Page 85 - The Jet Engine

Lubrication

system. Scavenge pumps return the oil to the tank need for large pumps and difficulty in matching the
via the oil cooler. On entering the tank, the oil is de- required oil flow at slower speeds.
aerated ready for recirculation.
8. The full flow system achieves the desired oil flow
Full flow system rates throughout the complete engine speed range
7. Although the pressure relief valve system by dispensing with the pressure relief valve and
operates satisfactorily for engines which have a low allowing the pressure pump delivery pressure to
bearing chamber pressure, which does not unduly supply directly the oil feed jets. Fig. 8-2 shows an
example of this system which may be found on a
increase with engine speed, it becomes an turbo-fan engine. The pressure pump size is
undesirable system for engines which have high determined by the flow required at maximum engine
chamber pressures. For example, if a bearing speed. The use of this system allows smaller
chamber has a maximum pressure of 90 lb. per sq. pressure and scavenge pumps to be used since the
in. It would require a pressure relief valve setting of large volume of oil which is spilled by the pressure
130 lb. per sq. in. to produce a pressure drop of 40 relief valve system at maximum engine speed is
lb. per sq. in. at the oil feed jet. This results in the obviated.

Fig. 8-2 A full flow type oil system.

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