Bendix Commercial Vehicle Systems SR-7 SPRING BRK MOD VLV 1/11 - Manual (Page 6)

6
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
MAIN PISTON MOVES UP
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 Bendix
® SR-7 ®
valve. The dash valve delivery air fl ows 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
IN-LINE SINGLE
CHECK VALVE