reveals that adequate volume is being supplied to
the affected valve bank, relief valves are properly
adjusted, and the component is not at fault, check
Do not attempt to loosen fittings in
the valve for scored or worn parts. Scoring is a sign
pressurized lines or while the hydraulic
pumps are in operation.
components or oxidized oil. Scored or severely worn
bleeding of air by loosening various clamp and
valve components must be replaced.
screw-type fittings may become necessary. If the
above procedures fail to eliminate air entrapment,
Warped mounting surfaces can distort the assembly
contact Grove Worldwide, Product Support.
and cause leakage and binding. To check for valve
distortion, loosen the mounting bolts slightly. If the
leakage stops when the bolts have been backed off
slightly, distortion was the problem. To correct this
Parts found damaged or out of tolerance when
condition, shim the valve assembly to level and
maintenance is being performed should be replaced.
retighten the mounting bolts.
Refer to the Parts Manual for proper replacement
Check valves in the control valves are designed to
permit a flow of oil in one direction only. If a piece of
dirt or rust has worked its way into the check valve
and lodges between the poppet and seat, it will keep
The control valves that control the crane functions
the valve open and allow a return flow of oil. The
are installed on the turntable assembly center
remedy is to clean the valve, but it is also a good
section. The valves are controlled hydraulically
idea to follow through and ensure the hydraulic
through pilot pressure signals from the hydraulic
system filters are still serviceable.
remote control valves in the cab.
Some of the most common causes for stiff spool
Inspect the control valves for visible damage, binding
movement or jammed spool action are; system
spools, and evidence of leakage. If excessive
overheating, excessive pressure, contaminated or
internal leakage is suspected during operation with a
deteriorated oil, or warped mountings.
spool in its center position, it is possible that the area
between the spool and working section bore of the
cause, flushing the system and replenishing with
valve body is worn beyond serviceable limits. If this
clean oil may solve the problem. If the spool bores
condition exists, the spool and body must be
are badly scored or galled, the valve must be
replaced as an assembly.
removed for servicing.
Warping occurs when mounting plates are not level
or they become distorted from machine damage. As
Dripping oil indicates some type of external leakage.
mentioned previously, the valve can be shimmed
The machine should be removed from service for
External leaks sometimes
develop at fittings and seals. Spool seals are
Also check the valve for rust. Rust or dirt collecting
susceptible since they are subject to wear. Seals
on the linkages can prevent free movement of the
may be damaged by temperatures that are too high,
spool, and keep it from the true center position.
or by dirt or paint accumulation on the spool.
Excessive system pressure can create both internal
Damaged seals must be replaced.
and external leaks in valves that are otherwise
sound. Therefore, it is extremely important that relief
A component functioning at reduced efficiency may
valves be adjusted only by qualified personnel using
indicate that the control valve for that component is
the proper equipment.
leaking internally. Assuming preliminary check-out