SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

Hi All -

First post here, looks like a great forum to get tips and advice. I inherited an irrigation system last year when we bought a house, so I'm still learning some of its quirks.

I have a problem that's really frustrating me, so I appreciate any opinions. I just fired up the system a couple weeks ago when I had a tech come out and do the backflow inspection. I wasn't home when he did it. A couple days later I turned on the system for the first time and we heard a constant banging noise in the indoor plumbing - kind of like water hammer, but rapid (probably 5-6 bangs per second) and constant as long as the sprinklers were on. Let it run, but left on vacation later that day so I couldn't do any troubleshooting. Did not have this problem at all last summer. System was purged last fall by the same tech who opened it for me a couple weeks ago.

Still having the problem. Occurs on all five zones, except not nearly as bad on the one zone that is sprays only (other four zones are rotors).

Here's what I have checked so far:

1. Checked the interior pipes in the crawlspace. Noticeable vibes when I feel the main copper supply line coming in. I added some foam pads in a few places where the pipes contacted a joist or other support, but it didn't help much. As far as I can tell, the supply for the irrigation tees off at the main control valve next to the water meter some 30 feet away from the house. The irrigation supply line does not enter the house.

2. Checked main irrigation supply valve at the water meter, it was fully open. Closed it fully and reopened it (with system off), still have the problem.

3. Checked the backflow valve - no noticeable vibes and cannot hear any noise. No indication that there would be a problem inside the house. Closed and reopened both ball valves on the backflow device (with system off) and problem still persists.

4. Water heater happened to die a couple days ago, so while the plumber was here I demo'd the problem. He said it sounded like a meter clanking and suspected the backflow (depsite the fact that I can't hear the noise at the backflow valve). He also checked house supply pressure and found it to be ~70 psi -- he said anything less than 80 psi is OK. I didn't ask him to investigate further. (And the noise was occurring before the water heater died, so it's not related to anything he did.) Does the backflow preventer have some sort of meter in it?

Called the irrigation tech today, he sounded fairly stumped but suggested a couple things:

5. Rotate the backflow ball valves to about 45 deg partially closed - "maybe the water is exceeding the speed limit with the valves full open" -- his words. I vaguely recall that they were set that way last summer when we moved in, but this did not help. I tried it with both ball valves together and separately.

6. Check the zone valves with the system off and see if one was hissing. Can't remember what this would be a symptom of, but no luck. Turned on the system while I was checking the zone valves and they sounded OK - no unusual sounds there other than typical open & close sound.

Any ideas?? It is really frustrating because the sound is fairly loud and therefore I can't run the sprinklers in the early morning, but I haven't even run them at all because I'm fearful it might cause damage to the plumbing if it's some sort of water hammer. I'm just puzzled as to what might have changed from last year to cause the issue this year.

Additional research on the Internet suggested too small of a water meter (but that hasn't changed from last year when there wasn't a problem) or air in the system (haven't tried to do anything there).

Appreciate any help. I may ask the tech to come out in a couple days to have a listen/look, but based on our conversation today, I'm not optimistic that he'll be able to identify the source of the issue.

Thanks,
John

Wet Boots -- Thanks for your thoughts on possible surging. I've got one zone in particular that has a low-head drainage issue that results in some air on that zone, just haven't had a chance to replace the heads with ones with built-in check valves. I'll do some troubleshooting (keep some heads closed while I run the zones) to see if reducing zone flow might help pinpoint the problem. But the noise occurs with all five zones, not just the one with the low-head issue...

I just keep coming back to the thought of "what has changed since last year" since I didn't have the noise problem last year.

Appreciate the advice, I'll keep trying stuff...

John