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

I just installed a new valve (Hunter HPV). Everything works well except when the value is opened there is a fairly violent sounding thump-thump-thump sound. After 3 quick thumps, everything works well. When the valve shuts off, everything is very smooth. I have about 78 PSI coming into the valve. This happens on a recurring basis. Reducing the flow control significantly makes this go away.

I am trying to understand this problem better. Wet Boots provided the following comment in another thread about banging when the zone is first opened (as opposed to closing).

Quoted

Also, note that there is banging when the zone is first opened, and that is not water hammer. It is something of an oscillation you can sometimes see when a system is first opened in the spring, where there is no water in the zone for the supply to 'push' against. When it happens on a recurring basis, you look to make changes. Installing check valves in the heads is one obvious choice nowadays, to keep a zone full of water, so there's something to 'push' against. Throttling down a zone valve flow control is another option. Changing zone valves is another.

So according to this, I have 3 options. 1) check-valves in the heads. I can try this, but I don't think anything is draining since the zone is very flat and nothing is noticeably draining. Should I still try this? 2) flow control - this works, but only if I reduce the flow significantly. 3) changing zone valves - what kind of zone valve would I try? What would it do (ie: feature) that the Hunter HPV isn't doing?

Thanks,
-Jeremy

Thanks for the help guys.

This particular zone is really small (ie: only 4 sprinkler heads on it). However, I'm not sure that I really have a problem because adjusting the flow control down to where it's quiet is still more than sufficient for the zones needs. I am just trying to understand more about the physics of what's going on. Blasting a full 3/4" line at 78 PSI into a small zone like that wide-open may not be a good idea anyway

Interesting the old valve on that zone (some sort of old 1" weathermatic) worked ok wide-open. It had a flow control, but it was always wide open because I thought it was just a shut-off valve back when I inherited the system and didn't understand very much about valves (even less than now since I'm still very much learning), so I just cranked it open full So, it's interesting that the hunter HPV causes banging when it's wide-open. Maybe it allows more flow on full (even though it's a 1" as well). (Everything else is the same with the new valve, 3/4" supply lines, etc).

-Jeremy

Thanks Wet Boots! This is the exactly the sort of knowledge/advice that I need.

Knowing this and how it is crucial for my setup, I can't imagine buying valves without flow control.