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What is water hammer?

Water hammer or banging pipes are different faults with your water reticulation system.

 In theory, you should never hear the water moving through your hot or cold pipes. Instead, all you should listen to is the water flow from the tap or fixture in the room it’s installed in.

 Essentially water hammer is a shock wave created inside your piping.

What are the causes?

Plumbing is essentially the movement of water through pipes. It, therefore, has the potential to be noise-creating and create what is referred to as a water hammer.

Water hammer that is noticeable occurs with copper water pipes. But plastic water pipes also suffer from water hammer, and it’s harder to hear.

Water hammer audible noise in copper pipes is generated primarily by:

  • High water pressure

  • Quick closing mixer taps

  • Quick closing solenoid valves

  • Faulty or worn brass seats in taps

  • Broken tap washers

  • Airlocks in pipes

  • Shock waves in pipes

Common noise complaints

  • Sharp banging or hammering sounds coming from pipes

  • A series of loud bangs when the washing machine or dishwasher is in operation

  • A loud bang from a valve or tap

  • Audible ticking sounds that diminish after the tap is turned on

An intense banging or hammering results from faulty valves, defective mixer taps, defective solenoid valves, broken taps or broken tap washers or poor clipping of pipes.

 A series of loud bangs while using the washing machine or dishwasher is caused by the machine’s instantaneous opening and closing of the solenoid valves as it traverses through its cycle.

Excessive water pressure can accentuate all of these causes as water pressure legally cannot exceed 500kPa inside the building.

 The ticking sound can build up and then diminish and are the sounds generated by pipe expansion. This is caused by the pipe heating up when the hot tap is turned on as the hot water replaces the cold water and then cools down.

The bangs you hear are from a shock wave

Water hammer will occur much more if your pressure is excessive. The common causes of water hammer are quick closing mixer taps or solenoid valves on washing machines and dishwashers.

In the picture above, the shock wave is generated at the face of a quick closing mixer tap because the flow of water moving under pressure is stopped suddenly by the instant turning off of the mixer tap. The shock wave then ricochets back from the face of the mixer tap cartridge through the stationary water in the pipe.  As a result, the shock wave creates enormous pressure moving at 1280 meters per second through the pipe.

 This same effect is replicated more intensely by the solenoid valves in your washing machine and dishwasher. Unlike mixer taps, they instantly open and shut as your machine moves through cycles.

Water hammer is an early warning alert

All of the sounds or the audible noise commonly referred to as water hammer tend to be highlighted in copper water pipes. Water hammer still exists in plastic piping systems, but it is diminished significantly as the plastic pipe absorbs the sounds.

 Your plumbing reticulation pipes, taps, valves and appliances are all susceptible to damage caused by the impact of shock waves, even if you hear no noise.

 The noise is essentially an early warning system telling you to rectify the problem before damage occurs.

Rectification is possible

Water hammer is avoidable and can be rectified regardless of whether you have copper or plastic water reticulation piping.

Banging or noisy pipes usually occur when the water reticulation pipes have not been clipped correctly as per AS/NZS 3500.1: 2018 when the house was initially constructed. This can be much more challenging to rectify compared to a water hammer.

To prevent damage to plumbing pipes, taps, fixtures, hot water valves and appliances, the water hammer’s noise and shock wave elements need to be eliminated.

The noise element is auditory. For example, when you turn off a tap or your washing machine is running, the loud bang of a water hammer alerts you to water hammer problems. Without the noise, there will be no indication of a problem until the damage is caused or your home is flooded by a burst flexihose or appliance hose.

The elimination of the water hammer eliminates the shock waves, which impose undesirable stresses on reticulation pipes, flexihoses and appliances.

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