Hi. I am designing a irrigation system and am making it gravity drained so that I don't have to pay someone to blow it out for the winter. I have been wondering though if I am going to run into problems were various valve types do not draining the way I hope. Now it is obvious that things such as my back flow preventer will trap water in between the double check valves, but I believe i can manually open the second check valve to let that drain. But for things such as my automatic control valves I am assuming that if left open they would drain whatever way they were tilted. I am assuming my pressure reduction valves would be able to drain from the outflow side. What I am worried about is small chambers within the valve that are constructed in such a way that water will be trapped or pooled inside the valves even if gravity drained, and will expand in winter and burst. Or with the control valves, maybe it does not open and close like a door, maybe it is a check valve that loosens or tightens all the way when switched on or off, and therefore would not drain backwards even when left open. Right now my design goes uphill from the water main to the backflow preventer, downhill to a manual drain valve, uphill to the controll valves, uphill to an anti sihpone, downhill to the sprinklers and downhill to a manual drain valve. You can see how if my controll valves dont drain backwards then there is water traped between them and the anti siphon (the anti siphone has to be uphill sense it has to be the highest point) Thanks for any help, feel free to ask me to expand on this if its unclear. I will be making drawings but wanted to get it at least somewhat right before I do cause I spend a long time on drawings.