Natural Vacuum

[BMaple]

A few years ago, I attended a workshop put on by the “experts” from a maple research group. They told us that you shouldn’t have more then 10-12 drops on one 5/16” line – even in a gravity system. So, I re-plumed my entire bush with pipeline to comply. It didn’t make any difference. Next, I decided to experiment by attaching a single 5/16” tubing right down the pipeline and connecting about 60 taps to it over a long run. It made a huge difference. I have since done this on another line with about 80 taps. The other day when the sap was running, I went up and pulled the top tap and it nearly sucked the hat off my head – not really, but you could hear the vacuum and feel it with you finger. I have about 220 taps on my pipeline and picked up just over 200 gallons of sap the other day with marginal conditions. My neighbor with over 400 taps tells me that he only got 150 gallons during the same period. Natural vacuum is working for me and I’ll be converting the rest of my system.

[paulslund]

I've only ever heard the "best is 5, no greater than 10" under mechanical vacuum. I recall reading somewhere that although more difficult, you can create vacuum on 5/16" but needed well over 60 taps (thinking 80+?)to create the volume of flow needed for the sap to create a proper column in the tubing. On 3/16" the number is around 30 iirc.

[Openwater]

I've got 1 run of 525' of 5/16 with 25 taps and it produces just fine. Vacuum gauge on 1st tree always pulls close to what the gauge at pump reads; usually between 25-27inHg when I got the recirc line dialed-in right. I always wondered about the 5-10 drop limit on a single lateral and if there's any science behind that rule of thumb.