How does a pneumatic control valve work? When should air-on valves and air-off valves be used respectively?
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rt ps: What is the difference between air-on valves and air-off valves in terms of the flow direction of air in the system? How to determine whether a valve is air-open/air-close?
Generally, valves that are actuated by air entering the upper diaphragm head operate in air-shut mode, while those with air entering the lower diaphragm head operate in air-open mode; however, there are exceptions to this rule. The most accurate way to determine this is by checking the valve’s nameplate – those marked FO operate in air-shut mode, while those marked FC operate in air-open mode. If there is no nameplate, and the valve technician permits you to do so, simply remove the valve’s inlet pipe or disconnect the DCS signal; a valve that remains fully open is a gas-shut valve, while one that does not remain fully open is a gas-open valve.
Reply to 2# ssln123: Thank you for your reply. I have another question: If a pneumatic control valve means that it opens fully when the air supply is cut off, then in Lurgi furnace operations, could there be any danger if the air supply to the control valve is suddenly interrupted and the valve opens fully? (As far as I know, the oxygen control valve on the Luchi furnace is air-shut.)
Another criterion for choosing gas on/off valves is that the valve must be in a safe position in the event of a gas supply interruption. It depends specifically on the different processes!
The most important principle when choosing between air-operated open and air-operated closed control valves is safety. For example, in the case of control valves for boiler water supply, it is essential that the valve remain in the open position in the event of an accident (i.e., when the air supply is interrupted); therefore, air-operated closed valves must be used. The working principle of the Lurgi furnace mentioned by the original poster is not clear, and safety considerations must take precedence here~~~
When selecting a control valve between air-open and air-close types, the key is to ensure the safety of the equipment and production process. It is mainly to prevent the equipment from filling with liquid, experiencing overpressure, or having an empty liquid level in case the air supply to the valve is disconnected due to a fault
Reply to 5# jlszhoujidai: Uh..... please explain the question regarding the Luchi furnace. The original purpose of the poster was to define what a gas on/off valve is. Because it is very dangerous when the air supply to the device is interrupted and the oxygen valve is fully open, I want to confirm whether the air shut-off valve remains in an open position when the air supply to the device is interrupted. But seeing that everyone’s responses were the same, the original poster decided to look for design reasons from other aspects and adopt everyone’s answers. I won’t reply to each one individually; thank you all again.