Slow flow from lateral lines

[wildacres]

Hi all -

I am in my 4th year of a small gravity tubing system. While I've had a much
more seasoned veteran give my tubing a 'Two Thumbs Up' - good downhill,
no sags, 10 taps per lateral, and a modest distance to traverse - I struggle
to understand why the sap from the lateral lines is backed up 10-15
feet behind each mainline saddle. The lines are full! In many places, the sap is backed up right to the tap itself. Rather than flowing into the mainline, it seems to drip out.

I've done a few experiments in the kitchen, and noted, predictably, that when you add water to the top of a drop line, and plug one of the openings,
in fact you get the same behavior. I've heard the point about this being a
desired effect, as it leads to natural vacuum - but to me, it seems ridiculously slow, and I have concerns about the sap being exposed to the sun for so long, come late March.

So my question is, is this normal? And, if not, what should I do to get things
moving? As you can tell from my message, I'm interested in the details, so please bring em' on - and thanks in advance!

Paul L.

[mark bolton]

I had the same problem last year on my 2 lateral lines draining into barrels. I did an experiment and vented the top of one line and it produced 2X as much sap/day as the non-vented line. This year I have 6 laterals draining into one main line and they will all be vented. I have heard the arguments that it may introduce bacteria, cause premature hole closure..., but non-vented lines just don't produce for me.

[PerryW]

I've seen it happen too. I've gone as far as cutting the lateral off at the mainline to make sure the fitting wasn't plugged up. I believe it is the result of the natural vacuum. If you pull a tap higher up, the sap will quickly run into the mainline.

[argohauler]

You need a vent somewhere. Either at the end of every lateral or at the end of your mainline.

[Wanabe1972]

I asked this question a few years ago. I had the same problem with sap not entering the main line. I was told I did a good job of sealing everything up and when the tree was ready it would push it all out. I tried venting a few lines so they would empty out but once they did empty the flow at the tank slowed up. I think the natural vacuum the main line creates helps over venting but I'm no expert.

[PerryW]

This seems to happen primarily on gravity laterals with only a few taps, or when the sap in NOT running at full bore. As long as nothing is plugged up, it is nothing to worry about.

[Haynes Forest Products]

I solved this problem with a VACUUM PUMP:lol: sorry

[NedL]

I had the same problem last year(my first year with tubing). It was pretty frustrating. I have switched to mainly tubing staright into buckets to see if that helps. This is one spot I will set up a string of 7 taps. I'll see which works best.

[Yellzee]

I have a gravity system and have this effect, but I think the natural vacuum helps when it's running well. IF you start to crack a seal on a tap at the end of the line you can hear the air getting sucked in, suggests a good vaccuum is present. first year I went vented, the last 2 without vents and found I get more volume if NOT vented.

[DanE.]

Not sure if this will help, but here are some observations from last year(1st with tubing) and what I'm doing this year.

Last year I set up the laterals, unvented, with 3-5 taps per going to a 1/2 mainline, 25 - 30 taps total. All on a descent slope. I saw the same thing you are, I ended up venting everyone of the lats.

So, between then and now I found this site and research tubing and found research papers on tubing. One of the research papers said if you had enough drop (50 feet) a 5/16 line would support 50 taps unvented. They would product more sap because of the natural vacuum created. and then then there were other traders that run many more taps per line than recommended for vacuum systems (~5) but they are on gravity. so what is someone to do? everyone has there own opinion and you need to do the best for what you have.

This year I decided to do my own research. I have 3 test cases. 1. 45 taps with 5 - 12 taps per lat into a 1/2 main line. 2. 24 taps all on one 5/15 line 3. The other 20 taps are single tap into there own pails, randomly placed through out the woods. Case 1 & 2 are unvented and 3 is vented.

So far case 1 produced 45 gallons on the first run. Case 2 was destroyed by heavy snow and tree limbs and I collected nothing. Case 3, only produced minor amounts. The second collection on sunday (24 gal) I averaged about the same for each tree. with the exception on one pail that was over flowing. Today I go into the woods to check on the sap and see what you are the sap sitting in the lines and nothing in the barrels, but I left it alone because all of the pails were empty too, except for that one darn tree. go figure.

I guess what I'm saying here is if you are concerned try different things, keep records and see what works best for you. And for me if case 2 does not pan out, that is ok, because I have a small evaporator and would be pushing the limits of it anyways or i'm going to have some long nights.

Dane.

[Hop Kiln Road]

First, everyone should read this report:

http://www.nysaes.cornell.edu/pubs/fls/OCRPDF/FLS-014.pdf

Now, I don't agree with how they conducted some the experiments and thus the conclusions they draw and many of the conclusion others draw, ie, on a 50 tap line of a 15% slope the vacuum was measured at the top and there was no vacuum if the line evened out at the bottom. But look at the results on Table 5, where they used 1/2" tubing. There was an obvious effect, but it seems they were vested in some conclusion about vacuum and they ignored it. Bruce

[wildacres]

Bruce -

Yikes! This article reminds me why I could never be a lawyer or an
engineer (and I am one :lol: ) ...There's an awful lot of conflicting detail here, and it's obvious that there are a ton of factors affecting the process. Nevertheless, it seems like general conclusions include that you don't lose anything over time with natural vacuum, and that a lot of taps is better than a few on a lateral.

I changed my laterals where I could to link 15 taps together - we'll see if that has any positive effect on the matter. A column of water 33 feet! No wonder my sap is backing up so much.

So few black and white answers in this domain...

[wildacres]

Perry -

I think you are right on with your generalization about about low flow and few taps. I noticed that the biggest, 'juciest' trees I have
produce very well on unvented gravity (21 taps on one lateral) - even though the slope is modest. You can see the sap 'pumping' through the line, even slightly uphill in places. The difference with the rest of my system seems to be the amount of sap and the number of taps I had on one lateral. I've modified things a bit to hook more taps into one line.

Hoping, praying, pleading with the gods that we get some cold nights around here. All these days of 32/45 low/high try a man's patience.

Paul

[Dill]

I'd like Cornell to refund me 15 minutes of my life I just wasted on that.
Too bad the research guys are focused on vacuum. I know all the big guys run it. But I'd say 85% of the nations producers are small (under 500) and that a huge number of us are still on gravity. And a study with 1/2 tubing doesn't help us at all, I know it was 1970 whatever, but I haven't seen that stuff for sale.

[danno]

I solved this problem with a VACUUM PUMP:lol: sorry

But on a tight vacuum system you are still going to see the sap moving very slowly through the lines (the desired effect I've been told). It's not unless you have a leak (vent) in your system does the sap take off.