wet dry lines on gravity

[jrthe3]

i was talking to a friend last night he wants to put up some tubin and sell me the sap we talked for awhile and wondered if there would be any benafit to running a wet dry set up on gravity system it will be vacuum in a few years

[ennismaple]

There would be little to no benefit for a gravity setup.

[mapleack]

It would be no benefit to a gravity system, but if its going to be a big enough tubing system that it would benefit when vacuum is installed, it might be easier to just put in the dry lines now, before you've got laterals in the way.

[DrTimPerkins]

i was talking to a friend last night he wants to put up some tubin and sell me the sap we talked for awhile and wondered if there would be any benafit to running a wet dry set up on gravity system it will be vacuum in a few years

A dual-line conductor system is designed to separate the transfer of liquid from the transfer of air in the tubing system. Air moves at a much higher velocity than sap in a system under vacuum, so if the two are in one pipe it results in turbulance, increasing friction and decreasing transfer of vacuum to the taphole. A dual-conductor separates the two spatially and allows each to move more optimally.

A gravity system is primarily set up simply to transfer liquid from the tree to the tank without concern for transfer of air (vacuum).

Because of the different objectives, gravity and vacuum systems are different in a few ways. The one major difference in setup is the number of taps to put on a lateral line. Under vacuum you should "strive for five, no more than ten" taps on a lateral line to achieve the highest sap yields. On gravity systems, it is best to have 20-30 taps per lateral line as long as there is a good downhill slope on the lateral lines, as this results in the development of natural vacuum, and higher yields on gravity than otherwise. Because of this, lateral lines in gravity systems can be significantly longer as well. Having long lateral lines in vacuum systems is definitely detrimental to good vacuum transfer.

So to change the system from gravity to vacuum you're going to have to retube or greatly modify at least your lateral lines to get the full benefit of vacuum. Given that, why not just add the second mainline (dry line) at the time you decide to add vacuum? Conversely, just bite the bullet and put in the vacuum system and get a pump/releaser.

[maple flats]

[QUOTE=DrTimPerkins;.............-

Given that, why not just add the second mainline (dry line) at the time you decide to add vacuum?

This is what I did. I have a wet line main set up, laterals only enter branch lines and branch lines enter the main at the beginnings of a manifold. When I add Vac the rest of the mainfold and the dry line will be added. If things go well, I will have vac and an RO for 2011.

[Hop Kiln Road]

"On gravity systems, it is best to have 20-30 taps per lateral line as long as there is a good downhill slope on the lateral lines, as this results in the development of natural vacuum, and higher yields on gravity than otherwise. Because of this, lateral lines in gravity systems can be significantly longer as well." - Cut & Paste from Tim Perkins

Reading Morrow's paper "Natural Vacuum and the Flow of Maple Sap" in 1971, I'm not convinvced that is the right conclusion. I think gravity systems work better, regardless of slope, with lateral citeria just like a vaccum system (short, five taps) connected to unvented 1/2" pipe. Amoung other points, notice on Table 5, Page 10, Chazy Woods 1970, where Morrow uses 1/2" pipe and gets the best results, but since he was studying vented/unvented tubing, he doesn't pursue it.

It appears that his study of the physics of liquid flow in tubing was done in a 6 story building, at 70 degrees with no gas in the lines. It is all the co2 in the tubing, which wants to rise against the downhill flow of the sap, that will slow down a long lateral. Couple that the extremely heavy sap flow at the very beginning of the runs, which will overwhelm the tubing but not the pipe, and I think the long laterals negate any advantage of the natural vacuum they may create.

Bruce

Bruce

[PerryW]

On my gravity system....

If I have less than 10 taps on a lateral, there is never enough sap to actually create columns of sap in the pipe which creates the natural vacuum.

If the sap does not create the columns of sap and instead, runs like water in a gutter, no natural vacuum is created.

Of course it is debatable whether the small amount of natural vacuum created actually does anything.

Video of columns of sap in a lateral:

http://s6.photobucket.com/albums/y235/perryW/?action=view&current=MapleSapLinesRunning.flv

[DrTimPerkins]

Reading Morrow's paper "Natural Vacuum and the Flow of Maple Sap" in 1971, I'm not convinvced that is the right conclusion.

There is a fairly substantial body of research work on this in addition to Morrow, as well as a great deal of practical information from producers in the field. Although not all studies are 100% consistent due to the large number of variables in doing research under field conditions (not atypical), most results show that a higher number of taps on a lateral line (up to a point) under gravity conditions, if flowing downslope, will create a natural vacuum. This results in a higher pressure gradient between the tree and tubing system, and thus higher flow.

[vtsnowedin]

About twentyfive years ago I had a gravity system set up on a steep hillside. No support wire was used and of course there were some sags in the mainline. Sap would collect in the sags until they filled up and started to siphon over the hump then race down the rest of the run to the sugarhouse. Sitting at the sugar house you would get a two gallon flush then a pause then another flush. When the pipe was running full you could hear air sucking into leaks up hill from the sag so quite a bit of vacume was being created by a full pipe dropping thirty feet or so. I don't know how you could build this accidental collector and releaser on purpose and as I repipe this same hillside this week I plan on doing everything I can to not repeat it.

[WESTVIRGINIAMAPLER]

One thing for sure I know about a larger numer of taps on lateral lines is that it is higher quality sap when you are not using mainlines or have long laterals with a lot of taps and short mainlines. The sap spends a lot less time in the lines due to the speed of it flowing thru the mainlines. This keeps the sap cooler as it gets to the tank faster and it keeps the lines flushed of bacteria better.

One key is to have the have the tank in a shaded area or a large enough cover on top to keep it cool. Gray reflective tarp on the side the sun hits keeps the sap much cooler.