Loud banging noise in one zone

Since a week or so I have a loud banging noise in one zone. Sounds like a washing machine that is overloaded with bulky items. It takes about 30 seconds initially when running the zone first time for the day until it stops. One or two bangs when stopping the zone. After that, it bangs only a couple of times when rerunning the zone.
It is not a water hammer, that feature makes no difference.
Backflow issue?
There are enough nozzles open to have sufficient water running.
Anybody having an idea?
Thank you in advance

It most likely is still water hammer. Is it the first zone that runs on the system? If so the water hammer feature would not help. More likely, there is there a minor leak in the zone? Is the zone on a hill? Check the lowest head to see if water is running out of it when the system is off. You may just need a check valve in the head to keep the pipes full, minimizing water hammer. Good luck.

Thank you Munch.
It is the t5th zone in the system and it repeatedly happens even if another zone is running prior.
I tested with the water hammer on and off, no difference. The zone is on a fairly level surface, just a minor slope.
No leak visible on any of the first and lowest heads, but the soil is slightly moist next to the valve box, where the pipe comes out, possibly for this zone. I have dug out the pipe and watch it, especially during the run of that zone.

Here is an update of the situation: All zones except Zone 5 are good.

Zone 5 is starting with a loud banging for about 30 seconds, which sounds like someone is ripping pipes out of the house. The it is quiet.
When I stop zone 5 and wait for few seconds, then start zone 5 again, it does only a short banging sound once and is the running nicely.
Same happens every time I re-run zone 5.

The pipes are staying dry at the point where I dug them out. No sign of a leak.

Still no clue what the issue is.
Thanks for sharing additional thoughts

@Munch - I would really appreciate your help. I have noticed this year a pretty bad water hammer situation with my irrigation system. Its been driving me and my plumber nuts how to address it. We have lowered the water pressure coming into my house and have considered installing a water hammer arrestor. As you noted, the water hammer feature in the Rachio app has not helped and my first 3 zones are on a hill. I do have a WFM and it hasn’t registered a leak in my system. Running a faucet in my home when the system turns on allievates the water hammer noise. Any advice? Can you explain about installing a check valve? The noise is driving me crazy and I can’t seem to find anybody locally who knows how to help. Thank you so much for your advice.

I had more serious issue. It starts with one zone but now it looks that every zone was effected. It will randomly start banging when the last zone stops. If I manually start a new zone than the banging will stop, but one the manually turned on zone stops, the banging will resume. I am frustrated, I need to wake up at 2:00pm to shut off the main valve to drain the water in my house then turn on the main water valve again. It happened just recently. Any idea about how to fix the issue? The banging stop function does not help at all.

A water hammer arrestor may not be a bad idea. The flow meter wouldn’t pick up the leak since the water is leaking out of the system between the valves and the last head causing a void in the pipes. When the zone is turned on the water behind the valve rushes in and slams into the water in the pipe causing the hammering sound. Check valves are super easy to install. It varies slightly with each type of head but you just open the head and stick the check valve in the bottom. I have attached pictures of a Toro 570z head check valve installation (the white thing). The part number for the Toro check valve is 570cv.

My guess (and it is a wild one) is that your valve or valves need rebuilding. The slow shut down process is causing the water to shutter through the system while it tries to shut down. I hope this helps and good luck.

Looks like the thread was hijacked by other topics. Any feedback on my issue? Thanks

I think you might have a bad valve; not functioning the way it is suppose to. Get a new one, gut out the old one and replace it with new guts from the new valve.

Loud banging/ pipes shaking is usually water hammer. Caused by noncompressable water accelerating through a pocket of air in the system and slamming into some more noncompressible water. Groaning/pipes vibrating is usually a bad valve. Usually caused by a weak spring shuddering against the water pressure trying to close a valve.

@Munch - After a bit of trial and error, I believe I have identified a failing pressure relief valve as the culprit causing the water hammer. After replacing the PRV the water hammer appears to be gone though it did cause my WFM to shut down every zone due to water usage slightly above my set rates. I assume this was caused by the higher pressure from the new PRV as my WFM was calibrated using the older valve. Thanks for your help.

I’m a little late to the party here, but my zones knocked and thought it was water hammer… The fact that only 1 of your zines is doing it… It might not be this, but my issue was the street side meter.

My water company came out and replaced my meter with a straight piece of pipe and the knocking went away. He replaced my meter with a new one but it’s back. I could put a larger diameter meter in, but then my monthly access fee goes up.

Again, it doesn’t sound like this is what you’re dealing with but figured I’d share.

I got 8 zones setup in the meantime and it happens mainly when the lawn zones are turning on (5 of them). I spoke with the builder as well and she described that this probably normal with the water being pumped up from the basement through the pipes into the backflow preventer on the ground level.
Would that make sense?