Troubleshooting guide

31
www.bendix.com 1-800-AIR-BRAKE (1-800-247-2725)
Trailer Spring Brake Valves
Trailer spring brake valves are designed for use in trailer
air brake systems.
The SR-4
™
trailer spring brake valve was an earlier
design that used a dedicated spring brake reservoir for
release of the trailer spring brakes. Note: This valve is
available for service only, due to changes made in
FMVSS 121 (superceded by SR-5
™
). All other Bendix
spring brake valves use service reservoir air for trailer
spring brake release.
Mounted on one of the trailer reservoirs, these valves
control both the parking and emergency brake functions
of the spring brakes and use internal pressure
protection and check valves to isolate reservoir failures
to prevent automatic application of the trailer spring
brakes. An anti-compound feature is part of these
valves.
With later government regulations allowing simplified
system plumbing, Bendix developed the SR-5
™
trailer
spring brake valve. It also mounts to a reservoir on
the trailer and, like the SR-2
™
& SR-4
™
trailer spring
brake valves, it controls the trailer spring brakes, but
unlike these valves, the SR-5
™
trailer spring brake valve
uses supply line pressure to release the trailer spring
brakes. Because dedicated or isolated reservoir
pressure is no longer required by law for spring brake
release, the SR-5
™
trailer spring brake valve system
needs only a one reservoir for service volume on single
axle trailers. Two reservoirs are generally required
for service volume requirements on tandem axle
Typical SR-2
™
Trailer Spring
Brake Valve
Tandem Axle
Trailer Air
System
SR-4
™
Spring
Brake Valve
(Original Design)
SR-4
™
Spring
Brake Valve
(Revised Design)
SR-2
™
Spring
Brake Valve
SR-5
™
Spring Brake Valve
Look for
drilled hole
ABS
Controller/
Relay
Assembly
Spring Brake
Reservoir
SR-2
™
Spring
Brake Valve
trailers. An integral anti-compound feature is part of
the SR-5
™
trailer spring brake valve. The SR-5
™
is a
"spring brake priority" trailer valve.
Trailer Spring Brake Valves
Service
Reservoir
Service
Reservoir
Note: The SR-5
™
trailer spring brake
valve looks very similar to the
original design of the SR-2
™
valve.
Look for a hole drilled into the flat
surface between the pressure
protection valve and the body for
positive SR-5
™
trailer spring brake
valve identification.