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42
BRAKES
Fig. 46
5.3 Balancing (Fig. 46) :
When the output force is conveyed through the
push rod to the master cylinder, the reaction
force from the master cylinder comes on the
rubber reaction disc and pushes it backwards.
This causes the valve body to traverse back
and the piston to contact the valve rubber cup,
thereby closing the air valve (Y) and vacuum
valve (X). In this condition both the vacuum
and atmospheric valves are closed. As a result,
there is a fixed pressure differential between
chambers 2 & 4 and chambers 1 & 3, so the
level of power assist and braking force remains
constant. The vacuum brake valve always
seeks balancing position whenever the brake
pedal force is constant.