I'm very happy with the 3/16 for gravity vacuum in general, but are having premature tap "drying" in the half of our tubing that is in its second year of use. I thought I'd see what kinds of solutions I could crowdsource on here.
Last year, after the season, we washed the tubing with calcium bleach with a long contact time. Each line and all drops were filled completely and let to stand for several days. I thought this would leave the lines almost as good as new. Not so. After 4 weeks, the flow from that bush was noticeably under-performing. Upon inspection, taps were dry and yeast was present in the clear spouts and lines. The new lines are still running great and are clear after 6 weeks. I suspect substantial backflow issues due to ice blocking the mainline at times as well as the normal negative tree pressure induced backflow. We are probably looking at a yield of about 15 gpt on the second year tubing and about 25+ gpt on the new.
Here are solutions that I've thought of and I'm curious what folks think about these solutions or have any of their own they'd like to suggest.
1. Run bleach solution through lines for longer and under higher pressure before capping off to dislodge more yeast etc.
2. Switch from 3/16 drops to 5/16 drops to make backflow less of a problem because the trees won't be able to slurp up as much sap at night.
3. Use Check valve spouts.
4. Add a vacuum pump of some kind to keep flow positive more often. (We have high gravity vacuum on most lines, but not all). I assume this would improve yields as well, but I don't know how well since we have many very long laterals and also maxed out mainlines that would be a pain to replace with larger ones.
5. Some combination of the above.