How to achieve fault location capability for control valve failures
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When selecting control valves, those with single-acting actuators are generally chosen in a fail-open or fail-close configuration； For control valves with double-acting actuators, the instruments are of fail-safe type. I recently read an article that described it as follows: For the selection of the operating mode of the control valve, a fail-safe positioning mode should be used, with a fail-open+fail-lock operation principle. That is, as the control signal from the instrument decreases, the opening degree of the control valve increases; when the instrument air supply is interrupted for a short period, the position of the control valve remains unchanged; and when the air supply is interrupted for a long time, the control valve opens fully. I don’t understand how, when the instrument air is interrupted, this control valve can maintain its position for a short time (hold position) before opening fully I would appreciate it if fellow sailors could help analyze this: to achieve this function, how should the control valve be set up, or what additional components are needed? Thank you!
I’ve never seen a similar setting for a locator; the air storage tank can definitely achieve the function you mentioned
Air tank + check valve – the correct answer. The main issue is that what you said is too general; a fixed-value element could also be added
This is more easily implemented for double-acting valves; it primarily requires a hold valve, an air reservoir, and a check valve. In the event of a loss of air supply, fault holding is achieved based on the pressure set by the hold valve, with the air in the reservoir used to maintain the valve’s position. Once the air in the reservoir is exhausted, the valve will move to its faulty position.