At some homes and buildings, there’s an annoying echo that sounds long after the last wrench is turned and hammer swung. 

In some instances, it’s as forceful as a sonic boom. Another variation sounds like ghosts rattling chains in the wall. 

Water hammer and a variety of a somewhat lesser annoyance — water chatter — are terms that describe the audible, rock n’ roll world of piped systems big and small.   

Water hammer is the term used to define the destructive forces, pounding noises and vibration that can develop in a piping system when a column of liquid flowing through a line is abruptly stopped. The tremendous forces generated at the stopping point can be compared to an explosion.

After a sudden valve closure, a shockwave passes back and forth through the water column at roughly 4,500 fps, like a mini tsunami, causing the vibrations known as water hammer.

“When water hammer happens, energy forces may cause damage throughout the piping system by the sudden shaking, pipe expansion and contraction,” says Keefer Rader, owner of Outlaw Mechanical, a mechanical installation firm based in Albuquerque, New Mexico. 

Damage can happen all along the piped system, especially with copper piping, not just at the point of stoppage. The weakest points in the system, typically where fittings are soldered, are most affected by the impact. If left unchecked, water hammer moves from a.) an annoyance to . . . b.) an expensive hazard if leaks develop.   

According to Gaurav Mathur, product manager for Watts, the most common cause of water hammer is the quick closing of a valve within a plumbing fixture — most often a fast-acting solenoid valve inside a dishwasher or clothes washer.


Whoa: 600 psi!

“When a piped supply of water, at 50 to 70 psi is in motion and then suddenly stops, a sonic wave surges backwards toward the supply,” Mathur says. “The problem can be especially challenging if the water piping is made of rigid copper. Modern PEX plumbing systems are more forgiving because the tubing is pliable and the shock is absorbed to some degree. However [similar in this way to copper fittings], it’s the crimped or otherwise coupled fittings that can be the weak links. There’s never an absolute, 100% elimination of the problem.”

Mathur explains the best solution is proper placement of a water hammer or “shock” arrestor. “The most effective location for the device is in the supply line as close to the fixture as possible,” he notes. “Typically, these are mounted in the wall very near where the line protrudes from the wall, going to the fixture.” 

The speed of the valve closure, especially during the last 15% of the valve’s closing, is directly related to the intensity of the surge pressure. An approximate pressure rise of 60 times the fluid’s velocity is produced. So, water traveling at 10 fps could produce a shock pressure of 600 psi!


Canada takes a stand

Water hammer problems became so pervasive in Quebec Province that the installation of water hammer arrestors was mandated several years ago. There, building codes now demand that all new homes must include the installation of the devices.

Mike Breault, senior technical instructor with Watts based in Burlington, Ontario, says the mandating of water hammer arrestors stems chiefly from the need to solve widespread water hammer problems in new home developments.

“Quebec is a fast-growing area,” he explains. “There are large, new subdivisions that place a strain on the water supply infrastructure. That leads to water pressure irregularity, so pressure-boosting stations are being installed. However, this introduces a new challenge: higher-than-normal water pressure with some homes getting between 80 psi or higher. We’ve learned of some homes receiving water pressure in excess of 105 psi.”

The higher the pressure within the piped system — and the greater the need. 

Temporary relief of water hammer shock can be achieved by installing a correctly-sized air chamber, generally a standpipe. Although effective for a short amount of time, air chambers lose their effectiveness rather quickly, either during the flow cycle, when water travels both ways, or by the air being absorbed through turbulence. Short of draining the entire pipe system and removing the chamber, there is no way to replenish the air in the chamber. 

“The only true, permanent solution to lessen the damage caused by water hammer is to install an engineered water hammer arrestor,” Breault states. 
Rader adds: “We don’t run into water hammer issues frequently, but they do come to our attention from time to time.” 

On a recent troubleshooting mission, Radar says that water hammer noise in a home was traced back to a well pump creating too much pressure, and a bathroom valve closing too quickly. Rader installed a Watts LF15M2 water hammer arrestor and that was the end of the problem.  

Are your customers hearing sonic waves? Catching the culprit may be an easy arrest — and you’ll be an instant hero.