Bang when toilet start flushing

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dacarra

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Hi,
this is a dual flushing toilet, around 10 years old. For some 6 months this happens: when the handle is turned and the water starts flushing, sometimes (maybe 1 out of 3 or 4 times), there is a loud bang that seems to come from the utility room, next to the washroom, where the pressure tank is located. Since the bang happens when the valve is opened, not when it closes, I don't think it is a water hammer. The pressure is 30-50, so it's not very high to begin with. It does not happen if the toilet is flushed with the supply valve closed, so it doesn't seem to be related to the toilet itself. By the way, I replaced both pressure tank and pump a couple of months ago, and it was happening before and continued happening after. I am baffled. I thought of installing a water hammer arrestor anyway, and probably would not do any damage, but if it is not a water hammer it probably would not do good either. Any ideas or suggestion would be greatly appreciated.
 

Reach4

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Do you have a submersible pump, and is there a check valve above ground?

I am thinking perhaps the pump starts, and the water from the pump slams against the above-ground check valve.
 

dacarra

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The pumps is drilled. No check valve above ground, is at pump. The pump and valve are new and anyway the bang happens when the pump is not on. As I mentioned, it was happening for some time with the old pump and valve, and it happens with the new as well.
 

Bannerman

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I thought of installing a water hammer arrestor anyway,
Your pressure tank will act as a large hammer arrestor. You need to investigate the cause of the problem, not add devices to address symptoms.

Ensure the pressure tank pre-charge pressure is calibrated correctly. The tank's air pre-charge should be 2-3 psi lower than the pressure switch cutin setting which you said is 30 psi. The pre-charge should then be 28 psi. When measuring the current pre-charge pressure with a tire pressure gauge, the pump will need to be turned off and a faucet opened to drain all pressure from the plumbing system.

If the tank pre-charge is equal to or above the pressure switch cut-in pressure, the home's plumbing pressure maybe dropping to 0 psi before the pump becomes activated. Once the pump is activated, the pressure may then immediately increase from 0 to 30 psi, which will likely then send a shockwave through the system.
 

dacarra

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The pre-charge is at 28, the pumps starts at 30 regularly, and anyway, as I mentioned, the bang happens not when the pump starts but immediatly after turning the toilet handle. It does not happen by the way, with the other toilet, or with any faucet.
 

Bannerman

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Since the sound seems to be pump system related, have you remained in the room where the pressure tank is located to attempt to identify the sound source while somene else flushes the toilet?

You said the pump is not running when the sound occurs. How long after hearing the sound does the pump activate? Since the sound does not occur with every flush, and since the pump will not likely activate after every flush, could there be a correlation between the sound only occurring when the pressure tank pressure is low enough for the pump to activate when filling the toilet tank?
 

Terry

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Sometimes the shutoff at the wall has a loose rubber washer that causes a vibration. I can normally open the valve up all the way and then back it in just a little and that often will fix the chattering. Even better is to replace with a 1/4 turn stop.
 

dacarra

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Bannerman: sometime the pump does not starts at all after flushing, if the tank happens to be full. Or the pump could start way after the noise is heard. I did try to stay next to the pressure tank while someone else was flushing, but could not determine where it came from, only that it seems to came from the room. But it could be reverberating.
Terry: I tried closing and then opening the valve several times to see if it makes a difference -it does not- and I normally back it off a little. I might try to change the valve anyway and see if that makes any difference. It is not a chattering by the way, it is a bang. I gather that to put an arrestor in would be a waste of time, as I was thinking?
 

dacarra

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Just an update: after the last post I closed the valve down another little bit - about a 1/4 turn - and since then , 5 days now, the noise has disappeared. I'm keeping the finger crossed, but that seems to have done the trick. Thanks Terry.
I still cannot figure out why the noise - a rather loud bang, similar to a water hammer, seemed to come from the utility room instead that from the valve itself. Maybe it was reverberating along the pipes?
 
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