Water Hammer: Annoying to destructive in 50 to 70 psi

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At some homes and buildings, there’s an obnoxious echo that sounds long after the last hammer is swung. In some instances, it’s as forceful as a sonic boom.

Water hammer, and a variety of somewhat lesser annoyance — water chatter — are terms that describe the audible traffic jam going on inside the pipes of some plumbing systems. But its affects aren’t limited to annoying noises. Water hammer can destroy pipe and fittings, regardless of the size of the system.

LF15M2-AThe 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, causing the vibrations known as water hammer,” said Steve Hamoen, at Zonelife Inc., a design/build plumbing and mechanical installation and engineering firm based in Cambridge, Ontario.

Water hammer can cause damage throughout the piping network by the sudden shaking, pipe expansion and contraction. Damage can happen all along the system, especially with copper piping, not just at the point of stoppage. The weakest points in the system, typically where fittings are soldered, often absorb the majority of the impact.

If left unchecked, water hammer can go from being an annoyance to being an expensive hazard if leaks develop.

According to Lisa Yezzell, national product manager for Watts Water Technologies, the most common cause of water hammer in a domestic water system is the quick closing of a valve within a plumbing fixture. Sometimes it’s a fast-acting solenoid valve inside a major appliance like a washing machine, but spinning a bathroom fixture closed quickly can create the same annoying result.

LF150A_50“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,” said Yezzell. “The problem can be especially challenging if the pipe is made of rigid copper,” she added. “Modern PEX plumbing systems are more forgiving because the tubing is pliable and much of the shock is absorbed. No matter what the pipe material is, it’s the valves and fittings that are often the weak link.”

“New, high-efficiency appliances, primarily dish washers and washing machines, conserve water by cycling more often for shorter periods of time,” she continued. “As the number of cycles increase, the wear on piping components increases due to water hammer.”

The best solution is proper placement of a water hammer or ‘shock’ arrestor. Locate the device on the supply line as close to the fixture that causes the problem as possible. Typically, these are mounted in the wall very near where the line protrudes from the wall, going to the fixture. Watts water hammer arrestors are available in a wide range of models suited for installations with icemakers, lavatory supply tubes, washing machines and dishwashers in sizes from 3/8” to 1”.

The speed of the valve closure, especially during the last 15% of 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.

Water hammer problems became so pervasive in Canada’s Quebec Province that the installation of water hammer arrestors was mandated. For the past five years, building codes now demand that all new homes must include the installation of the devices.
Mike Breault, product manager with Watts Canada, based in Burlington, Ontario, said that 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,” explained Breault. “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. But this introduces a new challenge: higher-than-normal water pressure with many homes getting 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, the bigger the water hammer potential, and the severity of its effects.

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 as the air is 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/surge absorber,” said Breault.

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