Alright- odd question- spile design!

So, I had a friend stop by today with some spiles he didn't think were any good.

You see, they had a hole on the bottom of the spile, not the top. In his way of thinking, they should have been on the top- so that gravity pushed the sap down the xylem/phloem.

Not being one to pay much attention to anything (heck, I'll probably ignore a bunch of these replies- just to show you I don't pay much attention), I went and grabbed one of mine just to check. Yep hole on the bottom- none on the top.

I explained that clearly, his thinking was all wrong, and that sap is largely coming from the roots of the tree, and he should be ashamed for being such a dunderhead.

However, it got me to thinking, why DON'T they have a hole on the top as well as the bottom? I mean isn't part of the attraction to 40 days and freezing nights that we can collect day and night as the sap runs up the tree during the day and returns at night? I never paid much attention because most of my spiles have a metal seam running over the top, but he had some of these new-fangled plastic jobbers- no seam. It's just unseemly to me.

I have some older metal spiles that didn't even have holes in them, just open seams pinched together. I opened then up straight out the back with a small drill bit which helped. Most of my taps have straight horizontal openings. I have some with just holes on the bottom as well. I think it's the pressure from inside the taphole from above the taphole which forces the sap out under gravity. On vac you have the bonus of pull from outside the tree. As long as there is a hole in the back of your spout and it's not constricted it will run.

Thats a great question.... Not odd at all.... And I don't have the answer.... But I will theorize....
My guess is - The hole is there, in case you bottom the tap out in the hole... ensuring that there is always spot for sap to enter the spile.
And - My guess is that it doesn't matter whether that hole is in the bottom or the top... Pressure will be pretty much equal 360 degrees around that spout... and the pressure decides how much sap to push out.

First, sweet sap from maples in the spring comes out of the xylem...the wood tissue, which is somewhat unusual.

It is likely whoever designed the tap thought that sap was pushed up from the roots, which is incorrect. During the sap exudation (flow) phase, sap on gravity collection systems is generally moving downward.