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BOOM CYLINDER HOLDING VALVE
A holding valve is built into the base of the boom lift cylinder barrel. This valve is
designed to hold the boom in position should loss of power or pressure line failure occur.
To check the boom lift cylinder holding valve, set the outriggers, place the boom in the
horizontal position over the front of the crane, and raise rated load about one foot above
the ground, using the boom lift cylinder (not the hoist). An example of rated load for the
IC-40-2D is 4150 pounds (1830 kg), at an 8-foot (2.5 m) load radius, with outriggers
extended, and the boom over the front. Turn the engine off and move the BOOM lever to
the LOWER position. If the boom moves down, adjust the holding valve.
W A R N I N G
Before working on the holding valves or plumbing to the boom cylinders, always
relieve trapped pressure by lowering the boom fully, turning off the engine, and
cycling the BOOM and TELESCOPE lever.
To adjust the holding valve, loosen the jam nut on the adjusting screw and tighten the
screw one-half turn and retest. Repeat until unpowered boom movement stops.
Retighten the jam nuts. If adjusting the valve does not help, the cylinder may have
internal leakage or the valve may be malfunctioning.
EXTENSION CYLINDER HOLDING VALVE
A holding valve is directly connected to the base of the primary extension cylinder rod.
The valve is designed to hold the boom in position should loss of power or pressure line
failure occur.
The holding valve should be checked with the boom elevated to the maximum angle and
the boom extended to a 4-foot (1.2 m) load radius. An 8,000 pound (3630 kg) load on a
two-part line is required for this test. Use the hoist to lift this load about six inches (15
cm) above the ground. The radius of the test load should be within the rating on the
capacity chart. Use great care to prevent the load from hitting the crane.
Turn the engine off and pull the TELESCOPE lever to the RETRACT position. If the
boom retracts, the valve should be adjusted.
To adjust the holding valve, loosen the lock nut on the adjusting screw and tighten the
screw until unpowered movement stops. Retighten the lock nut to hold the proper
adjustment.
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