I have two toilets in the house and just over the past trwo months whenever either one come to the end of the flush cycle(the incoming water stops filling the tank) I get a water hammer type banging in the pipes. The washing machine does not cause this when it closes the water valves. I looked for loose pipes and found none exposed. I also put my hand on the cold water pipe on a long run as the toilet was flushed. I can not feel excessive vibration and the nios seems to come from the floor under the uppermost bathroom in the house. Both toilets had fluidmaster 400a fillvalve replaced about 2 or 3 years ago.

Sounds like water hammer to me. "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 air chambers to cushion the hammer much like the shocks on your car.
Back in the 60's we were required to to put air chambers on all bath lavatories 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 began 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 and thank you for rating my reply. TOM

Thanks for the reply Tom. Let me give you a little more detail. The house was built in the mid 50's. It is a split level with originally one bathroom on the upper most floor. So far I have not found an air chamber under the kitchen sink. The kitchen and lower bathroom are above a crawlspace so I can see the pipes that run up into the cabinets and vanity (no air chamber). I took pictures of the plumbing and electrical when the new bathroom was framed(no air chambers there- it was built in the late nineties). The only place left would be behind the walls in the upper bathroom. Since I hate messing with plumbing would it be as effective if I turned off the main in the crawl space and then opened the faucet handles (hot and cold) in the uppermost sink and tub as well as the lowest faucet which would be an outdoor hose spigot to bleed the system? If so should I close all but the highest faucets when I turn the water back on? Another interesting thing is that the new washing machine does not cause the pipes to rattle. However, it is comnnected with the braided stainless steel hoses and the two toilets have ridgid chrome plated copped fill pipes from the angle stops.

When we install air chambers we install them just inside the wall ahead of the stub-out, (see image). In my area we are mandated to install them. If it really bothers you You could do one of two things.
Install a expansion tank in the attic off a cold water line to service the entire house or try changing the ball cocks to a float ball type,(see image). Good luck, Tom

Thanks Tom. I drained the water pipes today and still get the water hammer occasionally when either toilet finishes refilling the tank. I also looked for any signs of air chambers and the only place left would be behind an inaccessible wall behind the vanity in the upper most bathroom. Is it possible that eccessive pressure coming into the house could contribute to the problem? As I said in the beginning it just started a couple of months ago and we have not made any changes to the plumbing for about 3 years. It is odd that it does not do it every time (actually a good thing) and that the new washing machine does not cause the problem. I will look into a whole house chamber. Thanks again. BTW, I thought that the Fluidmaster 400A fill valves were a better setup than the older copper ballfloats. The toilets are about 7 years old and the original American Standard fill valves( yellow plastic units) were replaced about 3 years ago because they frequently over filled (start/stop) and I was frequently taking them apart to clean the rubber diaphram under the cap.


Just to clarify as I noticed that my terminology was incorrect. Both toilets have Fluidmaster 400A fill valves which are float type not the older ball type as in your diagram. Also my angle stops are not fully open. They are only about 1/4 to 1/2 turn opened. Is this a problem?

[QUOTE][, I thought that the Fluidmaster 400A fill valves were a better setup than the older copper ballfloats./QUOTE] Not in my area. It seems that in time our water swells the hole in the FCluidMaster seal,(see image) shut cutting down on the fill rate until finally it swells shut entirely. I woukd change out the noisy ball cock and see what happens. Also I would purchase a hose bib gage,(see image) and check my house pressure.
Do you have a PRV (pressure reducing valve) installed? Back to you, Tom

Okay. I tested the water pressure at a sillcock about 5 feet down the line from the water meter. It reads 85 lbs of pressure. Is it worth putting a prv on the system for that?

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It reads 85 lbs of pressure. Is it worth putting a prv on the system for that?

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You're right at the limit. If you wish to reduce your water hammer you will have to control your house pressure. I would install a PRV valve and set it at 45 PSI and work up from there. Good luck, Tom

Thanks again. I am looking into a prv now. The funny thing is that the water company said that 85 psi is normal and not to worry unless it was closer to 100 or higher...

Do the math. City water towers are 100 feet high for a reason. Because at 100 feet the head pressure is 43.4 PSIat the base, add the drop from the ground to the main and you come up with 45 PSI which is the national average. 80 Psi is putting a undue strain on both valves and pipe joints. Your water company was mistaken. Install the PRV valve. Good luck, Tom

I may have noted this before but the city brings in 3/4" copper to the meter in the crawlspace. from there the piping is all 1/2" until it gets to the addition where the plumber increased the main run (about 25 ft) to 3/4". He did this on the hot side as well. All the feeds to the new individual fixtures are tee'd and reduced to 1/2" again. My question is that is it necc to replace the original main run to 3/4"? It is also about 25 ft before it goes up to fixtures including the hot water heater.

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Originally Posted by Primo59

I may have noted this before but the city brings in 3/4" copper to the meter in the crawlspace. from there the piping is all 1/2" until it gets to the addition where the plumber increased the main run (about 25 ft) to 3/4". He did this on the hot side as well. All the feeds to the new individual fixtures are tee'd and reduced to 1/2" again. My question is that is it necc to replace the original main run to 3/4"? It is also about 25 ft before it goes up to fixtures including the hot water heater.

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For better volume I would increase the main to 3/4" and not tie more then three fixtures on a 1/2" branch. However I would still reduce the house pressure. I don't care what the water company said, 80 PSI is simply too damm much pressure. Regards, Tom

The PRV is a definite and I appreciate the advice on that. I was just looking to see if I should pursue the piping while I hade the plumber out at the house. Thanks again Tom!!

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the city brings in 3/4" copper to the meter in the crawlspace. from there the piping is all 1/2" until it gets to the addition where the plumber increased the main run (about 25 ft) to 3/4".

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Increasing the pipe size after it's been reduced one pipe size won't bring back the volume. I would replace the 1/2" main with 3/4" for the best volume to your house. Regards, Tom