How to Optimise your Water Hammer Arrestor Installation

Where is the best place to install water hammer arrestors?

Water hammer is created when a valve closes or a pump stops quickly and the momentum of the water creates a pressure wave that rebounds from the closed port, travelling back up the pipe. This is exacerbated when the frequency of the transient pulse resonates with the pipework or from standing waves in the system that can build to the extent that severe damage can be caused.

Determining the origin of the hammer effect can be difficult which makes picking the site for the hammer arrestor more complicated. The effect can be made obvious through insufficient pipe supports that allow pipes to move and vibrate loudly but this can be quite a long distance from the actual source. When hammer travels long distances it is harder to hear the onset to determine what the actuation point is and it is a matter of elimination sometimes to find the action that causes the problem.

Exactly where to place the hammer arrestor will depend on the actual piping arrangement. The best places are either close to the pump, isolation or check valve that is originating the hammer, or at more distant points where the pipe changes direction, for example at the top of a pump riser. Using an angle type arrestor such as the P12 in place of a pipe elbow can be very effective at reducing transient pressure spikes from either direction. Replacing pipe elbows with a tee and fitting a P14 arrestor is also an option and this allows for maximum transient suppression when in line with the returning wave.

Preventing hammer upstream of isolation valves can be achieved through fitting a hammer arrestor of either type at the last pipe bend or elbow prior to the valve inlet. Depending on the severity of the water hammer, several arrestors can be employed to reduce the impact throughout the system. One close to the pump or valve and one at the first high point or one in each of a pair of series elbows prior to a tall riser.

Serial elbows can cause a water hammer effect that can be removed by fitting a hammer arrestor at the first bend, possibly after a check valve.

If you are having problems with water hammer, call us and let us use our experience to suggest exactly where you will get the most benefit from water hammer arrestors.

How to adjust the water hammer arrestor for maximum efficiency?

The P12 and P14 water hammer arrestors are supplied already pressurised from the factory and can be installed and used without further adjustment. However, to get the most efficiency from them, they work best when pressurised at 30 to 50% of the normal working pressure. 

This is easy to adjust as they are fitted with a Schrader valve as used on car tyres so it is simple to bleed some air pressure out or put more in and evaluate the changes. The smaller arrestors would require an external gauge to check the pressure but the larger ones are supplied with a pressure gauge as standard. 

As many systems do not have the same pressure throughout, this enables adjustment of each arrestor to suit the inlet pressure conditions where each are sited. For systems with fluctuating pressures, the use of multiple arrestors that are all set to slightly different internal pressures, can effectively bracket the system pressure range so that they coordinate the effectiveness.