TM 5-3810-306-20BLEEDING AIR FROM HYDRAULIC SYSTEMTOOLS: NoneSUPPLIES: NoneEQUIPMENT CONDITIONS: NoneGENERAL:By design, air entering the hydraulic oilwill normally be removed automaticallyby passage of the oil over the baffles inthe hydraulic reservoir. However, aircan enter the system if a component hasbeen replaced, the reservoir level is toolow, or a leak develops in the suctionlines to the pumps.If air becomes entrapped in the hydraulicoil, it may be detectable in pumps andmotor-operated components such as theswing mechanism and hoist(s) causingthese units to become noisy duringoperation. Should noisy operationoccur, first check oil level in hydraulicreservoir and fill as necessary. Theninspect for leaks in suction lines leadingto pumps.Small leaks may be difficult to locate.Should you encounter a leak that is notreadily detectable, the following methodmay be used when checking for suchleaks.1.PRESSURIZE HYDRAULIC SYSTEM.a. Seal all normal openings (vents, etc.) inhydraulic system and reservoir.b. Using a positive means to control pressure (i.e.,a regulator), pressurize hydraulic system to 2 to4 psi (13.79 to 27.6 kPa/0.1379 to 0.276 bar).NOTEA soap solution applied to the fittingsand joints may also prove helpful indetecting small leaks while thesystem is pressurized.c. Inspect all joints and fittings for evidence ofleaks.d. Remove pressure, repair any leaks found andreopen any openings (vents, etc.) closed forinspection.e. Refill reservoir after completing any repairs orservice.f.Operate all hydraulic circuits several times inboth directions. This action should return anyentrapped air to the reservoir where it can beremoved from oil by the baffle system provided.2.REMOVE ENTRAPPED AIR IN CYLINDERS.CAUTIONLocate crane on a firm supportingsurface and position boom in moststable position when extending boomat low angles.16-52
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