High vacuum in gravity tubing research

[maplecrest]

Back in the early 80,s when i was playing with tubing. i had 400 taps on a 1/2 inch main line. gravity. the sap one day got a vac level going on the top of the system that was drawing on the lines as i walked down the main line. when i got to the last enterance before the tank the volume and pressure had built up so much that it blew the bottom lines off the main line. i then put a 3/4 line in place the 1/2 a couple of connecters above the blow off point.which controled the pressure. i just put vac on that system when i replaced the maine line and tubing.which is, i split the system in half with 2 - 3/4 inch lines.and cut the drops per lat from 10 or 12 to 4. for 20 plus years that system would get going and run great. since going to vac on this system 4 years now. and trees are older, not a young bush. but fairly steep, great slope. i do not see the volume of sap i did with that under sized and 12 tap per line set up. it does work. you have to think smaller diameter main lines and 10 to 12 taps per lat. to fill the lines.

[DrTimPerkins]

...Maybe Dr. Perkins could provide a link on here. It would give many others access to the study. Or, everyone can join their Maple Association and receive the Maple Digest.

All our current research papers are located at http://www.uvm.edu/~pmrc in the "Recent Publications" section on the right.

The 3/16" tubing paper is located at: http://www.uvm.edu/~pmrc/highvacuum.pdf

Please recognize that the papers available on our website are UVM publications only. Others also publish in the Maple Digest. It is very inexpensive....consider subscribing either through your local association or as an individual.

[lastwoodsman]

Didn't someone give a source for 3/16 tubing and fittings? I cannot find it. I would like to set up a 400 ft run.

[GeneralStark]

Didn't someone give a source for 3/16 tubing and fittings? I cannot find it. I would like to set up a 400 ft run.

The article referenced earlier provides more detail and sources for the materials. D+G makes the 3/16" tubing and most are getting the fittings from McMaster Carr I believe.

[heus]

Dr Tim Wilmot gave a nice presentation on this topic at LEME saturday. I am thinking about using 3/16 next year at the back of my property where there is enough fall.

[bnbmaplesyrup]

The article referenced earlier provides more detail and sources for the materials. D+G makes the 3/16" tubing and most are getting the fittings from McMaster Carr I believe.

I have found the tubing at McMaster. Where do you find the taps for the trees? We have some steep side hills that this sounds like a viable solution to get another 50 - 75 taps.

[CampHamp]

Thanks for the research, Tim (or Doc?)! I'm giving this 3/16" tubing a shot on 60 taps. It feels a bit risky, since that is most of my taps. After getting less than 5 gallons per tap last year on 5/16" (albeit, a bad year), I thought I'd take a shot. I have a decent slope, but many of the trees are low on the hillside. It is difficult to predict from the publication how the vacuum in the tubing changes based on average slope angle. For example, if I have some lines that are short (100') and steep (30' drop) and wonder how this vacuum will compare to a longer (400') line with a shallower slope (30' drop). I'll take readings from my pressure meter when it's flowing and report.

I have a 500' gravity line of 5/16" with 30 taps from last year. I'd like to extend this line another 200' down to my mainline and wonder if I should extend it with 3/16". My gut feel is that it will create better vacuum on this bottom part and may even improve upper-line gravity pull as sap backs-up at the transition point.

When I looked at my 5/16" lines last year, it seemed that most of the sap flowed under air along the slopes and in some shallow places the sap would form columns and move as a unit, like a cork out of a bottle. I wondered if I should even add water to the top of the line to get all that air out!

[DrTimPerkins]

Thanks for the research, Tim (or Doc?)!

Yes, it can be confusing....there are two "Tim's" at UVM PMRC.

Dr. Tim Perkins, aka Dr. Tim, UVM PMRC Director, Timothy.Perkins@uvm.edu
Tim Wilmot, M.S., aka Tim, UVM Maple Extension Specialist (stationed at UVM PMRC), Timothy.Wilmot@uvm.edu

If you have questions about the 3/16" tubing, they should be directed to Tim Wilmot

If it's easier to remember, I'm the handsome one.

[CampHamp]

Thanks for the clarification, Dr Tim Perkins (aka "the handsome one")!

Tim Wilmot, when the season comes, I'd be glad to provide vacuum stats for my lines (I have 4 gauges) along with length/slope attributes, if you think this would help you progress this research. I think it will be interesting to see what my "mixed-line" does (the one with 5/16" on the upper section and 3/16" on the lower part). Do you have a prediction?

BTW, I noticed that there are T-reducing fittings that will convert 1/4" directly to the 3/16" run. Do you see a problem using those to eliminate the need for the adapter in the drop line? I don't have a price yet, but it would save me time putting adapters in, if there are no expected issues with that. I don't have a need this season, but others might be interested.

Again, thanks for your research. I expect that it will make these small, hill-side runs much more productive without the need for vacuum equipment.

[DrTimPerkins]

Tim Wilmot does not monitor this list. If you wish to reach him, send an email to Timothy.Wilmot@uvm.edu