Water Hammer Question

[Marnoot]

I've got a water hammering issue with my pipes, and am a little confused by it. I generally think of water hammer being caused by a valve closing quickly, creating a shock-wave. I have a problem where the automatic sprinkler valves just outside the house cause water hammer in the pipes inside the house, when the valves open. When the cycle is done and the valve(s) close, there is no hammer.

I've attached a crudely drawn illustration of the setup. The water hammer is occurring in the pipes down stream, illustrated with the green arrow.

Any ideas? Should I install a water hammer arrester in between the green arrow and the regulator/valve? Water pressure is about 50PSI after the regulator.

[K Frame]

What might be happening is that when the sprinkler pops on, it creates a quick pressure drop in the house piping. When the pressure rebounds, it causes a water hammer. Not common, but I have heard of it.

Why it's not doing it when the system shuts down? That might have something to do with the location of the sprinkler heads in relation to the pressure regulator. The regulator might be insulating the house piping from the spike in water pressure that is the traditional cause of water hammers.

[Marnoot]

Well, I just ordered a hammer arrestor to install on a T a few feet after the pressure regulator. Hopefully that will take care of the problem.

[K Frame]

I always just made my own out of some spare copper pipe.

[Marnoot]

That's what my father's done at his house, but I was reading that apparently that's discouraged now as the dark moist voids can breed bacteria. And the air over time dissolves into the water thus losing the air pocket, requiring you to drain the house plumbing periodically to restore the air pocket. I don't know how common each issue is, but I figured I'd shell out $25 for the kind with the piston to avoid either.

[K Frame]

I put a schrader valve on mine... Air gone? Get the tire pump out.

Bacteria? Adds flavor.

Actually, that's a good point about the bacteria.

[Brad Johnson]

A simple pressure tank, even a small one, somewhere in the line will function as a pressure wave dampener without leaving places for the nasties to begin colonizing.

Brad

[cassandra and sara's daddy]

they make em sized for just that

[Leatherneck]

Are you on a well with pressure tank? Is it saturated?

TC

[Brad Johnson]

Forgot to say above, if the line from the pressure tank to the faucet is long enough you will still get hydraulic hammering.  Whatever "anti-hammer" device you use, it needs to be as close the faucet as possible.

Also, I think you can get a slow-action sprinkler valve made just for the problem you are experiencing.

Brad

[Marnoot]

I'm on municipal water. Regarding placement of the tank or arrester, what faucet do I place it near? Do I place it as close to the sprinkler valves as possible, or as close as possible to the nearest faucet indoors along the pipe?

The pipe runs through the foundation, the valve, the regulator, runs to the utility room, splits off one way to the water softener and another to two outside hose bibs. Then after the softener branches to the water heater and the rest of the house. The hammering is most noticeable in the pipe before it gets to the water softener, around where it branches to the hose bib and the softener.

I'm stating this all off of memory, I'll have to look closer when I get home tonight.

[Leatherneck]

When you look at it, try to figure out where that hammering is coming from and examine the devices (staples, clamps, etc.) that hold the pipes to the structure for looseness. Loose staples allow the tubing to reverberate, making the noise worse. Note that the right answer to all water hammer is NOT tighter fasteners; but the effects of mild hammering can be lessened-maybe to an acceptable level.

TC