How Do Copper Compression Fittings Work?

Will Charpentier

Copper lines are found in many places. A common household use is as the water supply line for a refrigerator ice maker. Copper lines are often used as fixed fuel lines on boats and as lines supplying fuel to the injectors in a diesel engine.

The Copper Compression Joint

The Anatomy of a Compression Joint

The Copper Compression Joint

There are two effective ways to join copper lines together: soldering, which requires a specialized skill, and compression joints, which require no more than the ability to use a pipe wrench.

Making a Connection

A compression fitting joins copper piping together with a fitting. This fitting may be bulky or unattractive; nonetheless, it is the quickest effective way to make a joint between two or more copper lines. One end of the fitting is threaded pipe, the receiver; the end of the receiver is slightly enlarged, to allow the insertion of the pipe to be joined to it. The other end is unthreaded pipe that passes through a compression ring called an olive, then through a compression nut, which will be tightened onto the threads of the receiver. Before assembling the compression joint, use steel wool to remove any burrs from both pipe ends and wrap the threads of the receiver with PTFE Teflon pipe sealing tape.

Under Pressure

The Copper Compression Joint Assembled

When the compression nut is tightened onto the threaded receiver, the olive acts as a bridge between the receiver and the compression nut along the direction of compression. The olive is designed to flatten along the length of the pipe---the direction of compression--rather than across the width of the pipe. Its slight deformation also crimps the pipe slightly, causing the olive to act as a washer between the threaded receiver and the compression nut without leaks, and as a firm seal around the pipe that prevents the joint from being pulled apart easily. Should a lead develop in a copper compression fitting over time, it usually can be repaired by simply tightening the nut.