Information on and causes of Water Hammer


  • Water hammering is caused by the quick shutoff of water supply pipes. The energy in flowing water has to go somewhere, and when a valve is shut off, the pipes can flex and “hammer” against anything close—like nearby studs within walls , floor joists or other water pipes. Solenoid-triggered valves( LG washing machines as an example) , like the ones in dishwashers, washing machines and water softeners, shut off almost instantly, not only causing the most ferocious hammering but also putting strain on rubber hoses and copper solder joints
  • Water hammer costs homes money in the medium to longer term causing premature failures of water pipes, hot water storage heaters and tanks, washing machines and dish washers, automatic control valves and flush tanks or valves
  • In the US and Australia Water Arresters are very common but not so in the UK & Europe until the recent release of more devices with Solenoid-triggered valves and the water pressure increasing in many homes.
  • Properly sized water hammer arresters should be installed on the Supply that is having issues , this is most likely to be the cold supply but in some cases it can be the hot supply as well.

    The closer you locate the arrester to solenoid valves, the better.

    There are two types of Water Arrester , single device units or multi device units. Single Device units: We sell two on for taps, basins and toilets and one for washing machines / Dish Washers Multi device units: If you are experiencing Water Hammer from a variety of devices in the home you need to pull together a little table of the number of devices and multiply them using the values in the scope table below; Then find a unit that meets your total scope

    Device Score
    Shower 1
    Bath 1.5
    Toilet/WC 1.5
    Basin/Sink 1.5
    Dish Washer 3
    Washing Machine 3
    Header Tank 1.5
    Garden Tap 2