When to use three-valve assemblies and five-valve assemblies?

Finally, the differential pressure was entered incorrectly; it should be the three-valve assembly

Both three-valve assemblies and five-valve assemblies are used for measuring liquid level or flow rate. The five-valve assembly simply has one additional drain hole (valve) compared to the three-valve assembly. For example, some orifice plates are installed on the pipe rack while the instruments are on the ground. If a fault occurs and the gauge head needs to be removed for inspection, is it easier to climb up into the pipe rack to close the root valve, or is it more convenient to close the three (five) valve assemblies inside the protection box? It also helps in diagnosing instrument faults, such as by opening the balance valve to check whether the instrument can return to zero. Early differential pressure transmitters were relatively fragile and could not withstand pressure from only one side. Relying solely on root valves is hardly sufficient to meet this requirement. By activating or deactivating the valve assemblies in the appropriate sequence, it is possible to prevent the instruments from being damaged due to pressure on one side only.

For single-flange differential pressure, the type with a measuring tube isn’t needed, right?

Mm-hmm, for the double-flange type that’s a measuring tube, it’s not necessary either, right?

The five-valve assembly includes a set of test ports for verifying the operation of instruments

Try to use a five-valve assembly; it has all the functions of a three-valve assembly. The drain valve in a three-valve assembly is prone to internal leakage, and it also requires additional welding points, which can lead to failures

In my opinion, there’s no significant difference between a three-valve assembly and a five-valve assembly; the three-valve assembly consists of a positive pressure valve, a negative pressure valve, and a balance valve, along with two small bolts for draining waste. In the five-valve assembly, those 2 valves are, in theory, the result of those 2 small bolts used for drainage being replaced with valve mechanisms. For the three-valve assembly, tools are needed to open the drain port, while the five-valve assembly comes with a handle, which makes it convenient. There shouldn’t be any difference in usage; it should work universally. They can be replaced with each other. In our factory, from high pressure to low pressure, it’s basically three-valve assemblies; there’s also a five-valve assembly provided by the manufacturer on the unit, which looks sophisticated, but in reality it’s not that complicated. The pressure isn’t very high either.

Two-valve assemblies, three-valve assemblies, and five-valve assemblies are all used for pressure transmitters or differential pressure transmitters. As for flanged pressure transmitters (or diaphragm pressure transmitters), or double-flange and single-flange differential pressure level transmitters (with capillaries), of course no valve assembly is needed... What kind of work does he do? He’s not working in the field of instruments, is he? It seems like someone from another field is trying to take advantage of this situation~~