6
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SERVICE APPLICATION WITH LOSS OF AIR IN
PRIMARY CIRCUIT (FIGURE 9)
With the parking brakes released (dash valve button in) and
the absence of air in the primary circuit delivery, a service
brake application from the secondary circuit causes the
pressure in the spring brakes to be exhausted proportionally
to this application. This is known as spring brake modulation.
A 30 psi service brake application will exhaust the spring
brake pressure to approximately 60 psi.
SECONDARY RESERVOIR
CONSTANT PRESSURE
AIR EXHAUSTS FROM
SPRING BRAKES
FIGURE 9 - SERVICE APPLICATION LOSS OF PRIMARY CIRCUIT
INLET VALVE SEATED
CONTROL LINE PRESSURE
BALANCE PORT - LOSS OF
PRIMARY CIRCUIT PRESSURE
CONTROL PORT - SECONDARY
CIRCUIT PRESSURE
SECONDARY RESERVOIR
NO PRESSURE
CONTROL LINE PRESSURE
DELIVERY TO
SPRING BRAKES
CONTROL PORT - LOSS OF
SECONDARY CIRCUIT PRESSURE
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MAIN PISTON MOVES UP
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BALANCE PORT - PRIMARY
CIRCUIT PRESSURE
SERVICE APPLICATION WITH LOSS OF AIR IN
SECONDARY CIRCUIT (FIGURE 10)
With the parking brakes released (dash valve button in) and
the absence of air in the secondary circuit reservoir, the
external single check valve in the supply port seals to prevent
air leakage to atmosphere from the SR-7
™
valve. The dash
valve delivery air flows through the in-line single check valve
and becomes SR-7
™
valve supply air. This air is delivered to
maintain at least 107 psi (nominal) in the spring brake
chambers.
FIGURE 10 - SERVICE APPLICATION LOSS OF SECONDARY CIRCUIT
à
IN-LINE SINGLE
CHECK VALVE
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