
ENGINE LUBRICATION 89
a tandem oil pressure and scavenge pump was employed
(Figure 4.21) and also that an oil cooler was included in
the scavenge return to the oil tank. Engine oil coolers
receive further mention later.
4.5 OIL PUMPS AND PRESSURE RELIEF VALVES
Developing oil pressure in the fully forced system
In modern practice, engine-driven positive displace- External gear pump
pressure developed by the oil pump depends entirely
upon the resistance offered to the flow of oil in the rest
of the lubrication circuit. The principal advantage of
using this type of pump is that it is compact in design.
Because it is not self-priming, the oil pum ...