5\16 tubing to 3\16 tubing=vacuum?

[cjf12]

Could you turn an existing gravity bush with 5\16 into one with vacuum by replacing the lower portion with 3\16 and leave everything else the same? Maybe combine a few lines to increase number of taps per lateral?

[optionguru]

I think you could but they only recommend about 30 taps per 3/16, some have had good luck with 40 taps.

[blissville maples]

I also questioned this, I believe whatever drop you have on the 3/16 portion only will dictate vac level. for instance if 5/16 hits the 3/16 and form there drops 20' elevation, should see 20x.88= 17.6'' vac level, I will be changing some lines this weekend in this manner

[blissville maples]

from what I read all based on elevation drop in the 3/16 nothing else, everything above this drop should be on vac

[DrTimPerkins]

Could you turn an existing gravity bush with 5\16 into one with vacuum by replacing the lower portion with 3\16 and leave everything else the same? Maybe combine a few lines to increase number of taps per lateral?

You will get some vacuum, but not nearly as much as if you used entirely 3/16" tubing.

[cjf12]

Any thoughts as to what limits the vacuum in that situation? And what do you consider "some vacuum"? 15hg.?

[blissville maples]

this is simple, 1 foot of elevation change in 3/16 line will create .88 inch vac. therefor if you have 40' plus drop in the 3/16'' line, all your taps could lead into the 5/16'' lateral, flow through the 3/16 for an elevation drop of 40'+ and you will achieve max vac 27+ possible at all taps even if they come into the 5/16 portion. you would not gain anything in this situation by using all 3/16'', however if you have only 10 feet drop in 3/16'' and 10 feet drop in the 5/16'' for a total of 20' drop, you will not achieve max vac, since if it was all 3/16'' your max at 20' drop could only be 17.6'' and this would only be on taps above the 20' drop. so figuring the 5/16 in on the first 10' of drop, your gain would be 8.8' above the 3/16'' to 5/16'' intersection

[cjf12]

That is what I had in mind. Connect all the 5/16 lines to 3/16 and be sure to have at least a 30 foot drop. In the sinkhole I have nearby I could easily gain a 70 foot fall in the line. Therefore all taps at high vac. In theory or reality though?

[blissville maples]

i'll know in a few weeks!! i am doing just that this weekend. i don't see how it cant be, the actual elevation drop will occur in the 3/16'' itself. it my take an extra couple gallons of sap to flow down the drop until it reach its full vacuum since it will have evacuate or pull on, the extra cubic area in the 5/16 above. but if theres no leaks, and drop is 35' plus and column is full of sap then i cant see how not. time tells all!

[markcasper]

So say you have a 40 feet run of 3/16 and a 40 ft run of 5/16, how many quarts or whatever unit of volume difference is there between the two assuming each line was full to capacity? My only concern with putting 3/16 is the sap that will be stagnating in there because of a full line all the time. So more taps on a line will decrease the amount of time its sitting in that pipe. When you only have 2-4 taps on a 5/16 and plenty of slope, the sap isnt sitting in there, its moving fast because of the air above the stream. there is no friction to slow it up.

[BreezyHill]

this is simple, 1 foot of elevation change in 3/16 line will create .88 inch vac. therefor if you have 40' plus drop in the 3/16'' line, all your taps could lead into the 5/16'' lateral, flow through the 3/16 for an elevation drop of 40'+ and you will achieve max vac 27+ possible at all taps even if they come into the 5/16 portion. you would not gain anything in this situation by using all 3/16'', however if you have only 10 feet drop in 3/16'' and 10 feet drop in the 5/16'' for a total of 20' drop, you will not achieve max vac, since if it was all 3/16'' your max at 20' drop could only be 17.6'' and this would only be on taps above the 20' drop. so figuring the 5/16 in on the first 10' of drop, your gain would be 8.8' above the 3/16'' to 5/16'' intersection

This is not my area but the numbers that Tim Wilmont the3/16specialist at UVM gave were different. 30' drop in elevation would provide maximum obtainable vac which is around 29.92".

Hopefully Dr Tim can weight in on this since Tim has retired.

I hate to have someone going 40' of drop when only30 was needed and possible sacrifice production as a result or just make more work for themselves.

[Thompson's Tree Farm]

At Verona, Tim Wilmont said that the .88 is the theoretical vacuum created per foot of drop. He suggested that in the real world to expect more like between.5 and .75.

[maple flats]

That would be my guess too, because the 30' drop in the 3/16 is not all sap, but rather sap-air (gaseous bubbles from the tree, not really air) sap-air-sap air and so forth. As such, if only 50% of the column is sap you only get half the .88" per foot of drop. That being said, any vac is better than no vac. If connecting to a few laterals of 5/16 you also will not be running the same way you should if all in 3/16. With that you go back and forth from the highest to the lowest in a series string and the only tees are where you run a drop. If tying a few 5/16 laterals you will be using tees to join multiple taps and t's or y's in a lateral should only be used for adding a drop.

[West Mountain Maple]

Dr Tim, can you explain why it matters if the upper portion of a straight run with say 25 taps on it is 5/16, and then transitions to 3/16 and drops 30-40 feet with no taps on it. I think alot of us are not understanding why this will not give us max vac to all the taps above. Also, am i going to decrease vac by using 5/16 drops into a full 3/16 run? thanks if you can explain

[blissville maples]

i agree, well said west. perhaps theres physics we're overlooking somewhere in this equation.

[West Mountain Maple]

still wondering, anyone??

[Moose Maple]

I just tried out my 5/16 to 3/16 setup this weekend - exactly like you have discussed - I tied in about 35 taps all on 600 feet of 5/16 going into about 150 feet of 3/16 with about 35 feet of fall. I tested the system with water and my upper most tap on the 5/16 was pulling 21 inches of vacuum. I'm thrilled with that!


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[DrTimPerkins]

Dr Tim, can you explain why it matters if the upper portion of a straight run with say 25 taps on it is 5/16, and then transitions to 3/16 and drops 30-40 feet with no taps on it.

I could tell you, but then I'd have to kill you. :)

I just had a short conversation with Tim Wilmot (the 3/16" Guru) about this, and basically he said he's tried it, and it doesn't tend to work well all the time.

I'll "TRY" to give you my explanation for it, but remember....you asked for it. It is somewhat related to the CFM capacity of mechanical pumps, and related to the problem of why can't you get 29" Hg out of your old dairy pump.

34' drop in elevation in a 3/16" tubing when completely filled with sap (assume no gases) will produce 30" Hg (the maximum). Realistically, there is some amount of gases/air bubbles in the tubing as well. At atmospheric pressure (0" Hg) the bubbles are a certain size, as you pull a vacuum, what you are actually doing is pulling the air molecules further apart, which makes the bubbles bigger. When you get to high vacuum (at least as considered high vacuum in the maple industry), the gas bubbles are WAY WAY WAY bigger.

So we have this 34' drop in elevation in 3/16" tubing filled with liquid and no gases. If it were closed with a valve at that point, we would have 30" Hg vacuum at the top of the line due to the weight of the sap in the tube pulling down on the liquid. Now assume we also have a 100' length of 5/16" tubing connected above that but it is valved off and filled with air. What happens if we open that valve? The air in the 5/16" tubing, at atmospheric pressure (0" Hg) would start to be pulled into the 3/16" tubing due to the weight of the liquid in the 3/16" line. As this happens, the vacuum level asserted on the gases in the 5/16" tubing begins to increase (which is what we want), however, the vacuum level at the top of the 3/16" line would decrease as air moved into the 3/16" line to displace the liquid. At the same time, as the liquid flowed out the end of the 3/16" line (as long as it were NOT being refilled), the potential vacuum in the 3/16" line would drop because of the decrease in the weight of the liquid in the line...because now there is some air occupying that space. Because the volume of air in the 5/16" line is SO much larger than the volume of the liquid in the 3/16" line, there is not enough weight of liquid in the line to form a high vacuum in the 3/16" line.

If we added in some liquid (sap flow) into the 5/16" tubing, we might eventually reach the point where there was a balance, and liquid could build up in the 3/16" tubing and build up the vacuum level, and perhaps eventually (if we had the correct volume of flow and no air leaks) then we might eventually achieve close to the maximum vacuum level. So there MIGHT be some ways to improve this by making the drop in the 3/16" line MUCH higher (thus getting more liquid weight in the line) in relation to the volume of 5/16" line, or doing that in combination with really loading up the 5/16" line, or during peak sap flows, but this would be somewhat hit or miss in terms of generating high vacuum at the top of the 3/16" line and beyond. Might work at some times, might not work at others. It would be least effective after a flow stopped, as it would take time to build the vacuum back up again each time because you would likely have to evacuate the air from the 5/16" tubing each time. This is not really a problem in a pure 3/16" tubing system since it doesn't really ever evacuate the line completely, so a vacuum can start to build as soon as the sap in the lines thaws out.

The analogy (although admittedly not perfect) to this is a rubber band. In 3/16" lines, you have one rubber band you're pulling on. Put a certain weight on it and you'll have a certain tension in that band. However if you tie one small rubber band (representing the 3/16" line) to a larger rubber band (representing the 5/16" line), then the tension in the small band is OK, but the tension in the 5/16" band is not very high.

So to sum it all up.....it just doesn't always work very well to try to put 5/16" tubing above a 30-40' drop on 3/16" tubing. You might find in your situation you can get it to work, but it probably depends upon the total drop on the 3/16" tubing in relation to the amount of 5/16" tubing you have, and interacting with the number of taps and volume of flow you experience at a given time. You might find that it works one day, but not so much the next. I think the far better option would be just to keep it simple and use 3/16" throughout to make sure you are generating the highest vacuum levels possible.

[DrTimPerkins]

I just tried out my 5/16 to 3/16 setup this weekend - exactly like you have discussed - I tied in about 35 taps all on 600 feet of 5/16 going into about 150 feet of 3/16 with about 35 feet of fall. I tested the system with water and my upper most tap on the 5/16 was pulling 21 inches of vacuum. I'm thrilled with that!

Now try adding some air to that (which the trees add to tubing systems along with sap). Your vacuum level will drop, although you will still get some amount of vacuum. To achieve the highest vacuum, use 3/16" the full length if possible.

[BAP]

Dr Tim, does using 5/16" drops with 3/16" make any difference in the vaccuum level?

[blissville maples]

dr. Tim, i understand now about how the gases are pulled and take more cubic area, i never figured on that. and like your saying with enough sap coming in the 3/16 and enough drop it may work. but i can see how it may take longer to get the "pull" established against the larger gas bubbles. so yes it may and will probably work, but perhaps at less potential for less time. i have a bush with nearly 50 feet of drop, i will try the section of 3/16'' here to gauge an understanding of this in the field!!

Also intersed in BAP"S question about the 5/16'' drops in to 3/16'' lat's.. this is what i went with to prevent 2 different drop line sizes, hoping with no negative affects. thanks for the info!

[DrTimPerkins]

Dr Tim, does using 5/16" drops with 3/16" make any difference in the vaccuum level?

The effect is small enough to be negligible.

[Moose Maple]

Dr. Tim - thanks for the insights on air in the system and its affect on a gravity vacuum system. I assumed that would not be a big issue so long as there were no leaks around the tap holes. I will report back on how this hybrid system works once the sap starts to run. Our objective is to gradually replace all the old 5/16 with 3/16 over the next couple of years.


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[markcasper]

The effect is small enough to be negligible.

Would you know why some equipment dealers are advocating 5/16" for drops and other dealers are saying it will be doomsday if you don't keep it all 3/16"? What gives?

[BAP]

The effect is small enough to be negligible.
Thanks for the prompt answer Dr Tim

[DrTimPerkins]

Would you know why some equipment dealers are advocating 5/16" for drops and other dealers are saying it will be doomsday if you don't keep it all 3/16"? What gives?

I don't know.