Quote Originally Posted by wnybassman View Post
...I am not sure why 3/16ths is being introduced into mechanical vac systems. Wasn't it developed for its great natural vac properties with the right slope conditions? And wouldn't mechanical vac negate any natural vac that might be created with slope?
The effect is additive (positive direction, not negative). Pumped vacuum + natural vacuum = total system vacuum.

Generally such hybrid systems are used in combination with low-moderate vacuum pumps (sap pullers, etc.). Pumped vacuum can aid in leak detection in 3/16" systems, and help to achieve high vacuum in trees that aren't as high up on the slope. Even in a high pumped vacuum setting, 3/16" tubing can add a little boost in production if you aren't quite at max vacuum levels with the pump alone and the 3/16" tubing is set up properly. The reason it isn't used more by producers with high vacuum pumps is that 3/16" clogs up a bit easier and is also more subject to sanitation-related drop off in yield due to higher backflow episodes.

Dr. Abby and I have an article coming out in an upcoming Maple News https://www.themaplenews.com/ that compares the hypothetical relationships between elevation, vacuum, and yield in gravity, natural (3/16") vacuum, hybrid, and pumped vacuum systems.