Pontiac FIREBIRD 1972 Service Manual page 1171

9-18 1972 PONTIAC SERVICE MANUAL
PUMP SHAFT THRUST PLATE
I
\
OPEN CAVITIES
ROTOR
C A M
R L
//
//
VANES
( 1
0)
CROSS OVER HOLES
t'
PRESSURE PLATE
Fig. 9-15 Power Steering Pump Components
end of the plunger screw is designed to keep dirt and
foreign material out of the ball check area. Due to selective
parts controlling calibration of this valve, the flow control
valve is only serviced as an assembly.
PUMP RING
CROSSOVER HOLE ( 2 )
I
UNDERVANE HOLE ( 1 0 )
I
DOWEL PIN HOLE ( 2 )
Fig. 9-16 Pump Ring, Rotor and Vanes
OPERATION
When the pump and power steering gear are completely
void of oil, adding oil to the reservoir will completely
envelope the pump housing assembly which is inside the
reservoir (Fig. 9-14). Oil is drawn into the intake portion
of the pump by suction (and weight of oil) causing it to
flow through a drilled passage in the lower portion of the
housing (4) to another drilled hole leading to a groove
around the rotor ring (3) to tend to fill this area and also
the two suction openings on the surface of the thrust plate
and two suction openings in the pressure plate. Oil fills the
lower opening in the thrust plate to feed the rising portion
of the rotor ring. Air is pumped out of the pump through
the gear oil circuit to the gear, then to return to the
reservoir and out the vented cap.
The mode of operation of the power steering pump is
based upon the demand of the power steering gear. The
various major modes of operation are: (1) Slow cornering,
(2) moderate to high speed straight ahead driving, and (3)
cornering against the wheel stop. The pump is designed to
recognize these conditions as required by the steering gear
rotary valve and compensates for them internally.
As the pump drive shaft turns the rotor, the vane tips
follow the inner cam surface of the pump ring, moving
outward and inward twice during each revolution. This
results in a complete pumping cycle every 180 degrees of
rotation (Fig. 9-16). Oil is moved in the spaces between the
vanes. As the vane tips move outward, oil is sucked into
the intervane spaces through four suction ports in the
pressure and thrust plates. The pressure of the oil is raised,
and the oil is discharged from the pump ring, as the vane