Figure 34-41. Vacuum-Over-Hydraulic Brake System - Released.
diaphragm to drop and close both the atmospheric and
making them inoperative and allowing the piston return
vacuum valves in the control valve. Thereafter, the
spring to move the pistons to the released position.
slightest foot pedal movement, either toward the
When the foot pedal movement stops at some
released or the applied position, will result in the opening
intermediate point between the released and fully applied
of either the vacuum or the atmospheric valve, and will
position, the pistons will move toward the lap position so
release partially or apply further the brakes.
that the fluid pressure under the relay-valve hydraulic
piston will be reduced the necessary amount to allow the