BENDIX ST-1 Quick Start Manual

®
Bendix ST-1 & ST-3
® ™
PRESSURE
BENDIX
®
ST-1 VALVE
™
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.
When reservoir pressure decreases sufficiently, 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 flat of the valve.
Safety Valve
™
EXHAUST
PORT
SETTING
150 PSI
BENDIX
®
ST-3 VALVE
™
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.
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 first, 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 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. 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).
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