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TM 55-1905-221-14-4
6-36. TRANSMISSION OIL PUMP (Continued).
8. Pumps are built for right-hand and left-hand rotation depending on the engine model on which they are
used. The direction of rotation is marked on the pump body.
9. A bleed hole in the oil pump body and the cover leads from the oil seal cavity to the intake side of the
pump to avoid a pressure build-up back of the oil seals.
b. Operation.
1. The intake and discharge ports in the pump cover and passages in the pump body are separated by the
respective castings so that, when the pump is operating, the two ports are sealed, one from the other. As the inner rotor
revolves, a vacuum is formed on the intake side of the pump as the cavity between the lobes of the inner and outer rotor
increases; consequently, oil is drawn into the rotor compartment until this cavity reaches the lower end of the port.
2. Oil drawn into the cavities between the inner and outer rotors on the inlet side of the pump is forced out
under pressure at the outlet side of the pump.
3. A loss of hydraulic oil pressure is an indication of worn parts within the pump or malfunction of either the
flow control valve or the pressure relief valve. The recommended oil pressure for the hydraulic oil system is between 90
psi and 150 psi (620.5 kPa and 1034.2 kPa). If the pressure drops below 90 psi (620.5281 kPa) inspect the pump.


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