How To Remove Water From Pipes So They Can Be Soldered

A pipe in a wall with a shut-off valve | Construction Pro Tips
Construction Pro Tips

Soldering with water inside a pipe is virtually impossible, due to the fact that the water acts as a coolant and cools the pipe as you’re trying to heat it. That means that making sure that pipes are free of water before soldering is a very frequent issue for service plumbers when doing repairs.

There’s a few reasons why there might still be water in the pipes- it could be that the main water valve isn’t sealing properly after it’s been shut, or just the fact that the system wasn’t given any air to evacuate the water adequately.

Opening up all the fixtures to give some air into the system helps to speed up the process immensely. But if after a couple of minutes the flow doesn’t seem to want to stop, you’d need to think of another solution. This leads me to my next option- purging at the lowest point. Normally, the best place to purge a pipe would be right at the main valve. If you have a valve with a small purge on it (like I do) you would just close the valve, empty as much water as you could from the fixtures nearby, and then finish the purge. (Note: these valves are often installed the wrong way, so make sure it’s installed correctly or else you’ll be purging the city’s water.)

Here are some other techniques for removing water from pipes so they can be soldered:

  • Use a wet-dry vacuum to suck out or blow out the water in the pipes. In order for this trick to work, you’ll need to open a fixture nearby to allow for the water to move, or else you’ll just be creating negative pressure inside the system.
  • The famous bread trick. You may have heard of this technique already and thought it was an urban legend. Truth is, the “bread trick” actually works. The idea is to shove a tightly knit ball of white bread far enough in the pipe to stop the water from flowing temporarily. Now, as much as this is a proven trick, it does have its downsides. The bread easily dissolves, and it 7piwill be pushed out if there is the slightest pressure build up in back of the pipe. The bread trick also doesn’t really work well on vertical pipes because the weight of the water will easily push it out.
  • Use a compression valve. The compression valve is more of a user-friendly option of closing off a pipe’s access to water, and would be installed right before the repair itself. Another good alternative is to use a push or Sharkbite valve to get the same results. Although this method does work, there’s a lot of controversy on whether this fitting should be installed in a wall or not, so do take some precautions when using them.
  • Use a drain coupling or elbow. These special fittings have the same little purge as the main water valve you saw before and allow for water and steam to be drained while soldering. Once again, just like the compression valve, this fitting would get installed on the side where the water is flowing and would be permanently soldered in place along with the repair. The only downside to them is that they aren’t readily available at your local hardware store. And personally, the fact that the purge relies on a small rubber gasket that could dry up in time, I wouldn’t install this in a closed wall, but that’s just my way of doing it.
  • Use a gadget called the Jet Swet. The Jet Swet is a device that allows for a leaking pipe to be temporarily blocked to solder on a shut off valve which could then be closed to complete the repair. This is by far the most reliable way of countering this problem as compression fittings and drain couplings aren’t recommended to be installed in a closed wall.