Pontiac FIREBIRD 1972 Service Manual page 297

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REAR SUSPENSION
AIR BY-PASS
T O RESERVOIR
Fig. 4 - 1 0 Pressure Regulator Valve
The intake and compression strokes are controlled by a
sliding distributor valve that is actuated through an arm
that is tripped by the piston as it nears the end of each
stroke. Each time the arm actuates the distributor valve,
a different set of holes are covered in the first stage hous-
ing. The distributor valve controls the flow of intake mani-
fold vacuum and air sides of the compressor diaphragm.
(Fig. 4-1 1 and 4- 12).
As the compressor cycles, the reservoir air pressure gradu-
ally increases causing a back pressure on the second stage
piston until it equals the push of pressure against the
diaphragm. At this point, a balanced condition is reached
and the unit stops operating. After reservoir pressure
drops due to system air usage, the compressor again begins
to cycle and replenish the reservoir.
Fig. 4 - 1
2
First Stage compression Stroke
Pressure balance will depend upon the prevailing manifold
vacuum and atmospheric pressure. Both are affected by
altitude above or below sea level. Balance pressure will
vary from approximately 150 to 275 psi.
The pressure regulator valve is preset and limits the reser-
voir outlet pressure to approximately 125 psi to avoid
damage to the height control valve and Superlift shocks
(Fig. 4-10).
HEIGHT CONTROL VALVE
The height control valve, which is mounted on the frame,
senses rear car height through a link attached to the right
rear upper control arm. When load is added to the car, the
over-travel lever is forced up causing an internal lever to
open the intake valve (Fig. 4-1
3).
When this valve is open,
Fig. 4-1 1 First Stage Intake Stroke Fig. 4 - 1 3 Load Added to Car