If you have water hammer, you usually have good water flow, which is a good thing. To prevent water hammer in an existing home, you can decrease the flow rate (not desireable) or install one or more dampeners. Dampeners can be bought, but you can just as easily make one. It is nothing but a piece of pipe capped on the end and installed vertically (with the capped end up) on the water pipes. Air will be trapped in this dampener and will "absorb" the shock created when the water flow is abbruplty stopped.

Water, like all fluids, is not compressible. You can put it under pressure, but can not compress it. When a valve is closed at the end of a run of plumbing the water in the pipe thinks that it is still going to be moving and continues to try to flow in that direction. The higher the water flow, the faster the water wants to continue moving. Since it is not compressible, it shakes the pipes as the molecules run into each other at the end of the run. This can damage the piping over time. Adding dampeners (filled with air that is compressible) gives the water somewhere to go and softens the blow at the end of the line.

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Integrity Inspection Service, LLC
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