How should one choose between normally open pneumatic diaphragm valves and normally closed pneumatic diaphragm valves?
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During normal operation, the valve needs to be in an open state; therefore, should a normally open pneumatic diaphragm valve or a normally closed pneumatic diaphragm valve be chosen?
Normally open means the valve is in the open position when there is no air supply, while normally closed is the opposite. Which one to choose also depends on the requirements of the operating conditions. The condition requiring the valve to be in an open state during production is not complete. Generally, it is determined based on the valve position when the air supply fails. In other words, if the gas supply fails (there is no gas available), it is important to know whether the valve is in the open or closed position, as this affects the operational conditions. This is the first principle. Secondly, consider factors such as whether it belongs to an interlocking mechanism and the pneumatic control solenoid valve used.
As per your request, a normally closed valve can be selected; it opens when there is air supply and the solenoid valve is powered, while it closes due to the spring force in emergency situations when power and air supply are lost.
When choosing between air-open and air-close valves, the decision is first made from a safety perspective – that is, to determine what state the valve should be in in the event of an accident (when the control valve loses air pressure) so as to prevent safety incidents. After ensuring safety, the choice is then made based on which state is more beneficial for process quality.
The selection of valves is not for normal production but for abnormal situations; this requires taking into account the characteristics of your production process, and no simple conclusions can be drawn. If possible, you can provide more information, similar to the data provided for HAZOP analysis, including PID, SDS, RC1 reports, process descriptions, etc.