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Thread: Reverse vacuum at the top of my line

  1. #1
    Join Date
    Mar 2018
    Location
    Upstate ny
    Posts
    12

    Default Reverse vacuum at the top of my line

    All my lines are 3/16 gravity fed with 3/16 drops, at the top of one of my lines the sap just sits there. If I unhook the last tee all the sap shoots down the line like crazy, I can figure out why it isn't running. If I unhook farther down the sap actually sucks back towards the top of the line. Everything is running at recommendation for pitch and all my lines end with a tap but this is the only one doing this. Any and all recommendations are appreciated.
    2012 - 12 taps into gallon jugs / 1 gallon syrup
    2013 - 12 taps into gallon jugs / 1 gallon of burnt syrup 🤔
    2014 - 20 taps on buckets / 2.5 gallons of syrup
    2015 - 20 taps on buckets / 3 gallons of syrup
    2016 - 30 taps on buckets / 3.5 gallons of syrup
    2017 - 45 taps on buckets / 6.5 gallons of syrup
    2018 - 70 taps on buckets / discovered mapletrader.com / 40 taps on 3/16 into 300 gallon poly tank / Fuel tank evaporator build / no sleep whatsoever / 22 gallons and counting...

  2. #2
    Join Date
    Jan 2010
    Location
    Covington, New York
    Posts
    1,514

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    Does sap come out of that line at the bottom?
    Noel Good
    1998 to 2009: 15 taps on buckets, scavenged fire pit and pans
    2010: New 2x4 SS flat pan w/preheater
    2015: New to me Lapierre 18x60 raised flue, new shack, new everything!! 59 taps 23.75 gallons made
    2016: 85 taps 19 gallons
    2017: Purchased 2.5 acres and tubed half with 3/16. 145 taps total 49.25 gallons made
    2018: 200 taps (162 on 3/16ths 38 on buckets) New NextGen RO 63 gallons made
    www.wnybass.com

  3. #3
    Join Date
    Mar 2018
    Location
    Upstate ny
    Posts
    12

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    Very little compared to the other lines
    2012 - 12 taps into gallon jugs / 1 gallon syrup
    2013 - 12 taps into gallon jugs / 1 gallon of burnt syrup 🤔
    2014 - 20 taps on buckets / 2.5 gallons of syrup
    2015 - 20 taps on buckets / 3 gallons of syrup
    2016 - 30 taps on buckets / 3.5 gallons of syrup
    2017 - 45 taps on buckets / 6.5 gallons of syrup
    2018 - 70 taps on buckets / discovered mapletrader.com / 40 taps on 3/16 into 300 gallon poly tank / Fuel tank evaporator build / no sleep whatsoever / 22 gallons and counting...

  4. #4
    Join Date
    Mar 2006
    Location
    Eden Prairie, MN
    Posts
    1,549

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    That is totally normal. There is a vacuum at the top tap. But you have a nice tight seal on that spile so no air is getting in the line. Thats good. The tree is apparently not giving off any gas, so no bubbles. If that is the case, the sap sill only move as fast as the tree releases it, which for a single tap is very slow. If you pull that tap, the vacuum is broken and the whole volume races down the hill. If you open the line half way down, the lower half will fall down the same way, but the vacuum in the upper half will suck the sap up hill a bit.
    John
    2x8 Smokylake drop flue with AOF/ AUF
    180 taps on sacks
    75 on 3/16 tubing with shurflo
    Eden Prairie, Minnesota

  5. #5
    Join Date
    Mar 2017
    Location
    Harvard, MA
    Posts
    121

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    Quote Originally Posted by RileySugarbush View Post
    That is totally normal. There is a vacuum at the top tap. But you have a nice tight seal on that spile so no air is getting in the line. Thats good. The tree is apparently not giving off any gas, so no bubbles. If that is the case, the sap sill only move as fast as the tree releases it, which for a single tap is very slow. If you pull that tap, the vacuum is broken and the whole volume races down the hill. If you open the line half way down, the lower half will fall down the same way, but the vacuum in the upper half will suck the sap up hill a bit.
    Id like to understand this better, why itís normal. Iím seeing similar results to Obidiah - multiple taps and drops with sap sitting in them not moving or flowing into the lateral. My lines are 3/16 gravity with 20 taps on slope between 10 and 20í, each 150-250í long. Taps and drops are all new. I started with all 5/16 drops but when I saw this problem I changed out some drops and tees to 3/16 cause I ran out of 5/16 fittings. So now I have some of each in drops. I think Iíve ruled out clogs in tees because when I pull a tap the sap flow right down the drop through tee into the lateral. Holding the tap in the tap hole by hand it looks like the natural vac is pulling sap out of the tree vs before there was no flow. What I ended up trying is lightly tap the tap back into the tree until this vac hissing stops but sap and bubbles still flow out the tap and down the drop. If I tapped just one bit harder the sap and bubbles stopped completely, so I back off a bit. I did this in a 3rd of drops and saw an increase in flow at the bottom collection tank.
    Still a newbie after 3 seasons.
    2016: 20 taps on buckets, 4 gallons made on a borrowed 2x3 steel arch.
    2017: 32 taps on buckets, 8 gallons of syrup, on a "loaner" Lapierre 19x48 Mini-Pro loaned by a friend. Makeshift 8x8 sugar shack.
    2018: 80 taps with 3 new neighbors on tubing. New 10x12 sugar shack, Lapierre Jr 2x5 evaporator. Made 17 gallons, Sold around 5 gallons of syrup.
    2019: 100 taps, 60 tapped on Feb 21. Added a small RO.

  6. #6
    Join Date
    Mar 2012
    Location
    Walpole, NH
    Posts
    963

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    You may have a small leak down the line.
    Sugaring for 45+ years
    New Sugarhouse 14'x32'
    New to Me Algier 2'x8' wood fired evaporator
    225 Sugar Maples Currently,(105 on 3/16" and 110 on Shurflo 4008 vacuum, 10 gravity), (16,000 before being disabled)
    1947 Farmall H and Wagon with gathering tank
    2012 Kubota with forks to move wood around

  7. #7
    Join Date
    Dec 2015
    Location
    Connecticut
    Posts
    90

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    Quote Originally Posted by tgormley358 View Post
    Id like to understand this better, why itís normal. Iím seeing similar results to Obidiah - multiple taps and drops with sap sitting in them not moving or flowing into the lateral. My lines are 3/16 gravity with 20 taps on slope between 10 and 20í, each 150-250í long. Taps and drops are all new. I started with all 5/16 drops but when I saw this problem I changed out some drops and tees to 3/16 cause I ran out of 5/16 fittings. So now I have some of each in drops. I think Iíve ruled out clogs in tees because when I pull a tap the sap flow right down the drop through tee into the lateral. Holding the tap in the tap hole by hand it looks like the natural vac is pulling sap out of the tree vs before there was no flow. What I ended up trying is lightly tap the tap back into the tree until this vac hissing stops but sap and bubbles still flow out the tap and down the drop. If I tapped just one bit harder the sap and bubbles stopped completely, so I back off a bit. I did this in a 3rd of drops and saw an increase in flow at the bottom collection tank.
    I think drops to individual buckets are the best unless you have the money to spend on a pump. Obviously they are not for those who do not enjoy exercise.

    CV's with drops to individual buckets outperform my tubing lines no matter what I do.

    I have not tried 3/16 tubing however, but the more I read about it the less sleep I get. And I have lost enough as is.

    I had a similar problem to you on 5/16 tubing back in February. I increased the pitch from my lowest tap to my collection barrel by shortening the distance between the two from about 90 feet to 30 feet (this steepened the pitch significantly ) and that helped a lot.

    It seems to me the final pitch to the collection barrel is what makes or brakes a good gravity run! The closer to vertical as you can get it the better. And no fittings in it to muck the flow up into the barrel. Class 5 rapid would be the best.

    But the hydrodynamics of sap in lines are very convoluted and while this is a very informative website on many frontiers nobody on it has yet to de-convolute hydrodynamics in sap lines to any great extent. Nothing personal to anybody. If somebody writes a good book on it I will buy six copies.

    40 taps for me this year so far. 8 to a barrel, 7 to a barrel, 6 to a barrel, 5 to same barrel as the 6, 2 to a bucket and 12 on individual buckets. I think that make 40. Some with CV taps some without.

    I have kept track of individual gallons of sap retrieved from each.

    The 12 on individual buckets and the 2 on a bucket have put out half my sap this year. One of the problems with it is I end up with 5 gallon buckets overflowing even on 1 tap.

    To date I have gotten 369 gallons of sap and about 9 gallons of syrup on the 40 taps.

    Hope this weekend does not knock anybody out. Me especially. I am all rock so that gives me a good chance.

  8. #8
    Join Date
    Feb 2012
    Location
    Fond du Lac, Wisconsin
    Posts
    855

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    Quote Originally Posted by tgormley358 View Post
    Id like to understand this better, why itís normal. Iím seeing similar results to Obidiah - multiple taps and drops with sap sitting in them not moving or flowing into the lateral. My lines are 3/16 gravity with 20 taps on slope between 10 and 20í, each 150-250í long. Taps and drops are all new. I started with all 5/16 drops but when I saw this problem I changed out some drops and tees to 3/16 cause I ran out of 5/16 fittings. So now I have some of each in drops. I think Iíve ruled out clogs in tees because when I pull a tap the sap flow right down the drop through tee into the lateral. Holding the tap in the tap hole by hand it looks like the natural vac is pulling sap out of the tree vs before there was no flow. What I ended up trying is lightly tap the tap back into the tree until this vac hissing stops but sap and bubbles still flow out the tap and down the drop. If I tapped just one bit harder the sap and bubbles stopped completely, so I back off a bit. I did this in a 3rd of drops and saw an increase in flow at the bottom collection tank.
    The weight of the sap in the line is what creates your vacuum. If you open a tap mid way down you have decreased the weight causing the vacuum and having less weight pulling down, the vacuum pulls the sap up until the weight of the sap equals the vacuum. It is like reducing the weight on a spring, it will pull upwards.
    Smoky Lake 2x6 dropflu pans and hoods on homemade arch
    Smoky Lake 6 gallon water jacked bottler
    Concentric Exhaust
    250 Deer Run RO
    325 taps

  9. #9
    Join Date
    Mar 2006
    Location
    Eden Prairie, MN
    Posts
    1,549

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    Another way to think about it is something you can try in your kitchen. Take a tall glass of water, insert a straw to the bottom, cover top of straw with your finger and lift it out. The water stays in the straw just like the sap stays in your line. The weight of it is actually pulling a very small vacuum on your finger. ( If the straw was 33 feet long, you would get a near perfect vacuum on your finger) Lift your finger and and it all flows out. Satisfying to watch, but it is over when the sap has run out and the vacuum is gone!


    It your try the same experiment with a bigger tube like a 1/2" inch hose, the trick doesn't work because bubbles of air can flow past the water and let the water run out. Diameter is even more critical with the straw held at a more horizontal angle since gravity pulls the water to one side and lets the bubble get past more easily. This is exactly why 3/16 tubing works creating natural vacuum and 5/16 doesn't. In such a small diameter, surface tension on the bubbles is stronger than the effect of gravity on the sap so the bubbles can't get past. So even with bubbles and sap in the line, the sap hangs there and it's weight pulls a vacuum on the upper end of the line.

    Quote Originally Posted by tgormley358 View Post
    Id like to understand this better, why itís normal. Iím seeing similar results to Obidiah - multiple taps and drops with sap sitting in them not moving or flowing into the lateral. My lines are 3/16 gravity with 20 taps on slope between 10 and 20í, each 150-250í long. Taps and drops are all new. I started with all 5/16 drops but when I saw this problem I changed out some drops and tees to 3/16 cause I ran out of 5/16 fittings. So now I have some of each in drops. I think Iíve ruled out clogs in tees because when I pull a tap the sap flow right down the drop through tee into the lateral. Holding the tap in the tap hole by hand it looks like the natural vac is pulling sap out of the tree vs before there was no flow. What I ended up trying is lightly tap the tap back into the tree until this vac hissing stops but sap and bubbles still flow out the tap and down the drop. If I tapped just one bit harder the sap and bubbles stopped completely, so I back off a bit. I did this in a 3rd of drops and saw an increase in flow at the bottom collection tank.
    John
    2x8 Smokylake drop flue with AOF/ AUF
    180 taps on sacks
    75 on 3/16 tubing with shurflo
    Eden Prairie, Minnesota

  10. #10
    Join Date
    Mar 2017
    Location
    Harvard, MA
    Posts
    121

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    Quote Originally Posted by RileySugarbush View Post
    Another way to think about it is something you can try in your kitchen. Take a tall glass of water, insert a straw to the bottom, cover top of straw with your finger and lift it out. The water stays in the straw just like the sap stays in your line. The weight of it is actually pulling a very small vacuum on your finger. ( If the straw was 33 feet long, you would get a near perfect vacuum on your finger) Lift your finger and and it all flows out. Satisfying to watch, but it is over when the sap has run out and the vacuum is gone!


    It your try the same experiment with a bigger tube like a 1/2" inch hose, the trick doesn't work because bubbles of air can flow past the water and let the water run out. Diameter is even more critical with the straw held at a more horizontal angle since gravity pulls the water to one side and lets the bubble get past more easily. This is exactly why 3/16 tubing works creating natural vacuum and 5/16 doesn't. In such a small diameter, surface tension on the bubbles is stronger than the effect of gravity on the sap so the bubbles can't get past. So even with bubbles and sap in the line, the sap hangs there and it's weight pulls a vacuum on the upper end of the line.
    Thanks John. I remember the finger straw experiment. It helps with my understanding. So when I see sap hanging in a drop seeming to not move down to the lateral, that can be ok since itís cintinuing to pull sap from the tree, I think youíre saying. But if the lateral has flow and the tee is not clogged, how does the stuck sap in the drop get moving? It sounds like my attempt at getting the sap moving, withdrawing the two slightly so I see sap and bubbles moving, but no vacuum leakage sound, are not really helping. Anyway, Iím getting more sap now that temps have warmed. Iím happy. But Iíll continue to noodle over it as everyone does.
    Still a newbie after 3 seasons.
    2016: 20 taps on buckets, 4 gallons made on a borrowed 2x3 steel arch.
    2017: 32 taps on buckets, 8 gallons of syrup, on a "loaner" Lapierre 19x48 Mini-Pro loaned by a friend. Makeshift 8x8 sugar shack.
    2018: 80 taps with 3 new neighbors on tubing. New 10x12 sugar shack, Lapierre Jr 2x5 evaporator. Made 17 gallons, Sold around 5 gallons of syrup.
    2019: 100 taps, 60 tapped on Feb 21. Added a small RO.

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