open end or closed end on gravity lines?

[wshaw932]

im here in central WI, so we will be experiencing first good flow later this week finally. this is my first year using the gravity lines, and i have 100 taps in them.

So. question folks. i have been told two different things. i was told by the first guy, that the beginning of my line should be tapped into the tree, which causes the line to be entirely sealed except for the end that runs into my tanks. a second guy who came out told me i needed to vent my line so the sap could run down.

Now, the second guy makes sense, but if the trees are pumping sap out, shouldnt it force the sap down anyways? secondly, on my downhill slopes, with 5 or ten taps above on the slope, my line begins to level out somewhat towards the bottom taps heading into the tanks. will my sap flow well as long as the beginning of the line is well above the bottom? i would think so.
Thanks-Wes-

[mapleack]

They should be sealed. Venting allows bacteria to enter and will net you 50% less sap. When lines are sealed natural vacuum is created by sap flow, equaling more sap. Always have fall on your lines the entire way, even it's only a little bit. This is the first time this year I've seen this question, amazing it took this long. :)

[Burnt sap]

To Echo Andy keep them closed you will gain more sap in the end. 5% slope will do in most cases.

[wshaw932]

yeah, i couldnt seem to find any threads about it. i was just wondering, because sap hasnt flowed well yet, but there is a little sap in some of my 3 ft drop lines leading to the mainline. in some of those lines, there is sag (didnt tap high enough, so the bottom of the drop line is lower than the mainline), and i am curious if the sap will push out of those drop lines when the trees begin to run better. my entire mainline starts about 20 ft taller than where they empty into my collection containers, but the end of my line that goes into the collection container is just a little lower than where it drains into the container.

pictures attached. any advice? (pictures the best i could do with my computer skills7533

[PerryW]

They used to vent lateral lines in the 1960's but quickly found out that unvented lines perform better for the following reasons:

1) Vented lines let lots of air down the pipe which reduces the amount of room for sap flow,

2) Unvented lines produce more natural vacuum

3) Unvented lines keep the sap cleaner by reducing microorganisms.

4) Vented lines will sometimes spew sap out when the downstream tubing is still frozen. An unvented line will crease pressure and help push the ice.

[mapleack]

Wshaw, add another post, wire, etc to eliminate the low spot before the tank.