Oil Pressure Gauge
by the pump's drive shaft, which, in turn, actuates the
other gear mounted on a stub shaft. The two gears are
The oil pressure gauge is mounted on the
in mesh and rotate in opposite directions. Oil is picked
instrument panel of the vehicle. Marked off on a dial in
up in the spaces between the gear teeth and the
psi, the gauge indicates how regularly and evenly the
housing. This oil is then carried around to the pump
oil is being delivered to all vital parts of the engine, and
outlet where it is discharged. Pressure is developed
because of restrictions in the system caused by closely
warns of any stoppages in this delivery. Pressure
mated parts in the engine and pump. The gear pump
gauges may be mechanical or electrical. In the
may be driven directly from the camshaft or indirectly
mechanical type, the gauge on the instrument panel is
by the distributor.
connected to an oil line tapped into the main oil supply
passage leading from the pump. The pressure of the oil
ROTARY PUMP.--The rotary pump (fig. 5-13)
in the system acts on a diaphragm within the gauge,
has an inner rotor with lobes that match similar shaped
causing a needle to register on a dial. In the electrical
depressions in the outer rotor. The inner rotor is off
type, the oil pressure operates a device on the engine
center from the outer rotor. As the inner rotor turns, it
that signals electrically to the pressure gauge, which
turns the outer rotor with it. As the two rotors turn, the
indicates the oil pressure.
openings between them are filled with oil. This oil is
forced out from between the rotors as the inner rotor
Some of the vehicles brought into the shop will not
lobes enter the opening in the outer rotor. As you can
be equipped with an oil pressure gauge, but will have
see in figure 5-13, the inner rotor lobes have very little
electrically operated warning lights on the instrument
clearance as they approach the discharge. This allows
panel, which flash on and remain lighted to indicate
the oil to be pressurized prior to discharge.
low oil pressures.
As a safety factor to assure sufficient oil delivery
Oil Strainers
under extreme operating conditions, the oil pump is
designed to supply a greater amount of oil than is
Most engines use at least one oil strainer or screen
normally needed for adequate lubrication. This
in the lubrication system. The strainer must have a
requires that an oil pressure relief valve, usually
mesh suitable for straining out undesirable particles
incorporated in the pump, as shown in figures 5-12 and
from the oil and yet pass a sufficient quantity of oil to
5-13, be used in the system to prevent excessive oil
the inlet side of the pump. The strainer is located so
pressure, especially at high speeds or when the oil is
that all oil entering the pump from the oil pan must flow
cold. The relief valve has a spring-loaded ball or
through it. Some screen assemblies also incorporate a
plunger that is forced off its seat when the desired
safety valve, which opens in the event the screen
pressure, which ranges from 30 to 50 psi, is reached,
becomes clogged, thus bypassing oil to the pump.
allowing the excess oil to be delivered to the inlet side
Strainer assemblies may be either the floating or the
of the pump or to return to the crankcase through a
fixed type.
drilled passage.
DRIVEN ROTOR
DRIVING ROTOR
OIL PUMP
PRESSURE
RELIEF
VALVE
ASf05013
INTAKE
Figure 5-13.--Rotary oil pump.
5-17
