Home / Repairing Household Plumbing / Soldered Capillary Plumbing Joints for Copper Pipes
A capillary plumbing joint consists of 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 strong connection that will not easily pull apart.
Because a capillary plumbing fitting costs much less than a compression fitting they are often used when a number of joints have to be made, such as when installing a new central heating system. They are also useful in cramped spaces, where it would be impossible to use wrenches to tighten a compression joint.
Many people are put off using capillary fittings because of the need to use a blow-torch. However, modern gas-canister blow-torches are easy to use and are not dangerous if used correctly.
If you joined two lengths of copper pipe by just soldering them end to end the join would be very weak because the contact area between solder and copper would be very small. Because the sleeve on a capillary fitting increases the contact area and also acts as a brace to strengthen the connection, a much stronger join is formed.
Molten solder is sucked into the space between the pipe and fitting by capillary action, and this combines with a thin layer of copper at the contact surface to bond the pipe to the fitting. To help the solder to 'take' the copper needs to be clean and shining. Flux is applied before soldering to prevent oxides forming which would impair the solder-copper bond.
The most common type of capillary joint has a ring of solder pre-loaded into the sleeve. It is known as an integral ring or 'Yorkshire' fitting (the name of a leading brand).
The 'end feed' type of capillary joint is virtually the same as an integral ring fitting, except that you have to add the solder when you make the joint. The sleeve is slightly larger than the pipe and liquid solder is drawn into the space between by capillary action.