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Removing Air From The Hydraulic System 3810-01-448-2619">

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TM 5-3810-307-24-1-1
When hydraulic oils are changed, recheck the
NOTE
reservoir oil level after brief system operation and
add oil as required.
On cranes with booms that can not be
lowered  to  below  horizontal,  the
Reservoir capacity, at full level, is 64.4 gal. (244 l).
outriggers may be used to raise the
Ensure the crane is in the travel mode of operation
machine in order to lower the boom nose
when the oil system is being filled. The system must
below horizontal.
be filled with all cylinders retracted and the boom at
rest.  Fill the reservoir to the full mark on the
CAUTION
reservoir sight gauge. After the reservoir is filled,
Locate the crane on a firm supporting
operate all circuits and recheck the reservoir sight
surface and position the boom in the
gauge. Add oil as required.
most stable position when extending the
boom at low angles.
REMOVING
AIR
FROM
THE
HYDRAULIC
SYSTEM.
On cranes with boom telescope cylinders attached
so the rod (ram) moves while the cylinder barrel
Due to the manner in which the hydraulic system is
remains stationary, cycling may not remove the air.
designed, air entering the hydraulic oil will normally
Lowering the boom to below horizontal and fully
be removed automatically by passage of the oil over
telescoping the boom in and out several times
the baffles in the hydraulic reservoir. However, if a
should remove entrapped air from the cylinders.
component has been replaced, the reservoir level is
too low, or a leak develops in the suction lines to the
However, if the air is not readily removed, lower the
pumps, air can enter the system. If air becomes
boom to below horizontal, extend the telescope
entrapped in the hydraulic oil, it may be detectable in
cylinders as far as practicable, and allow the boom to
pumps and motor-operated components such as the
remain in this position overnight. This should allow
swing mechanism and hoist(s), because it can cause
entrapped air to find its way to the holding valve
these units to become noisy during operation.
where telescoping the boom IN the next morning
Should noisy operation occur, first check the level of
should force the air back to the reservoir.
the hydraulic reservoir and replenish as necessary.
Then inspect for leaks in the suction lines leading to
While allowing the boom to remain in an extended
the pumps.
and lowered position overnight is helpful in removing
entrapped air from the hydraulic cylinder, ensure the
Minute leaks may be difficult to locate. Should you
boom is first telescoped IN (not OUT) in the morning.
encounter a leak that is not readily detectable, the
Telescoping OUT may cause air to be forced back
following method may be used when checking for
into a cylinder.
such leaks. Seal all normal openings in the hydraulic
system and the reservoir. Using a positive means to
control the pressure (i.e. a regulator), pressurize the
WARNING
hydraulic system to 2 to 4 psi (13.79 to 27.6 kPa)
and inspect all joints and fittings for evidence of
Extreme care must be used when
leaks. A soap solution applied to the fittings and
removing any plugs or restrictions from a
joints may also prove helpful in detecting minute
hydraulic system suspected to have
leaks while the system is pressurized. Remove the
entrapped air that may be pressurized.
pressure, repair any leaks found, and reopen any
openings (vents, etc.) closed for inspection. Refill
Entrapped air may be removed from cylinders having
the reservoir after completing any repairs or service.
wet rods by cycling. On certain cylinders, a plugged
Operate all hydraulic circuits several times in both
port is provided on the rod end to bleed-off
directions. This action should return any entrapped
entrapped air.
air to the reservoir where it can be removed from the
oil by the baffle system provided.
2-8-12

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