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Fig. 10PG-Oil Cooler and Lubrication Circuit
Fig. 12PG-Modulator and Booster Valve Circuits
against spring pressure until the third spool of the valve un
covers a port leading to exhaust (oil pump suction).
Any drop in mainline pressure, such as this exhaust, per
mits spring force to overcome the decreased hydraulic pressure
and return the valve to the left. This closes the exhaust passage
and allows mainline pressure to increase. The continual open
ing and closing of the exhaust port, which occurs rapidly,
regulates mainline pressure at the desired level (Fig. I IPG).
The regulated mainline pressure is then delivered to the
throttle valve, the detent valve, the vacuum modulator valve,
and the manual valve. These valves then regulate or direct the
mainline pressure to perform the various operational
functions.
Vacuum Modulator and Booster Valve Circuit
The vacuum modulator changes or modulates mainline
pressure to meet the needs of changing engine loads. This
modulation is controlled by hydraulic pressure, spring pres
sure, and engine vacuum. High manifold vacuum, such as that
created at idle, causes low modulator pressure and results in
lower mainline pressure. During periods of low engine vacuum,
such as occurs on acceleration, high modulator pressure is
produced, resulting in the higher mainline pressure needed to
control the increased planetary torque.
In all ranges, mainline pressure is supplied to the area
between spools 1 and 2 of the modulator valve (Fig. 12PG).
The spring in the sealed vacuum unit tends to keep the valve
bottomed in its bore. In this position, oil is delivered through a
drilled passage in the valve to the blind cavity at the left end of
the valve. Oil pressure in this area tends to oppose spring pres
sure and tries to move the modulator valve to the right. At this
same time, mainline pressure flows from the area between
spools 1 and 2 of the modulator valve into the booster valve
passage. Mainline pressure is directed to the right end of the
booster valve and applies force to the left on the small spool
rear face. This hydraulic force combined with the normal
spring force on the pressure regulator valve, results in a higher
mainline pressure.
Higher vacuum moves the modulator valve further to the
right which shuts off the source of mainline pressure to the
Fig. 11PG-Mainline Circuits and Pressure Regulation
Fig. 13PG-Manual Valve Linkage - Valve Body Removed
