SD-26-1852
Bendix® DC-4000™ Double Check Valve
In-line Mount

Frame Mount
DELIVERY

DELIVERY

SUPPLY

SUPPLY

SUPPLY

SUPPLY

SHUTTLE
MOUNTING
HOLE
O-RING

CAP
BODY

Shuttle valve symbol per
ISO 1219, Fluid Power
Systems and Components.

SHUTTLE
GUIDE

FIGURE 1 - BENDIX® DC-4000™ DOUBLE CHECK VALVE

DESCRIPTION

OPERATION

The Bendix DC-4000 double check valve is used
in an air brake system to direct a flow of air into a
common line from either of two sources, whichever is
at the higher pressure. The valves may be used for
directing air flow for specific functions or to select the
higher pressure of either of two sources of air as a
supply source.
®

™

Bendix manufactures multiple types of double check valves;
one type is mounted in the air line without being secured to
the vehicle frame, and another type contains a mounting
tab to secure it to the vehicle frame or chassis. Although
the valves are somewhat different physically, the same
function is performed by each type.

The DC-4000 is a flow and pressure-sensitive valve.
As air under pressure enters either end of the double
check valve (inlet port), the moving shuttle responds to the
pressure and seals the opposite port — assuming it is at
a lower pressure level than the other.
The air flow continues out the delivery port of the double
check valve. The position of the shuttle will reverse if the
pressure levels are reversed. Double check valves are
designed so that the shuttle can never impede the backflow
of air in the exhaust mode.

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Figure 2 illustrates a vertical configuration where the
double check valve is used to control a given device — such
as trailer brakes — from either of the two control sources.
The shuttle is bias by gravity, meaning when both supply
ports are unpressurized, the top (or higher) port will be
open to delivery.
Reservoir
Brake Valve

To Trailer
Brakes
Trailer Hand
Control Valve

Double
Check
Valve

FIGURE 2 - DOUBLE CHECK VALVE: CONTROL OF
SYSTEM FROM EITHER OF TWO CONTROL SOURCES

Figure 3 illustrates a typical double check valve used to
supply air to a system (or systems) from either of two
separate sources — whichever is at the greater pressure
level. In this type of installation, the pressure and flow
differential to which the valve is subjected may — under
certain conditions — be minimal. As a result, performance
of the double check valve may be optimized if it is mounted
in the horizontal position.

Bendix®
PP-7™ Valve
Bendix®
PP-1®
Valve

Trailer Supply
Spring Brake Control

Reservoir

Double Check
Valve

Reservoir

FIGURE 3 - DOUBLE CHECK VALVE: SYSTEM WITH TWO
SUPPLY SOURCES

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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.
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
Bendix® DC-4000™ double check valve should be inspected
every 6 months or 1500 operating hours, whichever comes
first, for proper operation. Should the DC-4000 valve not
meet the elements of the operational tests noted in this
document, further investigation and service of the valve
may be required.

SERVICE CHECKS
OPERATING AND LEAKAGE TEST
A. When the double check valve is used in conjunction
with a trailer control valve, the following operating and
leakage test can be made:
1. Apply and release the foot brake valve and note that
the brakes apply and release on both the tractor
and the trailer.
2. Apply and release the trailer control valve and note
that only the trailer brakes apply and release. With
the trailer control valve applied, check the exhaust
port of the foot brake valve for leakage with a soap
solution. Permissible leakage is a 1 inch bubble in
5 seconds (100 sccm).
3. Apply and hold a full foot brake valve application.
Check the exhaust port of the trailer control valve
for leakage with a soap solution. Permissible
leakage is a 1 inch bubble in 5 seconds (100 sccm).
NOTE: On some vehicles, an exhaust line is
connected to the exhaust port and piped outside the
cab. In this case it may be necessary to disconnect
this line to complete the leakage check.
B. When checking the double check valve — either bench
tested or tested on the vehicle — two separately
controlled air supplies must be connected to the inlet
ports.
1. Install an accurate test gauge in the outlet port or
in a line from the outlet port.
2. Apply and release air pressure to one inlet port and
note that the gauge registers an application and
release.
3. Repeat by applying and releasing air to the other
inlet port.

4. A leakage check should be performed at the inlet
ports of the valve in the following manner:
a. Disconnect the air line from one inlet port.
b. Apply air to the other inlet port and coat
the opposite inlet port with a soap solution.
Permissible leakage is a 1 inch bubble in
5 seconds (100 sccm).
c. Repeat Step “b” applying air to the other inlet
port while checking the opposite inlet port for
leakage.
If the double check valve does not function as described,
or if leakage is excessive, the valve should be repaired
or replaced with genuine Bendix® parts. The following
instructions should prove helpful:

DISASSEMBLY
1. Remove the end cap(s) from the valve.
2. Remove the grommets (if applicable).
3. Remove the shuttle and/or shuttle guide.

CLEANING AND INSPECTION
1. Clean all metal parts in mineral spirits and dry them
completely.
2. Inspect all parts for excessive wear or deterioration.
Inspect valve seats for nicks or burrs.
3. Inspect the bores of the valve housing for deep scuffing
or gouges.
Replace all parts that were discarded, and any parts not
found to be serviceable during inspection, using only
genuine Bendix replacement parts.

ASSEMBLY
Before assembling the Bendix® DC-4000™ double check
valve, lightly lubricate all o-rings and o-ring grooves with
silicone lubricant (291126N).
NOTE: When using pipe thread sealant during
assembly and installation, take particular care to
prevent the sealant from entering the valve itself.
Apply the sealant beginning with the second thread
back from the end.
1. Install the shuttle and shuttle guide.
2. Coat all static seals such as o-rings, grommets, etc. with
silicone lightly lubricant (291126N). It is not necessary
to lubricate the shuttle.
3. Install the grommets.
4. Install the end cap(s).
TESTING OF REBUILT DOUBLE CHECK VALVE
Perform operating and leakage tests as described in
“Service Checks” section.

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-HFi ® 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.

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Unless otherwise indicated, the trademarks used in this document, including Bendix, are United States
trademarks owned by, or licensed to, Bendix Commercial Vehicle Systems LLC.

SD-26-1852 Rev 001 © 5/2026 Bendix Commercial Vehicle Systems LLC, a member of Knorr-Bremse • All Rights Reserved.

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