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TM 10-3930-671-24
10.5. Main Hydraulic Control Valve
Description and Operation..................................................................................................... F-459
Main Hydraulic Valve Mounting & Control Lever Linkage (Typical)....................................... F-460
Main Hydraulic Valve Removal.............................................................................................. F-461
Main Hydraulic Valve Installation........................................................................................... F-462
Troubleshooting Guide .......................................................................................................... F-463
Description and Operation
The main hydraulic control valve features an open-
center, parallel-circuit type modular design. It has
adjustable
system
pressure
relief
valve
and
counterbalance (tilt lock) valve in the tilt circuit with
pressure-compensated flow control to regulate lift
speeds. All ports and connecting lines are on the bottom
of the valve.
When lift attachments are used, an auxiliary section may
be added to the outer (RH) side of the standard (lift/tilt
only) main valve. The optional aux sections also have an
adjustable relief valve and can be assembled with
optional flow control levels. The aux valve section is
added to the main valve by first removing a cover plate
and then bolting the add-on section to the valve.
The
valve
is
adjustable
for
pressure
and
flow
requirements for lift, tilt and auxiliary functions. The
hydraulic
system
relief
pressure
level
is
"tuned"
(adjusted) to match the need of each truck capacity.
Pressure is tuned by adjustable screws. Flow is tuned
with interchangeable flow cartridges.
The valve spools are arranged in standard sequence
(from the operator’s position) to first provide lift control,
then tilt, and finally auxiliary control. The control levers
are spring-loaded (by the valve spool centering springs)
to return them to neutral when released. Oil flow is
controlled by the amount or distance the control handles
are moved. Excess oil flow is returned to the sump. A
check valve prevents reverse flow.
F-459
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