Mainline minimum - gravity

[wkies]

Two quick questions for a gravity tubing system: 1) is there a minimum of taps per mainline and 2) is there a minimum number of taps per lateral line?

I have a few long stretches over which my lateral lines run (they end up slightly sagging no matter what I do). I could run another mainline to the area but would have limited number of taps (less than 20).

Thanks

[DrTimPerkins]

Two quick questions for a gravity tubing system: 1) is there a minimum of taps per mainline and 2) is there a minimum number of taps per lateral line?

I have a few long stretches over which my lateral lines run (they end up slightly sagging no matter what I do). I could run another mainline to the area but would have limited number of taps (less than 20).

There is no functional minimum on mainline tubing. The issue is more that you can heat up the sap quite a lot in a mainline that has little sap running in it, especially if it is black waterpipe. You should avoid doing this.

There is also not a functional minimum limit on # taps/lateral line. You could do 1 tap/lateral if you wanted, but it would be costly to do so (and probably result in lower yields....see below). The recommendations for # taps/lateral are very different for gravity versus vacuum systems. On gravity, having 20 taps on a lateral line is fine. On vacuum, you want to "strive for 5, no more than 10 taps/lateral).

Long runs on lateral lines under gravity conditions with 20 taps are fine as long as they are running downhill. You can actually develop a substantial natural vacuum under such conditions when the sap is running. You do want to eliminate the sags though, perhaps by using a few strategically placed side-ties.

[jfroe939]

Dr. Tim... you mentioned there is substantial natural vacuum on a gravity line. Any guess as to just how much - in terms of a quantifiable number? I'm sure the answer would be "it depends." I'm sure it depends on how tight your system is and how long it is or how many taps you have on and surely how steep of a slope you have on. Care to put together a plausible gravity tubing scenario that would have the most natural vacuum? or even maybe something you've actually run into in the woods that made you really take a closer look because of a noticeable or observable vacuum? Sort of a lame question I guess?!!

[DrTimPerkins]

Dr. Tim... you mentioned there is substantial natural vacuum on a gravity line. Any guess as to just how much - in terms of a quantifiable number? I'm sure the answer would be "it depends." I'm sure it depends on how tight your system is and how long it is or how many taps you have on and surely how steep of a slope you have on. Care to put together a plausible gravity tubing scenario that would have the most natural vacuum? or even maybe something you've actually run into in the woods that made you really take a closer look because of a noticeable or observable vacuum? Sort of a lame question I guess?!!

It depends....:)

Best thing to do would be to read the source.

http://www.nysaes.cornell.edu/pubs/fls/OCRPDF/FLS-014.pdf

But essentially it comes down to a few factors:

1. Leak-free system
2. Good slope (5% or better) and overall total elev difference of 50+ ft
3. Long laterals with minimum sag
4. Several taps/lateral (20-50+, depends upon slope....more taps with more slope)
5. Fast sap flow rates.

The other important thing....natural vacuum only works when the sap is actually running. It won't help get things going, or help much when the sap flow slows down.

[wkies]

The reason I ask about "minimum" numbers is I have a small number of trees that are located away from the main tubing system (completely different collection point). I can run a mainline with traditional 3/4 tubing like usual with wire and all and have a few laterals off of it or I can run a mainline of 5/16 tubing as a "mainline" and run the laterals off of that.

[DrTimPerkins]

The reason I ask about "minimum" numbers is I have a small number of trees that are located away from the main tubing system (completely different collection point). I can run a mainline with traditional 3/4 tubing like usual with wire and all and have a few laterals off of it or I can run a mainline of 5/16 tubing as a "mainline" and run the laterals off of that.

If you're on gravity with decent slope, go with the 5/16" tubing and forget the mainline. You'll get better results.