1
SD-03-4510
DESCRIPTION
In a trailer air brake system, the SR-2
™
spring brake
valve controls the functioning of the spring brakes during
parking and emergency applications. It is responsible for
automatically applying the spring brakes and preventing
trailer air pressure loss in the event of breakaway or supply
line failure. The SR-2
™
valve also prevents the automatic
application of the trailer spring brakes after the loss of trailer
service reservoir pressure while allowing failure indication
to occur in the tractor.
The SR-2
™
valve is provided with one 3/4” male pipe thread
connection for mounting the valve to the trailer brake
reservoir. Other porting includes:
One - 1/4” pipe thread supply port
Four - 3/8” pipe thread delivery ports
Two - 1/4” pipe thread service reservoir ports
One - 3/8” pipe thread exhaust port
OPERATION
CHARGING (Figure 2)
Air from the trailer supply line enters the SR-2
™
valve
trailer supply port and moves the control piston into contact
with the control inlet and exhaust valve, sealing off the
exhaust passage through the control piston, and opening
the inlet. Air entering the supply port is also conducted
to the underside of the pressure protection piston. When
air pressure builds to approximately 55 psi beneath the
pressure protection piston, the piston moves against the
force of the piston spring and the pressure protection inlet
valve opens and remains open. Air fl owing past the open
pressure protection valve opens the service reservoir check
valve. Air passing through the service reservoir check
Bendix
®
SR-2
™
Trailer Spring Brake Valve
RETAINER
DIAPHRAGM (11)
(19) SCREW
(20) WASHER
BODY
PARTIAL VIEW OF EXHAUST
FOR PC. NO. 287376
EXTERIOR
SECTIONAL
CHECK VALVES (10)
(SHOWN OUT OF
POSITION)
SCREW (16)
CHECK VALVE (10)
RETAINER (17)
SPRING (9)
PISTON (8)
O-RING (2)
COVER (12)
CAP SCREW (13)
O-RINGS (1)
CONTROL
PISTON (14)
SEAL RING (4)
EXHAUST PORT
SPRING (3)
VENT
INLET/EXHAUST
VALVE (5)
INLET VALVE
SPRING (6)
O-RING (7)
RES.
FTG.
(15)
FIGURE 1
