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Water Hammer

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A water hammer occurs for a great number of reasons and can be overwhelming in severe cases, even causing a lot of damage to appliances, tapware, and pipe fittings if left unchecked. The common opinion is that a water hammer cannot be fixed. We are here to tell you it can be fixed and to guide you through these processes.


What is a water hammer?

In plumbing terms, a water hammer occurs when a surge or wave is produced by forcing water in motion to stop or change direction suddenly, thus causing a change in momentum.

This most commonly occurs when a fast closing valve closes at an end of a plumbing system, and a pressure wave propagates in the pipe until the pressure is absorbed by the pipe or until there is a rupture in the pipe.

A water hammer can be extremely damaging to the plumbing system if left unchecked.

Watch this video for a visual explanation of what water hammer is.

Common causes of water hammers

The list below is not in any order of importance:

  • Water pipes inadequately clipped
  • Excessive water pressure
  • Use of fast closing valves in the plumbing system


How to locate a water hammer

It sounds strange because the noise is so clear, but the water hammer’s noise which is heard in one area may be caused by a problem from a different location.

How do you locate the source of the water hammer?

  • Ask yourself these few questions before you start:
    • How long has the water hammer been present?
    • Have any new appliances, such as dishwasher or washing machine been installed recently?
    • Is the water hammer getting worse?


For a newly built home

  • It is a great practice to do a water hammer test before all the walls are closed. You can do this by installing a ball valve and a gauge and seeing what happens when you turn the water on and off fast. This way, you can hear and see if you have a water hammer problem and fix it before it becomes hard to fix.


Existing Home

  • Check to see if a 500kpa pressure limiting valve has been installed and is working
  • Check the plumbing valves are all working around your home. The most common valves to be damaged by water hammers are the pressure limited valves to the dishwasher and the hot water system.
  • If the water hammer happens even if all the taps are off, it could possibly be caused by the neighbour’s plumbing pipes. This sometimes happens when the water entry taps into the mains have been done close together.
  • Check all the water pipe clips. Water hammers can loosen water pipe clips.
  • Check for faulty washers and install new ones
  • If your hose taps need to remain open, change the washers over to spring-loaded type washers. Installing a ball valve instead of the hose tap is another way to do this.
  • Check existing water hammer suppression devices (and if they have been installed correctly). If not, this can add to a water hammer problem.


How to fix a water hammer

There are hundreds of products on the market that claim to be the device that can fix water hammers. The problem is, water hammers can occur in so many locations and can happen without warning. The best solution is to install a combination of these devices. Adding water hammer devices is not expensive or even that time-consuming; it just takes a little bit of experience and know-how, and your water hammer problem could be fixed.

Sometimes, the water hammer has been happening for such a long time that pipe clips in the wall have become loose. Without cutting holes in the wall this cannot be fixed but it can be significantly improved.

  • Install a pressure control device in the house (500kpa).
  • Install pressure limiting valves in the hot water system, the dishwasher, and the washing machine.
  • Install spring-loaded washers on the dishwasher and the washing machine.
  • Install a water hammer suppression device on all quick closing devices (washing machine, dishwasher, mixer taps).

Watch this video for helpful hints on how to deal with a water hammer from a particular tap.

Reverse water hammer

This is where the water hammer occurs between the tap and the outlet. Two fixtures which experience this are the shower and the bath.

If this is happening, it is going to be hard to fix without access to the pipes in the wall. The good practice is to install an air chamber at the rough-in stage, so the shock wave can be absorbed. Option 2  is to limit the water pressure to 350kpa. Option 3 is to limit the flow of water flowing; this can be done by adding flow restrictors to the water outlet.


Water Hammer Fast Facts

  • Water hammers can occur without any noise.
  • When a quick closing tap is closed, the shock wave it produces can exceed 3000kpa.
  • When it comes to a water hammer, harder pipes such as copper or galvanised steel will produce more noise than its plastic counterpart.
  • All quick closing taps should be fitted with water hammer suppression devices, according to the Australian standards.
  • Water hammers can occur from slow closing spindle type taps.
  • The most common area for water hammers are the kitchen sink mixer and the basin mixer.
  • Water hammer was first mentioned back in the 1st century by Marcus Vitruvius when describing the effect of water hammers in lead pipes and stone tubes of the Roman public water supply.


Potential damage caused by water hammers

  • Rupturing plumbing pipes
  • Valve failure
  • Hot water system damage
  • Pipe welds and plumbing fitting failure
  • Failure of pipe supports
  • Internal damage to taps and appliances


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