Plumbers: Help with water hammer issue
 

Howdy,

I had a plumber install some new taps in a vanity unit and replace a toilet in the same bathroom. We never had any issues with banging pipes / water hammer before hand. Since the installation, every tap in the house causes banging / rattling of pipes. Especially annoying when flushing the toilet when people are sleeping. It sounds to be coming from immediately under the bathroom.

The only thing they really changed is the copper pipes running out of the floor into the vanity unit to the taps where replaced with braided steel covered flexible hose. When you turn the taps on and off, these wobble around - I'm thinking this could be causing the issue? They want to come back and spend hours pinning all the pipes under the house and installing some kind of valve in front of the hot water unit - but something tells me these boys either 'aint too sharp (they made so many silly little mistakes on a simple job I had thought of just setting the dog on them) or they are going for maximum invoice.........so anyone else here with experience in water hammer problems?

You need to do two things:

1. Find out which section of pipe is hammering. It normally occurs at the end of a long run of pipe where there's a termination or a 90-degree bend. When water flowing in the pipe is stopped suddenly, the "slamming" of the flow in the pipe into the termination can cause the noise you're hearing.

2. Once you find out which length of pipe is the culprit, a simple $10 shock dampener can solve the problem. It's simply a short run of pipe at the termination or elbow that extends up vertically a few inches and is partially filled with water and with an air space. The air remains trapped at the top of the pipe (which is capped) and can compress (unlike water) to absorb pressure fluctuations/shock in the pipe.

That'll be $500 please. :)

I'd check the valve that they cut off at the street or whereever first. Make sure it is fully opened.

Also check your water pressure. Excessive pressure (< 60 psi) can add to the problem.

Thanks guys - we do have notoriously high water pressure in my area. I had a limiter placed outside the meter already because we where contunually blowing out pressure valves in the hot water system.

Looks like I'll be crawling under the house this weekend.

So what's the best way to determine precisely where the hammering is coming from? Do you just go underneath and have someone turn taps on/off?

As P-O-P explained. The sudden 'stop' of a column of water is most likely your problem. You mentioned new vanities installed and no previous problem. The plumber apparently did not install a "T" with a short 4"-6" stub pipe. This allows somewhere for the water to 'buffer' to when the valve shuts off (as P-O-P explained). Basic science = you cannot compress a liquid.

If your plumbing is plastic CPVC pipe...it's an easy fix you could possibly do yourself. Hacksaw, CPVC pipe/ftgs. glue.

With toilets, and washers/dishwashers that don't use a water-fill timer, you can also just close the hand valve partway which will limit the flow and the hammer effect.

Eureka! A POP post I can agree with!

Something doesn't sound right here. Is it being suggested that a dampner be installed on the vanity side of the valve? If so, this will not solve the problem.