2
valve fl ows out the service reservoir port and then opens
the spring brake reservoir check valve, allowing air to fi ll
the spring brake reservoir. As air is fi lling the spring brake
reservoir, it also fl ows by the open control inlet and out
the delivery ports of the SR-2
™
valve into the spring brake
emergency ports releasing the spring brakes.
PARK APPLICATION (Fig. 3)
To park the trailer, either the trailer supply valve or the
parking control valve, which are located in the cab, are
actuated and the trailer supply line is exhausted. When
the trailer supply line is exhausted, air pressure is removed
from the control and pressure protection pistons. With
air pressure removed the control piston is moved by the
return spring, control inlet valve closes and the exhaust
passage through the control piston opens. Opening the
exhaust allows air in the spring brake emergency section
to be exhausted out the exhaust port of the SR-2
™
valve.
Spring force above the pressure protection piston closes
the pressure protection valve while the service and spring
brake reservoir check valves close and protect against the
loss of pressure in either reservoir.
SERVICE APPLICATION WITH PARKING BRAKES
APPLIED OPTIONAL ANTI-COMPOUNDING PIPING
(Fig. 4)
With the optional anti-compounding feature of the SR-2
™
valve in use, the exhaust port of the SR-2
™
valve receives
normal service application pressure through a line
connecting it to the delivery of the trailer service system.
If a service brake application is made while the spring
brakes are applied, compounding of both applications
is prevented by service air pressure entering the SR-2
™
valve exhaust port, fl owing through the exhaust passage
of the control piston, past the open exhaust valve and out
the SR-2
™
valve delivery port to the emergency section of
the spring brakes.
NOTE: During normal vehicle operation, with the spring
brakes released, service air pressure will enter
the SR-2
™
valve as described, but will stop at the
closed exhaust valve. See Figure 2.
SERVICE
RESERVOIR
CHECK VALVE
FIGURE 2 -
SR-2
™
TRAILER SPRING BRAKE VALVE
CHARGING ABOVE 55 PSI
SPRING BRAKE
RESERVOIR
CHECK VALVE
SPRING
BRAKE
RESERVOIR
CONTROL INLET &
EXHAUST VALVE
SPRING BRAKE
SERVICE
RESERVOIR
TRAILER SUPPLY
LINE
TRAILER SERVICE
LINE
RELAY VALVE OR
MODULATOR
PRESS.
PROTECTION
VALVE
PRESS.
PROTECTION
INLET VALVE
CONTROL
PISTON
SERVICE
RESERVOIR
CHECK VALVE
FIGURE 3 -
SR-2
™
TRAILER SPRING BRAKE VALVE PARK
APPLICATION
SPRING BRAKE
RESERVOIR
CHECK VALVE
SPRING
BRAKE
RESERVOIR
CONTROL INLET &
EXHAUST VALVE
SPRING BRAKE
SERVICE
RESERVOIR
TRAILER SUPPLY
LINE
TRAILER SERVICE
LINE
RELAY VALVE OR
MODULATOR
PRESS.
PROTECTION
VALVE
PRESS.
PROTECTION
INLET VALVE
CONTROL
PISTON
SERVICE
RESERVOIR
CHECK VALVE
FIGURE 4 -
SR-2
™
TRAILER SPRING BRAKE VALVE
OPTIONAL ANTI-COMPOUNDING
SPRING BRAKE
RESERVOIR
CHECK VALVE
SPRING
BRAKE
RESERVOIR
CONTROL INLET &
EXHAUST VALVE
SPRING BRAKE
RELAY VALVE OR
MODULATOR
PRESS.
PROTECTION
VALVE
PRESS.
PROTECTION
INLET VALVE
CONTROL
PISTON
SERVICE
RESERVOIR
TRAILER SUPPLY
LINE
TRAILER SERVICE
LINE
