Manitowoc 2250 Service Maintenance Manual

Reference Only
INTRODUCTION 2250 SERVICE/MAINTENANCE MANUAL
1-38
Published 07-19-16, Control # 249-01
Travel System Operation
General
See Figure 1-22 and Figure 1-23 for the following.
Each travel hydraulic pump drives one crawler system motor
and gearbox. Each pump and motor is controlled with the
travel control handle’s movement and the programmable
controller (PC). The travel control handles are inoperable
when the travel brake is applied. A gearbox for each crawler
is driven with a flexible shaft connected between the motor
output and the drive gearbox input.
To ensure that the crane travels in a straight line forward or
reverse direction, each travel drive system has shuttle valves
and pressure senders that monitor hydraulic pressure to
each closed-loop system. When traveling, the PC monitors
information from the pressure senders and adjusts the
displacement of the travel pumps to maintain equal pressure
in each travel drive system. This allows the crane to track in
a controlled straight direction.
The source hydraulic pressure for releasing the travel brakes
and enabling the motor servo systems is pilot pressure from
the boom hoist charge pump at 24 bar (350 psi). Continuous
changing of the closed-loop fluid occurs through leakage in
the pump, motor, and loop flushing valves that removes 11 L/
min (3 gpm) of fluid to when the system pressure is above
24 bar (350 psi).
When either travel control handle is moved from the OFF
position, an input signal is sent to the PC. The PC sends a
12 V output signal to enable the optional swing/travel alarm.
When the travel control handle is moved to the OFF position,
the PC sends a 0 V output signal to disable the swing/travel
alarm.
Travel Brakes
Hydraulic pressure required for releasing the travel brakes is
pilot pressure from the boom hoist charge pump at 24 bar
(350 psi). For travel brake operation, the system pressure
must be above 14 bar (200 psi) for the travel brakes to fully
release from each travel motor’s shaft. If system pressure is
below 14 bar (200 psi), the travel brake could be partially
applied and damage the brake.
When the travel brake switch is in the ON position, right and
left travel brakes are applied to hold the crane in position.
The travel brake solenoid valve HS-1 is open to allow
hydraulic flow from the brake to the tank.
When the travel brake switch is in the OFF position, an input
signal is sent to the PC and the travel system circuit is active,
waiting for a travel control handle command. When the travel
control handle is moved, the PC sends a 12 V output to
enable the travel brake solenoid valve HS-1. The brake
solenoid valve shifts to block the tank port and supplies
hydraulic charge pressure fluid from the boom hoist charge
pump to hydraulically release both crawler brakes. If brake
pressure or electrical power is lost when operating, the
brakes apply.
Two-Speed Travel Operation
The travel 2-speed switch allows the operator to select LOW
speed when a smoother start is required. LOW speed places
the travel motor in the maximum displacement (high-torque,
low-speed) position and prevents the motor from shifting to
HIGH speed. Hydraulic pressure for releasing the travel 2-
speed solenoid valve HS-35 is pilot pressure from the boom
hoist charge pump at 24 bar (350 psi).
When the travel speed switch is in LOW speed, the PC
sends a 12 V output to enable the 2-speed travel solenoid
valve HS-35, shifting the valve to direct hydraulic pilot
pressure to the end of the pressure compensator (P/C)
valve. The P/C valve shifts the pressure-compensating
override (PCOR) spool, placing the travel motor in the
maximum displacement position. The travel motors remain
in this position until the travel speed switch is placed in the
HIGH speed position.
NOTE: Place the travel speed switch in HIGH speed when
maximum available travel speed is required
(normal operation).
In the HIGH speed position, the travel motors shift to
minimum displacement (low-torque, high-speed)
automatically if the system pressure is below 270 bar
(3,915 psi). If the engine is below 1500 RPM, the 2-speed
travel solenoid valve HS-35 is enabled, although the travel
speed switch is in the HIGH speed position. The travel two-
speed solenoid valve HS-35 is disabled, shifting the valve
and removing hydraulic pilot pressure to the end of the P/C
valve, allowing the motor to operate in PCOR mode.
Travel Detent Selector
The travel detent selector on the right travel control handle
allows any travel command to be locked in. When moving at
the desired speed and direction, lift the travel detent selector
on the control handle. The PC locks in the information. Lifting
the travel detent selector again or moving the travel control
handle in the opposite direction opens the travel detent
circuit and returns the control of the travel system back to the
operator.
Travel Forward and Reverse
Both travel closed-loop systems operate the same, except
fluid flow to the motor ports are different for each track.
When a travel control handle is moved in a forward direction,
an input voltage of 5 or more volts is sent to the PC. The PC
sends a variable minus 0 to 2.8 V output that is applied to the
selected travel pump’s electrical displacement control
(EDC). The travel brake solenoid valve HS-1 is enabled to
release both the left and right crawler brakes, before the
selected travel pump strokes.

Manitowoc 2250 Specifications

General

Brand	Manitowoc
Model	2250
Category	Construction Equipment
Language	English