User manual BENDIX SR-7 SPRING BRK MODULATING VALVE

[. . . ] This maintains the spring brake hold-off pressure at 107 psi (nominal). à à à CONTROL LINE PRESSURE à à àà BALANCE PORT SECONDARY RESERVOIR CONSTANT PRESSURE CONTROL PORT à INLET / EXHAUST VALVE SEATED FIGURE 6 - CHARGING GREATER THAN 107 PSI 4 DELIVERY TO SPRING BRAKES à à à CONTROL LINE PRESSURE à à àà BALANCE PORT - PRIMARY CIRCUIT PRESSURE CONTROL PORT - SECONDARY CIRCUIT PRESSURE à 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 SR-7TM valve monitors the presence of air pressure in both primary and secondary delivery circuits. PARKING (FIGURE 8) Actuating the park brakes (by pulling the dash valve button out) exhausts spring brake air pressure through the SR-7TM valve exhaust port. MAIN AND CONTROL PISTONS MOVE UP à SECONDARY RESERVOIR CONSTANT PRESSURE FIGURE 8 - PARKING 5 à INLET VALVE SEATED à à CONTROL LINE PRESSURE à à à à à SECONDARY RESERVOIR CONSTANT PRESSURE à à à DELIVERY TO SPRING BRAKES BALANCE PORT CONTROL PORT AIR EXHAUSTS FROM SPRING BRAKES MAIN PISTON MOVES UP à à à CONTROL LINE PRESSURE à à INLET VALVE SEATED 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. 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-7TM valve. [. . . ] 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. 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-7TM valve delivery port. Place parking control valve in "release" position. 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. 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-7TM valve should be inspected every 6 months or 1500 operating hours, whichever comes first, for proper operation. Should the SR-7TM valve not meet the elements of the operational tests noted in this document, further investigation and service of the valve may be required. à à SECONDARY RESERVOIR CONSTANT PRESSURE à à BALANCE PORT PRIMARY CIRCUIT PRESSURE CONTROL PORT SECONDARY CIRCUIT PRESSURE à à 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-7TM VALVE. THE VALVE CONTAINS HIGH SPRING FORCES THAT COULD RESULT IN PERSONAL INJURY IF DISASSEMBLY IS ATTEMPTED! SERVICING THE SR-7TM VALVE 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. Park the vehicle on a level surface, apply the parking brakes, and always block the wheels. 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. [. . . ] 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. Prior to returning the vehicle to service, make certain all components and systems are restored to their proper operating condition. VALVE REMOVAL 1. Prior to removing the SR-7TM valve, apply the parking brakes and drain all the vehicle reservoirs. [. . . ]