Manitowoc 2250 Service Maintenance Manual

Reference Only
Manitowoc Published 07-19-16, Control # 249-01 1-47
2250 SERVICE/MAINTENANCE MANUAL INTRODUCTION
1
clutches from the drum shaft. The right rear drum clutch
solenoid AS-10 air pressure is exhausted so the clutch
remains spring-applied to the drum shaft.
The pump’s EDC tilts the swashplates in the UP direction to
satisfy pressure memory. The PC compares load-holding
pressure to pressure memory. When the system pressure is
high enough, the PC sends a 12 V output to release the right
rear brake solenoid AS-9. The valve is enabled and shifts to
allow manifold air pressure to release the spring-applied
brake.
The pump’s EDC tilts the swashplate to stroke the pump in
the DOWN direction. In the DOWN direction, fluid flow is
from the low-pressure side from pump ports B to port B of the
motor. Fluid from motor port A returns to pump ports A.
The PC output voltage to the pump’s EDC and the PC output
voltage to the motor’s pressure-control pilot (PCP) is relative
to the control handle’s movement. As the control handle is
moved forward, the pump’s swashplate angle is increased.
When pressure exceeds the PCOR valve setting of 340 bar
(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 the 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
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 load 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.
The PC controls the lowering speed by varying the voltage to
the EDC's in relation to the control handle’s movement to
program requirements. Each pump’s swashplate angle is
increased as the control handle is moved forward. As more
fluid is returned to the pumps, more fluid is pumped to the
motor, and the drum lowers the load faster.
When a 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 each
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 load-holding pressure in pressure
memory. After the control handle’s center switch opens, the
PC sends an output signal to the right rear brake solenoid
AS-9. The valve is disabled and shifts to block manifold air
pressure flow to the brake cylinder and applies the brake.
The brake applies before the drum’s pump de-strokes.
Dual Load Drum Motor Operation
See Figure 1-27, Figure 1-28, and Figure 1-29 for the
following.
The optional dual load drum motors are usually equipped on
cranes configured for duty cycle. The operation of the dual
load drum motors is similar to what is described for Load
Drum System—Full Power on page 1-44. Operation of the
brakes and clutches is the same. The operation that is
different includes the following:
• The sequence/flow valve for each motor opens when
system pressure exceeds 25 bar (365 psi). The
variable-speed motor removes 10 L/min (2.6 gpm),
while the fixed speed motor removes 5 L/min (1.32 gpm)
of hot fluid from the system by dumping the fluid in the
motor case where fluid returns to the tank through the
tank cooler.
• The motor electrical control is with a proportional
solenoid that is proportional to the electrical control
current applied (400 to 1200 mA).
• The motor PCP is replaced with the proportional
solenoid.
There is no hydraulic servo system to the motors. The servo
PC valve and the PCOR valve are replaced with the
proportional solenoid.

Manitowoc 2250 Specifications

General

Brand	Manitowoc
Model	2250
Category	Construction Equipment
Language	English