I am considering designing an irrigation system that does not need to be blown out in the winter, even in a Northern climate. Essentially, each zone would be sloped to a midway point between the sprinklers and the valve. The slope would be at least 1/4" per foot. The line would slope down from the valve to the middle point then slope back up at the same rate to the sprinkler, forming a V shape. The low point in the V would be roughly 4 foot under ground given the length of the zone. At that point, I would install a couple automatic valves (the kind that intentionally leak when there is no pressure in the pipe) and encase them in a valve box which would be above and below a couple feet of gravel, with soil piled on top. My hope for this design is that it would cause any water remaining in the pipe after a sprinkler session to drain down to the low point and out the valve, thereby ensuring that no water remains to freeze. I have three questions for this community:
1. Is this a pipe dream? (Pun intended). Am I missing something here that would make this system not feasible?
2. If so, is there a way to tweak it to make it work? If not, is there a way to tweak it to make it work better?
3. I have seen some say that automatic valves should only supplement a proper blowing out. Can anyone show the evidence or reasoning for this line of thought, or is it just speculation that is getting recirculated amongst the experts?
Thanks for any insights you can provide!