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What Is a Water Hammer? And How You Can Fix It

What is a water hammer? When something goes bump in the night, it could be water moving through your valves and pipes. But when you hear loud banging coming from your plumbing or valves, it’s a problem called a water hammer. If your house is more than a decade old, you can probably attest to hearing this sudden and often disturbing cacophony. (Light sleepers, you know all too well what we’re talking about!) But what’s the cause of a water hammer, anyway? Our crack plumbing expert explains all, including how to stop this crazy water noise from happening in the first place.


What is a water hammer, and what causes water hammer problems in pipes?

It’s a common misconception that water flows smoothly through pipes, valves, toilets, and the pump. In fact, water churns and tumbles in your water system as it moves from a tank, through pipes, and eventually out of valves and faucets.


Mostly, all of that water movement causes a steady sound that we hardly notice. But sometimes, when you shut off the valve or water suddenly, or when there’s a sudden pressure increase, water comes to a sharp halt, causing the familiar water hammer sound. The sound, or water hammer, is the result of in-line pipes moving and bumping around in their hangers.


Hammering can be caused by waterlogged air chambers, clogged chambers, or excess pressure in your plumbing system. It can also be the result of a valve or pipe clog, which can produce a staccato banging sound.


You find this banging mostly in older homes that have pipes with 90-degree angles, says Tom Bigley, director of plumbing services for the United Association. “The noise you hear is the pipe moving because of shock waves.”


Newer homes with flexible piping that snakes through walls rarely suffer from water hammers, Bigley says.


Yes, the hammering is vexing. But worse, prolonged water hammer noise like this can sometimes cause pipe fittings and valves to fail and pipes to burst. Properly installed plumbing contains air pockets or chambers that compress when a shock wave hits them, muffling that water sound. But water under pressure absorbs air and eventually erodes the air cushions. That’s when the water hammer trouble begins.


How to fix the water hammer yourself

If you feel at least somewhat confident in your plumbing skills (you can locate pipes and valves and know the difference between an open and closed valve), here are some quick-fix steps to eliminate the water hammer before you call in a professional water hammer arrestor.


  • If you can hear where the water hammer originates, for example in your bathroom, turn off the water supply behind the noisy soaked chamber, open the faucet, and let the water drain. When the water velocity stops dripping, air will again fill the pipes and restore the air cushion.


  • If the water hammer is located deep within the pipes, you can turn off the water valve to the house and drain the main water supply lines by turning on all of the faucets in the house, including hose bibs, and let the air flow into the pipes again. Then close all the faucets. Always check valves—or your pipes will flood the house!


  • Turn the water valve back on. Don’t be alarmed if the pipes spit air when you first turn on faucets. It’s normal after a valve closure.


When to call a plumber for a water hammer problem

If the easy water hammer fixes don’t work, your water pipes or valves might be clogged with mineral buildup and general gunk. This is when you need to throw in the towel (figuratively speaking) and call a plumber.


If the chamber is capped, the plumber will remove the cap and snake out the residue from the waterline and pipe systems. If you don’t have air chambers built into your system, the plumber will try to reduce the pressure spike by installing a pressure-reducing valve in the supply line (low pressure is usually measured in inches of water column). Or, if that’s not feasible, because the water pressure will be too low for a good shower plus running the dishwasher or a load of washing, the fix is to install air chambers to stop the water hammer. Either way, you should be free of the hammer—and sleeping well again in no time.



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