Arrow-right Camera
The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883

Ask the Builder: Kaboom! Why are your water pipes banging?

This is a large-diameter water manifold in my house. The smaller PEX lines are flexible. These are the two best things to use to prevent water hammer at home.  (Tim Carter)
By Tim Carter Tribune Content Agency

Q. Tim, every time I shut off a faucet in my home, my water pipes rattle and make a dreadful sound. It seems to me that they might burst. The problem is common in many houses on my street, as I’ve asked my neighbors if they have the same problem. What’s happening? Did the builder or plumber make a mistake when installing the pipes? Is there a danger of pipes bursting and flooding? Is there an easy fix, even DIY? Help before I need a life jacket! – Pam H., Clearfield, Pa.

A. I used to hear loud crashing noises caused by water hammer at one of the first homes I lived in when I was in my early 20s. At the time, I didn’t think much of it and had yet to sit for my master plumber exam. I lived in an area where the city water main pressure was close to 80 pounds per square inch. The high water pressure was wonderful for showers and garden hoses, but the noise was a nuisance, especially when the electronic washing machine and dishwasher valves would shut off.

If you dust off your high school physics textbook, you’ll discover why the water hammer is happening. First, water is a liquid, and most liquids are not compressible. Water also is pretty heavy. Stop for a moment and think of the velocity of water as it rushes out the end of your garden hose. That’s how fast, for the most part, the water is moving through your water lines.

Imagine if that water in the pipes instead was a tiny freight train chugging along. All of a sudden, right in front of the locomotive, a valve shuts off. The train crashes into the valve, and the energy sends a huge pulse wave through the piping. The pressure within the system can spike to well over 180 PSI. You bet that can cause problems over time. A catastrophic leak is absolutely possible from countless shock waves.

The plumber who installed your piping could have prevented the water hammer by installing larger-diameter pipes within the system. Larger pipes, by their very nature, slow the velocity of the water moving through the pipes. All he would have had to do was extend ¾-inch water lines to each fixture group and critical fixtures such as washing machines and dishwashers. These machines have electronic valves that slam shut when no more water is required.

PEX plumbing supply lines also could have helped. These flexible, innovative plumbing water supply lines install much like electric cable, and they can jiggle and move around to absorb the shockwave that pulses like a bomb going off in your water lines. Copper is rigid and it can bang and shudder, as you well know.

The good news is there are ways you can pretty much stop the water hammer within your home. If you possess moderate plumbing skills, it’s absolutely a DIY opportunity to get out your soldering torch and other tools.

I’d install two things to start: a spring-activated, pressure-reducing valve and one or two common expansion tanks. Both of these affordable accessories do a magnificent job of taming the wild stallions that are galloping through your water lines.

The pressure-reducing valve can be adjusted by turning a screw. Be sure you pay attention to the direction of the water flow on the body of the valve. Most of the time, this is installed just past the main shutoff valve for your home. While you have the water off, install a secondary main shutoff ball valve in case you have a wretched old gate valve. Ball valves allow for full flow, and they’re usually trouble-free for decades.

Just after this new ball valve, consider installing a tee fitting that will allow you to put in a boiler drain so you can easily drain out all the water in your water lines. Many plumbers fail to install this simple accessory. I also would install a second tee fitting in the main water line. This will allow you to install a water pressure gauge. You’ll never regret having one of these.

After you install all that, consider installing a 3-gallon expansion tank. These are wonderful devices that have a rubber bladder within the tank. The bladder separates the water in the system from a bubble of air inside the tank. Be sure to install this tank so the threaded inlet points down toward the floor. This allows the air bubble to be above the water, not below it.

The air bubble acts just like a shock absorber in your car or truck because air is compressible. These expansion tanks also do double duty protecting your storage water heater, as heated water also needs a place to expand.

I know this seems like a lot of plumbing work, but it’s not. You can do all of this in an hour or less if you know what you’re doing. Just follow the plumbing code and best practices, and soon your home will be as quiet as a lamb.

Subscribe to Carter’s free newsletter at