Pipe banging from water service provider

[I try]

Just curious what I can do to fix this pipe banging irritation. Every night at around the same time I hear the water line bang against the wall or ceiling. It only happens for a about 20 seconds and then goes away. It happens pretty consistently time wise. I know it's the water company because no water is being used in my home. I've actually been in the shower when this happened and there is a noticable change in presure while this banging is occuring. In other messages I red about a stand pipe, but am not sure what that is or where it is. In addition, I have a water sprinkler system, so I'm not sure if the banging is from the fire supply or the home use supply. Any ideas how to solve this problem without tearing my walls about to try and secure the pipe better? Should the water company provide water that doesn't experience rapid pressure fluctuations? I believe this happens when they do some kind of nightly maintanence on the system, like a pump transfer or back flush. I've talked with them briefly and know the fluctuations happen during this time when they are performing this task. Thanks for you help and suggestions.

[Speedy Jim]

Ah. You have a residential fire sprinkler system. (?)

Solving this one may take some more detective work. If there are check valves/backflow preventers on either service, these can contribute to the banging during periods when the pressure drops suddenly.

If there is a pressure reducing valve (PRV) on the household service, it likely has an internal check. I have seen cases where this internal check valve made godawful noises at night when the utility suddenly drops pressure.

If there is a thermal expansion tank, this reserve of pressure can make the banging period longer.

I have a hunch that solving this may take someone knowledgeable on the scene to evaluate just what is happening in your case. And I don't think the fix will be as simple as "adding a standpipe".

Jim

[David Martel]

Jim,

I've never heard of a stand pipe used on the potable water plumbing just on the septic side. Is this a name for an anti-water hammer shock absorber?

Dave M. "

[Speedy Jim]

Yes, I think that's what he was referring to. More properly an "air chamber". As long as they don't get waterlogged over time, they can be effective in controlling true water hammer, such as when a faucet is closed very rapidly. Jim

[I try]

Jim-

Yes, it is a residential fire sprinkler system, required by the lovely city I live in. I guess it's good in the case of a fire, but most likely will only add to my water bill, because a larger main is required. Sounds like you have a pretty good feel for this. The noise occurs pretty much on schedule and lasts for about 10 seconds. There is no water being used in the house so it is purely the result of pressure fluctuations on the city water. I could actually see one of the sprinkler heads move while the noise was occuring. Could a pressure regulator on the main fix this. The weird thing is it just started one day. It didn't start small and get worse. It sounds like you are saying the the valve itself is causing the problem in doing it's job to prevent a back flow of water or are you saying that because it isn't doing it's job, the pressure change is causing a water hammer? Are there regulations regarding the city provided water? Thanks for you help. Dave.

[Speedy Jim]

You'll have to track down what components are actually in the service line(s), such as regulator (press reducing valve), check valves, backflow preventers, expansion tanks.

In the event of a sudden drop in mains pressure, a check valve will slam shut and could cause a type of water hammer in the pipes. I just mention that as one scenario, not necessarily what you have.

I doubt that anyone on here will be able to nail it down for you; good bet you'll need someone competent to look the thing over.

Doubtful that the utility will cooperate.

Jim