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Compression Plumbing Joints for Copper Pipes

Joining copper pipe is one of the basic plumbing skills. Compression joints are easy to make after a bit of practice. People like using them as they don't require the use of blow-torches. There are two main types of compression joint, the non-manipulative fitting and the manipulative fitting.

A non-manipulative compression joint

This is the most commonly used type of compression joint for household plumbing.

Although it is more expensive than a capillary fitting, a non-manipulative fitting is easier to use and requires only the minimum of tools. It is made-up of a central body made of brass or gun metal with a cap-nut at the end and an olive to help give a watertight seal. When the cap-nut is rotated clockwise it squeezes an olive tightly between the pipe end and the casing. Olives have various profiles. If they have long and short sloping sides, the long side must face the body of the fitting.

Getting a watertight seal depends upon the ends of the pipe having been well prepared so they will butt up exactly to the pipe stop in the casing without any gaps. This forms a seal and ensures that the pipe is parallel to the movement of the rotating cap-nut. The cap-nut applies an even pressure to the olive so that it does not buckle under the strain of being tightened. Joint paste is sometimes used to help ensure against leakage.

Making a non-manipulative compression joint

Make sure that the end of the pipe is square and has no burrs or you won't get a watertight seal. Clean the end of the pipes and the olive with with steel wool or emery paper until they are shiny. Slip the cap nut over the end of the tube and then slide on the olive. Coat the outside of the tube and the olive with a joint paste if you wish (to give an extra safeguard against leakage) and insert the pipe end into the joint body as far as the stop. Use your fingers to screw the nut as tight as you can. Hold the joint body with one wrench, give the cap nut one and a half turns with another wrench. That should be enough to ensure the cap nut compresses the olive enough against the tube wall to make a watertight joint but does not damage it.

A manipulative compression joint

Manipulative compression joints are rarely used in indoor domestic water systems.

The joint consists of a male and a female union nut. These are slipped over the pipe ends which are then flared ('manipulated') using a special steel tool called a drift. Jointing compound is then smeared on the inside of the flares and a copper cone is inserted between them. The nuts are then screwed together with wrenches to complete the seal.