A union is a three-part fitting. The first part is a section which has a large thread on it and an O-ring inside which makes the seal. On the other side of this first part is a plain socket. The other half of the union consists of two parts: a union nut and a socketed section. The nut slides over the socketed section and, together, they pair up with the threaded section of the union. The O-ring sits against the flat surface of the socketed section to give you a good seal.
Unions are helpful in pipe systems because they enable you to take sections out quickly, service them, check them, or even replace them, and put sections back in again. It's especially important in process lines where something goes wrong, something needs changed, fixed, or replaced, and requires being put back in again as fast as possible. Unions enable you to do this, saving you the time of cutting and gluing pipe. All you have to do is unscrew the unions on either side of the piece of equipment that needs removed, take it out, check it, put it back, and screw the unions back up again. The period your system needs to be down is significantly decreased by using unions on your equipment. We recommend that any piece of equipment which might require servicing should have unions either side.
Unions are sold up to 4”/ 110mm in size. For pipe sizes larger than that, the equipment will require a flange on either side, rather than a union. Flanges work in a similar manner to unions, just for a larger pipe size – flanges are bolted together and can then be unbolted to remove the piece of equipment.
If you would like to watch a video explaining this a little more then you can visit our YouTube channel and watch the video!