BENDIX R-12DC DBL CHECK RELAY VALVE User manual

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Bendix®R-12DC™Relay Valve with Biased Double Check
DESCRIPTION
The relay valve in an air brake system functions as a relay
station to speed up the application and release of the
brakes. The valve is normally mounted at the rear of the
vehicle in proximity to the chambers it serves. The valve
operates as a remote controlled brake valve that delivers
FIGURE 1 - EXTERIOR VIEWS
EXTERIOR R-12DC™VALVE
(MODEL WITH 2 HORIZONTAL PORTS)
PRIMARY
SERVICE
DELIVERY
SUPPLY (2)
SD-03-1068
SECONDARY
SERVICE EXTERIOR
R-12DC™VALVE
(MODEL WITH
4 VERTICAL
DELIVERY PORTS)
EXTERIOR
R-12DC™VALVE
(MODEL WITH 2
HORIZONTAL AND 2
VERTICAL DELIVERY
PORTS)
PRIMARY
SERVICE
PORT
FIGURE 2 - R-12DC™RELAY VALVE WITH BIASED DOUBLE CHECK SECTIONAL VIEW
RELAY
PISTON
VALVE
RETAINER
EXHAUST
SEAT
RETAINING
RING EXHAUST
PORT
SECONDARY
SERVICE PORT
DOUBLE CHECK
DIAPHRAGM
GUIDE
SPRING
CAP SCREW
SEALING
RING
COVER
RELAY
PISTON
O-RING
SPRING
O-RINGS
INLET
EXHAUST
VALVE
or releases air to the chambers in response to the control
air delivered to it from the foot brake valve.
TheR-12DC™relayvalvesaredesignedforeitherreservoir
or frame mounting. (See Figure 1). For ease of servicing,
theinlet/exhaustvalvecanbereplacedwithouttheneedfor
lineremoval.

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OPERATION
APPLICATION
Under normal conditions, the internal biased double check
valve assures that the primary service signal controls the
valve. Air pressure delivered to the primary service port
enters the small cavity above the piston and moves the
pistondown. The exhaust seat moves down withthepiston
andseatsonthe innerorexhaust portionofthe inlet/exhaust
valve, sealing off the exhaust passage. At the same time,
the outer or inlet portion of the inlet/exhaust valve moves
off its seat, permitting supply air to flow from the reservoir,
past the open inlet valve and into the service brake
chambers. In the event of a loss of the primary service
line, (see Figure 4) the double check valve mechanism in
the cover of the R-12DC™valve will move, shutting off the
primaryserviceline,andinsteadallowthesecondaryservice
line to apply the air pressure needed to operate the valve.
Note: Secondary service line may leak out of the primary
service at control pressures up to 20 psi when the primary
signal is not present.
BALANCE
The air pressure being delivered by the open inlet valve
also is effective on the bottom area of the relay piston.
BRAKES
APPLIED
FIGURE 4 - R-12DC™APPLIED POSITION (SHOWING BIASED DOUBLE CHECK OPERATIONAL VIEWS)
SECONDARY
CONTROL LINE
SUPPLIES RELAY
PISTON
CONTROL LINE
FAILURE
NORMAL: BIASED
DOUBLE-CHECK VALVE
ALLOWS PRIMARY
CONTROL LINE SUPPLIES
RELAY PISTON
BRAKE PEDAL
APPLIED
BRAKE PEDAL
APPLIED
BRAKE PEDAL
APPLIED
R-12DC™
VALVE
ANTILOCK SENSOR
TONE RING
ANTILOCK
MODULATOR
BRAKE VALVE
(DELIVERY
LINES ARE
SHOWN)
RESERVOIR
BRAKE
CHAMBERS
FIGURE 3 - R-12DC™SECTIONAL VIEW WITH TYPICAL
SYSTEM COMPONENTS
RELAY PISTON
EXHAUST
PORT
INLET
EXHAUST
VALVE

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BRAKE
CHAMBERS
MAINTAIN
APPLICATION
FIGURE 5 - R-12DC™BALANCE POSITION
AIR PRESSURE
ABOVE RELAY
VALVE IS
EXHAUSTED
HERE
BRAKE
CHAMBERS
RELEASED
FIGURE 6 - R-12DC™EXHAUST POSITION
Whenair pressure beneath thepistonequalstheservice air
pressure above, the piston lifts slightly and the inlet spring
returns the inlet valve to its seat. The exhaust remains
closed as the service line pressure balances the delivery
pressure. As delivered air pressure is changed, the valve
reactsinstantlytothechange,holdingthe brake application
at that level.
EXHAUST OR RELEASE
When air pressure is released from the service port and air
pressure in the cavity above the relay piston is exhausted
through the brake valve. At the same time, air pressure
beneath the piston lifts the relay piston and the exhaust
seat moves away from the exhaust valve, opening the
exhaust passage. With the exhaust passage open, the air
pressurein thebrakechambers isthenpermittedto exhaust
through the exhaust port, releasing the brakes.
PREVENTIVE MAINTENANCE
Important: Review the Bendix Warranty Policy before
performinganyintrusivemaintenanceprocedures.Awarranty
maybevoided if intrusive maintenance is performed during
thewarrantyperiod.
No two vehicles operate under identical conditions, as a
result, maintenance intervals may vary. Experience is a
valuableguide in determiningthebestmaintenance interval
for air brake system components.At a minimum, the valve
shouldbeinspectedevery6monthsor1500operatinghours,
whichevercomesfirst,forproperoperation.Shouldthevalve
not meet the elements of the operational tests noted in this
document,further investigationandservice ofthevalve may
berequired.
REMOVAL AND INSTALLATION
REMOVAL
1. Block and hold vehicle by means other than air brakes.
2. Drain air brake system reservoirs.
3. Ifentirevalveistoberemoved,identifyairlinestofacilitate
installation. Prior to disassembly, remove as much
contaminationas possiblefromthe exteriorofthe device
taking care to keep all contamination from entering the
openports.
4. Disconnectairlinesfromvalve*.
5. Remove valve from reservoir or if remotely mounted,
remove mounting bolts and then valve.
*Itisgenerallynotnecessarytoremoveentirevalvetoservice
theinlet/exhaust valve.Theinlet/exhaust valveinsertcan be
removedbyremoving thesnapring,exhaustcoverassembly
andtheninlet/exhaust valve.
AIR PRESSURE
FROM BRAKE
CHAMBERS IS
EXHAUSTED
HERE
BRAKE PEDAL
POSITION
HELD
BRAKE
PEDAL
RELEASED

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*Crack Pressure is the amount of control
pressure required by the valve to initiate
air delivery. For Crack pressures other
than 4 psi, a differential spring is used in
the assembly to produce the required
valve response.
(Models designed to have a 4 psi crack
pressure do not require a differential spring.)
Key No. DESCRIPTION
1 VALVE COVER
2 VALVE SPRING
3 CHECK VALVE GUIDE
4 CHECK VALVE
5 O-RING
6 DOUBLE CHECK COVER
7 O-RING
8 O-RING
9 RELAY PISTON
10 VALVE BODY
11 INLET & EXHAUST VALVE
12 VALVE RETAINER
13 SPRING
14 O-RING
15 O-RING
16 EXHAUST COVER
17 RETAINING RING
18 DIFFERENTIAL SPRING (IF USED)
PRIMARY CONTROL
PORT 1/4 NPT
SECONDARY
CONTROL PORT
1/4 NPT
16
CAP SCREW
2
1
10
11
CAP
SCREW
3
45
6
7
9
8
DIFFERENTIAL SPRING
(CONTROLS CRACK PRESSURE*)
(NOT REQUIRED FOR MOST
MODELS.
SEE BELOW.)
17
15
14
13
12
VERTICAL
DELIVERY
PORTS
SUPPLY
PORT
HORIZONTAL
DELIVERY
PORTS
DIFFERENTIAL SPRINGS
FIGURE 7 - R-12DC™EXPLODED VIEW
1. Remove the four cap screws securing the mounting
bracket and cover to the body. Retain the cap screws
for reuse.
2. Discard the mounting bracket.
3. Removeanddiscardsealingring(7) from the cover (1).
a. Removethe2torxscrewssecuringthe doublecheck
cover(6)tothecover(1).
b. Remove the double check cover (6) from cover (1)
andremove anddiscardspring (2),guide(3),double
checkdiaphragm(4),and o-ring (5).
4. Removeanddiscardsealingring(7)fromthecover(1),
and mounting bracket.
Caution: Drain all reservoirs before attempting to remove
theinletexhaustvalve.
DISASSEMBLY
Note: Prior to disassembly, mark the location of the
mounting bracket to the cover and the cover to the body.
CAUTION:Thevalvebodymaybelightlyclampedinabench
viseduringdisassembly, however,over-clamping will result
in damage to the valve and result in leakage and/or
malfunction. If a vise is to be used, position the valve so
that the jaws bear on the supply ports on opposing sides of
the valve’s body.
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5. Removepiston(9)fromthebody(10)andretainforreuse.
6. Removeanddiscardo-ring(8)frompiston (9).
7. Depressandholdtheexhaustcover assembly (16) and
remove and discard retaining ring (17) from the valve
body (10).
8. Slowly release the holding force on the exhaust cover
assembly (16) to relax the spring.
9. Removeanddiscardthe following parts:
a. Exhaust cover assembly (16)
b. O-rings (14 & 15)
c. Spring (13)
d. Inletexhaustvalve(11)
e. Retainer (12)
CLEANING AND INSPECTION
1. Wash all metal parts in mineral spirits and dry them
thoroughly.
(Note: When servicing the R-12DC™valve, all springs
and all rubber parts should be replaced.)
2. Inspect all metal parts for deterioration and wear, as
evidenced by scratches, scoring and corrosion.
3. Inspect the exhaust valve seat on the relay piston for
nicks and scratches which could cause excessive
leakage.
4. Inspect the inlet valve seat in the body for scratches
and nicks, which could cause excessive leakage.
5. Inspectthecheck valveseatin theR-12DC™valvecover
and make sure all internal air passages in this area are
open and clean and free of nicks and scratches.
6. Replaceallpartsnotconsideredserviceableduringthese
inspections and all springs and rubber parts. Use only
genuine Bendix replacement parts, available from any
authorized Bendix parts outlet.
ASSEMBLY
Note:Alltorquespecifiedinthismanualareassemblytorque
and can be expected to fall off slightly after assembly. Do
notre-torque afterinitialassemblytorquefall. Forassembly,
handwrenches are recommended.
Priortoassembly, lubricate all o-rings, o-ring boresandany
sliding surface with a silicone lubricant equivalent to Dow
Corning#10.
Washallremainingpartsinmineralspiritsanddrythoroughly.
Using the lubricant provided in this kit, lightly lubricate all
o-rings,o-ring grooves, body boresany sliding surfaces.
1. Install o-rings (14 & 15) in the exhaust cover assembly
(16).
2. Install o-ring (8) on piston (9).
3. Installsealing ring (7) on cover(1).
4. Installretainer(12) on inletexhaustvalve(11) andinsert
both in the body (10).
5. Install spring (13) in the body (10).
6. Install exhaust cover assembly (16) in the body (10).
Depress and hold the exhaust cover assembly in the
body.
7. Install retaining ring (17) in the body (10). Make certain
the retaining ring is completely seated in the groove in
the body.
8. Install piston (9) in body (10).
9. Installo-ring(5)ondoublecheck cover (6), installspring
(2), guide (3) and double check diaphragm (4) in cover
(1). Install cover (1) and torque torx head screws to
80-100 in. lbs.
10. Referringto themarks madeduringdisassembly, install
cover(1).
11. Install the mounting bracket (not shown) on the cover
(1).
12. Installthe fourcap screwsin thecover (1)and torqueto
80-100inchpounds.
13. TestthevalveasoutlinedintheOperationalandLeakage
Test section before returning the valve to service.
INSTALLATION
1. Clean air lines.
2. Inspect all lines and/or hoses for damage and replace
as necessary.
3. Install valve and tighten mounting bolts.
4. Connect air lines to valve (plug any unused ports).
5. Testvalveasoutlinedin OperationalandLeakageTests.
OPERATIONAL AND LEAKAGE TEST
1. Chock the wheels, fully charge air brake system and
adjust the brakes.
2. Make several brake applications and check for prompt
application and release at each wheel.
3. Checkforinletvalveando-ringleakage. Makethischeck
withtheservice brakes released. Coat the exhaust port
andtheareaaroundtheretainingringwithasoapsolution;
a 1” bubble in 3 seconds leakage is permitted.
4. Checkfor exhaust valve leakage. Make this check with
the service brakes fully applied. Coat the outside of
the valve where the cover joins the body to check for
seal ring leakage; no leakage is permitted.
If the valves do not function as described above, or if
leakage is excessive, it is recommended that the valves
be replaced with new or remanufactured units or repaired
withgenuineBendixparts,availableatanyauthorizedBendix
parts outlet.
GENERAL SAFETY GUIDELINES

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ABS/TRACTION
WARNING
INDICATORS
DIAGNOSTIC
CONNECTION
ENGINE ECU
BRAKE
CHAMBER
AIR DRYER
SUPPLY
RESERVOIR
ANTI-COMPOUNDING
SPRING BRAKE
RELAY VALVE
FRONT AXLE
SERVICE
RESERVOIR
REAR AXLE
SERVICE
RESERVOIR
R-12DC™
RELAY VALVE
COMPRESSOR
FIGURE 8 - TYPICAL PIPING SCHEMATIC
DC-4™
DOUBLE
CHECK
VALVE
ANTI-COMPOUND
LINE
GAUGE
SR-1™SPRING
BRAKE VALVE
SERVICE
BRAKE
VALVE
SPRING
BRAKES
PARKING
VALVE
ABS
ECU
MODULATOR
LOW PRESSURE
WARNING
INDICATOR
SINGLE
CHECK
VALVE
MODULATOR
WHEEL SPEED
SENSOR TONE RING
QUICK
RELEASE
VALVE
TONE RING
WHEEL SPEED
SENSOR
MODULATOR
MODULATOR
WHEEL SPEED
SENSOR
TONE RING SPRING
BRAKES

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GENERAL SAFETY GUIDELINES
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURYOR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove 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
enginebe inoperation, EXTREME CAUTION should
be used to prevent personal injury resulting from
contact with moving, rotating, leaking, heated or
electrically charged components.
3. Do not attempt to install, remove, disassemble or
assemble a component until you have read and
thoroughly understand the recommended
procedures. Useonly the propertools andobserve
all precautions pertaining to use of those tools.
4. 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 an
AD-IS®air dryer system or a dryer reservoir
module, be sure to drain the purge reservoir.
5. Following the vehicle manufacturer’s
recommended procedures, deactivate the
electrical system in a manner that safely removes
all electrical power from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.
7. 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.
8. Use only genuine Bendix®replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specifically for such applications and
systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
notattempt repairs requiring machiningor welding
unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certain all components and systems are restored
to their proper operating condition.
11. For vehicles with Antilock Traction Control (ATC),
the ATC function must be disabled (ATC indicator
lampshould be ON)prior to performingany vehicle
maintenance where one or more wheels on a
drive axle are lifted off the ground and moving.

8BW1933 © 2007 Bendix Commercial Vehicle Systems LLC. All rights reserved. 3/2007 Printed in U.S.A.