BENDIX SR-2 TRAILER SPRING BRAKE VALVE

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SD-03-4510

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 ﬂ owing past the open

pressure protection valve opens the service reservoir check

valve. Air passing through the service reservoir check

Bendix

SR-2

™

Trailer Spring Brake Valve

RETAINER

DIAPHRAGM (11)

(19) SCREW

(20) WASHER

BODY

PARTIAL VIEW OF EXHAUST

FOR PC. NO. 287376

EXTERIOR

SECTIONAL

CHECK VALVES (10)

(SHOWN OUT OF

POSITION)

SCREW (16)

CHECK VALVE (10)

RETAINER (17)

SPRING (9)

PISTON (8)

O-RING (2)

COVER (12)

CAP SCREW (13)

O-RINGS (1)

CONTROL

PISTON (14)

SEAL RING (4)

EXHAUST PORT

SPRING (3)

VENT

INLET/EXHAUST

VALVE (5)

INLET VALVE

SPRING (6)

O-RING (7)

RES.

FTG.

(15)

FIGURE 1

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Summary

Operation

Charging Process

Explains how air pressure charges the SR-2™ valve and releases spring brakes.

Park Application

Details the process of applying trailer spring brakes for parking.

Service Application with Anti-Compounding

Describes how service application interacts with applied parking brakes.

System Failures and Maintenance

Service System Failure

Explains trailer spring brake behavior during service system air pressure loss.

Emergency Application with Service Failure

Describes emergency braking when the service system fails.

Service and Leakage Tests

Safety Precautions

General Safety Precautions

Critical safety instructions to follow when working on the vehicle.