Strange water hammer problem

[gmkaboulov]

Apologies if this has already been discussed:
I am having issues with water hammer, and the combination of symptoms doesn't really match with anything I've read online about it.

Opening/closing a sink valve: no noise
Dishwasher: no noise
Toilets: no noise
Garden hose: no noise
Open bathtub valve: loud banging, stops immediately when valve is closed
Washer: loud banging

Sounds like air in the pipes, but this is where I get puzzled:

Toilet tank is filling (cold water only of course), and when I open only the hot water valve in my sink, loud banging. Closing valve immediately stops the noise.

No matter what combination, hot or cold, there is loud banging whenever more than one valve is open, except the dishwasher (I can open the sink valve while the dishwasher is running and there is no noise), and also the washing machine makes noise even if nothing else is open (but I am guessing this is because it opens the hot and cold supply at the same time). There is never any noise when closing a valve. Also the water flow visibly changes with the banging.

Is my house supply pressure too high or too low? Or is pressure even an issue? I want to eliminate some possible causes before calling a plumber. Thanks

 

[LiQuId]

high pressures can cause problems and noises to become louder, do you have a pressure reducing valve on your water supply??

how long has this been going on, ie. is this new?

shut the valve off to the hot water tank and see if this remedys the problem, could be a loose washer.

does it bang once when you open and close a fixture Bang then Bang,,... or is is more like a machiene gun Bang bang bang .... machiene gun = washer, one bang = water hammer

its not usually due to pressure.............

 

[gmkaboulov]

I think there is a PRV and I think I know where it is. This has been going on for as long as we've had the house (about 7 or 8 years).
Will try to shut off the hot water valve tonight.
It is a machine gun banging, roughly 2-3 times per second.
The more valves that are open, the louder the banging. Also, if both hot and cold are fully open on the faucet it doesnt make noise

 

[johnjh2o]

Sounds like the PRV valve to me.

John

 

[LiQuId]

^Agreed, this is the most likely and a good place to start.

 

[bhamiltonjr]

You can also try and drain down the entire house but shutting off the water main and opening every fixture in home, getting all the water to release from line. Shut everything back up, Turn main water back on. Open fixture one at a time again to bleed air out of the system. You might have some Air Chambers in the wall that have filled with water and is now causeing an air hammering action.

 

[bhamiltonjr]

Do you have a 2/3 handle shower valve or a single handle style?

 

[LiQuId]

You can also try and drain down the entire house but shutting off the water main and opening every fixture in home, getting all the water to release from line. Shut everything back up, Turn main water back on. Open fixture one at a time again to bleed air out of the system. You might have some Air Chambers in the wall that have filled with water and is now causeing an air hammering action.

this wouldnt solve the problem they are experiencing, a machiene gun style banging is caused by a loose or worn washer usually.