Introduction

The fitting consists of three parts: a compression nut, a compression ring (also called a ferrule), and a compression seat.

Here are two sets of compression fittings. They come in various sizes and shapes.

Usage

The simplest application of a compression fitting is with metal tubing. As the ring is compressed, it squishes down around the tubing. The tubing gets compressed, too, making a strong connection.

You can also use a compression fitting on plastic tubing. It helps to stiffen the plastic tubing my putting a metal tubing sleeve into the plastic like this:

The compression ring can't be reused.
If you have to replace an old compresion fitting you have to cut the end off the tube.

Procedure:

• Start with a nice straight cut on the pipe. Remove any burrs, clean out any debris.
• If you have to bend the tubing, put the compression nut and ring on the tubing first. The ring fits snugly on the tubing, and probably won't go on if the tubing is bent. Avoid bending the final bit near the fitting.
• It is good practice to lubricate the threads of the compression nut before putting it together.
• Insure that the pipe is pushed all the way into the compression seat before you tighten the nut.
• Tighten using two wrenches: one on the compression seat, one on the nut.
• Do not overtighten the fitting. Once you encounter resistance in tightening, tighten no more than an additional half turn. Test the connection. If there is leakage, tighten the compression nut by no more than a quarter turn at a time until the leak stops.

• Inexpensive and easy to find.
• Easy to assemble and disassemble (i.e. no soldering).
• Does a good job of keeping the pipe from pulling out of fitting.
• Does a poor job of keeping pipe from rotating in the fitting, which will cause leaks.

• Compression fittings are designed to be used once. If a compression fitting fails, it is best to replace everything. You can sometimes get by with cutting the end off the tubing and putting on a new compression ring.
• When using plastic pipe, a plastic compression ring is better than a metal one.
• Solid brass compression fittings are much more expensive than copper, but last much longer. Prefer them when you need a durable connection.

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