What is a Compression Coupling?

In the field of plumbing, there is a wide variety of fittings and couplings that come into play. One of the more useful and versatile of these is the compression coupling. A compression coupling is a unique type of fitting used to connect tubing. These fittings are used in liquid and gas applications.

Compression couplings are manufactured from various materials, including brass, copper, plastic and cast iron. The most common compression couplings are made of brass. They also are available in a variety of shapes and sizes. The size of a compression coupling is determined by the outside diameter of the tube or pipe it holds.

There are two types of compression couplings. Type A, referred to as non-manipulative, is used in liquid plumbing systems. Type B, known as a manipulative fitting, is found in gas applications.

A compression coupling works by using clamping force to seal the fitting. The unit consists of a compression nut, a compression ring and a seat. The compression ring, often called a ferrule, is placed on the tubing with the nut behind it. The tubing is then inserted into the seat, and the nut is screwed onto the seat. As the nut is tightened, it compresses the ring around the tubing, creating a leak-free seal.

One of the reasons for the widespread popularity of the compression coupling is the ease with which it can be installed. Except in the case of type B compression couplings, no special tools are required. For type B fittings used in gas systems, a special flaring tool is needed to flare, or spread, the end of the tubing in order to facilitate a tight seal. A compression coupling does not have to be soldered.

Another property lending to the wide use of compression couplings is the availability of fittings in a choice of varied shapes and configurations. There are straight fittings, called unions, that simply connect two lines together. When a directional change is needed in the system, compression couplings are available in elbow shapes of different degrees. An elbow fitting helps to eliminate the need to try to bend the tubing.

A multi-port compression coupling can be used when it is necessary to connect more than two lines. These are very useful in adding additional water or gas outlets to an existing system. Compression couplings also are manufactured as combination fittings. Combination fittings have a compression coupling on one end and another type of fitting, such as a straight pipe nipple, on the other end. These types of fittings serve to connect different types of tubing and pipe.

Though highly versatile and adaptable to numerous plumbing situations, a compression coupling should be used only in a system in which it will be fairly stationary. These fittings do not fare well with a lot of movement or flexing. Common areas where they are found are in water faucet connections and water inlets on toilets.