Explain it to me like I'm twelve...pls

[NTBugtraq]

I have a closed system. Taps to drops to laterals to mainline...all dropping in elevation. So I have a collection tank at the lowest point. Why will sap flow to it?

I asked based on this; if I suck fluid up a straw and then put my finger over the top of the straw, the fluid does not come out of the straw.

So why will sap flow to the lowest point when, essentially, the tree is my finger over the top of the straw? With no air entering at the top of the system, how does it flow to the lowest point?

Please forgive me for such a question, but I have drops with sap up to the tree, and others that are empty. I'd just like to understand the physics better.

Cheers,
Russ

[wnybassman]

i think because the sap coming out of the tree has pressure to it. And I think that's why vacuum is so effective, because it makes it easier for the tree to push the sap out into the line. I could be wrong though.

[Maplesapper]

Sap and gases exit the taphole.
Once there is a large column of sap starts heading down hill, the vacuum effect will kick in and pull sap from the taps.
The weight of the column of sap overcomes the initial back pressure that your finger has on a straw, because more sap, more weight is being added,

[SPILEDRIVER]

and once your straw is full and capped with your finger theres nothing else coming in

[happy thoughts]

Your straw example is not a good model because the pressure of fluid inside the straw doesn't change. No more water is being taken up by the straw so the pressure remains constant. When sap flows within the tree it causes the pressure inside the tree to increase. When the pressure inside the tree is higher than the pressure outside the tree, sap escapes out the tap hole or any where else it can such as broken branches.

[WestWind]

Your mainline/lateral/drop/tap/tree is NOT a closed system. The end of your mainline is not immersed in sap or anything else, it hangs in the air. Thus, air enters the mainline as sap exits. Keep in mind, the sap doesn't fill the entire lumen of the mainline, rather it flows along the lower half with freely flowing air in the top 1/2 of the tube's cross section. The drops you mentioned which are filled with sap to the tree are like your straw example and they don't flow; (that may be because of lack of pitch in that section). The rest of your flowing system is not closed and not like the straw.

[NTBugtraq]

Ok, so if I take your advice (everyone's), at least part of my problem has been the centrifugal pump I had at the very end of my mainline. It was preventing air from getting back into the mainline. I had been able to get some 100 gals from the line with that pump, but several times it would just pump air and leave the sap in the line.

So here's what I am doing now. I got a sump, which I will bring the end of the mainline into. An automatic sump pump in the sump will then pump the sap into my storage tank. Hopefully this solves the issues.

One question: My mainline will have to be elevated to enter the sump, approximately 2' above where the lowest point is now. The lowest point in the mainline in the bush is about 8' above where the sump sits, and at least 150' away from the sump. So it will only be going back up 2' for about the last 6' of that run. So the entry to the sump is still 6' below the lowest point on the mainline in the bush. Problems?

Cheers,
Russ

[NTBugtraq]

I moved the sump location so that 2' rise isn't necessary, now my sump is the lowest point in my mainline. Got about .5 gal of sap into the sump today, hopefully tomorrow is going to be gang busters (or so the forecast says...)

Cheers,
Russ

[PerryW]

since you said "twelve year-old" I was gonna say "Because I said so"

but Stabbing your finger with a knife before putting it over the straw would be a better analogy. The blood squirting out of your finger would fill the straw and the column of blood in the straw would add vacuum to pull the blood out faster.

[TerryEspo]

Great analogy Perry.
Kinda yucky thought but so true. :o

[CampHamp]

I see sap columns in my drop lines only in two cases, when the trees are running and (1) the tubing is blocked with ice or (2) I stop my pump (because I block my mainline when I transfer sap to the shack to keep the vacuum in the lines).

Once any obstruction is cleared, the columns will go away because there is air coming out of a tap and that will push the column downwards. If you see columns on some trees and not others, it could be that the trees closest to the blockage had taller columns or that some haven't started to run yet (no air to push the column down).