TM 5-3810-307-24-1-1
Relief Valves
DESCRIPTION
Relief valves are used to protect a component, a
valves, but some are located in the line between
circuit, or a system from over pressurization. Most of
components (e.g., double cross-over relief valve),
the relief valves are located in the directional control
while others are part of a component.
MAINTENANCE
GENERAL.
The following test tables list Main and Circuit Relief
Valve Settings. If the pressure setting of any relief
Relief valves are checked and adjusted by causing a
valve is not 100 psi ( 689.5 kPa) of that listed in
given circuit to reach its prescribed pressure limit
the tables, adjustment is necessary.
(stall). At this point, the relief valve opens, returning
oil to the reservoir. Hydraulic motor circuits may be
CAUTION
stalled by preventing rotation of the motor shaft prior
Do not overtighten the adjustment screw
to actuating the control valve. Cylinder circuits may
or locknut.
be stalled by extending or retracting a cylinder to its
limit of travel.
CAUTION
By placing a pressure gauge in the proper line or
Do not hold the relief valve open for
port, a pressure reading will indicate the point at
more than one minute at a time.
which the relief valve opens. The needle on the
meter face will climb until it reaches the relief valve
setting. At that point the needle will stop climbing
NOTE
and fluctuate, indicating the relief valve is open and
To adjust a relief valve, turn the
returning oil to the reservoir.
adjustment screw (in to increase or out
to decrease) until the proper setting is
Correct relief valve adjustment is mandatory if any
reached.
hydraulic circuit is to function properly. Settings must
be within specified tolerances. Therefore, after the
need for adjustment has been established, it should
MAIN RELIEF SETTINGS TABLE
be performed only by qualified technicians using the
correct equipment.
Valve Bank
Setting - psi (kPa)
One Section (Swing) . . . . . . . . . . . 1,500 (10,342)
The hydraulic system utilizes two valve banks. A
Five Section . . . . . . . . . . . . . . . . 3,500 (24,132)
single section valve bank directs oil flow for operation
of the Swing Circuit. The five section valve bank
directs flow for operation of the Telescope, Lift,
NOTE
Auxiliary Hoist, Main Hoist, and Clamshell/
Release the control lever after taking
Attachments Circuits.
each reading and while making
adjustments.
Each valve bank has one main relief valve limiting
maximum operating pressure of the component(s) in
that circuit. In addition, circuit relief valves further
limit operating pressures as required by circuit
design.
2-8-26
