BENDIX ST-1 ST-3 SAFETY VALVE User manual

DESCRIPTION

The safety valve protects the air brake system against

excessiveairpressurebuild-up.Thevalveconsistsofaspring

loaded ball valve subjected to reservoir pressure which will

permit air to exhaust reservoir pressure to atmosphere if

reservoirpressure risesabove thevalves pressure setting,

which is determined by the force of the spring.

OPERATION

Toillustratetheoperationofthesafetyvalve,weshallassume

that the governor cutout pressure is set at 125 psi.Asafety

valve with a setting of 150 psi could then be used. Should

system pressure rise to approximately 150 psi air pressure

would force the ball valve off its seat, and allow reservoir

pressure to vent to atmosphere through the exhaust port in

the spring cage.

When reservoir pressure decreases sufficiently, the spring

force will seat the ball check valve, sealing off reservoir

pressure.This wouldoccur atapproximately135psiforthe

150psivalve.Itisimportanttonotethatthedesiredpressure

setting of the safety valve is determined by the governor

cutout pressure. The opening and closing pressures of the

safety valve should always be in excess of governor cutout

pressure setting. The pressure setting is stamped on the

lowerwrench flatofthevalve.

Normally, the safety valve remains inoperative and only

functionsiffor anyreasonreservoirpressure risesabovethe

settingof thevalve. Constant“poppingoff”orexhaustingof

thesafetyvalvecanbecausedbyafaultysafetyvalve,faulty

governor, faulty compressor unloading mechanism, or a

combination of any of the preceding.

PREVENTIVE MAINTENANCE

Important: Review the Bendix Warranty Policy before

performinganyintrusivemaintenanceprocedures.Awarranty

maybe voidedif intrusivemaintenance isperformed during

thewarranty period.

No two vehicles operate under identical conditions, as a

result, maintenance intervals may vary. Experience is a

valuableguide indeterminingthe bestmaintenance interval

for air brake system components.At a minimum, the safety

valveshouldbe inspectedevery6monthsor1500operating

hours, whichever comes first, for proper operation. Should

the safety valve not meet the elements of the operational

testsnotedinthisdocument,furtherinvestigationandservice

ofthe valvemay berequired.

OPERATING AND LEAKAGE CHECKS

OPERATING TEST: With air pressure in the system, pull

theexposed endof thevalvestemremovingthe springload

fromtheballcheckvalve.Airshouldexhaustfromthevalve’s

exhaust port. Release the stem, the air flow should stop.

Failure of valve to pass operating test would indicate the

valve should be disassembled, cleaned and rebuilt. (See

“Disassembly and Assembly” section). If adjustment is

necessary, see “Adjustment” section.

LEAKAGE CHECK: Coat the exhaust port with soap

solution.Aleakage ofa 1”bubble in5 secondsis permitted.

Excessiveleakage indicatesdirt invalve,faultyballvalve or

seat. Valve should be disassembled, cleaned and rebuilt.

(See “Disassembly and Assembly” section).

REMOVING AND INSTALLING

REMOVING

1. Block wheels or otherwise secure vehicle and drain

reservoirs.

2. Usingwrenchflatclosesttoreservoir,unscrewvalvefrom

reservoir.

INSTALLING

Safety valve should be installed in same reservoir that

compressor discharge line is connected to. Install in a

convenient location in a top port of the reservoir. If safety

valveisinstalledhorizontally,exhaustportshouldpointdown,

stemof thevalve shouldfacerearofvehicle.

PRESSURE

SETTING

150 PSI

EXHAUST

PORT

ST-3™

VALVE

ST-1™

VALVE

SD-03-1901

Bendix®ST-1™& ST-3™Safety Valve

DISASSEMBLY: ST-1™ADJUSTABLE VALVE

1. Clamplower wrenchflatinvise (flatnearestpipethread).

2. Usingupper wrenchflat,unscrew locknut.Unscrew and

removespring cagefrombody ofvalve.

3. Remove ball valve, spring and release pin from spring

cage.

DISASSEMBLY: ST-3™NON-ADJUSTABLE VALVE

1. Clamp spring cage in soft jawed vise.

2. Using wrench flat, unscrew body from spring cage.

3. Remove ball valve, spring and release pin from spring

cage.

CLEANING AND INSPECTION

Clean all parts in mineral spirits. Inspect all parts.All parts

notconsideredserviceableshouldbereplaced withgenuine

Bendix replacement parts.

ASSEMBLY: ST-1™ADJUSTABLE VALVE

1. Place the ball valve in body.

2. Installspringandreleasepininspringcagewithadjusting

screw.

3. Positionthe releasepin overballvalve. Screwbody with

ball into the spring cage. Tighten securely.

4. Adjust for proper setting (see “Adjustment” section).

ASSEMBLY: ST-3™NON-ADJUSTABLE VALVE

1. Install spring, release pin in spring cage.

2. Position ball valve in body and screw spring cage onto

body.

3. Hold spring cage in soft jawed vise and tighten body

securely.

TO RAISE PRESSURE SETTING

1. Loosen lock nut.

2. Turn adjusting nut clockwise to obtain correct pressure

setting.

3. Tighten lock nut.

TO LOWER PRESSURE SETTING

1. Loosen lock nut.

2. Turn adjusting nut counter clockwise to obtain correct

pressure setting.

3. Tighten lock nut.

TESTING OF REBUILT SAFETY VALVES:

Performoperating and leakagechecks.

ADJUSTMENT OF SAFETY VALVE

NOTE:The ST-3™safety valveis notadjustable.

The pressure setting of the safety valve is stamped on the

cover wrench flat (closest to the pipe thread). The vehicle

manual may also provide the proper pressure setting. If

setting is not known, determine governor cutout pressure

settingandadjustsafetyvalvesothatthesafetyvalvecloses

at a pressure setting somewhat above governor cutout

pressuresetting(See “Operation” section).

To adjust, the safety valve must be connected to an air

system with air pressure in excess of desired setting. It is

importantthatan accurategaugebe usedtocheckpressure

settings while making adjustments.

WARNING! PLEASE READ AND FOLLOW

THESE INSTRUCTIONS TO AVOID

PERSONAL INJURYOR DEATH:

When working on or around a vehicle, the following

general precautions should be observed at all times.

1. Park the vehicle on a level surface, apply the park-

ing 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 work-

ing 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 electri-

cally charged components.

3. Do not attempt to install, remove, disassemble or

assemble a component until you have read and

thoroughly understand the recommended proce-

dures. Use only the proper tools and observe all

precautions pertaining to use of those tools.

ST-3™SAFETY

VALVE

ADJUSTING

NUT

SPRING

CAGE

LOCK

NUT

SPRING

RELEASE

BALL

VALVE

PIPE

THREAD

BODY

ST-1™SAFETY

VALVE

BODY

SPRING

CAGE

PIPE

THREAD

BALL

VALVE

SPRING

RELEASE

4. If the work is being performed on the vehicle’s air

brake system, or any auxiliary pressurized air sys-

tems, make certain to drain the air pressure from

all reservoirs before beginning ANY work on the

vehicle. If the vehicle is equipped with an AD-IS®

air dryer system or a dryer reservoir module, be

sure to drain the purge reservoir.

5. Following the vehicle manufacturer’s recom-

mended 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 con-

taining pressure; it may whip. Never remove a

component or plug unless you are certain all

system pressure has been depleted.

8. Use only genuine Bendix®replacement parts, com-

ponents 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 weld-

ing unless specifically stated and approved by the

vehicle and component manufacturer.

10. Prior to returning the vehicle to service, make

certainallcomponentsandsystemsarerestoredto

their proper operating condition.

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