Flushing away water hammer

Answer's in the toilet

Get Smarter. Grow Your Referral Network.
Limited seating available for Inman Connect San Francisco

Q: It happened suddenly. The plumbing pipes in the bathroom would "hammer" whenever the toilet was flushed. We read your suggested remedy (drain the system) and tried it. It worked until my husband wanted more water pressure and turned the main shutoff valve another turn to bring more pressure upstairs.

Now the hammering continues until the toilet’s water tank is filled. We turned off the water at the main again, and this time did not open the valve all the way, but it didn’t help. Is there anything else that can be done to stop the noisy pipes?

A: We hope it didn’t happen suddenly on a "dark and stormy night"!

There is something else you can do but it may take a little pipe reconfiguration.

Anyone who’s been startled by a boom when the water is suddenly turned off or machine gun staccato when pipes are flowing can relate to a "water hammer." One type occurs when a fixture is shut off suddenly, and water rushing through the pipe is brought to a quick halt. The sudden stop creates a shock wave and the "boom." Another type can occur when water flowing through pipes under fairly high pressure is partially restricted — the "staccato."

Because the noise is limited to the bathroom, occurs only when you flush the toilet and stops when the toilet tank fills, we think the problem is in the shutoff valve for the toilet or in the fill valve in the toilet tank. …CONTINUED

When dealing with plumbing, we always recommend trying the simple fix first. You tried that by draining the system. Properly installed plumbing has air chambers that compress when the shock wave hits, softening the blow and preventing hammering.

The chambers can fail when water under pressure gradually absorbs the air. You can cure water hammer caused by failed air chambers by permitting the system to drain. Once all the water drains from the chamber, air will fill it again and restore the cushion.

In your case, draining the system fixed the problem for a little while. But it came back. So the problem probably isn’t compromised air chambers. When your husband restarted the system, he only partially opened the main shutoff valve, reducing the pressure in the system. This pressure reduction stopped the noise for a bit. Increasing the pressure to get acceptable water flow in the upstairs fixtures brought back the noise.

We suggest you focus your attention on the toilet. First make sure the shutoff valve is open all the way. Turn the handle counterclockwise to fully open the valve. Flush the toilet and see if that stops the noise. If the noise persists, close the valve by turning it clockwise. Then open it and flush again. Sometimes small bits of debris become lodged in the valve, restricting water flow. Opening and closing the valve often will dislodge the debris.

It’s also possible that the washer inside the valve is torn. If manipulating the shutoff valve doesn’t eliminate the noise, we suggest you replace it. It’s a cheap and simple process. A new shutoff valve can be found at any hardware store.

While you’re at it, consider replacing the fill valve in the toilet tank. It’s a second likely suspect for the noise. Over time, especially in areas prone to hard water, scale can build up in both valves, restricting the water flow and causing the noise you hear. Replacing these two parts should make your water hammer a thing of the past.

***

What’s your opinion? Leave your comments below or send a letter to the editor. To contact the writer, click the byline at the top of the story.