User Manual

4
OPERATION - NORMAL SERVICE APPLICATION
(FIGURE 4)
When a service application is made by actuating the dual
brake valve, air from the primary circuit is delivered to the
lower side of the control piston through the balance port,
and air from the secondary circuit is delivered to the top
of the control piston through the control port. Because air
pressure from the primary and secondary circuits are not
equal, there will be a slight movement of the control piston.
OPERATION - SERVICE APPLICATION WITH LOSS OF
AIR IN PRIMARY CIRCUIT (FIGURE 5)
A service application made with a loss of air in the primary
circuit would result in reduced air pressure delivered to
the lower area of the control piston. Air pressure from the
secondary circuit on top of the control piston would force
the piston down, opening the exhaust valve and allowing air
pressure in the spring cavity of the spring brake actuator to
release and the spring brake actuator to apply the brakes.
FIGURE 4 - NORMAL SERVICE APPLICATION
FIGURE 5 - SERVICE APPLICATION LOSS OF PRIMARY
CIRCUIT
FIGURE 6 - SERVICE APPLICATION LOSS OF SECONDARY
CIRCUIT
The pressure differential between the primary and
secondary circuits regulates the amount of air pressure
released from the spring cavity of the spring brake actuator.
This results in a total brake application on the rear axle
which is proportionate to the braking on the other axles.
OPERATION - SERVICE APPLICATION WITH LOSS OF
AIR IN SECONDARY CIRCUIT (FIGURE 6)
A service application made with a loss of air in the
secondary circuit would result in less, or no, air delivered to
the top of the control piston. However, the piston would not
move and braking on the rear axle(s) is assured because
the primary circuit supplies rear axle service brakes. The
spring brake actuators will not be actuated.