Bendix® DC-4® Double Check Valve
SD-03-2202
Frame MountIn-line Mount
SUPPLY
DELIVERY
O-RING
CAP
BODY
FIGURE 1 - BENDIX® DC-4® DOUBLE CHECK VALVE
SUPPLY
SHUTTLE
VALV E
SHUTTLE
GUIDE
MOUNTING
SUPPLY
HOLE
SUPPLY
DELIVERY
DESCRIPTION
The Bendix® DC-4® 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 ow for specic functions or to select the
higher pressure of either of two sources of air as a
supply source.
Bendix manufactures two double check valves; one is
mounted in the air line without being secured to the vehicle
frame, and the other 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.
OPERATION
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 ow 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 backow of air in the exhaust mode.
Figure 2 (see page 2) illustrates a typical double check
valve used to control a given device—such as trailer
brakes—from either of the two control sources.
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PREVENTIVE MAINTENANCE
Reservoir
Brake Valve
To Trailer
Brakes
Trailer Hand
Control Valve
FIGURE 2 - DOUBLE CHECK VALVE: CONTROL OF
SYSTEM FROM EITHER OF TWO CONTROL SOURCES
Bendix®
PP-7™ Valve
Bendix®
PP-1®
Valve
Trailer Supply
Spring Brake Control
Reservoir
Reservoir
FIGURE 3 - DOUBLE CHECK VALVE: SYSTEM WITH TWO
SUPPLY SOURCES
Double
Check
Valve
Double Check
Valve
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 differential
to which the valve is subjected may—under certain
conditions—be minimal. As a result, performance of the
double check valve will be optimized if it is mounted in the
horizontal position.
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-4® double check valve should be inspected
every 6 months or 1500 operating hours, whichever comes
rst, for proper operation. Should the DC-4 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” 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.
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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” 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 scufng
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-4® double check
valve, lubricate all o-rings and o-ring grooves with silicone
lubricant (Bendix piece number 291126 or equivalent).
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 lubricant (Bendix piece number 291126 or
equivalent). 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
Bendix
AD-9si™ 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. Never remove a component or
plug unless you are certain all system pressure has
been depleted.
▲ Use only genuine Bendix
components and kits. Replacement hardware, tubing,
hose, fi ttings, etc. must be of equivalent size, type
and strength as original equipment and be designed
specifi cally 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
specifi cally stated and approved by the vehicle and
component manufacturer.
▲ Prior to returning the vehicle to ser vice, 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 Bendix
Advanced
▲ You should consult the vehicle manufacturer's
operating and service manuals, and any related
literature, in conjunction with the Guidelines above.
®
DRM™ dryer reservoir module, or a Bendix
™
-equipped vehicle.
®
AD-IS® air dryer system, a
®
brand replacement parts,
®
Wingman®
®
.
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BW1582 © 2014 Bendix Commercial Vehicle Systems LLC, a member of the Knorr-Bremse Group • 8/2014 • All Rights Reserved.
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