SIDE SHIMMING OF BOOM SECTIONS 800D
7-12
Published 5-27-2018 Control # 039-06
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 hoist 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-blocking
occurrence or an 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: None of the
internal parts of the unloader valves are serviceable.
In the event that one of these three functions will 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 hoist 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.
CRANE VALVE
SPOOL ACTION
BONNETS
WORKPORTS
INLETCOVER
OUTLETCOVER
OUTLET
INLET
TURN RELIEF
LOOSEN NUT TO
ADJUST RELIEF
DUAL PRESSURE MAIN RELIEF
LINKAGE END
OF SPOOL
9420
Fo
r
Reference
Only
To Next Page
Loading...
