Instruction Manual

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Bendix

SR-7

Spring Brake Modulating Valve

SD-03-9043

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).

MOUNTING

STUDS (2)

EXHAUST

CONTROL

PORT

DELIVERY

SUPPLY PORT

BALANCE

PORT

FIGURE 1 - EXTERIOR VIEW

EXHAUST

DELIVERY

4-1

PARK CONTROL

(FROM DASH VALVE)

PIPE PLUG

(INCLUDED IN QUICK

RELEASE VALVE

APPLICATIONS)

Summary of content (8 pages)

PAGE 1
SD-03-9043 Bendix® SR-7® Spring Brake Modulating Valve MOUNTING STUDS (2) 41 BALANCE PORT 4-1 PARK CONTROL (FROM DASH VALVE) 42 CONTROL PORT 2 DELIVERY EXHAUST 1 SUPPLY PORT 3 EXHAUST 2 DELIVERY PIPE PLUG (INCLUDED IN QUICK RELEASE VALVE APPLICATIONS) FIGURE 1 - EXTERIOR VIEW DESCRIPTION 3. Prevents compounding of service and spring forces.
PAGE 2
MAIN PISTON CONTROL PISTON DOUBLE CHECK VALVE O-RING SPRING GUIDE CHECK VALVE COVER UPPER BODY RETAINING RING O-RING PARK CONTROL PORT O-RING SPACER IN-LINE SINGLE CHECK VALVE MAIN PISTON SPRING STATIC PISTON SPRING O-RING O-RING O-RING SUPPLY PORT STATIC PISTON SPRING O-RING CHECK VALVE GUIDE O-RING O-RING O-RING LOWER BODY BALL CHECK VALVE SPRING VALVE RETAINER SPRING O-RING 1/4-20 MACHINE SCREWS O-RING INLET / EXHAUST VALVE VALVE SEAT LOWER VALVE GUIDE RETAINING RING EXHAUST POR
PAGE 3
PP-DC® VALVE SYSTEM FOR A 4X2 OR 6X4 STRAIGHT TRUCK WITH PP-DC® PARKING CONTROL R-12® Relay Valve SR-7® valve w/ single check valve Ref: 5010914 FIGURE 3 - SYSTEM SCHEMATIC WITH PP-DC® PARK CONTROL PP-1® VALVE SYSTEM FOR A 4X2 OR 6X4 STRAIGHT TRUCK WITH PP-1® PARKING CONTROL ® R-12 Relay Valve SR-7® valve w/ out single check valve DC-4® VALVE FIGURE 4 - SYSTEM SCHEMATIC WITH PP-1® PARK CONTROL AND DC-4® DOUBLE CHECK VALVE 3
PAGE 4
CONTROL LINE PRESSURE BALANCE PORT SECONDARY RESERVOIR CONSTANT PRESSURE CONTROL PORT DELIVERY TO SPRING BRAKES INLET / EXHAUST VALVE OPEN FIGURE 5 - CHARGING LESS THAN 107 PSI CHARGING SPRING BRAKE ACTUATORS BELOW 107 PSI (FIGURE 5) CHARGING SPRING BRAKE ACTUATORS ABOVE 107 PSI (FIGURE 6) With the air brake system charged and the parking brakes released (by pushing the dash valve button in), air enters the park control port.
PAGE 5
CONTROL LINE PRESSURE BALANCE PORT - PRIMARY CIRCUIT PRESSURE SECONDARY RESERVOIR CONSTANT PRESSURE CONTROL PORT - SECONDARY CIRCUIT PRESSURE DELIVERY TO SPRING BRAKES INLET / EXHAUST VALVE SEATED FIGURE 7 - NORMAL SERVICE APPLICATION NORMAL SERVICE APPLICATION (FIGURE 7) PARKING (FIGURE 8) During a service brake application, the valve remains in the lap position. The Bendix® SR-7® valve monitors the presence of air pressure in both primary and secondary delivery circuits.
PAGE 6
MAIN PISTON MOVES UP CONTROL LINE PRESSURE BALANCE PORT - LOSS OF PRIMARY CIRCUIT PRESSURE SECONDARY RESERVOIR CONSTANT PRESSURE CONTROL PORT - SECONDARY CIRCUIT PRESSURE AIR EXHAUSTS FROM SPRING BRAKES INLET VALVE SEATED FIGURE 9 - SERVICE APPLICATION LOSS OF PRIMARY CIRCUIT SERVICE APPLICATION WITH LOSS OF AIR IN PRIMARY CIRCUIT (FIGURE 9) 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 prim
PAGE 7
NO CONTROL LINE PRESSURE BALANCE PORT PRIMARY CIRCUIT PRESSURE SECONDARY RESERVOIR CONSTANT PRESSURE CONTROL PORT SECONDARY CIRCUIT PRESSURE DELIVERY TO SPRING BRAKES INLET / EXHAUST VALVE OPEN FIGURE 11 - ANTI-COMPOUNDING ANTI COMPOUNDING (FIGURE 11) OPERATING TEST The Bendix® SR-7® valve provides anti-compounding of the service and spring brake forces.
PAGE 8
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® VALVE.