Page 86 - The Jet Engine

Lubrication

9. To prevent high oil pressures from damaging the total loss oil system is generally used. The
filters or coolers, pressure limiting valves are fitted to system is simple and incurs low weight penalties
by-pass these units. These valves normally only because it requires no oil cooler, scavenge pump or
operate under cold starting conditions or in the event filters. On some engines oil is delivered in a
of a blockage. Advance warning of a blocked filter continuous flow to the bearings by a plunger-type
may be indicated in the cockpit by a differential pump, indirectly driven from the compressor shaft; on
pressure switch which senses an increase in the others it is delivered by a piston-type pump operated
pressure difference between the inlet and outlet of
the filter. by fuel pressure (fig. 8-3). In the latter, the oil supply
is automatically selected by the high pressure fuel
Total loss (expendable) system shut-off valve (cock) during engine starting and is
10. For engines which run for periods of short delivered as a single shot to the front and rear
duration, such as booster and vertical lift engines, bearings. On some engines provision is made for a

Fig. 8-3 A total loss (expendable) oil system.

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