BENDIX DUAL RELAY VALVE User manual

1
PRIMARY
CONTROL
PORT (41)
CAST PORT
IDENTIFICATION
SECONDARY
CONTROL
PORT (42)
RESERVOIR
SUPPLY
PORT (11) MOUNTING
BRACKET STUDS
EXHAUST
PORT (1)
DELIVERY
PORT (22) RESERVOIR
SUPPLY
PORT (11)
Bendix®Dual Relay Valve
SD-03-1000
DESCRIPTION
The Dual Relay Valve is a special purpose, multifunction
relay valve. It is typically used on articulated vehicles with
three or more axles. Normally mounted at the rear of the
vehicle,inproximitytothevalvesandchambersserved,its
functionis similar to a pilotrelayandspeedsthe application
and release of control air pressure to the service relay
valve(s) on the rear most axle or axles of the vehicle. The
Dual Relay Valve is a pilot relay valve that responds to the
controlairdelivered to it from both circuits ofthefoot brake
valve. The Dual Relay Valve is controlled independently
bythefront (secondary) and mid (primary) deliverycircuits
of the dual circuit foot brake valve.
The Dual Relay Valve is supplied air from the rear axle(s)
service reservoir that is isolated from the other service
reservoirs forming a third service brake circuit on the
vehicle.Withtheaddition of a third brake circuit the vehicle
will maintain braking on at least two axles in the event of a
single service system malfunction. In systems where this
valve is used, the brake circuits are designated as Front
(steering) Axle, Mid-Axle and Rear Axle.
Although typically nipple mounted to the rear service
reservoir the valve can be bracket mounted. Only four (4)
ports are utilized in the die cast body of the Dual Relay
Valve.Allair connectionsareidentifiedwithraised numerals
with the following designations:
Port ID Size Designation
41 3/8 NPTF Primary Control Port
42 3/8 NPTF Secondary Control Port
12, 43 Plugged Not used
22 3/8 NPTF Delivery
11 3/8 NPTF Rear Service Reservoir
OPERATION
Refer to figures 1 and 2. Each service reservoir is isolated
andisprotected from loss of air in otherservicereservoirs.
Thefront and mid-axle service reservoirs supply air directly
to the secondary and primary circuits of the foot brake
valve,as well as antilock and traction componentsfortheir
respectivecircuits.The rear axle service reservoir supplies
airto the Dual Relay Valve,as well as therear axle service
antilock relay and traction components.
FIGURE 1 - DUAL RELAY VALVE

2
BVA-85™
MID
REAR
TO ACCESSORIES
BA-922®
TWIN CYLINDER
COMPRESSOR
AD-IS EP
EXTENDED PURGE
AIR DRYER
PP-DC™
PUSH-PULL VALVE WITH
INTEGRAL DOUBLE CHECK
RAM
REAR AXLE MODULE
FAM
FRONT AXLE
MODULE
ABS-6
WITH
TRACTION CONTROL
DOOR
INTERLOCK
VALVE WITH
CONTROL
MODULE
DUAL
RELAY VALVE
FRONT
Secondary
Control
Primary
Control
System Normal
With the system normal and air pressure available in all
servicereservoirs, brakeapplicationpressure istransmitted
from the primary and secondary circuits of the foot brake
valve.
Application pressure is transmitted simultaneously to the
frontand mid-axlebrakesand to theprimaryand secondary
controlports of theDualRelay Valve. TheDual Relay Valve
appliesorreleasestherearaxlebrakesindirectproportion
to the control signals received from the foot brake valve.
The brake on each axle are applied using pressure from
their dedicated respective reservoirs.
Loss of Front Axle Service Reservoir
A service application made with a loss of air in the
secondary circuit results in a no or low application of the
front axle brakes. Air pressure from the primary circuit of
thefoot brake valve applies the mid-axle brakes and enters
the primary control port of the Dual Relay Valve. The Dual
Relay Valve responds to primary control and applies the
rear axle brakes. Brake release occurs when foot brake
valve pressure is removed.
Loss of Mid-Axle Service Reservoir
Aservice application made with a loss of air in the primary
circuit results in a no or low application of the mid-axle
brakes.Air pressure from the secondary circuit of the foot
brake valve applies the front axle brakes and enters the
secondary control port of the Dual Relay Valve. The Dual
RelayValve responds to secondary control and applies the
rear axle brakes. Brake release occurs when foot brake
valve pressure is removed.
Loss of Rear Axle Service Reservoir
With a loss of rear axle service pressure, the front and
mid-axle brakes will be applied by the foot brake valve.
Primaryandsecondary control pressure is received by the
Dual Relay Valve however, a no or low application of the
rear brakes will occur due to a loss of pressure in the rear
service reservoir. Front and mid-axle brakes will release
when foot brake valve pressure is removed.
PREVENTIVE MAINTENANCE
GENERAL
Important: Preventive maintenance for the Dual Relay
Valve consists entirely of inspections and tests. The Dual
RelayValve is notserviceable and must be replaced when
testingor inspection warrants it.Kitsandreplacementparts
are not available.
Because no two vehicles operate under identical
conditions, maintenance and maintenance intervals will
vary. Experienceisavaluable guide in determiningthebest
maintenance interval for any one particular operation.
Perform the tests and inspections presented at the
prescribedintervals. If the Dual Relay Valve fails to function
as described or leakage is excessive, it must be replaced
with a genuine Bendix unit, available at any authorized
parts outlet.
Every 3 months, or 25,000 miles or 900 operating
hours:
1. Remove any accumulated contaminants and visually
inspect the exterior for excessive corrosion and
physical damage.
FIGURE 2 - TYPICAL ARTICULATED COACH SCHEMATIC

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2. Inspect all air lines connected to the Dual Relay Valve
for signs of wear or physical damage. Replace as
necessary.
3. Test air line fittings for excessive leakage and tighten
or replace as necessary.
4. Perform the Leakage Test described in this manual.
Every year, 100,000 miles, or 3,600 operating hours:
1. Perform the Operation and Leakage Tests described
in this manual.
GENERAL SAFETY GUIDELINES
WARNING! PLEASE READ AND FOLLOW
THESEINSTRUCTIONSTOAVOIDPERSONAL
INJURY OR DEATH:
When working on or around a vehicle, the
following generalprecautions 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. Stoptheengineand remove ignition key when working
underoraroundthevehicle. Whenworkingintheengine
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. Iftheworkisbeingperformedonthevehicle’sair brake
system,oranyauxiliarypressurizedair systems, make
certain to drain the air pressure from all reservoirs
before beginning ANY work on the vehicle. If the
vehicle is equipped with anAD-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.Priortoreturningthe vehicle to service, make certainall
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.
OPERATION & LEAKAGE TESTS
LEAKAGE TESTS
1. Fullychargetheairsystemmaking certain that the rear
service reservoir is fully charged.
2. Withthe system fully charged, check for leakage at the
rubber exhaust flap of the valve. Coat the exhaust flap
with a soap solution.A1 inch bubble in not less then 3
seconds is permitted (175 sccm max.).
3. Makeafullbrake application and hold it while checking
for leakage at the rubber exhaust port check of the
valve. Coat the exhaust port with soap solution. A 1
inch bubble in not less then 3 seconds is permitted
(175 sccm max.).
OPERATION TESTS
General
To complete the operational tests two accurate testgauges
and the appropriate fittings to “tee” the gauges into the
variouslines are required.Testingrequires that one gauge
beinstalled and remain in the line connectedtothedelivery
port 22 throughout the operational testing. The second
gaugewillbe alternately installed in the primary control line
leading to port 41 and the secondary control line leading
to port 42.
1. Install the gauge in the delivery line leading to port
22.
2. Install the gauge in the primary control line leading to
port 41.
3. Remove and PLUG the line leading to the secondary
control port 42.

4BW2591 © 2006 Bendix Commercial Vehicle Systems LLC. All rights reserved. 11/2006 Printed in U.S.A.
4. Charge the air system to governor cutout. While
observing both test gauges, make, hold and release
several brake applications at various pressures.
Delivery port (22) pressure should rise to the pressure
indicated below (+/- 5 psi) and promptly return to zero
pressure upon release of the brake valve.
Primary Control (41) Delivery port (22)
20 psi 20 psi
40 psi 40 psi
60 psi 60 psi
100 psi 100 psi
5. UNPLUG the line leading to the secondary control port
42.
6. Remove the gauge from the line leading to the primary
control port 41. Remove and PLUG the line leading to
the primary control port 41.
7. Install the gauge in the line leading to the secondary
control port 42 and reinstall the line in port 42.
8. Charge the air system to governor cutout. While
observing the test gauges installed in the secondary
controlline leadingtoport42 and deliveryport22 make,
hold,andrelease several brake applications at various
pressures. Delivery port 22 pressure should rise to the
pressureindicated below (+/- 5 psi) and promptlyreturn
to zero pressure upon release of the brake valve.
Secondary Control (42) Delivery port (22)
20 psi 10 psi
40 psi 30 psi
60 psi 50 psi
100 psi 95 psi
9. Remove the gauge from the secondary control line
leading to port 42.
10.UNPLUGand reconnecttheprimary controllineleading
to port 41.
11. Remove the gauge from the line leading to the delivery
port 22.
12.Make certain all lines and fittings are returned to their
original pretest positions and tightened sufficiently to
preventleakage. Make and hold a full brake application
and test all lines and fittings for leakage and note that
the Dual Relay Valve is operating correctly.
If the valve does not function as described or if leakage is
excessive, replace the Dual Relay Valve with a genuine
Bendix replacement.