Let’s talk about whether this is a confirmation error

I really admire the dedication of the original poster. I consulted our instrumentation engineers regarding the question in this post, and the answer given here should be correct.   Air-open control valve + reverse positioner = air-close valve; Air-close control valve + reverse positioner = air-open valve. Depending on safety requirements, pneumatic diaphragm control valves are available in either air-open or air-close versions. Depending on the safety and operational requirements of different production processes, the degree of harm caused to the production process when the signal pressure is interrupted depends on whether the control valve is in the open or closed position. If the hazard is low when the valve is in the closed position, a normally open valve should be used, as it keeps the control valve in the closed position when the signal pressure is interrupted; otherwise, a normally closed valve should be chosen.     These types of valves all have reverse positioners, so sometimes people make the opposite interpretation when trying to understand them. In fact, we often encounter ambiguous issues at work; if everyone had a skeptical attitude like the original poster’s, solving problems should be quite easy! This post was last edited by Bincheng Watcher on 2007-12-6 10:27.]

There aren’t any major issues with the original answer, but the open-on-air valve and the close-on-air valve, as mentioned by the poster, are determined by the state of the control valve when the instrument air supply is interrupted. When the instrument air supply is cut off, the open-on-air valve remains fully closed, while the close-on-air valve remains fully open. It seems quite appropriate.

Gas open and gas close are concepts based on the valve position in the event of an accident, aimed at ensuring the safety of personnel and equipment as well as reducing material consumption. As mentioned by the people above: the most accurate way is to simply determine the opening and closing state of the valve when energy (instrument air) is lost.   The reply from Building 4#, which I rated, was too long ； The last sentence is the standard answer.   The first two sentences are also correct; he took into account the spring starting torque of the valve’s actuator – that is, for some valves, a range of 20 kPa to 100 kPa corresponds to the full stroke ； Some are between 40 kPa and 200 kPa.   Often, it is necessary to consider lifting the mood and encouraging discussion ； Sometimes, even when there are differing opinions upstairs and downstairs, I still give a “actively involved” score.   At the same time, it opposes the extremely high requirement from previous posts, which demanded that instructors and engineers be able to identify the correct answer in discussions (acting as referees).   It’s already very difficult for most people.   This post was last edited by cocain on 2007-12-6 14:21]