BENDIX SD-03-1901 User Manual
®
Bendix® ST-1™ & ST-3™ Safety Valve
EXHAUST
PORT
SD-03-1901
Normally, the safety valve remains inoperative and
only functions if for any reason reservoir pressure rises
above the setting of the valve. Constant “popping off” or
exhausting of the safety valve can be caused by a faulty
safety valve, faulty governor, faulty compressor unloading
mechanism, or a combination of any of the preceding.
PRESSURE
SETTING
150 PSI
®
BENDIX
ST-1™ VALV E
ST-3™ VALV E
BENDIX
®
DESCRIPTION
The safety valve protects the air brake system against
excessive air pressure build‑up. The valve consists of a
spring‑loaded ball valve subjected to reservoir pressure
which will permit air to exhaust reservoir pressure to
atmosphere, if the reservoir pressure rises above the
valves pressure setting. This pressure is determined by
the force of the spring.
OPERATION
To illustrate the operation of the safety valve, we shall assume
that the governor cut‑out pressure is set at 125 psi. A safety
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.
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 safety valve should be inspected every 6 months or
1500 operating hours, whichever comes rst, for proper
operation. Should the safety valve not meet the elements
of the operational tests noted in this document, further
investigation and service of the valve may be required.
OPERATING AND LEAKAGE CHECKS
OPERATING TEST: With air pressure in the system, pull
the exposed end of the valve stem removing the spring
load from the ball check valve. Air should exhaust from the
valve’s exhaust port. Release the stem, the air ow 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.
When reservoir pressure decreases sufciently, the spring
force will seat the ball check valve, sealing off reservoir
pressure. This would occur at approximately 135 psi for
the 150 psi valve. It is important to note that the desired
pressure setting of the safety valve is determined by
the governor cut‑out pressure. The opening and closing
pressures of the safety valve should always be in excess
of governor cut‑out pressure setting. The pressure setting
is stamped on the lower wrench at of the valve.
LEAKAGE CHECK: Coat the exhaust port with soap
solution. A leakage of a one (1) inch bubble in 5 seconds is
permitted. Excessive leakage indicates dirt in valve, faulty
ball valve or seat. Valve should be disassembled, cleaned
and rebuilt. (See “Disassembly and Assembly” section).
1
REMOVAL AND INSTALLATION
REMOVAL
1. Block the wheels or otherwise secure the vehicle and
drain the reservoirs.
2. Using the wrench at closest to reservoir, unscrew valve
from reservoir.
INSTALLATION
The safety valve should be installed in the same reservoir
that the compressor discharge line is connected to. Install
the valve in a convenient location in a top port of the
reservoir. If the safety valve is installed horizontally the
exhaust port should point down and the stem of the valve
should face the rear of the vehicle.
DISASSEMBLY: BENDIX® ST-1™ ADJUSTABLE
VALVE
1. Clamp the lower wrench at in a vise (at nearest the
pipe thread).
2. Using the upper wrench at, unscrew the locknut.
Unscrew and remove the spring cage from body of
valve.
3. Remove the ball valve, spring and the release pin from
the spring cage.
DISASSEMBLY: BENDIX® ST-3™
NON-ADJUSTABLE VALVE
1. Clamp the spring cage in soft jawed vise.
2. Using the wrench at, unscrew the body from spring
cage.
3. Remove the ball valve, spring and release pin from
spring cage.
CLEANING AND INSPECTION
Clean all parts in mineral spirits. Inspect all parts thoroughly.
All parts not considered serviceable should be replaced
with genuine Bendix replacement parts.
ASSEMBLY: ST-1 ADJUSTABLE VALVE
1. Place the ball valve in the body.
2. Install the spring and release pin in the spring cage with
the adjusting screw.
3. Position the release pin over the ball valve. Screw the
body with the ball into the spring cage. Tighten securely.
4. Adjust for proper setting (see the “Adjustment” section).
RELEASE
ADJUSTING
NUT
SPRING
CAGE
BALL
VALV E
PIPE
THREAD
SPRING
CAGE
BODY
PIPE
THREAD
PIN
LOCKNUT
SPRING
BENDIX® ST-1™
SAFETY VALVE
BODY
RELEASE
PIN
SPRING
BALL
VALV E
BENDIX® ST-3™
SAFETY VALVE
TO RAISE THE PRESSURE SETTING
1. Loosen the locknut.
2. Turn the adjusting nut clockwise to obtain the correct
pressure setting.
3. Tighten the locknut.
TO LOWER THE PRESSURE SETTING
1. Loosen the locknut.
2. Turn the adjusting nut counter clockwise to obtain the
correct pressure setting.
3. Tighten the locknut.
TESTING OF REBUILT SAFETY VALVES
Perform the operating and leakage checks.
ASSEMBLY: ST-3 NON-ADJUSTABLE VALVE
1. Install the spring and release pin in the spring cage.
2. Position the ball valve in the body and screw the spring
cage onto the body.
3. Hold the spring cage in a soft jawed vise and tighten
the body securely.
2
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