Backward Bubbles

[SognSyrup]

We've got 3/16th gravity vacuum lines going. Last night as things were slowing down with dropping temps, one gauge read 11"hg and the line below the last tap was full. But some of the drops had bubbles moving UP toward the spile. Any thoughts? Is this some sort of backpressure after tree shut down for the night?

[maple flats]

How cold was it out when you saw that? When a tree gets to a certain temp, it draws water in thru the roots, and it will pull sap in from the line. If your line is 3/16 and steep enough the sap will freeze before it gets pulled back in.

[Cedar Eater]

I think when sap flow out of a tree stops, bubbles will naturally rise up the drops as sap slips around them under the influence of gravity. So it's more of a neutral flow situation where the tree just isn't being sucked hard enough for the sap to overcome the natural tendency for bubbles to rise.

[SognSyrup]

Thanks for the input folks. I just don't want to give much back to the tree! :lol: