How to choose an actuator for a fault-tolerant control valve?
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For valves with fault hold (FL) functionality, I usually opt for double-acting cylinder actuators or single-acting cylinders equipped with safety valves. But for valves of the (FL/FO) or (FL/FC) type, I’m unsure about the best choice of actuator; I’d like to hear the opinions of those experienced in this field
Failures are limited, and the retention bits cannot guarantee everything in the end; therefore, this aspect is taken into account during design.
Regarding (FL/FO) or (FL/FC), in my opinion, FO and FL here refer to the position of the valve in the event of a failure, without the use of a check valve. The design institute provides FL, but the manufacturer will also require you to specify whether it is FC or FO. It is possible to consider whether it is FO safety or FC safety in the case where a position-holding valve fails to maintain the position!
(FL/FO) or (FL/FC): First, the FL function is implemented, causing the valve to move toward FO or FC while remaining in place; this is achieved using a single-acting actuator plus a lockout valve. FL/FO is a gas-shut valve + lock valve, while FL/FC is a gas-open valve + lock valve
Could it be specified as follows: in the event of a gas supply failure, it is required to maintain FL; once the gas supply is restored, it is necessary to ensure whether the valve tends to stay open or closed.