Question regarding how many valve limit switches are required
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Dear seniors, mechanical valve limit switches mainly come in SPDT and DPDT types; moreover, some manufacturers’ switches may be 2*SPDT or 2*DPDT. I would like to ask: if it is necessary to feedback both the open and closed positions of the valve, how many switches are required? Two SPDT, one DPDT, one 2*SPDT, one 2*DPDT or two 2*SPDT, two 2*DPDT? I do understand the principle differences between SPDT and DPDT, but I’ve never been to the site, so I’m not aware of how they are actually configured. After all, the valve’s travel also affects the switches, making it impossible to use a 2*DPDT setup to detect the switch positions.
What do your requirements have to do with limit switches? I don’t believe that two limit switches cannot detect the switch position simultaneously. One for opening and one for closing; no matter how you put it, there are just two positions. What’s the need for a third limit switch? It’s It’s baffling.
The limit switch does not distinguish between on and off; it detects whatever position it is installed in.
I might not have explained it clearly enough; I just want to know whether there is any difference between using a switch with two dry contacts and one with two switches, each having only one dry contact, when it comes to sending feedback on the on/off status of a valve, and what limitations, if any, there are in terms of usage. When I asked the manufacturer earlier, I was told that for a switch with two contacts, if the travel distance of the actuator is too short, only one position can be detected effectively; as a result, two switches still need to be installed.
I might not have explained it clearly enough; I just want to know whether there is any difference between using a switch with two dry contacts and one with two switches, each having only one dry contact, when it comes to sending feedback on the on/off status of a valve, and what limitations, if any, there are in terms of usage. When I asked the manufacturer earlier, I was told that for a switch with two contacts, if the travel distance of the actuator is too short, only one position can be detected effectively; as a result, two switches still need to be installed.
SPDT and DPDT indicate different contact configurations for detecting the operation mode of the switch; they achieve the same function but have different safety characteristics