SD-03-2205
Bendix® SC-3™ Single Check Valves

INLET

OUTLET

SPRING

INLET

OUTLET

ONE SC-3™ VALVE MODEL
FEATURES A
1/16” PIPE PLUG

STRAIGHT SINGLE
CHECK VALVE

FIGURE 1 - SC-3 SINGLE CHECK VALVES

DESCRIPTION

FIGURE 2 - STRAIGHT SC-3 SINGLE CHECK VALVE
(EXTERIOR/CROSS-SECTIONAL VIEWS)
INLET

The Bendix® SC-3™ single check valve is a device placed
in an air line to allow air flow in one direction only, and to
prevent the flow of air in the reverse direction.
The two types of SC-3 single check valves are:

SPRING
OUTLET

OUTLET

1. Straight (wafer-type) single check valve (See Figure 2).
2. Angled (shuttle-type) single check valve (See Figure 3).
An arrow indicating the direction of air flow is found on the
body of the valve.
SHUTTLE

OPERATION
Air flow in the normal direction moves the SC-3 single check
valve from its seat, and the flow is unobstructed. Air flow
in the reverse direction is prevented by the seating of the
shuttle - or wafer-type disc - which is caused by a drop in
upstream air pressure and assisted by the spring.

PREVENTIVE MAINTENANCE
IMPORTANT
Review the Bendix warranty policy before performing any
intrusive maintenance procedures. A warranty may be
voided if intrusive maintenance is performed during the
warranty period.

FIGURE 3 - ANGLED SC-3 SINGLE CHECK VALVE
(EXTERIOR/CROSS-SECTIONAL VIEWS)

No two vehicles operate under identical conditions; as
a result, maintenance intervals may vary. Experience is
a valuable guide in determining the best maintenance
interval for air brake system components. At a minimum,
the SC-3 single check valve should be inspected every six
(6) months or 1500 operating hours, whichever comes first,
for proper operation. Should the SC-3 single check valve
not meet the elements of the operational tests noted in this
document, further investigation and service of the valve
may be required. Replace any SC-3 single check valve(s)
that is leaking or showing signs of wear or deterioration.
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INSTALLATION

GENERAL SAFETY GUIDELINES

WARNING! PLEASE READ AND
FOLLOW THESE INSTRUCTIONS
TO AVOID PERSONAL INJURY OR DEATH:

When working on or around a vehicle, the following
guidelines should be observed AT ALL TIMES:
▲Park the vehicle on a level surface, apply the parking
brakes and always block the wheels. Always wear personal
protection equipment.
▲Stop the engine and remove the ignition key when working
under or around the vehicle. When working in the engine
compartment, the engine should be shut off and the ignition
key should be removed. Where circumstances require that
the engine be in operation, EXTREME CAUTION should be
used to prevent personal injury resulting from contact with
moving, rotating, leaking, heated or electrically-charged
components.
▲Do not attempt to install, remove, disassemble or
assemble a component until you have read, and thoroughly
understand, the recommended procedures. Use only the
proper tools and observe all precautions pertaining to use
of those tools.
▲If the work is being performed on the vehicle’s air brake
system, or any auxiliary pressurized air systems, make
certain to drain the air pressure from all reservoirs before
beginning ANY work on the vehicle. If the vehicle is
equipped with a Bendix® AD-IS® air dryer system, a Bendix®
DRM™ dryer reservoir module, a Bendix ® AD-9si ®, AD-HF®,
or AD-HF® i air dryer, be sure to drain the purge reservoir.
▲Following the vehicle manufacturer’s recommended
procedures, deactivate the electrical system in a manner
that safely removes all electrical power from the vehicle.
▲Never exceed manufacturer’s recommended pressures.
▲Never connect or disconnect a hose or line containing
pressure; it may whip and/or cause hazardous airborne
dust and dirt particles. Wear eye protection. Slowly open
connections with care, and verify that no pressure is
present. Never remove a component or plug unless you are
certain all system pressure has been depleted.
▲Use only genuine Bendix ® brand replacement parts,
components and kits. Replacement hardware, tubing, hose,
fittings, wiring, etc. must be of equivalent size, type and
strength as original equipment and be designed specifically
for such applications and systems.
▲Components with stripped threads or damaged parts should
be replaced rather than repaired. Do not attempt repairs
requiring machining or welding unless specifically stated
and approved by the vehicle and component manufacturer.
▲Prior to returning the vehicle to service, make certain all
components and systems are restored to their proper
operating condition.
▲For vehicles with Automatic Traction Control (ATC), the ATC
function must be disabled (ATC indicator lamp should be
ON) prior to performing any vehicle maintenance where
one or more wheels on a drive axle are lifted off the ground
and moving.
▲The power MUST be temporarily disconnected from the
radar sensor whenever any tests USING A DYNAMOMETER
are conducted on a vehicle equipped with a Bendix ®
Wingman ® system.
▲You should consult the vehicle manufacturer's operating
and service manuals, and any related literature, in
conjunction with the Guidelines above.

See Figure 4. The straight Bendix® SC-3™ single check
valve consists of a two-piece body. When installing the
straight single check valve, tighten using the hex surface
that is closest to the port that it is being installed in. This will
prevent breaking the seal between the two halves which
would cause leakage. Angled SC-3 single check valves
can be assembled finger tight and then further tightened to
the original orientation in no more than two full revolutions.

USE THIS SURFACE
FOR TIGHTENING

DO NOT USE THIS
SURFACE FOR
TIGHTENING

FIGURE 4 - STRAIGHT AND ANGLED SC-3 SINGLE
CHECK VALVES

OPERATION AND LEAKAGE CHECKS
NOTE: Depending on installation, it may be easier or
necessary to completely remove the single check valve
so the following checks may be made.
•

With air pressure present at the outlet side of the single
check valve and the inlet side open to atmosphere,
coat the open end of the single check valve with soap
suds; a 1-in. bubble in five (5) seconds is permissible
(100 SCCM).

•

If the single check valve does not function as described,
or leakage is excessive, it is recommended that it be
replaced with a new genuine Bendix® part available at
any authorized Bendix parts outlet.

REMOVAL
•

Block and hold the vehicle by means other than the
air brakes.

•

Completely drain all reservoirs.

•

Disconnect the air lines at the single check valve and
remove the single check valve.

DISASSEMBLY/ASSEMBLY
NOTE: There are no disassembly or assembly procedures
for SC-3 single check valves. They are non-serviceable
items. If a valve does not meet the operational and leakage
tests, it should be replaced at any authorized Bendix parts
outlet.

TESTING AND TROUBLESHOOTING
Perform the Operation and Leakage Checks noted above.

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SD-03-2205 ©2021 Bendix Commercial Vehicle Systems LLC, a member of Knorr-Bremse • 4/21 • All Rights Reserved