BENDIX BW2271 User's Manual
Contents
1. SCHEMATIC WITH PP 1 PARK CONTROL AND DC 4 DOUBLE CHECK VALVE CONTROL LINE PRESSURE SECONDARY RESERVOIR CONSTANT PRESSURE INLET EXHAUST VALVE OPEN FIGURE 5 CHARGING LESS THAN 107 PSI 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 Bendix 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 LINE PRESSURE SECONDARY RESERVOIR CONSTANT PRESSURE INLET EXHAUST VALVE SEATED FIGURE 6 CHARGING GREATER THAN 107 PSI 4 BALANCE PORT CONTROL PORT DELIVERY TO SPRING BRAKES CHARGING SPRING BRAKE ACTUATORS 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 BALANCE PORT CONTROL PORT DELIVERY TO SPRING BRAKES CONTROL LINE PRESSURE SECONDARY RESERVOIR CONSTANT PRESSURE INLET EXHAUST VALVE SEATED FIGURE 7 NORMAL SERVICE APPLICATION NORMAL SERVICE APPLICATION FIGURE 7 During a service brake application the valve remains in the lap position The Bendix SR 7 valve monitors the presence of air pressure in2. MOUNTING STUDS 2 41 03 9043 41 BALANCE PORT PARK CONTROL FROM DASH VALVE CONTROL PORT 2 DELIVERY EXHAUST 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 I SUPPLY PORT 3 EXHAUST 2 DELIVERY 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 MAIN PISTON DOUBLE CHECK VALVE CONTROL PISTON O RING SPRING GUIDE CHECK VALVE COVER i PARK CONTROL PORT _ IN LINE SINGLE CHECK VALVE SPRING O RING SUPPLY 9 CHECK VALVE GUIDE O RING BALL CHECK VALVE PRIN O RING O RING VALVE SEAT RETAINING RING EXHAUST PORT DIAPHRAGM 10 TORX HEAD SCREW DIAPHRAGM WASHER UPPER BODY RETAINING RING O RING O RING SPACER MAIN PISTON
3. RE 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 Bendix 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 BALANCE PORT PRIMARY All CIRCUIT PRESSURE CONTROL PORT LOSS OF SECONDARY CIRCUIT PRESSURE DELIVERY TO SPRING BRAKES FIGURE 10 SERVICE APPLICATION LOSS OF SECONDARY CIRCUIT 6 NO CONTROL LINE PRESSURE SECONDARY RESERVOIR CONSTANT PRESSURE INLET EXHAUST VALVE OPEN FIGURE 11 ANTI COMPOUNDING ANTI COMPOUNDING FIGURE 11 The Bendix 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 procedur
4. SPRING STATIC PISTON O RING O RING STATIC PISTON SPRING O RING O RING O RING LOWER BODY VALVE RETAINER SPRING 1 4 20 MACHINE SCREWS INLET EXHAUST VALVE LOWER VALVE GUIDE RETAINING RING FIGURE 2 SECTIONAL VIEW OF SR Z SPRING BRAKE MODULATING VALVE USED IN RELAY VALVE APPLICATIONS OPERATION The operation guidelines shown in this manual represent the relay valve based Bendix 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 SYSTEM FOR A 4X2 OR 6X4 STRAIGHT TRUCK WITH PP DC PARKING CONTROL gt BRAKE 5 8T 2 PLACES a 3 8H 4 PLACES VALVE SD 1 2T Es cael SR 7 valve w ar Ie single check valve Ref 5010914 1 2H 4 PLACES 3 8H 2 PLACES 5 8T ALL TUBING 3 8 INCH O D UNLESS OTHERWISE NOTED FIGURE 3 SYSTEM SCHEMATIC WITH PP DC PARK CONTROL SYSTEM FOR A 4X2 OR 6X4 STRAIGHT TRUCK WITH PP 1 PARKING CONTROL 3 8H 4PLACES 1 2T 2 PLACES IFS x SR 7 valve w out I single check valve 3 8H 2 PLACES ALL TUBING 3 8 INCH O D UNLESS OTHER WISE NOTED FIGURE 4 SYSTEM
5. VED 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 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 a Bendix 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 rem
6. both primary and secondary delivery circuits BALANCE PORT PRIMARY lli CIRCUIT PRESSURE CONTROL PORT SECONDARY 48 CIRCUIT PRESSURE DELIVERY TO SPRING BRAKES 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 MAIN AND CONTROL PISTONS MOVE UP CONTROL LINE SECONDARY RESERVOIR CONSTANT PRESSURE INLET VALVE SEATED FIGURE 8 PARKING BALANCE PORT CONTROL PORT AIR EXHAUSTS FROM All SPRING BRAKES MAIN PISTON MOVES UP CONTROL LINE PRESSURE SECONDARY RESERVOIR CONSTANT PRESSURE BALANCE PORT LOSS OF PRIMARY CIRCUIT PRESSURE CONTROL PORT SECONDARY CIRCUIT PRESSURE FIGURE 9 SERVICE APPLICATION LOSS OF PRIMARY 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 CONTROL LINE PRESSURE IN LINE SINGLE CHECK VALVE SECONDARY RESERVOIR NO PRESSURE SERVICE APPLICATION WITH LOSS OF AIR IN SECONDARY CIRCUIT FIGU
7. es 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 BALANCE PORT lt ii PRIMARY CIRCUIT PRESSURE CONTROL PORT All SECONDARY CIRCUIT PRESSURE DELIVERY TO SPRING BRAKES 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 Alag more than 3 sec
8. isassembly TESTING THE REPLACEMENT 5 7 SPRING BRAKE MODULATING VALVE Perform operating and leakage tests as outlined in Operating Tests section BW2271 2011 Bendix Commercial Vehicle Systems LLC 1 2011 Printed in U S A All rights reserved
9. onds 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 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 THE VALVE CONTAINS HIGH SPRING FORCES THAT COULD RESULT IN PERSONAL INJURY IF DISASSEMBLY IS ATTEMPTED SERVICING THE SR 7 VALVE GENERAL SAFETY GUIDELINES 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 OBSER
10. ove a component or plug unless you are certain all system pressure has been depleted 8 Use only genuine Bendix brand 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 Automatic 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 VALVE 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 VALVE INSTALLATION 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 d
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