How does a union differ from a coupling in pipefitting?

A union is a type of fitting specifically designed to allow for the easy disconnection of pipes, making it a versatile choice in situations where maintenance or replacement of piping might be necessary. Unlike other fittings such as couplings, which typically provide a permanent connection between pipes, unions are equipped with a mechanism that lets a pipefitter easily separate the joined sections without cutting the pipe. This feature is particularly useful in systems where accessibility and the ability to service or replace sections of piping are important.

In many applications, such as plumbing, heating, and cooling systems, quick disconnection can save significant time and effort. Unions generally consist of three parts: a male end, a female end, and a nut or fitting that brings the two ends together securely. This construction permits straightforward disassembly while maintaining a strong, leak-proof connection when assembled.

In contrast, couplings are used to connect two pieces of pipe together, often in a permanent or semi-permanent manner, and do not provide the same level of convenience for disconnection. Understanding the distinct functions of unions and couplings is critical for effective pipefitting practices, especially when planning for future maintenance work.