Troubleshooting guide

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Trailer Spring Brake Valves
Trailer spring brake valves are designed for use in trailer
air brake systems.
The Bendix
®
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: The valve
(superseded by the Bendix
®
SR-5
™
valve)is available for
service only, due to changes made in FMVSS 121. 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. They
incorporate an anti-compound feature in the valve design.
With later government regulations allowing simplifi ed
system plumbing, Bendix developed the Bendix
®
SR-5
™
trailer spring brake valve. It also mounts to a reservoir
on the trailer and, like the Bendix SR-2 & SR-4 trailer
spring brake valves, it controls the trailer spring brakes.
Unlike these valves, however, the Benidx 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 one reservoir
for service volume on single axle trailers. Two reservoirs
are generally required for service volume requirements
on tandem axle trailers. An integral anti-compound
feature is part of the SR-5 trailer spring brake valve. The
SR-5 model is a “spring brake priority” trailer valve.
Parking and Emergency Systems: Trailer Spring Brake Valves
Note: The Bendix SR-5 trailer
spring brake valve looks very
similar to the original design of
the Bendix SR-2 valve. Look for
a hole drilled into the fl at surface
between the pressure protection
valve and the body for positive
Bendix SR-5 trailer spring brake
valve identifi cation.
ABS Controller/
Relay Assembly
Bendix
®
SR-5
™
Trailer Spring Brake
Valve
Typical Bendix
®
SR-5
™
Trailer
Spring Brake
Valve Tandem
Axle Trailer Air
System
Service
Reservoir
Service
Reservoir
Some System Designs use a Single Two-Compartment Reservoir
Bendix
®
SR-5
™
Spring Brake Valve
Look for drilled
hole
Bendix
®
SR-2
™
Spring Brake
Valve
Bendix
®
SR-4
™
Spring
Brake Valve
(Revised Design)
(Original Design)
Bendix
®
SRC-7000
™
Spring Brake Valve
(See next page)