TM 5-3810-306-20
BLEEDING AIR FROM HYDRAULIC SYSTEM
TOOLS:
None
SUPPLIES:
None
EQUIPMENT CONDITIONS: None
GENERAL:
By design, air entering the hydraulic oil
will normally be removed automatically
by passage of the oil over the baffles in
the hydraulic reservoir. However, air
can enter the system if a component has
been replaced, the reservoir level is too
low, or a leak develops in the suction
lines to the pumps.
If air becomes entrapped in the hydraulic
oil, it may be detectable in pumps and
motor-operated components such as the
swing mechanism and hoist(s) causing
these units to become noisy during
operation. Should noisy operation
occur, first check oil level in hydraulic
reservoir and fill as necessary. Then
inspect for leaks in suction lines leading
to pumps.
Small leaks may be difficult to locate.
Should you encounter a leak that is not
readily detectable, the following method
may be used when checking for such
leaks.
1.
PRESSURIZE HYDRAULIC SYSTEM.
a. Seal all normal openings (vents, etc.) in
hydraulic system and reservoir.
b. Using a positive means to control pressure (i.e.,
a regulator), pressurize hydraulic system to 2 to
4 psi (13.79 to 27.6 kPa/0.1379 to 0.276 bar).
NOTE
A soap solution applied to the fittings
and joints may also prove helpful in
detecting
small
leaks
while
the
system is pressurized.
c. Inspect all joints and fittings for evidence of
leaks.
d. Remove pressure, repair any leaks found and
reopen any openings (vents, etc.) closed for
inspection.
e. Refill reservoir after completing any repairs or
service.
f.
Operate all hydraulic circuits several times in
both directions. This action should return any
entrapped air to the reservoir where it can be
removed from oil by the baffle system provided.
2.
REMOVE ENTRAPPED AIR IN CYLINDERS.
CAUTION
Locate crane on a firm supporting
surface and position boom in most
stable position when extending boom
at low angles.
16-52
