Oil pump (internal
The oil pump in an closed combustion engine is usually a gear pump
driven by the auto parts
such as camshaft or crankshaft. Oil pressure varies quite a bit during
operation, with lower temperature and higher RPM's increasing pressure
to a maximum of about 4 bar.
To ensure that the oil pressure does not
exceed the rated maximum, a spring-loaded pressure relief valve routes
oil back to its source once pressure exceeds a preset limit.
The oil pump usually sucks the oil out of the engine's oil pan through a
wire mesh strainer and pumps the oil through an oil filter before it
goes to the bearings.