Bendix® R-12DC™ Relay Valve with Biased Double Check
PRIMARY
SERVICE
SUPPLY (2)
EXTERIOR R-12DC
(MODEL WITH 2 HORIZONTAL PORTS)
FIGURE 1 - EXTERIOR VIEWS
™
VALVE
SECONDARY
SERVICE
DELIVERY
EXTERIOR
R-12DC™ VALVE
(MODEL WITH
4 VERTICAL
DELIVERY PORTS)
EXTERIOR
R-12DC™ VALVE
(MODEL WITH 2
HORIZONTAL AND 2
VERTICAL DELIVERY
PORTS)
SD-03-1068
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
PRIMARY
SERVICE
CAP SCREW
SEALING
RING
RELAY
PISTON
O-RING
EXHAUST
SEAT
SPRING
O-RINGS
RETAINING
RING
FIGURE 2 - R-12DC™ RELAY VALVE WITH BIASED DOUBLE CHECK SECTIONAL VIEW
PORT
COVER
RELAY
PISTON
VALVE
RETAINER
EXHAUST
EXHAUST
PORT
or releases air to the chambers in response to the control
air delivered to it from the foot brake valve.
The R-12DC™ relay valves are designed for either reservoir
or frame mounting. (See Figure 1). For ease of servicing,
the inlet/exhaust valve can be replaced without the need for
line removal.
SECONDARY
SERVICE PORT
INLET
VALVE
SPRING
DOUBLE CHECK
DIAPHRAGM
GUIDE
1
OPERATION
APPLICA TION
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
piston down. The exhaust seat moves down with the piston
and seats on the inner or exhaust portion of the 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
primary service line, and instead allow the secondary service
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.
™
R-12DC
VALVE
RELAY PISTON
INLET
EXHAUST
VALVE
RESERVOIR
ANTILOCK SENSOR
TONE RING
FIGURE 3 - R-12DC
SYSTEM COMPONENTS
™
SECTIONAL VIEW WITH TYPICAL
BRAKE VALVE
(DELIVERY
LINES ARE
SHOWN)
ANTILOCK
MODULATOR
EXHAUST
PORT
BRAKE
CHAMBERS
BRAKES
APPLIED
BRAKE PEDAL
APPLIED
BRAKE PEDAL
APPLIED
NORMAL: BIASED
DOUBLE-CHECK VALVE
ALLOWS PRIMARY
CONTROL LINE SUPPLIES
RELAY PISTON
CONTROL LINE
FAILURE
BRAKE PEDAL
APPLIED
SECONDARY
CONTROL LINE
SUPPLIES RELAY
PISTON
FIGURE 4 - R-12DC
2
™
APPLIED POSITION (SHOWING BIASED DOUBLE CHECK OPERATIONAL VIEWS)
BRAKE PEDAL
POSITION
HELD
BRAKE
CHAMBERS
MAINTAIN
APPLICATION
AIR PRESSURE
FROM BRAKE
CHAMBERS IS
EXHAUSTED
HERE
BRAKE
PEDAL
RELEASED
AIR PRESSURE
ABOVE RELAY
VALVE IS
EXHAUSTED
HERE
BRAKE
CHAMBERS
RELEASED
FIGURE 5 - R-12DC
™
BALANCE POSITION
When air pressure beneath the piston equals the service 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
reacts instantly to the change, holding the 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
pressure in the brake chambers is then permitted to exhaust
through the exhaust port, releasing the brakes.
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
FIGURE 6 - R-12DC
™
EXHAUST POSITION
valuable guide in determining the best maintenance interval
for air brake system components. At a minimum, the valve
should be inspected every 6 months or 1500 operating hours,
whichever comes first, for proper operation. Should the valve
not meet the elements of the operational tests noted in this
document, further investigation and service of the valve may
be required.
REMOVAL AND INSTALLATION
REMOVAL
1. Block and hold vehicle by means other than air brakes.
2. Drain air brake system reservoirs.
3. If entire valve is to be removed, identify air lines to facilitate
installation. Prior to disassembly, remove as much
contamination as possible from the exterior of the device
taking care to keep all contamination from entering the
open ports.
4. Disconnect air lines from valve*.
5. Remove valve from reservoir or if remotely mounted,
remove mounting bolts and then valve.
*It is generally not necessary to remove entire valve to service
the inlet/exhaust valve. The inlet/exhaust valve insert can be
removed by removing the snap ring, exhaust cover assembly
and then inlet/exhaust valve.
3
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)
18
DIFFERENTIAL SPRING
(CONTROLS CRACK PRESSURE*)
(NOT REQUIRED FOR MOST
MODELS.
SEE BELOW.)
HORIZONTAL
DELIVERY
PORTS
CAP SCREW
PRIMARY CONTROL
2
PORT 1/4 NPT
3
5
4
1
6
7
8
CONTROL PORT
SECONDARY
1/4 NPT
CAP
SCREW
9
10
SUPPLY
PORT
DIFFERENTIAL SPRINGS
*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.)
VERTICAL
DELIVERY
PORTS
FIGURE 7 - R-12DC™ EXPLODED VIEW
Caution: Drain all reservoirs before attempting to remove
the inlet exhaust valve.
DISASSEMBLY
Note: Prior to disassembly, mark the location of the
mounting bracket to the cover and the cover to the body.
CAUTION: The valve body may be lightly clamped in a bench
vise during disassembly, 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 .
4
11
12
13
14
15
16
17
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. Remove and discard sealing ring (7) from the cover (1).
a. Remove the 2 torx screws securing the double check
cover (6) to the cover (1).
b. Remove the double check cover (6) from cover (1)
and remove and discard spring (2), guide (3), double
check diaphragm (4), and o-ring (5).
4. Remove and discard sealing ring (7) from the cover (1),
and mounting bracket.
5. Remove piston (9) from the body (10) and retain for reuse.
6. Remove and discard o-ring (8) from piston (9).
7. Depress and hold the exhaust cover 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. Remove and discard the following parts:
a. Exhaust cover assembly (16)
b. O-rings (14 & 15)
c. Spring (13)
d. Inlet exhaust valve (1 1)
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. Inspect the check valve seat in the R-12DC™ valve cover
and make sure all internal air passages in this area are
open and clean and free of nicks and scratches.
6. Replace all parts not considered serviceable during these
inspections and all springs and rubber parts. Use only
genuine Bendix replacement parts, available from any
authorized Bendix parts outlet.
ASSEMBLY
Note: All torque specified in this manual are assembly torque
and can be expected to fall off slightly after assembly. Do
not re-torque after initial assembly torque fall. For assembly ,
hand wrenches are recommended.
Prior to assembly, lubricate all o-rings, o-ring bores and any
sliding surface with a silicone lubricant equivalent to Dow
Corning #10.
Wash all remaining parts in mineral spirit s and dry thoroughly.
Using the lubricant provided in this kit, lightly lubricate all
o-rings, o-ring grooves, body bores any sliding surfaces.
1. Install o-rings (14 & 15) in the exhaust cover assembly
(16).
2. Install o-ring (8) on piston (9).
3. Install sealing ring (7) on cover (1).
4. Install retainer (12) on inlet exhaust valve (1 1) and insert
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. Install o-ring (5) on double check cover (6), install spring
(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.Referring to the marks made during disassembly , install
cover (1).
11. Install the mounting bracket (not shown) on the cover
(1).
12.Install the four cap screws in the cover (1) and torque to
80-100 inch pounds.
13. Test the valve as outlined in the Operational and Leakage
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. T est valve as outlined in Operational and Leakage T ests.
OPERA TIONAL 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. Check for inlet valve and o-ring leakage. Make this check
with the service brakes released. Coat the exhaust port
and the area around the retaining ring with a soap solution;
a 1” bubble in 3 seconds leakage is permitted.
4. Check for 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
with genuine Bendix parts, available at any authorized Bendix
parts outlet.
GENERAL SAFETY GUIDELINES
5
SPRING
BRAKES
TONE RING
LINE
MODULATOR
ANTI-COMPOUND
RELAY VALVE
SPRING BRAKE
ANTI-COMPOUNDING
™
RELAY
VALVE
R-12DC
SPRING
BRAKES
SENSOR
WHEEL SPEED
SPRING
™
BRAKE VALVE
SR-1
VALVE
PARKING
WARNING
INDICATORS
ABS/TRACTION
ABS
ECU
SERVICE
VALVE
BRAKE
ENGINE ECU
™
DC-4
MODULATOR
CHECK
DOUBLE
BRAKE
CHAMBER
VALVE
AIR DRYER
GAUGE
SERVICE
RESERVOIR
FRONT AXLE
SINGLE
SUPPLY
RESERVOIR
REAR AXLE
VALVE
CHECK
SERVICE
RESERVOIR
WARNING
INDICATOR
LOW PRESSURE
DIAGNOSTIC
CONNECTION
QUICK
MODULATOR
VALVE
RELEASE
MODULATOR
COMPRESSOR
TONE RING
SENSOR
WHEEL SPEED
SENSOR
WHEEL SPEED
TONE RING
FIGURE 8 - TYPICAL PIPING SCHEMATIC
6
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
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
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.
3. 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.
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
not attempt repairs requiring machining or 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
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.
7
8
BW1933 © 2007 Bendix Commercial Vehicle Systems LLC. All rights reserved. 3/2007 Printed in U.S.A.
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