Joining copper pipe is one of the basic plumbing skills. Compression and capillary joints are easy to make and once you’ve mastered the techniques, you’ll be prepared for a whole range of plumbing projects.
Connecting pipes effectively is the basis of all good plumbing as most leaks result from poorly constructed joints. For virtually ail domestic plumbing purposes you will only have to use compression or capillary joints. Compression joints are easy to use but expensive, while capillary joints are cheap but need some care in fitting. If you are making a join into an existing pipe system remember to make sure the water supply has been turned off at the relevant stop-valve either on that section or below the cold water storage cistern, and the pipe has been completely drained.
Preparing the pipes
Before joining pipes together, check that the ends are circular and have not been distorted. If they have been dented, cut back to an undamaged section of the pipe using a hacksaw with a sharp blade or a wheel tube cutter. The ends should also be square. Use a file to make any correction and remove ragged burrs of metal. If you’re using a capillary joint clean up the sides of the pipe with abrasive paper or steel wool.
Compression joints (friction joints)
A compression joint, as its name implies, is made by compressing two brass or copper rings (known as olives or thimbles) round the ends of the pipes to be joined, so forming a watertight seal. There are two main types of compression joint – the non-manipulative fitting and the manipulative fitting. Although not the cheapest means of joining a pipe, a non-manipulative joint is the easiest to use and requires only the minimum of tools. It comprises a central body made of brass or gunmetal with a cap-nut at each end which, when rotated, squeezes the olive tightly between the pipe end and the casing. This is the most commonly used type of compression joint suitable for most internal domestic plumbing purposes.
A manipulative joint is now rarely used in indoor domestic water systems. Because it cannot be pulled apart it is sometimes used for underground pipework, but capillary joints will do equally well in these situations. The joint usually comprises 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 smeared on the inside of the flares and a copper cone is inserted between them. The nuts are then screwed together to complete the seal.
How a compression joint works
The olive (thimble) is the key part of a non-manipulative compression joint. When the cap-nut is rotated clockwise the olive is forced between the casing and the pipe and is considerably deformed in the process.
A watertight seal is dependent upon the pipe ends having been well prepared so they butt up exactly to the pipe stop in the casing. This forms a primary seal and ensures that the pipe is parallel to the movement of the rotating cap-nut. An even pressure is then applied to the olive so that it does not buckle under the strain of tightening.
What size of pipework and fittings?
Pipework is now sold in metric dimensions, but plumbing in your home may be in imperial sizes. The metric sizes are not exactly the same as their imperial equivalents. These differences can cause problems. With capillary joints you have to use adaptors when converting pipe from one system to another. Adaptors are also needed for some compression joints although the 12mm, 15mm, 28mm and 54mm sizes are compatible with their imperial equivalents. This means if you already have imperial compression joints you can connect in new metric pipework, without replacing the joints. Adaptors are made with different combinations of metric and imperial outlets to fit most requirements. A plumbing supplier or a plumber will advise on what replacements to use.
Capillary joints
A capillary joint is simply a copper sleeve with socket outlets into which the pipe ends are soldered. It is neater and smaller than a compression joint and forms a robust connection that will not readily pull apart. Because it is considerably cheaper than a compression joint it is frequently used when a number of joints have to be made and is particularly useful in awkward positions where it is impossible to use wrenches. Some people are put off using capillary fittings because of the need to use a blow-torch. But modern gas-canister torches have put paid to the fears associated with paraffin lamps and are not dangerous.
How a capillary joint works
If two pipes to be joined together were just soldered end to end the join would be very weak because the contact area between solder and copper would be small. A capillary fitting makes a secure join because the sleeve increases this contact area and also acts as a brace to strengthen the connection. Molten solder is sucked into the space between the pipe and fitting by capillary action, and combines with a thin layer of copper at the contact surface thus bonding the pipe to the fitting. To help the solder to take’ the copper needs to be clean and shining, flux is applied to prevent oxides forming which would impair the solder-copper bond.