Anti-siphon valve making noise (irrigation system)

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Tamales
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Anti-siphon valve making noise (irrigation system)

Post by Tamales » Sun Apr 15, 2018 1:29 pm

The anti-siphon valve (or backflow preventer, or vacuum breaker, or whatever the correct term is) is on a water line that is branched off my main water line (i.e. after a T-joint), and the valve's output feeds the irrigation system. It's making a noise (sort of a buzzing sound) when certain zones of the irrigation system are on.

The valve is a Febco 765, and it was replaced a little over a year ago so it's not an age-related issue.

But it only does this for 2 of the 7 irrigation zones, which seems strange. Both the noisy zones are drip irrigation zones, but none of the other drip zones make noise, and none of the sprinkler zones make noise.

Any ideas what this might be?
It's definitely the anti-siphon valve making the noise, not the sprinkler valves (which are all at least 50 feet away).

bill88
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Re: Anti-siphon valve making noise (irrigation system)

Post by bill88 » Sun Apr 15, 2018 3:11 pm

My backflow valve (20+ yrs. old Wilkins 700 Dual Check) is making the same rattling/buzzing noise, quite loud. The only thing that stops it is turning off the shut-off valve for the sprinkler system.

My guess, and it's only that, is your problem is your Febco valve, and not anything else in your sprinkler system. Repairing or replacing your valve should fix it.
Bill | | (Formerly bill99)

Mudpuppy
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Re: Anti-siphon valve making noise (irrigation system)

Post by Mudpuppy » Sun Apr 15, 2018 7:24 pm

My guess is that those two drip zones do not have the same flow rate as the other zones and this is causing the noise at the anti-siphon valve. Have you tried adjusting the valves for that zone to increase or decrease the flow rate to see if it affects the noise?

Edit: You could also have air in those two zones. Depending on how the zone is set up, there may be a drip line that can be left uncapped to flush the air out of the zone.

neilpilot
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Re: Anti-siphon valve making noise (irrigation system)

Post by neilpilot » Sun Apr 15, 2018 7:55 pm

A backflow preventer will often chatter at very low flow rates, since it's designed to close if flow stops. Unless you can increase the flow on those drip zones, the noise will persist.

Replacing it with the same spec valve will not stop the chatter. Try partially closing the BFP's discharge valve to reduce the noise.

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fortfun
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Re: Anti-siphon valve making noise (irrigation system)

Post by fortfun » Sun Apr 15, 2018 8:01 pm

Mudpuppy wrote:
Sun Apr 15, 2018 7:24 pm
My guess is that those two drip zones do not have the same flow rate as the other zones and this is causing the noise at the anti-siphon valve. Have you tried adjusting the valves for that zone to increase or decrease the flow rate to see if it affects the noise?

Edit: You could also have air in those two zones. Depending on how the zone is set up, there may be a drip line that can be left uncapped to flush the air out of the zone.
This makes sense. All of my drip zones have a pressure regulator immediately after their valves. I wonder if those 2 zones are missing such a regulator, or if there is a leak on those lines, OR the valve on those zones could be damaged. Do you see any water leaking on the the valves associated with those drip lines? Are those drip lines emitting water?

Tamales
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Re: Anti-siphon valve making noise (irrigation system)

Post by Tamales » Sun Apr 15, 2018 8:23 pm

Good ideas. Thanks.
I don't have much control over the flow rate, other than adding emitters. I clipped off one of the emitters on one of the buzzing zones (as a quick way to increase flow rate), and that did indeed make the buzzing stop. But that's not a practical solution since the clipped-off emitter (i.e. open 1/4" tube) is probably equivalent to adding about a 50 new 2GPH emitters.

Maybe I'll see if I can find some 5 GPH emitters and replace a few of the 2 GPH with 5 GPH and hope that is enough of an increase. I wonder why it would just start all of a sudden.

Partially shutting off the outlet valve is an interesting idea too (is the idea that this puts some back pressure on the anti-siphon?). But the much higher flow sprinkler zones might not function very well after doing that. Anyway, I'll try that out and see if it makes a difference.

Any idea if the buzzing can eventually damage the anti-siphon valve, or is simply an annoying sound that could persist indefinitely without issue?

neilpilot
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Re: Anti-siphon valve making noise (irrigation system)

Post by neilpilot » Sun Apr 15, 2018 8:32 pm

Tamales wrote:
Sun Apr 15, 2018 8:23 pm

Partially shutting off the outlet valve is an interesting idea too (is the idea that this puts some back pressure on the anti-siphon?). But the much higher flow sprinkler zones might not function very well after doing that. Anyway, I'll try that out and see if it makes a difference.

Any idea if the buzzing can eventually damage the anti-siphon valve, or is simply an annoying sound that could persist indefinitely without issue?
If there are manual valves going to the drip zone, throttling back on those valves would also serve to put back pressure on the anti-siphon valve. Also, some zone valves can be adjusted to only open part way when energized.

The chatter means the backflow preventer internal seals and/or diaphragms are possibly subject to premature wear.

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