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SD-03-4510 |
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Bendix® SR-2™ Trailer Spring Brake Valve |
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SCREW (16) |
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RETAINER (17) |
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SPRING (9) |
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CHECK VALVE (10) |
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PISTON (8) |
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CHECK VALVES (10) |
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O-RING (2) |
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COVER (12) |
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(SHOWN OUT OF |
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POSITION) |
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CAP SCREW (13) |
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RES. |
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FTG. |
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O-RINGS (1) |
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(15) |
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CONTROL |
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PISTON (14) |
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SEAL RING (4) |
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O-RING (7) |
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VENT |
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INLET VALVE |
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EXHAUST PORT |
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SPRING (6) |
INLET/EXHAUST |
SPRING (3) |
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VALVE (5) |
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SECTIONAL |
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BODY |
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RETAINER |
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EXTERIOR |
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DIAPHRAGM (11) |
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(20) WASHER |
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(19) SCREW |
PARTIAL VIEW OF EXHAUST |
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FOR PC. NO. 287376 |
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FIGURE 1 |
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DESCRIPTION
In a trailer air brake system, the SR-2™ spring brake valve controls the functioning of the spring brakes during parking and emergency applications. It is responsible for automatically applying the spring brakes and preventing trailer air pressure loss in the event of breakaway or supply line failure. The SR-2™ valve also prevents the automatic application of the trailer spring brakes after the loss of trailer service reservoir pressure while allowing failure indication to occur in the tractor.
The SR-2™ valve is provided with one 3/4” male pipe thread connection for mounting the valve to the trailer brake reservoir. Other porting includes:
One - 1/4” pipe thread supply port
Four - 3/8” pipe thread delivery ports
Two - 1/4” pipe thread service reservoir ports
One - 3/8” pipe thread exhaust port
OPERATION
CHARGING (Figure 2)
Air from the trailer supply line enters the SR-2™ valve trailer supply port and moves the control piston into contact with the control inlet and exhaust valve, sealing off the exhaust passage through the control piston, and opening the inlet. Air entering the supply port is also conducted to the underside of the pressure protection piston. When air pressure builds to approximately 55 psi beneath the pressure protection piston, the piston moves against the force of the piston spring and the pressure protection inlet valve opens and remains open. Air flowing past the open pressure protection valve opens the service reservoir check valve. Air passing through the service reservoir check
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valve flows out the service reservoir port and then opens the spring brake reservoir check valve, allowing air to fill the spring brake reservoir. As air is filling the spring brake reservoir, it also flows by the open control inlet and out the delivery ports of the SR-2™ valve into the spring brake emergency ports releasing the spring brakes.
PARK APPLICATION (Fig. 3)
To park the trailer, either the trailer supply valve or the parking control valve, which are located in the cab, are actuated and the trailer supply line is exhausted. When the trailer supply line is exhausted, air pressure is removed
SERVICE |
PRESS. |
SERVICE |
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RESERVOIR |
PROTECTION |
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CHECK VALVE |
VALVE |
RESERVOIR |
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PRESS. |
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SPRING BRAKE |
PROTECTION |
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INLET VALVE |
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RESERVOIR |
CONTROL |
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CHECK VALVE |
PISTON |
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SPRING |
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TRAILER SUPPLY |
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BRAKE |
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LINE |
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RESERVOIR |
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TRAILER SERVICE |
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CONTROL INLET & |
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LINE |
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EXHAUST VALVE |
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RELAY VALVE OR |
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SPRING BRAKE |
MODULATOR |
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FIGURE 2 - SR-2™ TRAILER SPRING BRAKE VALVE |
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CHARGING ABOVE 55 PSI |
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SERVICE |
PRESS. |
SERVICE |
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PROTECTION |
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RESERVOIR |
VALVE |
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RESERVOIR |
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CHECK VALVE |
PRESS. |
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SPRING BRAKE |
PROTECTION |
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INLET VALVE |
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RESERVOIR |
CONTROL |
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PISTON |
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CHECK VALVE |
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SPRING |
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TRAILER SUPPLY |
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BRAKE |
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LINE |
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RESERVOIR |
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TRAILER SERVICE |
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CONTROL INLET & |
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LINE |
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EXHAUST VALVE |
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RELAY VALVE OR
MODULATOR
SPRING BRAKE
FIGURE 3 - SR-2™ TRAILER SPRING BRAKE VALVE PARK APPLICATION
SERVICE |
PRESS. |
SERVICE |
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RESERVOIR |
PROTECTION |
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CHECK VALVE |
VALVE |
RESERVOIR |
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PRESS. |
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SPRING BRAKE |
PROTECTION |
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INLET VALVE |
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RESERVOIR |
CONTROL |
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CHECK VALVE |
PISTON |
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SPRING |
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TRAILER SUPPLY |
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BRAKE |
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LINE |
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RESERVOIR |
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TRAILER SERVICE |
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CONTROL INLET & |
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LINE |
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EXHAUST VALVE |
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RELAY VALVE OR |
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SPRING BRAKE |
MODULATOR |
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FIGURE 4 - SR-2™ TRAILER SPRING BRAKE VALVE |
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OPTIONAL ANTI-COMPOUNDING |
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from the control and pressure protection pistons. With air pressure removed the control piston is moved by the return spring, control inlet valve closes and the exhaust passage through the control piston opens. Opening the exhaust allows air in the spring brake emergency section to be exhausted out the exhaust port of the SR-2™ valve. Spring force above the pressure protection piston closes the pressure protection valve while the service and spring brake reservoir check valves close and protect against the loss of pressure in either reservoir.
SERVICE APPLICATION WITH PARKING BRAKES APPLIED OPTIONAL ANTI-COMPOUNDING PIPING (Fig. 4)
With the optional anti-compounding feature of the SR-2™ valve in use, the exhaust port of the SR-2™ valve receives normal service application pressure through a line connecting it to the delivery of the trailer service system. If a service brake application is made while the spring brakes are applied, compounding of both applications is prevented by service air pressure entering the SR-2™ valve exhaust port, flowing through the exhaust passage of the control piston, past the open exhaust valve and out the SR-2™ valve delivery port to the emergency section of the spring brakes.
NOTE: During normal vehicle operation, with the spring brakes released, service air pressure will enter the SR-2™ valve as described, but will stop at the closed exhaust valve. See Figure 2.
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