Water Hammering - What Is It?

Water hammer (sometimes erroneously called air hammer) is that banging noise you hear in the wall when a faucet is turned off abruptly. The source of the noise you hear is the piping moving laterally and striking the framing or wall surface materials inside the wall cavity. This condition often occurs with appliances such as clothes washers or dish washing machines that stop the flow of water rapidly. Another common location is at shower risers when a single handle fixture is in use that tends to “shear off” the flow of water when the fixture is turned off.

To see a visual example of this phenomenon, turn on your garden hose with a self-closing handle nozzle. Hold your hand on the nozzle handle spraying full blast. Let go of the nozzle quickly. The nozzle shuts off, and the garden hose jumps around wildly. This same movement can occur in the wall when you hear piping noise caused by water hammer. The higher the pressure, the more hydraulic energy and the more noise you will encounter.

How do your clients repair this condition? If the pipes are accessible, additional securing of the pipes with piping fasteners will help. Sometimes lowering the water pressure reduces the noise. If no pressure regulator exists, it may be beneficial to add one. A sure way to correct the problem is to have a plumber install air chambers in the water piping near the offending fixture. Air chambers have an air bladder inside for the hydraulic energy to release against. Air works well to absorb energy since it is compressible. In the case of adding piping straps or adding air chambers it may be necessary to cut open wall surfaces to gain access. Potentially some of the problem piping may be accessed from a closet or cabinet near the fixture where a wall cut may not be as noticeable.

Water hammer is usually not a major issue in a properly installed plumbing system. Most homeowners that have lived with water hammer simply learn to turn fixtures off more slowly. In extreme cases it is possible to experience piping leaks within wall cavities caused by poorly installed piping solder joints. Water hammer in most cases, however, is a repair if desired condition.