Fail-Open (FO)
An actuated valve that opens automatically on loss of instrument air or power. Used where the safe failure mode is to maintain flow: e.g., cooling water supply to heat exchangers, quench water to fired coils.
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What is a Fail-Open (FO)?
An actuated valve that opens automatically on loss of instrument air or power. Used where the safe failure mode is to maintain flow: e.g., cooling water supply to heat exchangers, quench water to fired coils.
How is a Fail-Open (FO) sized for a valve?
Actuator sizing requires the valve's breakaway torque (BTO), running torque (RTO), and end-to-close torque (ETO) at the maximum differential pressure and operating temperature. The actuator output torque at minimum supply pressure must exceed the valve BTO by a safety factor (typically 1.25x minimum). For pneumatic actuators, the supply pressure range, fail-safe direction (spring return FC or FO), and speed requirements must also be specified.
When is a Fail-Open (FO) required versus manual operation?
Automation is required when: (1) the valve is in a remote or hazardous location, (2) rapid opening/closing is needed for emergency shutdown (ESD), (3) the valve must respond to a control signal (4–20 mA, HART, or fieldbus), (4) the operating torque is too high for manual operation, or (5) the valve is part of a Safety Instrumented System (SIS) requiring SIL certification. Contact Vajra Industrial Solutions for fully automated valve packages including actuator, limit switch, solenoid, and positioner.
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