Dealing with Water hammer Problems

What is Water Hammer?

Water Hammer is caused by the closing of a shut-off valve on a high pressure water supply. It usually occurs when a shut-off valve closes quickly, which causes a shock wave to reverberate in the water pipe, sometimes throughout the whole water system. It can usually be heard as one or more ‘thumps’ in the pipework immediately following the closing of the valve.

Can Water Hammer Cause Damage?

Yes, the shock wave caused when Water Hammer occurs can eventually cause damage in the system. It may cause a burst at any weak point in the pipework or at a joint, and it can also cause damage to the inlet valves on washing machines, dishwashers, thermostatic showers etc. Likely Causes of Water Hammer Quick shut-off valves, as fitted to washing machines, dishwashers, thermostatic shower valves and other electricity controlled water operated appliances. Float operated inlet valves fitted in cisterns and other installations incorporating a water storage tank can suffer from certain symptoms of Water Hammer, particularly noisy vibrations.

How to deal with Water Hammer

HYDRA-RESTERS and MINI-RESTERS have been specially designed and developed by the Sioux Chief Manufacturing Company Inc. in the U.S.A. to provide an acceptable solution to the problem. These unique fittings are effective shock absorbers in a range of different sizes, capable of taking up the shock wave in pipes from 1/2” to 2” dia. according to the size fitted.

Where to fit Hydra-Resters and Mini-Resters

Best results are normally obtained when the Water Hammer Arrester is fitted as close as possible to the shut-off valve causing the shock wave.

MINI-RESTERS were designed small enough to fit unobtrusively behind or beneath typical installations with quick shut-off valves likely to cause Water Hammer. MINI-RESTERS are most effective when fitted close to the shut-off valve causing the Water Hammer. Their effectiveness will diminish the further they are from the shut-off valve, and it is recommended that they should not be more than 2m from the valve.

It is important that all pipework is secured with appropriate pipe clips to prevent lateral movement and to hold away from adjacent surfaces to minimise the effects of shock waves or vibrations within the pipes.

In water systems with very high pressure, particularly where there are extended pipe runs which may not be secured, such as up in roof spaces or under floors, the effect of Water Hammer is likely to be more severe and the fitting of a 1/2” HYDRA-RESTER or even a 3/4” HYDRA-RESTER is recommended, according to pipe sizes and lengths of run.

A 1/2” HYDRA-RESTER fitted within 6m of a shut-off valve on a 15mm direct pipe run is likely to absorb the shock wave in that part of the system, but pipe runs to other shut-off valves in an extended system may need to be fitted with additional HYDRA-RESTERS of the appropriate size to suit each pipe run.

Complex Water Systems

Complex water systems serving many appliances, taps, cisterns and shower valves may need a MINI-RESTER fitted close to each of the valves causing the most serious Water Hammer, supplemented by a 1/2” or 3/4” HYDRA-RESTER fitted in the main pipe run as close to the offending shut-off valves as is convenient.

Hardly any two water systems are identical, hence it is only possible to provide guidance rather than rules to the installer. For a typical three bedroom house with severe Water Hammer problems, we would recommend the installer to take a minimum of two MINI-RESTERS and one 1/2” HYDRA-RESTER, together with at least six 15mm to 1/2” FI tees with provision for blanking off up to four of the tees. For houses with many appliances and larger houses the numbers of MINI-RESTERS and sizes of HYDRA-RESTERS may have to be increased appropriately.


Guide for Installers of Plumbing Systems in Areas of High Water Pressure

It is recommended that installers in areas of high water pressure should take account of the likelihood of Water Hammer arising if quick shut-off valves are used in the new system, and to allow for the cost of supplying and fitting the appropriate number of MINI-RESTERS likely to be required to ensure that the system will function free from Water Hammer.

Back to Water hammers


Masefield-Beta Limited
Unit 17, Coneygre Ind Est,
Tipton, West Midlands
Tel: 0121 557 3433
Fax: 0121 520 6369