JLG 601S ANSI Service Manual - Manual (Page 161)

SECTION 5 - HYDRAULICS
3120746 – JLG Lift – 5-13
Inspections and Adjustments
CHECK/HIGH PRESSURE RELIEF VALVES
The system check/relief valves have the dual purpose of
providing make-up oil during by-directional rotation and
providing protection from system over pressure. When the
problem occurs in one direction only, interchange the
check/relief valves to see if the problem changes to the
other direction. If so, one check/relief valve cartridge is
either malfunctioning or does not have the proper setting.
THE RELIEF VALVES ARE FACTORY SET AND SHOULD NOT BE
TAMPERED WITH EXCEPT FOR REPLACING THE ENTIRE CAR-
TRIDGE. DISASSEMBLY MAY CHANGE THE SETTING AND
CAUSE ERRATIC UNIT OPERATION OR PREMATURE FAILURE.
PUMP CHARGE RELIEF VALVE
If charge pressure is low (less than 220 psi [15.2 Bar]
above case pressure), the charge relief valve should be
inspected. Inspect for foreign material holding the poppet
open, and for scoring or wear on the poppet and seat in
the housing.
Adjustments of the charge pressure is accomplished by
changing the shim thickness behind the spring.
Figure 5-17. Troubleshooting - System Will Not Operate in Either Direction