如何选择阀门在故障状态下的正确位置？

注意：以下定义并不是唯一的，不同项目、不同标准可能有不同的定义，例如：FC、FO中的F，有的代表气源故障和无信号，有的只代表气源故障而不包括无信号。

FC，FAIL CLOSED (VALVE TO CLOSE ON AIR OR ELECTRICAL FAILURE)

FO，FAIL OPEN (VALVE TO OPEN ON AIR OR ELECTRICAL FAILURE)

FL，FAIL LOCKED (LAST POSITION)

FLC，FAIL LOCKED (AIR FAILURE) CLOSED IN CASE OF SIGNAL FAILURE

FLO，FAIL LOCKED (AIR FAILURE) OPEN IN CASE OF SIGNAL FAILURE

LO，LOCKED OPEN

3. Definitions

PIP PCECV003-2017 Guidelines for Application of Remotely Actuated On-Off Valves

7. Actuators

7.3 Failure Position

7.3.1 Failure position is an important consideration for remotely actuated on-off valves. Failure position, also called failsafe position, is the action of the valve upon failure of motive force (e.g., instrument air) or loss of signal (e.g., signal to the solenoid valve). The failure action of the valve should be evaluated based on the valve’s effect on the operation of the process. The valve should be designed to fail to the position that would result in a safe process condition which should be determined based on a broad overview of the process plant operation.

7.3.2 Failure position may be open, closed, last position or indeterminate.

3. Definitions

fail closed (FC): Characteristic of an automated valve that causes the valve to close as a result of specific malfunctions, including loss of signal or motive power. (Reference ISA 5.1)

fail indeterminate (FI): Characteristic of an automated valve that causes the valve to move to an unknown position as a result of specific malfunctions, including loss of signal or motive power. Some automated valves will not stay at the last position upon failure and instead move with the process differential pressure. Additional equipment may be needed to meet the definition of FC, FO, or FL. (Reference ISA 5.1)

fail locked (FL) last position: Characteristic of an automated valve that causes the valve to remain in the last (locked) position as a result of specific malfunctions, including loss of signal or motive power. Automated valves may fail indeterminately without additional equipment. (Reference ISA 5.1)

8. SPECIFICATION OF CONTROL VALVE ACTUATOR

8.1.1 Spring action

Spring-to-open and spring-to-closeare fail-saferequirements which shall be determined by process engineering and which shall be indicated on the PEFS. If no particular fail-safe action is required the position of the valve can either be fail last (stay-put) or floating. Fail last(stay-put) means that devices are in place to retain the position the valve had at the moment when the supply failed. Floating means that the position of the valve is determined by the balance of forces acting on the plug and the actuator (the final position is undetermined). This choice shall be indicated in the requisition (IEC 60534-7:2010, line 29).

Double acting actuators without spring shall not be used on applications that require operational adjustments of the valve in case the plant air supply is lost unless the required fail-safe action can be achieved by a pneumatic supply buffer vessel.

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