When undertaking any plumbing project in the home, knowing how to properly cap a water line is an essential skill. Whether you need to temporarily disconnect a line to make repairs, or permanently close off an old unused pipe, capping a line correctly is crucial to prevent leaks and ensure safety.
Why Cap Off a Water Line?
There are a few common reasons you may need to cap a water line in your home:
- Making repairs – Capping allows you to temporarily shut off flow to that section of pipe.
- Renovations – Capping prevents contamination while walls are open.
- Taking lines out of service – Permanently capping abandoned lines.
- Pressure testing – Capping to isolate lines for leak tests.
- Code requirements – Some local regulations require capping.
Choosing Your Capping Method
There are three main types of pipe caps to choose from:
Threaded caps screw onto threaded pipe fittings. They provide a solid metal-to-metal seal and are suitable for permanent caps. Installation can be slightly more difficult and requires the right tools.
Push-to-connect caps use internal seals and barbs to grip the pipe when pressed on. They’re extremely easy to install but may not be as durable for permanent caps.
Soldering a cap onto a copper pipe creates a permanent watertight seal. This method takes more skill but is very robust.
Preparing to Cap a Pipe
Before capping, take a few key steps:
- Locate the main shutoff valve – Turn water off before starting.
- Drain the plumbing system if possible.
- Measure pipe length precisely for cap fit.
- Inspect pipe end and sand smooth if needed.
- Have all tools and materials ready.
Installing Threaded Caps
Follow this process when using threaded caps:
- Ensure pipe is properly threaded.
- Wrap threads with Teflon tape or pipe dope.
- Hand tighten cap until snug.
- Finish tightening with a wrench – don’t overtighten.
Installing Push-to-Connect Caps
When using push-to-connect caps:
- Cut pipe end squarely and deburr the edges.
- Push cap fully onto pipe until it stops.
- Pull on cap to ensure a tight seal.
Soldering On Caps
Follow these steps when soldering a cap:
- Clean pipe end with emery cloth and flux paste.
- Apply solder paste inside the cap and fit onto pipe.
- Heat evenly until solder melts and flows into joint.
- Allow to fully cool before water pressure is restored.
Take these additional steps when capping lines:
- Open valves slowly to prevent water hammer.
- Don’t enclose push-to-connect caps inside walls.
- Check for leaks using soapy water or a pressure test.
- Make repairs if any drips, pooled water, or bubbles appear.
It doesn’t need to be hard to cap a water line. Follow our guide to properly stop flow in pipes and prevent problems down the line.