Manitowoc Published 11-06-15, Control # 040-13 1-101
2250 SERVICE/MAINTENANCE MANUAL INTRODUCTION
Drum 9 Lowering (MAX-ER Mode)
See Figure 1-64 and Figure 1-65 for the following procedure.
See Hydraulics Schematics supplied with crane to confirm
whether Drum 9 hydraulics are used for Propel (travel) or
Swing functions.
When left control handle (drum 9) is moved forward to
(LOWER), handle neutral switch closes, sending an output
voltage of 5 volts or less to crane PC. The PC sends an
output signal to shift diversion solenoid valve HS-54 to allow
fluid flow from crawler travel pumps through diverting valve
to drum 9 motors.
The crane PC sends a negative output signal to stroke the
crawler travel pumps momentarily in the raise direction to
satisfy pressure memory. The PC compares drum-holding
pressure to value stored in pressure memory. When system
pressure is high enough, the PC sends a positive output
signal to enable brake solenoid HS-56. Brake solenoid shifts
to block tank port and opens port to system charge pressure
to release brake.
The PC sends a positive output signal to stroke each crawler
travel pump EDC in the LOWER direction and a positive
output signal to each motor PCP. The crane PC checks that
block-up limit switches are closed with no other systems
operating limits present.
The crane PC sends a negative output voltage to each pump
EDC that tilts pump swashplate in the lower direction.
Hydraulic fluid at system pressure up to 5,900 psi (407 bar)
maximum then flows from pump ports B to port B of motors.
Fluid from motor ports A returns to pump ports A.
The load weight attempts to drive motor faster than return
fluid is available to pumps. System charge pump maintains
fluid supply at a positive pressure to motors. The position of
each pump swashplate restricts returning fluid flow. Pressure
builds on this return fluid side of closed-loop, acting as a
brake against the motor to control lowering speed.
The crane PC controls the lowering speed by varying voltage
to EDC’s in relation to left control handle movement to
program requirements. Each pump swashplate angle is
increased as handle is moved forward. As more fluid is
returned to pumps, more fluid is pumped to motors, and the
drum lowers the load faster.
When left control handle is moved to neutral position, the
crane PC sends an output signal to crawler travel pump
EDC’s to decrease swashplate angle, reducing oil flow
output. The crane PC stores the load holding pressure in
pressure memory. After control handle neutral switch opens,
the PC sends an output signal to disable brake solenoid HS-
56 to apply brake before crawler travel pumps de-stroke.
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