BENDIX TCH-001-040 User Manual

Technical Bulletin

Bulletin No: Effective Date: Cancels: Page: 1 of
Subject:

The Bendix® ST-4™ safety valve is available for installation into the cylinder head of the Bendix® Tu-Flo® 550,
Tu-Flo® 750, BA-921® and BA-922® compressors to prevent excessive cylinder head pressure in the event the
discharge line is blocked. The excessive pressure typically results in compressor damage and may cause
subsequent engine damage.

These safety valves are installed in the unused compressor discharge port. During normal operation the air
pressure in the compressor exerts a force on the safety valve piston, which is held against its seat by the safety
valve spring. When the operating pressure acting upon the safety valve piston exceeds the force of the safety
valve spring, the safety valve piston opens and vents the pressure to atmosphere. The safety valve is preset
to relieve pressures above 250 psi and comes in a variety of thread sizes as shown in the table below.

Because these safety valves are designed specifi cally for this application, a standard safety valve must not be
used in lieu of the valves shown here.

TCH-001-040

10/25/2011

SAFETY VALVE FOR INSTALLATION ON BENDIX COMPRESSORS

Hex

Install In Unused

Compressor Discharge Port

PRO-01-40 dated 12/1/94

1

Thread

Size

ST-4™ Safety

Valve

Typical Compressor

Cylinder Head

Bendix®

ST-4™ Safety Valve

Piece No. Thread Size Hex Size

131081

(includes washer)

800154 1/2-14 7/8” 2
800533 3/4-16 7/8” 2
800534 M16 7/8” 2

801116 7/8-14 15/16” 2

© 2011 Bendix Commercial Vehicle Systems LLC, a member of the Knorr-Bremse Group • 10/2011 • All Rights Reserved.

1/4-18 9/16” 2

Number of

Exhaust

Holes

Pressure

Setting

250 psi

Hole