How to install unions in copper pipe

The usual way to fix connections to copper pipe is to sweat them, which means welding lead with solder. Sweat connections are permanent, so when you need to be able to separate the pipes, as you do when connected to a removable device such as a water heater, you need to install a Union. It is a special type of plumbing installation with two threaded halves and a central nut to hold them together. Joints for copper tubing can be made of copper or brass, and have sliding joints to make the connections.


  1. Cut the copper tube with a pipe cutter if you are installing the Union in the middle of an existing line. Turn off the water, then unscrew the cutting disc, adjust the cutter around the tube and tighten the disc until the blade contacts the metal. Rotate the tool around the tube, tightening the disc in each turn until the tube separates. Let the water in the drain pipes in a bucket.
  2. Clean the ends of the tubes with a brush wire to eliminate oxidation and offer better bonding for welding. Some tube cutters have a brush attached for this purpose.
  3. Separate a union of brass or copper by unscrewing and removing the center nut. Disseminate the flow within the sliding connections in both halves of the Union and at both ends of the tubes that you want to form using the brush that comes with the flow. Slide each half of the Union into the end of one of the tubes.
  4. Heat one of the connections with a propane torch, holding the flame about six inches of metal. The flow back to black, liquefy and finally begin to bubble. When this happens, remove the flame.
  5. Touch the end of a lead coil from the weld on the joint immediately. The tin will melt and disappear in the joint, where they emerge from the connection to the pipe as it cools. Move the tip of the weld around the pipe to make sure that the weld fills the entire space between the fitting and the pipe. When one half of the connection is welded to a pipe, weld the other half to the other pipe in the same way. Allow the metal to cool for 10 to 20 minutes.
  6. Close the nut in one half of the Union, then join the tubes and continue screwing in the same direction. The opposite half of the Union has reverse thread to screw in one direction to tighten the nut in two halves. When you have tightened the nut with your hand as much as possible, continue tightening with a socket wrench.
  7. Turn over the water and check for leaks. If the Union is leaking, tighten the nut with the pipe wrench until it stops escaping.

Tips and warnings

  • Do not try to weld pipes that have water in them. The water vaporizes, and in doing so will absorb enough energy to keep the tubes hot enough to melt the solder enough to make a tight seal.
  • Safety glasses and copper accessories to protect your eyes from hot flow and sweat welding.

Leave a Reply

Your email address will not be published. Required fields are marked *