or luffing jib pawl out
air solenoid AS-15. The solenoid valve shifts to exhaust air
pressure from piston end of pawl cylinder and to supply
manifold air pressure to rod end of cylinder. The cylinder
retracts the pawl out of drum flange.
Boom Hoist/Luffing Jib Raise
The following description is for the boom hoist system. The
luffing jib system is similar.
When left side console control handle is moved back for
booming/luffing up, an input voltage of 5 volts or more is sent
to the PC. The PC sends a variable minus 0 to 2.8 volt output
that is applied to pump EDC. The PC sends a variable 0 to
2.19 volt output that is applied to boom hoist motor PCP. The
PC checks that system limit switches are closed and that a
system fault is not present.
The pump EDC tilts swashplate in the up direction to satisfy
pressure memory. The PC compares drum-holding pressure
to value in pressure memory. When system pressure is high
enough, the PC sends a 12 volt output to enable brake
solenoid valve HS-6. The brake solenoid shifts to block drain
port and opens port to pilot pressure from boom hoist charge
pump to release selected drum brake.
The pump EDC continues to tilt the swashplate up as
hydraulic fluid flow is from pump outlet port to motor inlet
port. Return fluid is from motor outlet port to pump inlet port.
The PC output voltage to pump EDC and the motor PCP is
relative to control handle movement. As boom hoist control
handle is moved back, 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 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 pump.
When boom hoist 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
boom hoist 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 to disable boom hoist brake solenoid
valve HS-6. Drum brake solenoid valve shifts to block pilot
pressure to brake and opens a line to tank. Brake applies
before drum pump de-strokes.
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