A hammering sound was occurring whenever a shower or sink were turned on or a toilet flushed. Also occurred when water entered the washing machine. The sound occurred consistently. Sometimes the hammering was extremely loud and accompanied by an equally loud groaning / deep sounding knocking or rumbling. Anti-hammering devices were put on the sinks, washing machine and toilets. The sound is no longer as consistent ( I could make it happen anytime I wanted before), but it is louder. The anti-hammering devices have apparently done nothing. A pressure valve at the front of the house was also replaced. The house is approximately 10 years old. A new bathroom was installed approximately one year ago. These noises started occurring around the end of April 2007. Obviously need them to stop. Need suggestions and ideas. Thanks.

"Water hammer" happens when you abruptly shut off the water. You have at least 40 pounds of pressure pushing the water flow. The weight of the water hitting a 90 degree bend causes the sound that you hear. We put in shock absorbers,(air chambers) to cushion the hammer much like the shocks on your car.
Back in the 60's we were required to to put shock absorbers,(air chambers) on all bath lavatorys and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is important.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will begain to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them in a two bath home. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back.
You have just recharged your air chambers and saved yourself a hefty service call bill. Hope this helps you out TOM

Thanks for the answer on pipe noise problem. Understand that hammering can occur when water is shut off, but my noise occurs when water is turned on. Appreciate your advice on recharging -- that should eliminate the loud groaning bumping sound as well? Is that all part of the hammering issue? At its worst, it sound like a slow moving train rumbing through the house.

Operating air chambers will eliminate most pipe noises. Recharge yours and get back to me. Good luck, Tom