Regarding explosion-proof limit switches
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To create a pneumatic knife valve, the customer provided a diagram showing that an explosion-proof limit switch should be used, as illustrated. However, it was found that the explosion protection rating of this switch was not sufficient; another type of switch was then chosen. Since this type of explosion-proof limit switch is being used for the first time and little is known about such devices, the user requires that the switch reach its intended position. Can this type of limit switch be connected to a controller to provide feedback on whether the switch has reached that position?
A travel switch consists of dry contacts; if you have no special requirements, it will definitely work.
Two things to pay attention to: 1. The explosion protection rating is sufficient； 2. The form of the travel switch must be compatible with the system it is connected to in order to function properly ；
There are no special requirements, as it’s my first time using it and I’m still learning*.
No problem – it’s just about opening and closing them fully; there are only two DI points. However, attention should be paid to the installation location, taking into account the spacing between the mounting holes and the size of the bolt holes
In some companies with strict management requirements, explosion-proof instruments must have an explosion-proof rating and a corresponding code, which need to be clearly indicated on the nameplate; otherwise, they are considered non-compliant. The poster should be careful, as many domestically produced explosion-proof products fall short in this regard. Furthermore, if a signal is required for both the opening and closing positions, then two limit switches need to be installed – one for detecting when the valve has reached the open position and another for detecting when it has reached the closed position. The product diagram provided by the owner shows a relatively large area; it’s not clear whether there will be enough space on the valve body to install both switches together.
I contacted several manufacturers of explosion-proof limit switches, but none of them could provide an explosion-proof certification; the nameplates were simply printed by them themselves. In other words, it’s products that lack any proper certifications. It’s better to spend more money to get a reliable product. Making money is secondary; safety comes first. There’s nothing that can be done regarding installation, as it’s a pneumatic knife valve with two switches, one above and one below; it can only be processed on-site. The layer owner’s two suggestions are very practical; thank you.
A travel switch is simply a set of dry contacts, and basically any such contact will do
Two things are important to consider: first, the switch must be able to be installed on your valve, and second, the explosion-proof rating of the switch must meet the requirements. A switch is a dry contact, which can be accepted by most controllers.
The explosion protection rating of the second image is Ex dII CT6; this type of switch is larger and heavier, so it should be processed and installed after purchase. The pictures show a relatively cheap and lower-quality version available on the market; it will work fine for installation purposes.
Honeywell switches are good too; we’ve been using them.