Manitowoc National Crane 500E2 Service Manual

2-6 Published 08/16/19 Control # 112-05
HYDRAULIC SYSTEM 500E2 SERVICE MANUAL
Unloader Valve Service
Refer to ATB System Diagnosis if an electrical problem has
occurred.
This crane has three work sections equipped with unloader
(dump) valves. The functions connected to the unloader
valves are winch up, boom down and boom extend. The
purpose of these unloaders is to stop control oil from
reaching the functions in the event of a two-block occurrence
or overload condition. Hydraulic lines extend between the
unloader valve on each of these sections to a single solenoid
(dump) valve. The hydraulic oil in these lines can drain out
over a period of time, when the pump is not engaged, or may
be lost during servicing the unit. Air may enter these lines at
such a time. If the unloader hydraulic lines have air in them,
these three functions may not operate or may exhibit a delay
in their operation.
NOTE: Internal parts of the unloader valves are not
serviceable.
In the event that one of these three functions do not operate
or operates with a delay and the crane is not overloaded or
two-blocked, the following air purging procedure should be
followed. If no improvement is seen after completing the
following procedure twice, follow the troubleshooting steps
outlined for checking and inspecting the solenoid valve and
unloaders in this hydraulic circuit outlined below.
1. Purposely trip the ATB switch to open the solenoid
(dump) valve.
2. Operate winch up, boom down and boom extend
separately for about a minute, longer if the oil is cold.
3. Operate all three functions simultaneously.
4. Release the ATB switch.
5. Check the operation of each function.
6. Repeat procedure if necessary.
In the event that one of these three functions will not operate
and the crane is not overloaded or two- blocked, the
following procedure is used to diagnose the problem.
Linkage End
of Spool
Spool Action
Bonnets
Inlet Cover
Outlet
Inlet
Main Relief
Work
Ports
Outlet
Cover
NOTE: Remove cap
to adjust main relief.
Spool Seal
Backup Washers
Retainer Plate
Crane Valve Cover
10 ft-lb (13.5 N.M)
Winch Valve Cover
5 ft-lb (6.7 N.M)
Bonnets
Assembly
Crane Valve Cover
10 ft-lb (13.5 N.M)
Winch Valve Cover
5 ft-lb (6.7.8 N.M)

Manitowoc National Crane 500E2 Specifications

General

Brand	Manitowoc
Model	National Crane 500E2
Category	Construction Equipment
Language	English