3/16 tubing with vacuum pumps

[Scribner's Mountain Maple]

I am wondering if anyone out there who has a high vacuum pump system, is choosing, or is being advised to install 3/16 instead of 5/16.

From what I have heard, when used with a high vacuum pump, 3/16 will provide a higher level of vacuum to the last tap on a given lateral than when compared to 5/16.

First, can anyone verify what "I've heard".

And second, is anyone doing this. Installing 3/16 in new bush set ups where you have high vacuum pumps?

I am setting up a new bush this year, and after the mains are done, should I buy 5/16, or 3/16. I have a high vac pump already.

Which tubing size is the future of maple production?

Thanks,
Ben

[maple flats]

I'm just guessing, but my guess is that 3/16 will reduce vacuum transfer when coupled with a vacuum pump. The exception might be if you have ideal elevation drops for 3/16 in the first place.
3/16 advantages come from natural vacuum, when the small tubing fills with sap. While the small tubing won't carry vacuum well, if you have the drop needed to use 3/16, a high vacuum pump might help boost the vacuum level, especially at the lower end of the tubing. As you go up steeply in elevation you still won't gain much, since you will likely have good vacuum by design and thus little room for more. As you approach total vacuum, gains become much harder to achieve.

[Chicopee Sap Shack]

At maple mania Glenn goodritch said to use 3/16 as it will give a little extra free vacuum making a marginal system better and a good system almost perfect. Any new lateral line I buy will be 3/16 now I'm just hoping for more fittings and saddles to be 3/16.

Scott

[500592]

I know somebody who has been using on vacuum with minimal slope and we figured that is was almost like the sap acted like a piston and was able to transfer the vacuum that way he was amazed at the stuff I will probably try it next year.

[Scribner's Mountain Maple]

I wonder what the research says. Has anyone done this, or is this just the tubing supplier sales pitch? I too heard just what you are saying Chicopee. I was interested to hear if Proctor or Cornell has tested this theory?

[Walling's Maple Syrup]

I wonder what the research says. Has anyone done this, or is this just the tubing supplier sales pitch? I too heard just what you are saying Chicopee. I was interested to hear if Proctor or Cornell has tested this theory? Tim Wilmot has researched this 3/16" tubing extensively. He can probably answer all your questions. He is a great guy to talk to. His email is timothy.wilmot@uvm.edu
Neil

[BreezyHill]

So lets do some simple math:
5/16 is .3125
3/16 is .1875...making the smaller tubing nearly half the size of 5/16. So for sap to pass the same amount, in the same time... then the speed of the sap must be double in the smaller line to be consistent to the capacity of 5/16.

Since the line is half the size, a larger amount of the sap is rubbing on the side wall causing frictional losses to factor in also.

Now when we talk about main line and vac transfer there needs to be sufficient slope to make certain there are no pools of sap that block the full diameter of the tubing. When this happens the transfer of vacuum past the pool is vastly limited. Now this affect is limited when a dry line is added to the system supplying additional vacuum to the line before and after the blockage point; but does not eliminate the reduction totally.

Vacuum transfer is also limited over distance due to frictional affects. Conventional wisdom is to increase the size of the tubing to pass more vacuum from the pump thru the lines to the last tap hole. When building a vacuum transfer system you start at the pump; with over sized pipe to the releaser, add dry lines to get vacuum to the laterals past the flow of sap, to the furthest tap hole.

Seems that basic math and physics shows that 3/16 in a high vac situation would be a limiting transport tool.

While 3/16 is showing great worth for gravity systems to produce natural vacuum by plugging the line full of sap and falling down hill. One must never forget that frictional losses on a liquid is also increased on a full line greater than on a non full line.

We have seen the affects of reducing the number of taps on a 5/16 lateral to 5 or less; would this mean that 3/16 will need 2 or less to be able to keep up with the flow of sap at peak flow times and transfer vac at maximum potential? We must not forget that vacuum is an absence or void. If the line is full all the way to the spout, vac is limited to some extent.

Not long ago it was predicted that most sugar bushes would be running 2" mains; but 1" is the sales leader by far, with 3/4" doing well.

If I were forced to make a prediction...it would be that 5/16 will stay the mainstay for laterals and drops for the majority of producers using high vacuum(24"+), as it will have the ability to keep up with the peak flow the best, and not leave sap in the tree when the lines are full from the spout all the way to the main.

If the line is full...how much more could have been pulled during each days peak flow, at a respectably cost that will not limit profitability for the producer?

Ben

[Scribner's Mountain Maple]

I emailed Dr. Wilmot and will post when I hear back from him.

Breezy, I tend to agree with all that you said. Accept I don't dare to make a prediction on which tubing will be the future.

The one thing that keeps coming to mind is that while a 5/16 has more room for sap transfer and air, the 3/16 will be full of sap. With the 3/16 being full, Sap is being pulled into the main line at 27". It will be pulling the same on every tap on the line. Thus, getting more vac to the last tap.

example:
When using 5/16 for laterals often times you are only getting 25" at the last tap on a 5 tap line even though you have 27" at the pump. Then using 3/16 you are able to get 27" at the last tap because of the smaller amount of air in the system to remove. Which will produce more?

I am not sure still and look forward to hearing from the good Dr.

Ben

[DrTimPerkins]

I know somebody who has been using on vacuum with minimal slope and we figured that is was almost like the sap acted like a piston and was able to transfer the vacuum that way he was amazed at the stuff I will probably try it next year.

3/16" tubing is definitely NOT indicated for tubing with low or no slope. Rather than developing natural vacuum, you will instead develop backpressure, which will reduce sap yield. The use of 3/16" tubing requires some slope to function.

I will refrain from answering, as Mr. Wilmot (he is not a Ph.D., although he does have a tremendous wealth of research experience) is definitely the 3/16" tubing guru, and will most likely be responding at some point himself, other than to say that we are putting in a new section of our woods on 3/16" tubing as a larger-scale test of combining natural vacuum with pumped vacuum.

[DrTimPerkins]

Since the line is half the size, a larger amount of the sap is rubbing on the side wall causing frictional losses to factor in also.

Ben,

I agree almost completely with everything you've said.....except that your conclusion is probably incorrect. To be very upfront, three years ago I felt exactly the same way (smaller lines = more friction = lower vacuum at taphole = lower sap yield), so we were testing increasing lateral line size of 1/2" diameter and using dual-5/16" lines (wet/dry) as ways to increase vacuum levels at the taphole (and yes, what we are actually talking about is transferring air out of the lines faster to achieve better vacuum). While those approaches do work to some degree, there are some difficulties in making them work well.

In any case, the hydraulics of maple tubing systems are quite a bit more complex than can be conceptualized in simple terms. It appears that 3/16" tubing, when used properly (leak-free system, good elevation drop), can generate a substantial amount of natural vacuum without the use of a pump. And while it is in many ways quite counter-intuitive, research examining combining natural vacuum and pumped vacuum, while fairly recent, has shown rather good results. This causes me to think that this might be the correct direction to go in...at least enough so that we will look into it considerably more at UVM PMRC over the next couple of years in larger field studies. To that end, we are retubing several hundred taps of our woods for that exact purpose (to test pumped vacuum with 5/16" tubing against combined pumped+natural vacuum in 3/16" tubing).

As I said in my previous post, I'll let Tim Wilmot respond in more detail, as he is the originator of the concept and the most knowledgeable person with respect to 3/16" tubing.

The other approaches we've been looking into, particularly dual-line lateral/dual drop-line tubing, might work better on low slope applications where natural vacuum with 3/16" tubing is not indicated.