®
Bendix® R-7™ Modulating Valve
SD-03-4504
MOUNTING
HOLE (2)
DELIVERY (2)
MOUNTING
HOLE (2)
BALANCE
BALANCE
PORT
EXHAUST
EXHAUST
CONTROL
PORT
SUPPLY
PORT
SUPPLY
CONTROL
INLET
EXHAUST
VALVE
MOUNTING
SURFACE
INLET
VALVE
SEAT
INNER SPRING
INLET
VALVE
SPRING
BALANCE
PISTON
OUTER SPRING
EXHAUST
CONTROL
PORT
CONTROL
PISTON
DOUBLE CHECK
VALVE (SUPPLY
PORT & BALANCE
PORT)
SINGLE
CHECK
VALVE
DELIVERY
PORT (2)
ADJUSTING SCREW
FIGURE 1 - EXTERIOR & INVERTED VIEW
DESCRIPTION
The R-7™ modulating valve is used in conjunction with a
dual air brake system and spring brake actuators, and
performs four functions:
1. Limits hold-off pressure to the spring brake actuators
(adjustable).
2. Provides for quick release of air pressure from the spring
cavity of the spring brake actuator allowing a fast
application of the spring brake actuators.
3. Modulates spring brake actuator application should a
failure occur in the service brake system.
4. Prevents compounding of service and spring forces.
The valve has one 1/4" control, one 3/8" supply, one 1/4"
balance, two 3/8" delivery NPTF ports, and an exhaust port
protected by an exhaust diaphragm. The valve incorporates
two 13/32" holes for mounting.
FIGURE 2 - SECTIONAL VIEW
Note for model year 2001 and later International Trucks only:
There is an inverted R-7™ valve, which appears inverted from
the other pictures in this document. A standard R-7™ valve
and an inverted R-7™ valve are not interchangeable. See
Figure 1 for a picture of an inverted R-7™ valve.
OPERATION - CHARGING SPRING BRAKE
ACTUATORS (FIGURE 3)
Air pressure used to control the spring brake actuators enters
the valve through the supply port, passing through one side
of the double check valve, through the open inlet valve, over
the balance piston, and out the delivery ports to the spring
brake actuators. When air pressure in the spring brake
actuator cavity has released the spring brake actuators and
when air pressure on top of the balance piston is sufficient
to overcome the force of the balance piston spring, the
balance piston moves allowing the inlet valve spring to close
the inlet valve, shutting off further air pressure from the
reservoir supplying the modulating valve.
1
SPRING
BRAKE
ACTUATOR
PRIMARY SECONDARY PARK -
SECONDARY SERVICE CIRCUIT
CONTROL
PORT
INLET/EXHAUST
VALVE
EXHAUST
PORT
CONTROL
PISTON
BALANCE PISTON
DUAL BRAKE
VALVE
PRIMARY
SERVICE
CIRCUIT
BALANCE
PORT
DOUBLE
CHECK VALVE
SUPPLY
PORT
SINGLE
CHECK
VALVE
+ SPRING BRAKE HOLD-OFF PRESSURE
- SERVICE AIR PRESSURE
o ATMOSPHERE PRESSURE
#1 RES.
#2 RES.
PARK
CONTROL
VALVE
SPRING
BRAKE
ACTUATOR
PRIMARY SECONDARY PARK -
SECONDARY SERVICE CIRCUIT
CONTROL
PORT
INLET/EXHAUST
VALVE
EXHAUST
PORT
#1 RES.
CONTROL
PISTON
SINGLE
CHECK
VALVE
BALANCE PISTON
+ SPRING BRAKE HOLD-OFF PRESSURE
- SERVICE AIR PRESSURE
o ATMOSPHERE PRESSURE
#2 RES.
DUAL BRAKE
VALVE
PRIMARY SERVICE
CIRCUIT
BALANCE
PORT
DOUBLE
CHECK
VALVE
SUPPLY
PORT
PARK
CONTROL
VALVE
FIGURE 3 - CHARGING
DUAL BRAKE
VALVE
PRIMARY SERVICE
CIRCUIT
BALANCE
PORT
DOUBLE
CHECK VALVE
SUPPLY
PORT
#1 RES.
#2 RES.
CONTROL
PARK
VALVE
SPRING
BRAKE
ACTUATOR
PRIMARY SECONDARY PARK -
SECONDARY
SERVICE
CIRCUIT
INLET/EXHAUST
VALVE
CONTROL
PORT
EXHAUST
PORT
CONTROL
PISTON
SINGLE
CHECK
VALVE
BALANCE PISTON
+ SPRING BRAKE HOLD-OFF PRESSURE
- SERVICE AIR PRESSURE
o ATMOSPHERE PRESSURE
FIGURE 4 - NORMAL SERVICE APPLICA TION
NOTE: The force of the spring below the balance piston is
adjustable by an external screw on the modulating
valve. This adjustment is normally made so that
the inlet valve will close at a slightly greater pressure
than the hold-off pressure of the spring brake
actuator, but below maximum system pressure.
OPERATION - NORMAL SERVICE APPLICATION
(FIGURE 4)
When a service application is made by actuating the dual
brake valve, air from the primary circuit is delivered to the
lower side of the control piston through the balance port,
and air from the secondary circuit is delivered to the top of
the control piston through the control port. Because air
pressure from the primary and secondary circuits are not
equal, there will be a slight movement of the control piston.
FIGURE 5 - SERVICE APPLICA TION LOSS OF PRIMARY
CIRCUIT
OPERA TION - SERVICE APPLICA TION WITH LOSS OF
AIR IN PRIMARY CIRCUIT (FIGURE 5)
A service application made with a loss of air in the primary
circuit would result in reduced air pressure delivered to the
lower area of the control piston. Air pressure from the
secondary circuit on top of the control piston would force
the piston down, opening the exhaust valve and allowing air
pressure in the spring cavity of the spring brake actuator to
release and the spring brake actuator to apply the brakes.
The pressure differential between the primary and secondary
circuits regulates the amount of air pressure released from
the spring cavity of the spring brake actuator. This result s
in a total brake application on the rear axle which is
proportionate to the braking on the other axles.
SECONDARY
SPRING
BRAKE
ACTUATOR
PRIMARY SECONDARY PARK -
SERVICE
CIRCUIT
INLET/EXHAUST
VALVE
CONTROL
PORT
EXHAUST
PORT
CONTROL
PISTON
SINGLE
CHECK
VALVE
BALANCE PISTON
+ SPRING BRAKE HOLD-OFF PRESSURE
- SERVICE AIR PRESSURE
o ATMOSPHERE PRESSURE
FIGURE 6 - SERVICE APPLICA TION LOSS OF SECONDARY
CIRCUIT
#1 RES.
#2 RES.
DUAL BRAKE
VALVE
PRIMARY SERVICE
CIRCUIT
BALANCE PORT
DOUBLE
CHECK VALVE
SUPPLY
PORT
PARK
CONTROL
VALVE
2
OPERA TION - SERVICE APPLICA TION WITH LOSS OF
AIR IN SECONDARY CIRCUIT (FIGURE 6)
A service application made with a loss of air in the secondary
circuit would result in less or no air delivered to the top of
the control piston; however, the piston would not move and
braking on the rear axle(s) is assured because the primary
circuit supplies rear axle service brakes. The spring brake
actuators will not be actuated.
OPERA TION - P ARKING (FIGURE 7)
When the handle of the parking control valve is placed in the
“park” (exhaust) position, the modulating valve’s supply air
pressure and the air pressure in the spring brake actuator
cavities is exhausted. The single check valve speeds the
exhaust of air from the actuator cavities by allowing the air
on top of the balance piston to exhaust by the double check
valve through the supply port to atmosphere. When air
pressure drops sufficiently, the balance piston opens the
inlet valve thus opening the larger passage in the modulating
valve insuring rapid exhaust of the balance of air pressure in
the spring cavity of the spring brake actuator.
SECONDARY
SERVICE
CIRCUIT
SPRING
BRAKE
ACTUATOR
INLET/EXHAUST
VALVE
PRIMARY SECONDARY PARK -
FIGURE 7 - PARKING
CONTROL
PORT
EXHAUST
PORT
CONTROL
PISTON
SINGLE
CHECK
VALVE
BALANCE PISTON
+ SPRING BRAKE HOLD-OFF PRESSURE
- SERVICE AIR PRESSURE
o ATMOSPHERE PRESSURE
#1 RES.
#2 RES.
DUAL BRAKE
VALVE
PRIMARY SERVICE
CIRCUIT
BALANCE
PORT
DOUBLE
CHECK VALVE
SUPPLY
PORT
PARK
CONTROL
VALVE
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
valuable guide in determining the best maintenance interval
for air brake system components. At a minimum, the R-7
valve should be inspected every 6 months or 1500 operating
hours, whichever comes first, for proper operation. Should
the R-7™ valve not meet the elements of the operational
tests noted in this document, further investigation and service
of the valve may be required.
SERVICE TESTS
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
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.
at all times.
™
3
OPERATING TEST
Block vehicle and hold by means other than vehicle brakes.
Charge air brake system to governor cut-out pressure.
1. Place parking control valve in “park” position. Observe
that spring brake actuators apply promptly. Remove
one line from delivery port of valve and install test gauge
known to be accurate. Place parking control valve in
“release” position. Observe that spring brake actuators
release fully .
2. With parking control valve in “release” position, note
gauge pressure reading. (Check vehicle manual for
correct spring brake actuator hold-off pressure.) If
pressure reading is incorrect, modulating valve should
be adjusted. (See section “Adjustment of Modulating
V alve - Spring Brake Actuator Hold-Off Pressure”.)
3. Place parking control valve in “park” position - gauge
reading should drop to zero promptly . A lag (more than
1 second) in drop of pressure would indicate faulty
operation of the single check valve (within the modulating
valve).
4. With the parking control valve in the “park” position fully
apply foot brake valve several times and note a pressure
reading increase on the gauge each time the brake is
applied. If pressure reading does not occur, the
modulating valve requires servicing or replacing.
5. Place parking control valve in “release” position.
Determine the reservoir which supplies balance port and
drain completely .
Apply foot brake valve several times and note that pressure
reading on gauge decreases each time foot brake valve is
applied. After foot brake valve has been applied several times,
pressure on gauge will drop to the point where release of the
spring brake actuators will no longer occur.
LEAKAGE TEST
Place the park control valve in the “release” position; using
a soap solution, coat exhaust and vent hole (in proximity of
adjusting screw). Slight bubble leakage permitted.
If the valve does not function as described, or if leakage is
excessive, it is recommended that it be repaired or replaced
with a genuine Bendix service replacement valve.
ADJUSTMENT OF MODULATING VALVE - SPRING
BRAKE ACTUATOR HOLD-OFF PRESSURE
Block vehicle by means other than vehicle brakes. If it has
been ascertained that hold-off pressure for the spring brake
actuators is incorrect (see section “Operating Test”),
adjustment should be made as follows:
1. Build system pressure to governor cut-out
(approximately 120 psi). It is important that system
leakage for a single vehicle not exceed a 2 psi drop in
one (1) minute with brakes released. Correct system
leakage before proceeding with adjustment.
2. Place parking control valve in “park” position and install
an accurate test gauge in a delivery port of the
modulating valve. Place parking control valve in “release”
position and observe pressure reading on the test gauge.
Refer to vehicle manual for recommended pressure.
Adjust as necessary.
TO RAISE HOLD-OFF PRESSURE
Loosen lock nut. Turn adjusting screw clockwise and observe
reading on gauge. T o raise hold-of f pressure, turn adjusting
screw clockwise - to lower hold-off pressure, turn adjusting
screw counterclockwise until pressure is below that desired
and then turn screw clockwise to desired pressure. Tighten
locknut securely after completing adjustment.
DISASSEMBLY
1. Remove exhaust cover screw, exhaust cover and
exhaust diaphragm.
2. Remove four (4) cap screws and lockwashers and cover.
Remove o-ring from cover.
3. Remove control piston and remove three (3) o-rings from
control piston.
4. Remove large retaining ring from body and remove inlet/
exhaust valve assembly .
5. Remove ring from inlet/exhaust valve assembly. Remove
o-ring retainer, remove o-ring from o-ring retainer.
Remove washer and spring. Remove valve retainer and
valve from valve body.
6. Remove four (4) cap screws from other cover. (Do not
disturb center cap screw unless spring brake hold off
pressure is to be adjusted). See Section “Adjustment
of Modulating V alve”.
7. Remove cover and inner and outer springs.
8. Remove balance piston. Remove o-ring from balance
piston.
9. Remove retaining ring from supply port and remove
supply adapter and double check valve assembly.
Remove o-ring from supply adapter. Remove double
check valve from shuttle guide. (NOTE: T o ease removal
of supply adapter, a pipe nipple can be screwed in
adapter.)
10. Remove allen head plug from single check valve service
port. Remove single check valve assembly . (If single
check valve is difficult to remove, it can be dislodged
inside bore of body of valve).
4
ASSEMBLY
Before assembly, lightly lubricate all o-rings, bores and
mating surfaces with silicone lubricant BW-650-M (Bendix
Pc. No. 291 126).
1. Install single check valve assembly and allen head plug.
Tighten securely .
2. Install o-ring on supply adapter, install shuttle guide over
supply adapter and install double check valve in guide.
3. Install adapter and double check valve assembly in
supply port. Install retaining ring, making certain the
retaining ring is engaged in groove.
4. Install o-ring on balance piston and install balance piston
in bore of body .
5. Install inner and outer springs and spring seat (note
that cone shaped protrusion on spring seat faces
springs).
6. Install cover with four (4) cap screws, torque to
approximately 45 in. lbs. (Do not disturb center cap
screw unless spring brake hold-off pressure is to be
adjusted. See section “Adjustment of Modulating
V alve”).
7. Install valve on valve body. Install valve ret ainer, spring,
and washer. Install o-ring on o-ring retainer. Install
o-ring retainer , compress ret ainer and install retaining
ring, making certain retaining ring is engaged in groove
of valve body .
8. Install inlet/exhaust valve assembly in body. Install
retaining ring making certain the retaining ring is engaged
in groove in bore of body .
9. Install three (3) o-rings on control piston. Install control
piston in body . (Larger diameter stem should point up).
10.Install o-ring on cover. Install cover with four (4) cap
screws and lockwashers. T orque to approximately 100
in. lbs.
1 1. Install exhaust diaphragm and exhaust cover.
TESTING REBUILT R-7™ MODULATING VALVE
Perform operating and leakage tests as outlined in “Service
Tests” section.
5
6
BW1445 © 2004 Bendix Commercial Vehicle Systems LLC. All rights reserved. 3/2004 Printed in U.S.A.
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