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Arresting Water Hammering

Image Source: Sioux Chief

Water Hammering

Water hammering is a phenomenon that occurs when water flowing in a piping system suddenly changes in direction or stops abruptly. This sudden change in flow can be attributed to common processes in the system such as pumps being turned off or a quick closing valve shutting close. As a result of the sudden change in flow, a pressure surge is created in the piping system. This surge in pressure is then released through the form of a shockwave, which results in the vibration of the pipes or even potential damage to the fittings and connections of the piping system.

What has been depicted is the typical nature of water hammering and its potential harmful effects it brings about to piping systems. Having the capability to minimize the effects of water hammering would not only reduce the noise it produces from the vibrating pipelines, but also ensures that the piping system will be less susceptible to damage in the long run; hence it is important to be able to restrict water hammering to maintain a quality piping system.

Water Hammer Arrestor

A water hammer arrestor enables the piping system to be able to ‘arrest’ the water hammering phenomena. The primary function it employs to control water hammering is to absorb the pressure spike into the arrestor’s body and cushion it with a specific mechanism depending on the type of water hammer arrestor, with the most common variant being the piston-type water hammer arrestor. The piston-type water hammer arrestor employs the use of a distinct air column that is separated by a moving piston from the flowing water in the pipes. This piston would absorb the shockwave generated by the pressure spike from usual culprits such as quick closing valves and dissipate the shockwave using the air column as a cushion.

Placement of Water Hammer Arrestor

Water hammer arrestors should be placed near the end of a water supply branch line between the last 2 fixtures. If the piping of the branch line exceeds 20 feet (or approximately 6m) an additional water hammer arrestor should be placed, with subsequent 20 feet lengths adding another water hammer arrestor. This is to ensure that the water hammer arrestor can effectively capture the water hammering caused by the fixtures; rather than causing a water hammer arrestor to be overloaded, or fixtures that are too far away for the water hammer arrestors to capture.

Sizing of Water Hammer Arrestor

Water hammer arrestors also come in different sizes that have differing capacity, to suit the needs of different piping systems. Sizing of water hammer arrestors for point of use fixtures are done by tabulating the number of fixture units and assigning suitably sized water hammer arrestors to each branch line. For sizing of water hammer arrestors for larger systems, calculations must be performed to ensure the sized water hammer arrestor capacity is compatible with the system. Having the correctly sized water hammer arrestor is crucial in maintaining the effectiveness of the water hammer arrestor, otherwise costs can pile on when there is a need for additional water hammer arrestors or a replacement for a higher size/capacity model.

We at Val-Technik would be able to provide professional opinion on the appropriate sizing for water hammer arrestors and suggest optimal placements for the arrestors to function effectively in piping systems.

For more information and consultation regarding the sizing and placement water hammer arrestors, please email us at or call 6742 2770.


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