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Sorry if this is out of the blue, but I have a plumbing question. Sometimes when I shut off the faucet or the toilet stops running, it makes noise. Any idea how to quiet it down?
 

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That seems like water hammer. I saw this on This Old House. When you shut off the valve just right, all the water in the pipes suddenly stops. This creates a pressure wave which hits something, making the banging noise. Google water hammer for more info.

To solve water hammer, put an air damper close to the valve. You can buy small cylinders that you attach to your pipe at lowes but they're junk. Sooner or later, they fill up with water and it doesn't absorb the pressure wave. What you need is a sealed chamber with a rubber bottom. This way, the air bubble doesn't dissapate into the water over time and it stays effective.
 

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Some more facts on water hammer

http://en.wikipedia.org/wiki/Water_hammer

the small brass cylinders work, but they will fill up with water over time. You have to shut off the main water and drain at the lowest point. this lets them fill back up with air. obviously, this is not very efficient so a sealed air vessel is best. The other problem is that you can't put them under a toilet - it'll look like poo, so you have to tap the line somewhere else.
 
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