Pipe Hammering - How Should I Fix?

Background: I live in a condo, second floor. After taking a shower I noticed a very loud noise coming from within the wall (or floor?), usually happened 4-5 minutes later. Neighbor reported same issue and agreed with me, it sounds like a rifle shot.

After two years of this I came home one evening to find a letter from my HOA stating that the neighbors ceiling directly below my shower stall was leaking water. The second plumber I hired located the problem, it was the pipe behind my shower head (about 3 feet above my floor). It had a hairline crack and was leaking. He cut out a section (about 6â€) and glued in a new one. This is 1/2†PVC pipe and as far as I can tell about 10’ of it is hanging vertically unsecured.

The plumber seemed confident that the “banging†didn’t cause the damage and it was a defective pipe but I am not so sure. Other units in this development (which is only 5 years old) have this problem.

This is costing a great deal of money and though I’m aware that an arrester may be the best solution it would require yet another visit by a plumber (already two and a third coming tomorrow as the water shutoff valve he turned is now leaking).

As the pipe is still exposed what can I do to help with the banging? Should I cover it in some insulation to pad it?

I have a banging in my other bathroom as well. Would it help to turn off the water very slowly from all the bathroom fixtures (or turn on slowly as well?) to delay the onset of this issue?

Thanks for your replies in advance. This is my first time as an owner and I had expected a new development not to have these kinds of problems but apparently the builder skirted the more rigorous requirements by constructing it as apartments (lower state code requirements) then flipping to a condo (more rigorous building codes IF it starts out as a condo dev.) development the next year. Live and learn…

A water hammer is caused by quickly turning off water - the fluid in motion tries to stay in motion and if it can't flow, it moves the pipe. If the pipe doesn't hit anything, often you won't hear it. PVC shouldn't be used for supply pipes - CPVC can. Both of these change size a fair amount if heated. If they can't slide easily, they can 'pop' when then eventually generate enough force to move through that restriction. If a pipe is not suppported properly and there's a tight spot, the thing can bend (take a piece of paper flat on the table and push the edges towards each other - it doesn't take much change in length to create a big bow in the paper - same with the pipe). Constant flexing of pipe not properly installed or spec'ed could cause it to eventually break/fracture.

If the wall is open, post a picture so we can see what you're talking about.

A hammer arrestor should normally only be needed on quick acting valves like ice makers, washing machines, and some toilet valves. A valve you open and close normally wouldn't cause a water hammer, and a true water hammer doesn't wait 5-minutes to happen...it is immediate upon closing the valve.

Thanks Jim, I'll post a picture this evening.

noise

Hammering does not occur 4 or 5 minutes after the water is turned off. But if the piping was installed in such a way that the pipe can expand when hot water flows through it, but is then "trapped" as it cools off, then when the force is great enough, it can release with a bang. IF that is what is happening, then that stress before it can break free COULD cause damage, especially if the pipe is pulling against a fitting joint.