®
Bendix® SR-7™ Spring Brake Modulating Valve
MOUNTING
STUDS (2)
4-1
PARK CONTROL
(FROM DASH
VALVE)
42
CONTROL
PORT
EXHAUST
2
DELIVERY
1
SUPPLY
PORT
3
EXHAUST
SD-03-9043
41
BALANCE
PORT
2
DELIVERY
PIPE PLUG
(INCLUDED IN
QUICK RELEASE
VALVE
APPLICATIONS)
FIGURE 1 - EXTERIOR VIEW
DESCRIPTION
The Bendix® SR-7™ spring brake modulating valve is used in
conjunction with a dual air brake system and spring brake
actuator and performs the following functions:
1. Provides a rapid application of the spring brake actuator
when parking.
2. Modulates the spring brake actuator application using
the dual brake valve should a primary failure occur in
the service brake system.
3. Prevents compounding of service and spring forces.
The valve has one park control, one service control, one
supply, one balance, four delivery NPTF ports, and an
exhaust port protected by an exhaust diaphragm. The valve
incorporates two mounting studs for mounting the valve to
the frame rail or cross member (where applicable).
1
MAIN PISTON
DOUBLE CHECK
VALVE
CHECK VALVE
COVER
PARK CONTROL
PORT
IN-LINE SINGLE
CHECK VALVE
SPRING
SUPPLY PORT
CHECK VALVE
GUIDE
O-RING
O-RING
O-RING
CONTROL PISTON
SPRING GUIDE
UPPER BODY
RETAINING RING
O-RING
O-RING
SPACER
MAIN PISTON SPRING
STATIC PISTON
O-RING
O-RING
STATIC PISTON
SPRING
O-RING
O-RING
O-RING
LOWER BODY
BALL CHECK
VALVE
SPRING
FIGURE 2 - SECTIONAL VIEW OF SR-7™ SPRING BRAKE MODULA TING VAL VE USED IN RELA Y V A LVE APPLICA TIONS
O-RING
O-RING
VALVE SEAT
RETAINING RING
DIAPHRAGM
DIAPHRAGM WASHER
EXHAUST
PORT
#10 TORX HEAD SCREW
VALVE RETAINER
SPRING
1/4-20 MACHINE
SCREWS
INLET / EXHAUST
VALVE
LOWER VALVE
GUIDE
RETAINING RING
OPERATION
The operation guidelines shown in this manual represent
the relay valve based SR-7™ (refer to system schematic
shown in figure 3). A quick release based valve functions
similarly to the relay valve based version with the exception
that all air delivered to spring brakes passes through the
park control port through the in-line single check valve. The
SR-7™ quick release style can be easily identified by the
pipe plug in the supply port of the valve.
2
PP-DC
VALV E
™
SYSTEM FOR A 4X2 OR 6X4
STRAIGHT TRUCK WITH
PP-DC PARKING CONTROL
™
™
SR-7 Valve w/single check
Ref: 5010914
FIGURE 3 - SYSTEM SCHEMATIC WITH PP-DC™ PARK CONTROL
™
PP-1
VALV E
SYSTEM FOR A 4X2 OR 6X4
STRAIGHT TRUCK WITH
™
PP-1 PARKING CONTROL
SR-7 valve
w/o single check
™
FIGURE 4 - SYSTEM SCHEMATIC WITH PP-1
™
DC-4
VALVE
™
P ARK CONTROL AND DC-4™ DOUBLE CHECK VALVE
3
CONTROL LINE PRESSURE
à
à
à
à
à
à
BALANCE PORT
SECONDARY RESERVOIR
CONSTANT PRESSURE
INLET / EXHAUST VALVE OPEN
FIGURE 5 - CHARGING LESS THAN 107 PSI
à
à
à
CHARGING SPRING BRAKE ACTUATORS
BELOW 107 PSI (FIGURE 5)
With the air brake system charged and the parking brakes
released (by pushing the dash valve button in), air enters
the park control port. This opens the SR-7™ valve to supply
air pressure to the spring brake chambers. As illustrated,
air pressure in the chambers is below 107 psi (nominally).
CONTROL PORT
à
DELIVERY TO SPRING BRAKES
à
CHARGING SPRING BRAKE ACTUA TORS ABOVE
107 PSI (FIGURE 6)
Once the SR-7™ valve delivery pressure reaches 107 psi
(nominal), the inlet and exhaust are closed (valve lap
position). This maintains the spring brake hold-off pressure
at 107 psi (nominal).
CONTROL LINE PRESSURE
à
SECONDARY RESERVOIR
CONSTANT PRESSURE
INLET / EXHAUST VALVE SEATED
FIGURE 6 - CHARGING GREA TER THAN 107 PSI
4
à
à
à
àà
à
BALANCE PORT
CONTROL PORT
DELIVERY TO SPRING BRAKES
à
CONTROL LINE PRESSURE
à
à
à
à
à
à
BALANCE PORT - PRIMARY
à
CIRCUIT PRESSURE
SECONDARY RESERVOIR
CONSTANT PRESSURE
INLET / EXHAUST VALVE SEATED
FIGURE 7 - NORMAL SERVICE APPLICA TION
NORMAL SERVICE APPLICATION (FIGURE 7)
During a service brake application, the valve remains in the
lap position. The SR-7™ valve monitors the presence of air
pressure in both primary and secondary delivery circuits.
à
CONTROL PORT - SECONDARY
à
CIRCUIT PRESSURE
DELIVERY TO SPRING BRAKES
à
PARKING (FIGURE 8)
Actuating the park brakes (by pulling the dash valve button
out) exhausts spring brake air pressure through the SR-7
valve exhaust port.
™
CONTROL LINE PRESSURE
SECONDARY RESERVOIR
CONSTANT PRESSURE
FIGURE 8 - PARKING
MAIN AND CONTROL PISTONS MOVE UP
à
à
INLET V AL VE SEA TED
à
à
à
à
à
à
à
BALANCE PORT
CONTROL PORT
AIR EXHAUSTS FROM
à
SPRING BRAKES
5
CONTROL LINE PRESSURE
à
MAIN PISTON MOVES UP
à
à
à
à
SECONDARY RESERVOIR
CONSTANT PRESSURE
à
à
à
à
à
INLET VALVE SEATED
FIGURE 9 - SERVICE APPLICA TION LOSS OF PRIMAR Y CIRCUIT
SERVICE APPLICATION WITH LOSS OF AIR IN
PRIMARY CIRCUIT (FIGURE 9)
With the parking brakes released (dash valve button in) and
the absence of air in the primary circuit delivery, a service
brake application from the secondary circuit causes the
pressure in the spring brakes to be exhausted proportionally
to this application. This is known as spring brake modulation.
A 30 psi service brake application will exhaust the spring
brake pressure to approximately 60 psi.
LOSS OF
à
à
BALANCE PORT -
PRIMARY CIRCUIT PRESSURE
CONTROL PORT - SECONDARY
à
CIRCUIT PRESSURE
à
à
AIR EXHAUSTS FROM
à
SPRING BRAKES
à
SERVICE APPLICATION WITH LOSS OF AIR IN
SECONDARY CIRCUIT (FIGURE 10)
With the parking brakes released (dash valve button in) and
the absence of air in the secondary circuit reservoir, the
external single check valve in the supply port seals to prevent
air leakage to atmosphere from the SR-7™ valve. The dash
valve delivery air flows through the in-line single check valve
and becomes SR-7™ valve supply air. This air is delivered to
maintain at least 107 psi (nominal) in the spring brake
chambers.
à
à
à
CONTROL LINE PRESSURE
à
à
à
IN-LINE SINGLE
CHECK VALVE
SECONDARY RESERVOIR
NO PRESSURE
FIGURE 10 - SERVICE APPLICATION LOSS OF SECONDARY CIRCUIT
6
à
à
à
à
à
à
BALANCE PORT - PRIMARY
à
CIRCUIT PRESSURE
CONTROL PORT - LOSS OF
SECONDARY CIRCUIT PRESSURE
DELIVERY TO
SPRING BRAKES
à
NO CONTROL LINE
PRESSURE
SECONDARY RESERVOIR
CONSTANT PRESSURE
à
à
à
à
à
à
à
à
à
à
à
à
à
BALANCE PORT -
PRIMARY CIRCUIT PRESSURE
à
SECONDARY CIRCUIT PRESSURE
CONTROL PORT -
à
à
INLET / EXHAUST VALVE OPEN
FIGURE 11 - ANTI-COMPOUNDING
ANTI COMPOUNDING (FIGURE 11)
The SR-7™ valve provides anti-compounding of the service and
spring brake forces. When the park brakes are actuated
(by pulling the dash valve button out), a service brake
application will cause the SR-7™ valve to deliver air pressure
to the spring brake chambers. Thus the vehicle is held
stationary using a service brake application. When the
service brake application is released, the delivery pressure
is exhausted from the spring brake chambers and the vehicle
remains parked using the spring brake actuators.
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 SR-7
valve should be inspected every 6 months or 1500 operating
hours, whichever comes first, for proper operation. Should
the SR-7™ valve not meet the elements of the operational
tests noted in this document, further investigation and service
of the valve may be required.
DELIVERY TO SPRING BRAKES
à
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 the SR-7™ 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. (Correct spring brake actuator
hold-off pressure is 107 psi nominally .)
3. Place parking control valve in “park” position - gauge
reading should drop to zero promptly . A lag (more than
3 seconds) in drop of pressure would indicate faulty
operation.
4. With the parking control valve in the “park” position,
gradually apply foot brake valve and note a pressure
reading increase on the gauge installed in the SR-7
™
valve delivery port.
5. Place parking control valve in “release” position.
6. Drain the reservoir, which supplies the rear service brake
circuit, apply the foot brake valve several times and note
that pressure reading on gauge decreases each time
foot brake valve is applied (spring brake modulation).
After the 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.
™
7
LEAKAGE TEST
Place the park control valve in the “release” position; using
a soap solution, coat all ports including the exhaust port. A
1" bubble in 3 seconds is permitted (175 SCCM).
If the valve does not function as described, or if leakage is
excessive, it is recommended that it be replaced with a new
or remanufactured unit available from a Bendix parts outlet.
DO NOT ATTEMPT TO DISASSEMBLE THE SR-7
V AL VE. THE VAL VE CONT AINS HIGH SPRING FORCES
THAT COULD RESULT IN PERSONAL INJURY IF
DISASSEMBL Y IS A TTEMPTED!
SERVICING THE SR-7™ VA LV E
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.
V AL VE REMOVAL
1. Prior to removing the SR-7™ valve, apply the parking
brakes and drain all the vehicle reservoirs.
2. Identify all air lines before disconnecting.
3. Remove the two mounting nuts that secure the valve to
the frame rail and remove the valve.
V AL VE INST ALLA TION
1. Align the mounting studs with the mounting holes on
the vehicle frame rail. Tighten the mounting nuts to
180-220 in. lbs.
2. Install the valve onto the vehicle ensuring all ports are
connected as marked during disassembly .
TESTING THE REPLACEMENT SR-7™ SPRING
BRAKE MODULA TING VALVE
Perform operating and leakage tests as outlined in “Operating
™
Tests” section.
8
BW2271 © 2004 Bendix Commercial Vehicle Systems LLC 3/2004. Printed in U.S.A. All rights reserved.
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