Are there self-acting control valves with air-close and air-open functions?
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Are there self-acting control valves that operate on air-close or air-open principle? I only know that pneumatic valves come in air-open and air-close types; are there such options for self-acting valves as well? If so, how can one tell whether it is an air-close or air-open type? It seems I’ve only heard of pre-valve and post-valve ones.
This post was last edited by ylb913 on 2018-8-11 at 11:19. Self-acting pressure control valves are typically used to regulate the pressure behind a control valve; when the pressure being controlled drops to zero, the spring force causes the valve to open fully in order to replenish pressure. When the pressure reaches a certain level, the pressure of the medium causes the valve to close completely, stopping pressure supplementation. This concept is similar to that of ordinary control valves, as both are designed to ensure equipment safety. However, the pressure source that controls the opening and closing of these valves is different; they cannot be referred to as being operated by air or failing to operate due to air issues, nor can they be called to open in case of a failure or to close in such situations. Instead, they open when pressure is low and close when pressure is high.
No, many domestic PCVs these days are made imitating pneumatic control valves.
1. Self-acting control valves do not have terms such as air-operated shut or air-operated open； 2. Self-acting control valves can be indicated as “normally open” or “normally closed”. Normally open, as the name implies, means it is not in use; the valve is in a fully open state.
It can be set to stay open or stay closed – you can choose; generally, it’s set to stay closed more often