natural vac in 1/2 main??

[blissville maples]

dr tim, or anyone else who may have experience or thought on this one!! if you forced 500 taps through a 1/2'' miainline on a steep slope say over 50' drop, would it not achieve the same effect as the 3/16" natural vacuum. thought about it quite a bit today and don't see why it wouldn't work, I think it would take a longer column than it would on 3/16'', but if you flooded a 1/2'' line with a steep grade it has to go down and if the line is full it has to make vac right?? I may have to try this.........maybe im overlooking something?

[log cabin luke]

It will create some vacuum for sure from my experience and some others I have spoken to. The big issue with it would be that if you are using standard 5/16 tubing you will not have any sap flowing on those marginal days and at the end of the season when it just doesn't stop with the 3/16. A 1/2 line with 400 taps on it on 3/16 line will overflow and create back pressure in the lines on a good flow unless it is very steep. If the 1/2 line is vented it can just barely handle it. That's from my own experience. I tried experimenting last year with 105 taps on a single 5/16 line that was steep. I ripped it out this year and am replacing it with 3/16 didn't work well.

[mellondome]

3/16 works due to the size of the drop of sap and surface tension within the tubing. This doesn't allow the ability for air to bypass the sap, allowing a full column to form. Larger than 3/16, air will flow past the sap droplet to allow the sap out of the line, keeping the vacuum from being formed.

[blissville maples]

luke-you have seen vac in the mainline from this effect or the 3/16 lines?? I think with enough slope, im talking 100' of drop in 100' of distance, nearly a 45degree angle. I would think the sap would have to go down not creating any pressure. only thing I womnder is if the 500 taps would actually even can fill the 1/2'' line since there is so much slope. once the line is full vac has to ensue, unless enough vac to hold sap there. I know if was flat you would have very much pressure and blow something apart, but this would be on serious slope. on this same slope I did what you said, took 5/16, went full roll up hill, put on 25-30 taps on 500 foot roll. I had 250 taps into tank, and on avg run would get 300-350 gals a day, one 24 hr period nearly 500 gallons, ran all night! was pretty amazing, easily 15 inches, but drained off before it froze, which makes re-establishment of vac slow next day. I hear the 3/16 freezes full, cant wait to try some!

[dbeitz1891]

Although you could achieve some vaccuum with the column completely full, just as in a siphon, there would a point where you couldn't achieve more. 3/16ths works so well because the ID is small enough for the properties of water to hold a solid column even in a very steep slope and those are, cohesion between individual molecules or surface tension, and adhesion of the molecules to sidewalls of the tubing. At 1/2 in diameter it is to great of a distance for cohesion between the molecules to keep a solid column of sap behind it when working against the effects gravity pulling it down. Not to mention you would need a very large volume to begin with unlike a normal slow trickle the trees would yield.
Those same principles are what allow the last sap of a run remain in the 3/16 tubing and continue to keep constant vacuum. These are all ideal situations with a leak free system, any variable you introduce could drastically change the results

[log cabin luke]

I have witnessed vac on a 1/2 main line but did not measure it at the time. I doubt I achieved much of anything over 3". I have done a lot of different experiments over the last few years because its all part of the fun. My experiment days are now over. I am only buying 3/16 line from here on out. had 750 taps on it last year and it ran until April 25th in mass. I stopped boiling a little before that because it was practically water at that point. 3/16 line does not drain even if you lift it up vertically. It just stays in there and freezes then starts vac the next thaw.

[mellondome]

You could use any size pipe for natural vaxc, as long as you didn't let air in the end of it. You you would need 30 ft of drop and the end of it has to stay submerged in liquid once the column is full. And even then, the gases given off by the tree won't flow down it, constantly reducing the vacuum.

[blissville maples]

luke- so on your 1/2'' main is that where you had the 750 taps running into? if not how many taps did u have on that particular line where you had seen the vac?? I would like to try this experiment not sure if ill have time this year, maybe ill go with your results! and am wondering if its even worth it as dbeitz said, and im not that great with physics etc, the 1/2'' line may just be too big regardless of volume or drop. I had initially thought enough trees would fill it, however velocity will be so high due to diameter that no column may form. thanks for weighing in

[log cabin luke]

On the 750 I had 2 ,1/2 inch main lines going into a 3/4 line. I had about 400-450 on one 1/2" line the rest on the other. I vented the lines and on a really good run the line with 400 would bubble a little sap out the top of the vent that was 10 feet up in a tree. I saw natural vac on a 1/2" line I once had with about 200 taps on it that was fairly flat and dropped about 15 feet over 500 foot distance. I pulled a couple taps to check on it and it sucked vacuum on my finger over the tap. I did not have a gauge but it was not a lot for sure.