How consistently downhill does 3/16 tubing have to be?

[dvnwvt]

I have three runs of 3/16 on natural vacuum (11 taps, 22 taps, 22 taps) with a decent drop of 30 ft or so. I'm pretty precise about making sure every tubing section between trees is downhill, all the way to the end, going back and forth with a small level. Is this overkill? Is vacuum dependent only on the height difference between highest and lowest tap, or, does every little uphill segment reduce overall vacuum?

[buckeye gold]

You want to keep it with some fall, but what matters is fall differential from top tap to bottom. That will dictate your vacuum. I actually raise mine 8 foot to cross a raod and it still flow up and over. Best to keep it tight and no leaks, don't worry too much about tree to tree fall. Your working on a siphon and overall head dictates the vac

[jpatriquin]

300 taps all 3/16 50' drop all lines have 30+taps per line Average 22" vacuum. Keep a close eye or ear for leaks and or a T getting pugged or partially so. Watch your drops at the end of line and and the flow move down the hill 5 or 6 taps and walk across each line and see if the flow is at about the same rate on lines and on both sides of the T it should be about the same you should see the tree gasses are collecting into larger bubbles, work your way down and do the same. I do that once a week. The tree gasses will compress further down and on a day of a very good run I find the taps at the bottom will slow and accumulate sap in the drops until they are almost full. I probably have to many taps per line. I note your question was asked in 2016 and feel you probably know all this by now and have more taps.

[Rodmeister]

First year sugaring and researching for gravity feed:

I also have 3 gravity feed lines - all on a 65' drop of about 40 degree slope, 23, 22 and 28 taps. I have good prospects for tapping on top of the hill for about 600' feet back from slope but flat terrain.

Question is if I run a line from back to slope and to bottom, will I get vacuum as line fills and drains? Or is a vacuum/tubing system the only practical solution?
BTW, gravity feed is working like a charm! 22 buckets and for 3 days nada, zip, zero - zilch.....gravity has been working round the clock!

Paul

[DrTimPerkins]

Anytime you have 3/16" tubing installed on flat ground you will cause an increase in pressure due to friction in the small line. My suggestion would be to use 5/16" tubing on the flat ground on top of the hill to reduce that factor, then transition to 3/16" once you hit the slope. You're at the top end of the recommendations for 3/16" now, so don't add more to those lines going down the hill. Use separate lines.

[DrTimPerkins]

Is vacuum dependent only on the height difference between highest and lowest tap, or, does every little uphill segment reduce overall vacuum?

While vacuum can pull sap up and over a low spot in 3/16" tubing (or even in 5/16" tubing), it is best to avoid this. Vacuum is additive in that you can think of each segment as an individual piece, and add/subtract as you move along. So if you have a drop, you'll gain vaccum, then if the tubing goes up, you'll drop some of that due to resistance (moving uphill), then gain more again as it starts back downhill.

[Rodmeister]

Thanks for the response Dr. Perkins
I watched a video of a gravity collection system (apparently in Vermont) that used 3/16 laterals into 5/16 mainlines. But this was on a mountain and ran over 1,000'. I wasn't sure if my much smaller drop of approx 70' is enough.
Response appreciated.

Paul Rodman

[maple flats]

Dr Tim is right, I used to maintain a down slope but likely not a constant degree of slope back when I ran my first lines 3/16 on a hill. That hill had a 60' fall in elevation from the top tap to the mainline it terminated at. Then one day I was checking lines for leaks. I had a large limb (about 6-7" diameter) fall on one of the laterals near the upper part of the lateral in a moderate wash. It was fascinating to watch the sap/air/sap go down, under the limb (which had not pinched the lateral) and back up to the next tree and continue down to the mainline (which was still about 40' lower elevation).
While not scientific by any means, it looked to be moving at the same speed as the 2 adjacent laterals.
Yes, I'm sure it slowed some, but without a stop watch I could not detect it. The adjacent lines both had about the same number of taps both above and below that area and those laterals were 3 of about 7 or 8 that emptied into a 3/4" mainline I had run in that direction off a 1" main just to catch those laterals. As such, I think if you have enough drop in elevation after a spot that may not have a good slope and if you have laterals that are not over powered you will be fine.
What I mean by not over powered, is that the number of taps above the flatter section is not too many, and below that area you have a good number of taps you will be OK. On my laterals I try to have 25-30 taps, BUT I also have a hybrid system. My mainlines had 19" vacuum on them by a mechanical pump and a vacuum tank. That might have also skewed my results significantly.

[DrTimPerkins]

Think of it as a roller coaster. When going downhill the cars will gain momentum (and your lines will gain vacuum). On a flat and especially on an uphill, there is friction and gravity working against you, so you will lose speed (and vacuum). If set up properly you'll have enough momentum to get you up the hill or across the flat area, but you will lose speed (and vacuum) in that section.

It is extremely difficult and unreliable to view the speed of sap within a line. You can't see it well, and sap can slip by bubbles in places, so it might appear there is more or less movement when there is not.

On a related subject, it is also impossible to tell how contaminated your lines are by looking at them. They can look clean, but be full of microbial biofilms. Conversely they can look dirty, but if the microbes are dead it doesn't matter. What is often more important is the spore population, which you can't really see at all.

[Sugarmaker]

Tight and down hill.
Regards,
Chris