Hydrodynamics question

[Dinorocks]

Thanks for looking! I have some trees with two taps that connect to tubing which empties into a reservoir at the bottom of a steep hill (a couple other trees are also connected into the downhill lateral)...total length from trees to reservoir is about 50 feet. I have collected very little compared to the buckets hanging on the trees that have no tubing. When I look at the tubing near the trees and connectors, I see that the tubing is full of sap. I put a very small hole in the tubing near the tap (top side of tubing) and watched the line drain into the reservoir...and continue to drip sap). There are no low areas in the tubing. The sap in the tubing reminds me of putting a straw in a glass of water, putting my thumb on end of straw and then pulling the tubing out of the glass...the straw is full of water until I remove my thumb.

Should I put small pinholes at the top of my tubing? If the tubing was connected to a vacuum system I could see how it would pull on the sap.

Thanks for any insight on my fluid dynamics dilemma!

Dino

[wmick]

What size is your tubing, and how many feet of elevation drop do you think you have.... from top to bottom, and from mid-laterals to bottom? how many taps, etc, etc.

My first instinct is to say.... No - Don't put any holes in your system, because the drop in elevation should be creating vacuum for you... (The fuller the pipe, the more vacuum created)..
But something doesn't seem to be working right... Describe your system with a little more detail...

PS - You mention having some buckets flowing better.. Is it possible that you have your buckets on trees that get more sun and have just thawed out further than your trees in the bush? Just asking because I think I have a similar situation today.... I have 2 small mainlines on shurflow in the same bush... After a deep freeze the last few days, one line is flowing an the other is not... Line one has some roadside trees that get better sun. I think that's the difference for me.

[maple flats]

If you have 20' or more drop in elevation, and even better 30', if you use 3/16 tubing you will get vacuum by gravity. In 5/16 tubing that doesn't work. For the 3/16 you are best if you have at least 10 taps, fewer still works, just it doesn't give as much vacuum, and ideal is 25-35 taps on one line. If less than 10, 5/16 is likely better and just wait to see if it runs when the buckets are doing very well, if not, look for drill shavings that might be plugging a fitting or even the taps. If you do have or go to 3/16 in year 1 it will perform very well, after that it requires maintenance for good performance. Shortly after the season you need to sanitize the tubing, first flush it with calcium hypochlorite and rinse (or in Canada you can still use isopropyl alcohol) then rinse with clean water, drain and let hang so all tubing dries inside. Then next year, just after the first flow, change all tees and any connectors, many will be plugged with debris that can't pass thru the small inside diameter of the fittings. I use 5/16 taps and drops into 3/16 lines (called laterals).

[DrTimPerkins]

A shorter answer is "do not vent maple tubing" unless your goal is to collect LESS sap over the season.

[Dinorocks]

Thanks for your responses. To answer some questions above, taps/tubing/connectors are 5/16. The taps are about 4 to 30 ft above the buckets on the side of a steep hill. I removed tubing from a tap and the sap in tubing flowed into bucket...I do not think there are any obstructions at tubing connectors.4AF9BDE1-15C0-437C-AF7D-BDC926102581.jpgDA230E31-07C2-4214-8191-3E575B8923BC.jpg

[wmick]

Thanks for your responses. To answer some questions above, taps/tubing/connectors are 5/16. The taps are about 4 to 30 ft above the buckets on the side of a steep hill. I removed tubing from a tap and the sap in tubing flowed into bucket...I do not think there are any obstructions at tubing connectors.Attachment 22169Attachment 22170

I'm still not quite following your setup.... but I think everything is likely OK... you might be just dealing with slower flow than you've imagined... If there are no restrictions, then the trees will give sap at the rate they feel like... Just like having a bucket.

You mentioned your finger over the straw analogy.... Not sure if you can feel it on your finger, (you could likely feel it on your tongue,) but the weight of that water in the straw, is actually pulling down or "sucking" on your finger... Gravity in maple lines works the same way.. If you have a line full of sap, dropping down an incline.... the weight of that sap in the line, under gravity is "pulling down" or creating vacuum on your fittings at the top of the incline. A 30ft drop, full of sap will actually create nearly perfect vacuum at the top. (approx 30inhg) This will increase your yield from those trees at the top, considerably.

This process typically works best with 3/16" line, because it is so small that air bubbles will not be able to pass by the sap and rise up the line and allow the sap to just run out..... You want the line to stay as full of sap as possible..

If your runs down the incline are not staying full of sap, then they wont create any vaccum. You may want to consider changing them to 3/16". You could likely leave the laterals and spouts at 5/16"

PS - Im jealous of your 30ft drop.... This is a great scenario... If there are more trees at the top,... tap them .... and run a 3/16" line down to your reservoir...

[DrTimPerkins]

I removed tubing from a tap and the sap in tubing flowed into bucket...

That is normal. Just leave it alone and DO NOT VENT the lines.

When you pull the spout or create a pinhole, you let all the sap run out of the line, but at the same time AIR goes into the line. That air will carry microbes and cause taphole drying MUCH faster than if you leave it unvented. This has been shown numerous times in a bunch of studies.

When you vent the spout, all the sap runs out of the line very quickly, but then you go back to one drop in, one drop out (on average). It might appear that sap runs faster when you vent. This is true, but this happens for only for a very short time, then all the sap is out of the line and you are back to one drop in, one drop out. When measured over an entire season, your sap yields will be considerably higher if you DO NOT VENT. Sap will move in 5/16" tubing just fine even if it looks like it isn't. Sap will move past/around bubbles in the line...you just can't see it very well, but it is happening.

So it is your choice....vent and get less sap or don't vent and get more sap. Most people choose not to vent.

In case you missed it...the recommendation is DO NOT VENT.

[berkshires]

Thanks for looking! I have some trees with two taps that connect to tubing which empties into a reservoir at the bottom of a steep hill (a couple other trees are also connected into the downhill lateral)...total length from trees to reservoir is about 50 feet. I have collected very little compared to the buckets hanging on the trees that have no tubing. When I look at the tubing near the trees and connectors, I see that the tubing is full of sap. I put a very small hole in the tubing near the tap (top side of tubing) and watched the line drain into the reservoir...and continue to drip sap). There are no low areas in the tubing. The sap in the tubing reminds me of putting a straw in a glass of water, putting my thumb on end of straw and then pulling the tubing out of the glass...the straw is full of water until I remove my thumb.

Should I put small pinholes at the top of my tubing? If the tubing was connected to a vacuum system I could see how it would pull on the sap.

Thanks for any insight on my fluid dynamics dilemma!

Dino

The hydro-dynamics are just as you observe: the sap is supposed to stay in the 3/16 line.

The column of sap in the line below the tree acts as a vacuum, helping to pull more sap out. If you vent the line, all it will pull is air above it.

It stands to reason that at the beginning, you will get more sap in buckets without the tubing, because the first flow on buckets is going right into the bucket, while the first flow on tubing is creating that column of sap in the tubing, which will help suck more sap out of the trees.

Make sense?

Gabe

[Dinorocks]

Thank you very much for the explanations! The vacuum makes sense, I was just concerned I was dead-heading the flow. All the tubing that goes from the tree tap directly to the buckets are open...all the the tubing that is joined with a three-way connector have sap in the lines above the connectors (the taps, tubing, and 3-way connectors are the same size and I confirmed that there are no obstructions). I’m not having very productive runs so far over all...now that I have more than just a “snapshot” assessment of sap flow so far this season, I see that the low flow is pretty uniform across all my trees and that Mother Nature just doesn’t want to give it up yet. I will be patient and not put pin holes in my tubing.

Thanks again for your help!!

[82cabby]

I’m just south of you in West Falls. It’s been a terrible start to the season so far. I’m averaging less than 3/4 gallon per tap per day for the last week. It’s the weather. Next week looks more promising.