BENDIX R-12P PILOT RELAY VALVE User manual

1
SD-03-1063
FIGURE 1 - CUTAWAYAND EXTERNAL VIEW
DESCRIPTION
The R-12P™pilot relay valve is designed to speed up
control signal application and release on long non-towing
trailers,towingtrailers, dollies,andlong wheelbasetractors.
It does this without adversely affecting the control signal.
The R-12P™valve replaces the current R-8P™valve.
Unlike a standard relay valve used as a “booster,” which
typically has a 2-4 psi differential between control and
delivery,the R-12P™valvehas zero differential.It“speeds”
up control line signal application and release in a train
of vehicles, and it delivers the same air pressure that it
receives. This provides a uniform brake signal to all trailer
and dolly brakes, even during light applications.
The unique R-12P™valve feature is that it uses a supply
air pressure load to quicken the valve’s response time. By
balancingthe pressure signalto alltrailer and dollybrakes,
the R-12P™valve aids in achieving overall vehicle brake
pressure balance, timing balance, and stability.
It also substantially improves brake lining wear balance
on combination vehicles by making even the most distant
brake contribute its share of braking effort.
Figure 2 shows the R-12P™valve in a trailer air brake
schematic. Note that additional air lines for a towing trailer
are shown as dashed lines.
The R-12P™valve uses the R-12™valve family lower body
and standard Bendix mounting brackets. It can also be
reservoir-mounted.
Thebody andcover aredie-cast aluminum,and thevalve’s
weight is approximately 2.3 lbs. Porting is as follows:
Qty. Size
Supply (SUP) 2 1/2”
Delivery (DEL) 4 3/8”
Control (CON) 1 1/4”
Exhaust (EXH) 1 --
Bendix®R-12P™Pilot Relay Valve
3/8”
DELIVERY
1/2” SUPPLY (2)
RESERVE
SPRING
1/4” CONTROL
LOAD
PISTON
BODY
EQUALIZING
ORIFICE
EXHAUST
INLET/EXHAUST
VALVE
COVER
1/2”
SUPPLY
3/8” DELIVERY (4)
RELAY
PISTON 1/4” CONTROL

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FIGURE 2 - TYPICAL R-12P™PILOT RELAY VALVE SYSTEM SCHEMATIC
DELIVERY
SPRING
BRAKE
VALVE
SUPPLY SERVICE RELAY
VALVE QUICK
RELEASE
VALVE
VENTED
CUT-OUT
COCK
SINGLE
CHECK VALVE
VENTED
CUT-OUT
COCK
RESERVOIR
CONTROL
BRAKE CHAMBER
SLACKADJUSTER
SUPPLY
CONTROL R-12P™
VALVE
OPERATION
CHARGING
When the air brake system is charging, the relay piston’s
exhaust seat is against the inlet/exhaust valve due to
the force of the reserve spring. Reservoir air enters the
R-12P™valve supply port and becomes active upon the
inlet/exhaust valve.At the same time, reservoir air passes
through the R-12P™valve body channel to the load piston.
Supplyairbuildssimultaneouslyandequallyunderneaththe
inlet/exhaustvalve andabove theload piston.While supply
pressure continues to hold the inlet/exhaust valve against
TRAILER BRAKE SYSTEM WITH R-12P™PILOT RELAY VALVE
its seat, it also moves the load piston into contact with the
relay piston. However, even though force is increasing on
the relay piston, it does not move the inlet/exhaust valve.
The effective area of the inlet/exhaust valve is larger than
theeffective areaof the load piston.Therefore,load piston
forcecannot overcomeinlet/exhaust valveforce. Sosupply
air builds to governor cut-out and the inlet/exhaust valve
remains closed. This is the position of the R-12P™valve
in normal run mode, as shown in Figure 3.
-- -- -- -- --ADDITIONALPLUMBING FOR TOWING TRAILER

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FIGURE 4 - NORMAL (RAPID) APPLICATION
LOAD PISTON
INLET/EXHAUST
VALVE
CONTROL
PORT
FIGURE 5 - BALANCE
FIGURE 3 - CHARGING
DELIVERY
PORT
SUPPLY PORT
NORMAL (RAPID) APPLICATION
Figure 4 shows an R-12P™valve receiving a “normal”
service brake application. “Normal” means the control
signal is applied rapidly enough to build up pressure on
the relay piston and “open” the inlet valve, causing the
R-12P™valve to react like a relay valve. The relay piston
opens the inlet, allowing supply air to flow out the delivery
port to the next valve in the system.
Note that these events occur quickly, due to the “preload”
on the relay piston. This preload, provided by supply air
pressure acting on the load piston, is a feature unique to
the R-12P™valve.
BALANCE
Air pressure being delivered by the open inlet valve is
also effective underneath the R-12P™valve relay piston.
When air pressure beneath the piston approaches control
pressure on top of the piston, the piston and inlet valve lift
together and close the inlet valve. The exhaust remains
closed, and the valve achieves “force balance.” That is,
the piston and inlet/exhaust valve are in their neutral
state. This is the position commonly known as “balanced”
when referring to conventional relay valves. However,
conventionalrelay valves cannotachieve true airpressure
balancebecause oftheir inherentdifferentials.The R-12P™
valve achieves this balance because of its equalizing
orifice. The orifice allows control pressure and delivery
pressure to be “common” and equalize. In this position,
shown in Figure 5, sustained service brake applications
can be held, with no “residual” differential.
RELAY PISTON
LOAD PISTON
INLET/EXHAUST
VALVE
CONTROL
PORT
SUPPLY PORT
RELAY PISTON
LOAD PISTON
INLET/EXHAUST
VALVE
CONTROLPORT
DELIVERY
PORT
SUPPLY PORT
RELAY
PISTON
EQUALIZING
ORIFICE
PROVIDESAIR
PRESSURE
BALANCE

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FIGURE 6 - RAPID EXHAUST FIGURE 7 - EQUALIZING (SLOW) APPLICATION
FIGURE 8 - EQUALIZING (SLOW) EXHAUST
LOAD PISTON
INLET/EXHAUST
VALVE
CONTROLPORT
DELIVERY PORT
SUPPLY PORT
RELAY PISTON
EXHAUST
LOAD PISTON
INLET/EXHAUST
VALVE
CONTROLPORT
DELIVERY PORT
SUPPLY PORT
RELAY PISTON
LOAD PISTON
INLET/EXHAUST
VALVE
CONTROLPORT
DELIVERY PORT
SUPPLY PORT
RELAY PISTON
RAPID EXHAUST
Figure 6 shows a rapid service brake release. Air above
the relay piston travels back out the control port to be
exhausted. With the lack of air pressure above the
piston, air pressure below lifts the piston, closing the inlet
and opening the exhaust. Delivery air then exhausts to
atmosphere.
EQUALIZING (SLOW) APPLICATION
When a control signal enters the R-12P™valve, it acts
on the relay piston. However, Figure 7 shows the control
signal passing through the valve without causing piston
movement. The air is passing through the relay piston’s
equalizing orifice, directly through the valve and out the
delivery port to the next valve in the air system. This
situation occurs if air pressure build-up is slow and the
pressure above the relay piston is not strong enough to
open the valve. (Air pressure above the piston must be at
least 3 psi greater than air pressure below the piston to
cause movement.)
In the equalizing application, even though the inlet valve
doesnot open,the controlsignal isnotdecreased because
the equalizing orifice allows it to pass directly through the
R-12P™valve. Note that this condition exists during very
slow service brake applications.
For example, if a vehicle is traveling over a long downhill
grade, the driver may want to limit speed and maintain
vehicle control through proper gearing, engine speed and
a light service brake application.

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FIGURE 9 - REDUCTION OF SUPPLY PRESSURE
LOAD PISTON
INLET/EXHAUST
VALVE
CONTROL
PORT
DELIVERY PORT
SUPPLY PORT
RELAY PISTON
RESERVE SPRING
SEALS EXHAUST
If, during the light brake application, the driver modulates
thetreadle slowly,and notenough toopen theR-12P™inlet
valve, the desired control pressure will still pass on to the
next valve, maintaining zero differential.
EQUALIZING (SLOW) EXHAUST (SEE FIGURE 8)
As described earlier, the result of any service brake
application with an R-12P™valve is air pressure balance
above and below the relay piston. If the brake valve is
modulated slowly upon release so that pressure beneath
thepiston isnot greatenough toopen theexhaust, delivery
air will pass through the equalizing orifice and out the
control port to be exhausted.
REDUCTION OF SUPPLY PRESSURE
Figure9 shows the R-12P™valvewith no supplypressure.
With no supply air, the reserve spring is strong enough to
holdthe relaypiston onthe exhaustseat, butit isnot strong
enough to overcome the force of the inlet/exhaust valve
spring. So both inlet and exhaust valves are closed.
Service Brake Applications with Reduced Supply
Pressure
Rapid Application - Use of Supply Line Single Check
Valve
Ifarapidservicebrakeapplicationismade,controlairmoves
the relay piston and opens the inlet valve; but there is no
supplyair to deliver. Controlairthen travels intothe supply
port. The single check valve in the R-12P™valve supply
port (shown in Figure 2) prevents this air from escaping to
atmosphere through the open or damaged supply source.
Control air also passes through the equalizing orifice and
outthe deliveryport,assuring noreductionorlossof control
signal to subsequent vehicles.
Equalizing (Slow) Application
If an equalizing (slow) service brake application is made
with reduced supply air pressure, control air passes
through the equalizing orifice and out the delivery port to
subsequent vehicles in the train.
Control air cannot escape to atmosphere because the
reserve spring keeps the exhaust closed.
WARNING! PLEASE READ AND FOLLOW
THESEINSTRUCTIONSTOAVOIDPERSONAL
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 bein operation, EXTREME CAUTIONshould
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 proper toolsand 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 dryersystem or adryer reservoir module,
be sure to drain the purge reservoir.

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5. Followingthevehiclemanufacturer’srecommended
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 beON) prior to performing anyvehicle
maintenance where one or more wheels on a drive
axle are lifted off the ground and moving.
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
valuableguidein determiningthebestmaintenanceinterval
for air brake system components.At a minimum, the valve
should be inspected every 6 months or 1500 operating
hours,whichever comes first, forproper 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.
SERVICE CHECKS
1. Remove any accumulated contaminants. Visually
inspect the valve’s exterior for excessive corrosion
or physical damage. Repair/replace the valve as
necessary.
2. Inspect all air lines connected to the valve for signs
of wear or physical damage. Repair/replace as
necessary.
3. Test air line fittings for excessive leakage and tighten
or replace as necessary.
OPERATIONAL AND LEAKAGE TESTS
1. Block the vehicle’s wheels and fully charge the air
system.
2. Apply and release the service brakes several times
and check for prompt response of the brakes at all
appropriate wheels.
3. Withthe air systemfully charged,apply a soapsolution
to the R-12P™valve exhaust port. Leakage of a 1”
bubble in 5 seconds is permissible.
4. Make and hold a full brake application and again apply
a soap solution to the R-12P™valve exhaust. Leakage
of a 1” bubble in 3 seconds is permissible.
5. With the brakes still applied, apply a soap solution
around the valve where the cover meets the body. No
leakage at this point is permitted.
If the valve does not function as described; or if leakage is
excessive, repair the valve or replace it at any authorized
parts outlet.
NOTE: If a supply line single check valve is present (see
Figure2), checkit forleakage. Disconnectthe inlet
side of the single check valve and coat the open
end with a soap solution. Make and hold a full
brakeapplication. Leakage ofa oneinch bubble in
five seconds is permissible. If the valve’s leakage
is excessive, replace it with a 1/2” single check
valve.
REMOVAL
1. Drain all system air pressure.
2. Identify and mark or label all air lines and their
connections to the R-12P™valve and the single check
valve, if present. Then disconnect the air lines.
3. Remove the R-12P™valve from the vehicle.

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FIGURE 10 - EXPLODED VIEW
1
98
2
3
LOAD
PISTON
4
10
5
11
12
FASTENER
RELAY PISTON
7
BODY
COVER
RESERVE
SPRING
6
INSTALLATION
1. Use the mounting bracket provided, or, if securing the
valve to a reservoir, use a Schedule 80 (heavy wall)
short couple pipe nipple.
2. Reconnect all air lines to the valve using the
identificationmade duringremoval. Besure to usepipe
thread sealant.
3. Test all air fittings for excessive leakage and tighten as
needed.Also,performOPERATIONALANDLEAKAGE
TESTS before placing the vehicle back into service.
DISASSEMBLY
The following procedure is for reference only. Always
have the appropriate maintenance kit on hand, and use
its instructions in lieu of those presented here. Refer to
Figure 10 throughout.
CAUTION: The R-12P™valve may be lightly clamped in
a bench vise during disassembly. However,
overclamping will cause damage to the valve
and result in leakage and/or malfunction. If a
vise is used, position the valve so the jaws
bear on the supply ports on opposing sides
of the valve’s body.
1. Remove the four fasteners that secure the cover to the
body. Then slowly remove the cover.
2. Remove and discard the small o-ring(1) that seals the
internal channel and the large o-ring(2) between the
cover and the body.
3. Remove the load piston from the cover. Note: If
necessary, use approximately 20 psi of shop air,
directed into the load piston’s air passage in the cover,
todislodge it.CAUTION:The pistonwill leavethe cover
with some force.
4. Remove and discard the load piston’s o-ring(3).
5. Removethe reservespringand therelaypiston fromthe
body.Remove and discardthe relay piston’s o-rings(4)
and (5).
6. While holding exhaust cover(7), remove and discard
the snap ring(6) that secures the cover to the body.
7. Removeand discardexhaust cover(7)andits o-rings(8)
and (9).
8. Removeanddiscardvalvespring(10),valveretainer(11),
and inlet/exhaust valve(12) from the body.

8BW1711 © 2007 Bendix Commercial Vehicle Systems LLC. All rights reserved. 7/2007 Printed in U.S.A.
CLEANING & INSPECTION
1. Usingmineral spiritsor anequivalentsolvent, cleanand
thoroughly dry all metal parts. Do not damage bores
with metal tools.
2. Washall non-metallic componentsin a soapand water
solution. Dry thoroughly.
3. Inspectinterior andexteriorof allmetal partsfor severe
corrosion, pitting, and cracks. Superficial corrosion
and/or pitting on the exterior of the body and cover
is acceptable. Replace the entire valve if the body or
cover interior show signs of corrosion or pitting.
4. After washing, inspect relay piston for cracks, wear,
or distortion. Replace the valve if these conditions are
found.
5. Make certain the air channel running from the cover
through the top surface of the body to the supply port
is clear and free of obstruction.
6. Inspect the pipe threads in the body. Make certain they
are clean and free of thread sealant.
7. Inspect all air line fittings for corrosion. Replace as
necessary. Remove all old thread sealant before
reuse.
ASSEMBLY
1. Beforeassembly,lubricateallo-rings,seals, andpistons
as well as body and cover bores, using the lubricant
providedin themaintenance kit.Use allof thelubricant,
and spread it evenly on all rubbing surfaces.
2. Install valve retainer(11) on inlet/exhaust valve(12) so
that the flange of the retainer surrounds the rubber
portion of the valve.
3. Install inlet/exhaust valve(12) in the body.
4. Install valve spring(10) over the inlet/exhaust valve in
the body.
5. Install large and small diameter o-rings(8) and (9) in
exhaust cover(7).
6. Place the exhaust cover on the inlet/exhaust valve
spring. Then depress the cover against the spring’s
force into the body. Secure the cover with snap
ring(6).
7. Install o-rings(4) and (5) onto the relay piston. Then
place the reserve spring in the piston and install the
piston into the body.
8. Install the load piston’s o-ring(3) onto the load piston.
Then install the load piston into the cover, small end
first.
9. Install small o-ring(1) that seals the internal channel
and large o-ring(2) onto the cover.
10. Place the cover on the body and secure with its four
fasteners. Torque to 120 - 150 in. lbs.
11. PerformOPERATIONALANDLEAKAGETESTSbefore
returning the vehicle to service.