SUB-SECTION 4D
CONTROL VALVES
chart.
for the control and compensator spools, and the valve
bodies. If either a valve body or spool is damaged, the com-
During disassembly, particular attention should be given to
plete valve section must be replaced.
identification and orientation of parts for reassembly. The
spools are selectively fitted to the valve body and must be
Control valve repairs, however, should be limited to the
returned to the same body from which it was removed.
steps listed in the REMEDY column of the troubleshooting
TABLE 4D-7
TROUBLE, CAUSE AND REMEDY CHART
TROUBLE
PROBABLE CAUSE
REMEDY
Compensating spool stuck open.
Entire valve inoperative.
Remove compensating spool -
examine for contamination, clean
and replace.
Pilot relief poppet stuck open.
Remove pilot poppet - examine
for contaminents, clean and
replace.
Remove spool, clean and flush
Compensating spool stuck.
High pressure thru neutral (When
inlet section.
valve plungers are centered)
Clean orifice.
Compensating spool orifice
partially plugged.
Contamination under relief valve.
Remove relief, clean, install and
One valve section does not
reset pressure.
operate.
Spool sticking.
Remove spool and clean, flush bore.
Valve response slow.
Remove poppet and clean, flush
Pilot poppet held open due to
housing.
contamination.
Remove and clean.
Response orifice partially plugged.
Eliminate causes such as restrictions in
Excessively high oil temperature.
Sticking plungers.
lines and filter.
Change oil, clean system.
Dirt in oil.
Loosen mounting bolts & check.
Valve warped from mounting.
Excessively high pressure.
Chock pressure with gauge on inlet
and cylinder ports.
Handle or linkage binding.
Free up linkage.
Plunger bent or damaged.
Replace entire section.
Return spring damaged.
Replace faulty parts.
Spring or detent cap binding.
Loosen cap, recenter & retighten.
Valve temperature not equal.
Let system warm up.
Paint or dirt on or under seal.
Leaking seals.
Remove and clean.
Excessive back pressure.
Check back pressure at tank port.
Scored plunger.
Replace valve section.
4D-20
