Water Shock Arrester
Water Hammer (hydraulic shock) is by far the loudest and most common plumbing noise problem in the home. You hear it in a home having high water flow rates (around 10 feet per second) when a faucet or water valveis shut off quickly.
Older homes have (or should have) what is called an “air chamber” located on each hot and cold water line at or near each faucet or water inlet valve. The purpose of the air chamber is to act like a shock absorber for water when it is flowing at high speed under pressure. Since air compresses (it’s a vapor) and water doesn’t, the air chamber allows the water a place to temporarily expand into and softens the blow of the water shock wave when the faucet is turned off quickly.
Air chambers are often fabricated on-site by the plumber and installed at the faucet’s water supply. They typically consist of a vertical length of capped pipe about 12″ long or longer and are the same diameter as the water supply pipe. The problem with these things is that they are sometimes made too short and undersized and eventually fill up with water and you have no more shock absorber. The result? Water hammer!. If you have a water filled air chamber it can be easily fixed by draining and recharging the plumbing system.
A better solution to alleviate the problem is to have a mechanical or engineered water hammer arrestor installed. These mechanical plumbing devices are charged with air or gas and will not fail like typical air chambers.