Where Is Water Hammer Common?

Water hammer damage typically occurs in specific areas of your plumbing system. Key locations include spaces with high water pressure, fast-closing valves, and long pipe runs, including:

  • household appliances, such as dishwashers and washing machines — especially high-efficiency models with quick-closing solenoid valves.
  • toilets and faucets due to their rapid shut-off valves.

Areas with high municipal water pressure entering a building are more prone to water hammer. Due to the high velocity at which water travels through the system, the rapid closure of a valve can produce a sudden change of motion and transfer energy throughout the system, putting extreme stress on joints and directional fittings.

For these reasons, a system's incoming pressure should be evaluated to ensure it does not exceed 80 pounds per square inch (psi). If it does, a pressure-reducing valve (PRV) should be installed to reduce the possibility of water hammer damage.

Hammer arrestors should be used in conjunction with PRVs in these types of high-pressure areas; likewise, where there is frequent opening and closing of valves: shower diverters, washing machines, dishwashers, and sensor-operated valves.

Why Assess Visible Water Lines?

While water hammer is audible, the sound may be deceiving and not pinpoint the issue's exact location; e.g., washing machine location. The sound may appear to be coming from the valve area but could result from an unsecured pipe within the wall cavity. Once a water hammer sound is verified, check for unsecured or loose supply lines or pipes making contact with a finished surface.

Water hammer can be absorbed by any of these unsecured lines, resulting in partial to extreme movement — creating contact with adjacent surfaces. Pipes should be properly supported and insulated to prevent them from touching surrounding building materials. Pipes that are not adequately secured will move and cause a knocking or vibrating sound when coupled with even the slightest amount of water hammer.

Locate any internal or external holes that water lines pass through to see whether these lines touch the sides of the hole in any direction when gently pushed. Any water line that passes through a hole should have a support installed or expandable foam applied. Both can also keep pests and insects from traveling through a hole. A combination of a j-hook and foam pipe insulation wrap on large holes in wood plates can cushion them against any wood or drywall.

For new installations of water distribution systems, check with your local building officials to ensure individual lines are properly secured and insulated to reduce the possibility of water hammer.

How to Fix Banging Water Pipes

In the past, plumbers were required to install a 12-in. capped vertical riser (air chamber) on a fixture(s) supply run to dead-end the line. As the system filled, this riser would fill with displaced air and create an air chamber.

But soon after putting the system into service, plumbers discovered that the air within this chamber had been replaced by water. The only way to restore the hammer protection was to drain and refill the system continuously.

This inconvenient practice led us to the modern-day water hammer arrestor.

As mentioned previously, high-efficiency washing machines, notably the newer models, are often more prone to causing water hammer. The mechanics behind this are not entirely clear, but it is likely associated with the washer valves, which close faster or more frequently than their counterparts in older models. That’s why it is not uncommon for homeowners who never had issues with water hammer to experience problems immediately after upgrading to a high-efficiency washer.

Oatey tip: One practical idea to reduce water hammer in washing machines involves the hoses, which are usually left hanging loosely between the washing machine and the wall or the box valve. This positioning can cause water hammer when the hoses flop around during the closing of the valve.

Securing these hoses — for example, by zip-tying them together and then to a pipe or something sturdy — can help eliminate water hammer. While these hoses are flexible and, therefore, challenging to secure, this simple preventative measure can effectively reduce water hammer and potential damage to a piping system.

Other Considerations

To prevent future piping damage, failure and leaks, incorporate hammer arrestors into a plumbing design blueprint early on.

Proper sizing and placement of hammer arrestors are equally crucial; otherwise, they cannot perform correctly or achieve longevity. Incorrectly sizing a hammer arrestor by miscalculating fixture units or failing to follow a manufacturer’s installation recommendations could end up doing little to remedy a water hammer problem.

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