Hop Kiln Road 2011

[PerryW]

Under marginal tempertures when mechanical vacuum will produce flows, natural vacuum won't.

I agree, you need the good sap flow before you get any natural vacuum.

the flow resistance from sidewalls on the gravity tubing systems restricts peak flows. Therefore gravity systems should strive for short laterals with as few taps as possible inorder to get the sap and gas separated and into a mainline.

Not sure i agree with this one. If there was enough sidewall resistance to restrict peak flows, then if you pulled a tap, sap would squirt out. I have some laterals with over 30 taps on them. When the sap is running at peak; If I pull any tap on the lateral, I can still hear and feel the natural vacuum. So, my theory is; As long as you can feel some natural vacuum, then the line can NOT be overloaded. Now I doubt the small amount of natural actually increases the sap flow; but I still like to hear the sucking sound so know things are running properly and I can more easily find any small pinhole leaks.

In spite of this, I think it is probably still a good idea to keep laterals short and not more than 10 taps on them in case you ever want to go vacuum. Plus, from my experience, the animals don't seem to ever chew through the mainline, wheras they seem to have an appetite for 30P. AND you probably have less problem with the lateral freezing up if you "strive for 5".