4
CHARGING SPRING BRAKE ACTUATORS
BELOW 107 PSI (FIGURE 5)
With the air brake system charged and the parking brakes
released (by pushing the dash valve button in), air enters
the park control port. This opens the SR-7 to supply air
pressure to the spring brake chambers. As illustrated, air
pressure in the chambers is below 107 psi (nominally).
CHARGING SPRING BRAKE ACTUATORS ABOVE
107 PSI (FIGURE 6)
Once the SR-7 valve delivery pressure reaches 107 psi
(nominal), the inlet and exhaust are closed (valve lap
position). This maintains the spring brake hold-off pressure
at 107 psi (nominal).
BALANCE PORT
SECONDARY RESERVOIR
CONSTANT PRESSURE
FIGURE 5 - CHARGING LESS THAN 107 PSI
à
CONTROL LINE PRESSURE
DELIVERY TO SPRING BRAKES
INLET / EXHAUST VALVE OPEN
à
à
à
à
à
à
à
à
à
à
CONTROL PORT
FIGURE 6 - CHARGING GREATER THAN 107 PSI
INLET / EXHAUST VALVE SEATED
CONTROL LINE PRESSURE
DELIVERY TO SPRING BRAKES
BALANCE PORT
CONTROL PORT
SECONDARY RESERVOIR
CONSTANT PRESSURE
à
à
à
à
à
àà
à
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