3/16 versus 5/16, line volume and ideas

[YoungFamilyFarm]

So, back in the day people used to put allot more trees on 5/16 lines than today. Now the "strive for five" recommendations steer toward a low number per "lateral". Then, 3/16 comes out and 25 trees is a base line I have heard multiple times. Now, the cross sectional volume of 3/16 versus 5/16 is almost exactly a 3x value. So mathematically speaking, 75 trees (taps, whatever) on 5/16 would produce the same volume/velocity/fill as 25 taps on 3/16. Now, minus the voided volume at the drop the line; the progressive fill/volume behavior and linear progression over the course of the run would be the same. Would the natural vacuum characteristic still be present? Has anyone tried this or proved it out? Tell me this logic makes sense?

[ttowle3]

I have thought that this 3/16 phenomenon should work on any larger size pipe but my friend said it must be because of the meniscus - tendency for water to curve and the larger pipe prevents this. Just my theory. Thoughts?
Look it up on wikipedia.

So, back in the day people used to put allot more trees on 5/16 lines than today. Now the "strive for five" recommendations steer toward a low number per "lateral". Then, 3/16 comes out and 25 trees is a base line I have heard multiple times. Now, the cross sectional volume of 3/16 versus 5/16 is almost exactly a 3x value. So mathematically speaking, 75 trees (taps, whatever) on 5/16 would produce the same volume/velocity/fill as 25 taps on 3/16. Now, minus the voided volume at the drop the line; the progressive fill/volume behavior and linear progression over the course of the run would be the same. Would the natural vacuum characteristic still be present? Has anyone tried this or proved it out? Tell me this logic makes sense?

[ttowle3]

oh I did a test this year and the 3/16 outperformed the 5/16 hands down though I didn't have the 5/16 on the 30 ft elevation - well some were but no questions about it 3/16 is superstar if you got the 30 ft sweet spot elevation. I had 25-30 on several runs of over 700 ft. they are still running sap but no good now.
Still I wonder why the experts cannot explain how it works.

[mapleguy]

ttowie3, you make a very good point. Maybe Dr. Tim can give us some insight. But this really makes sense, but I'm sure something is missing here.

[DrTimPerkins]

A 5/16" line will develop natural vacuum with enough taps on it. The problem is that when a flow ends, the sap all runs out, so that if it doesn't freeze overnight, then there is not enough flow to get it started again the next day. With 3/16" tubing, the small inner diameter holds some sap in the line, and just a small amount of flow will be enough to initiate vacuum development. It has to do with the cohesiveness and capillarity of water in small tubes. So while you could achieve similar results with 5/16", it is more difficult to do so and more problematic to keep it going.

[Mel]

I haven't posted in a long time, and just went through the process of changing my name to something a bit more relevant to myself to start posting again - just to post on this almost exact same topic/issue. So instead of starting the thread I was going to start - I'll just jump on this one.

As said, I haven't posted in a while but have been browsing quite a bit the past couple of weeks or so, a lot on the 3/16 topic. The principal seems to have a lot of merit - but it also seems it should be able to be applied a lot broader. We have a lot of trees, a lot of mainlines, and a lot of 5/16. The bottom parts of our runs have good slope, but it tapers off as you go up the hill - most of the slope is just before the 5/16 hits the mainlines. It would be a very costly proposition to replace all of our 5/16 with 3/16 - and I don't think the benefit would be proportional to the expense as a lot of our 5/16 is actually not on a decent slope itself, at the upper parts of the mainlines once you get above the initial rise in slope. So I guess long story short - has there been work done on determing if this '3/16 effect' can also be seen in 5/16 that has say 3x the number of trees per line (and good slope for the bottom part of it - this would apply to a lot of our lines), and/or/also can it be seen in/from the mainline itself if the bottom part of the mainline has the good slope? I am wondering if we would possibly see a benefit by leaving all our 5/16 as-is and perhaps look at only decreasing the size of our mainline on the bottom sharp slope section? It would seem that we should? I'd suggest that further research into this increased natural vacuum principal be expanded to those areas - as the potential benfits could be quite significant given the very significant cost of replacing all 5/16 with 3/16 in a large operation. Having said that, we have always suspected we are seeing some of this effect in our current setup but have never actually done any vacuum measuring - so I think I will try to round up some guages for next season to try to get somewhat of a handle on it.

Looking forward to more input from others - nothing like in-the-bush experimentation & R&D.

EDIT: Tim replied while I was typing - slow fingers strike again.

[Mel]

Our flowing usually ends due to a freeze - so in that case, there would be sap left, frozen in the lines. Plus the odd bit left due to the odd belly in the lines, even though we do our best to eliminate those. Also thinking it shouldn't take much flow the next day to get the lines filled again even if starting from empty? The possible mainline aspect (each mainline finishing its run with a sharp drop to the tank) is what really has me wondering - much easier to reduce the size of a section of mainline than rolls upon rolls of 5/16. I wish I had started thinking about this more a couple of months ago, I would have done some vacuum measuring across a few of our mainlines & lines. Way too late for here for this year for that - will have to do that the next.

[DrTimPerkins]

So I guess long story short - has there been work done on determing if this '3/16 effect' can also be seen in 5/16 that has say 3x the number of trees per line (and good slope for the bottom part of it - this would apply to a lot of our lines), and/or/also can it be seen in/from the mainline itself if the bottom part of the mainline has the good slope?

A few thoughts:

1. There are a huge number of permutations of sugarbush layouts and geography out there, some that would be retrofitted to 3/16" and some that would replace 5/16" with 3/16" when they go back and retube. We are only able to test so many given our resources and the land that we actually have here, along with the other studies that are ongoing. It is not due to a lack of interest, but simply one of time and resources (both in terms of land, money, and personnel).

2. The natural vacuum effect in 3/16" is derived from sap flowing downhill in a (nearly) filled tube. So it really doesn't matter so much what you're doing on the top of the hill, but what really matters is what is on the hill. You could have a large number of trees on really long 5/16" tubing, or a smaller number on 3/16" (which will develop vacuum faster and more consistently), as long as there is good drop involved. You could have 5/16" on the top, with 3/16" on the slope. It is particularly good if this drop is near the bottom, as more vacuum will be applied to those up the line as opposed to drop near the top of the slope and gentle near the bottom. Once the sap hits the mainline, unless the mainline is on pumped vacuum, the natural vacuum goes away from there on. I don't think you'd want to replace all your mainline with 3/16" and tie many 3/16" lines together in mainline fashion unless you want to have many individual 3/16" lines, otherwise you'd overload them at some point and reduce flow (and thus reduce vacuum as well).

3. If you are retubing a section of woods, then it would make the most sense to change over to 3/16" at that time if you desire to try it. But if you already have high vacuum, you might decide to leave it at 5/16". If you are setting up a new woods, and want vacuum but aren't buying a pump, then it is easiest to just go 3/16". Many people won't want to deal with a mixed 3/16" and 5/16" system due to the added complexity, and will just go one way or the other. It all depends upon what you have in terms of geography and what you have in terms of existing system, and whether you're going to pull out the entire system or try and retrofit what you have. Lots of choices.

[Mel]

Once the sap hits the mainline, unless the mainline is on pumped vacuum, the natural vacuum goes away from there on.

If the mainline was sized to the point that the last 30' or so of drop it was full of sap (not sure how many trees per diameter that would be), would that not introduce some vacuum as well? Upstream of that? Or maybe more than 30' would be needed in that case?

We do have 50 rolls of 3/16 that we will be putting out somewhere in our woods over this summer, to try. Makes it hard though to try to quantify results if we've never measured our vacuum before - but we could try measuring next spring on those 3/16 sections vs. similar 5/16 sections in that area.

We're lucky that most of our woods has some good slope - but most of that slope is at the bottom of the runs, and most of the runs are way too long to go from top to bottom without having to run to a mainline before it hits the best of the slope (gradual slope on top 3/4 or so of woods). Some of our mainlines are 1km+ long, and most start out 1/2" at the top and end up at 1" at the bottom.

Lots of food for thought - will definitely consider maybe using the 50 rolls just on the steeper slopes, and over more lines, although yes mixing fittings & sizes will likely be a bit awkward.

[DrTimPerkins]

If the mainline was sized to the point that the last 30' or so of drop it was full of sap (not sure how many trees per diameter that would be), would that not introduce some vacuum as well? Upstream of that? Or maybe more than 30' would be needed in that case?

Yes, if it were sized appropriately and you had the right amount of flow (it would have to have hundreds of taps, all running at the same time in order to start the vacuum), then it would generate some vacuum. However it would not self-starting very well at all (5/16" builds vacuum slower and doesn't hold it well when the sap stops), so a bigger mainline would be even more problematic in that regard. So while theoretically it is possible, it would not be practical and would not be easy to achieve. With 3/16" the vacuum starts as soon as you get the slightest amount of liquid in there, and it remains operational (in most cases) for long periods of time and self-starts again quickly and easily after a freeze event.