Does mainline diameter affect natural vacuum?

[TrentonMaple]

I'm new to tubing. I'm switching over our back sugarbush, which is on a wicked slope, from buckets to 3/16 tubing.

I just got an my order of 3/16 tubing from Bascoms. I bought saddles for a 1" mainline, as I was planning on using black plastic water line we had leftover from building our house.

I know 1" mainline is probably overkill for the 100 or so taps that I will have on tubing, but does the diameter of the mainline affect the "pull" of natural vacuum? I understand the physics behind why 3/16 produces more, as the column of sap pulls downhill, but does the mainline have to be full of sap as well? I thought I had read that the mainline functions only as a trough to convey sap to the tank.

Oh, one more thing - I bought a plug for the end of the mainline. Do I want it plugged (like the laterals) or open?

[psparr]

You are correct that the mainline only acts as a "trough". No need to leave the mainline open. They're will be enough air in it to not back up. This will be my second year with 3/16 line.
I was very pleased with the amount of sap I got. Here's a video of my setup. Good luck!

http://youtu.be/kQnQ-SZhBI0?list=UUKxgCYB7fY07atFbhTA5LAQ

[maple flats]

Never vent a lateral nor a mainline, you don't want bacteria to get in. The 3/16 will generate the vacuum, as long as you have 30'+ drop after the lowest tap. The mainline will be good at 1". If you ever did have a full mainline, your mainline is too small.

[adk1]

Explain the reason for a 30" drop after the lowest tap? This season my tubing will b 4 seasons old already. Thinking about starting to switch some of my laterals over to 3/16" tubing. I have wicked slope

[maple flats]

Sorry (typo), please note I corrected it to 30' drop. As stated in the article (Dec 2014 Maple News) by Tim Wilmot who is credited with designing the 3/16 idea, the 30' drop AFTER the last tap is to generate the vacuum on the lowest tap too. If you don't have that last drop below that last tap, you will have less, (or no, or actually pressure) on that tap, while you have good vacuum on the top of the hill.

[TrentonMaple]

My lowest trees wont have 30' of drop before the mainline. They're too close. I'll just have to see what happens with it.

I'm going to try to put up my mainline this weekend if the weather improves.

[DrTimPerkins]

My lowest trees wont have 30' of drop before the mainline. They're too close. I'll just have to see what happens with it.

The amount of vacuum you get is related to the height difference between the taphole and where the sap enters the mainline (or a tank). Trees on the lower slope will get some, but less -- however any amount of vacuum is better than none. Trees higher up will get more vacuum up to the point where you've exceeded about 35' of height, at which point you've reached maximum vacuum (assuming there are no leaks along the way).

[noreast maple]

I thought that 30 FT. drop in elavation was from your farthest tap to the bottom of the slope ,not from your tap just before it enters the mainline or tank. If your mainline runs along the bottom of steep slope , some of your taps will be right beside the mainline. hopefully someone can clarify this or there has been alot of misled custumers.

[DrTimPerkins]

I thought that 30 FT. drop in elavation was from your farthest tap to the bottom of the slope ,not from your tap just before it enters the mainline or tank. If your mainline runs along the bottom of steep slope , some of your taps will be right beside the mainline. hopefully someone can clarify this or there has been alot of misled custumers.

I don't know what you've been told, or who told you, however natural vacuum in a 3/16" gravity line is proportional to the height difference between the open-air exit (a tank or mainline typically) of the line to the taphole, up to the maximum vacuum you can achieve at the site, at which point you can't go any higher.

It is the weight of the sap pulling on the sap in the tubing next to it (since water and sap are cohesive...the water molecules like to "stick" together) that generates the "pull", producing the vacuum. Therefore it is the weight of the sap BELOW the taphole to where the sap exits the tube that generates the vacuum. The weight of the sap ABOVE the taphole (from the other trees further up the slope) doesn't affect the vacuum level.

What this means is that tapholes near the tank or mainline at the bottom of the slope will experience the least amount of vacuum (least amount of height difference), whereas those higher up on the slope will experience more.

One way to deal with this is to have some amount of vacuum on the mainline along the bottom of the slope, which is then additive to the natural vacuum in the 3/16" line.

With pumped vacuum, it is best to have air space to allow the air molecules to be moved out quickly. Hence the use of high CFM pumps, larger mainline, and short 5/16" lateral lines. With gravity vacuum, the vacuum is generated by the pull of the liquid and there is little CFM movement of air, and longer laterals work well.

[Machinist67]

To maintain theoretical perfect vacuum for your elevation you need to have 30FT+ AFTER the last tap to have full vacuum on that tree. Also the 30FT+ after the lowest tap must be 3/16"tubing. If this is not maintained then the vacuum will be less at the lower taps.

Take a column of liquid 30FT tall, plug the bottom, fill with liquid, install a vacuum gauge. Now remove the cap and the reading on the gauge will read perfect vacuum for your elevation.
If you would only have a column of liquid 10FT of drop from your lowest tap then that tap would only see vacuum around 8-10 in/Hg and the tap going up the hill from there will be gradually higher until you reach the 30FT elevation difference. The key is the column of sap must be full and have 30FT+ of drop below the last taps to maintain full vacuum.
Here is a video that does a good job and you can see how this was done. https://www.youtube.com/watch?v=QQX9L1KnBh8

[noreast maple]

Thanks dr Tim For explaining it better, and to Machinist67 also. both good explanations, and great video too. so I guess if you want your last tap to have better vac. than you would want to run down your mainline furter away from your last tap to try and get the amount of drop before entering the mainline, is that correct? If I cant get the reqired drop by doing that is it going to slow down the trees on the steep part of the bank? when i say steep, It is about 100 ft. drop or better from top to bottom of hiil where the mainline will come across the bottom.

[Machinist67]

I do not think it will slow the flow from the upper taps unless you would have a large number of taps on the same line. I average 25.7GPT for the season and I missed the first 2 weeks. Some of my sap in the lines travel as fast as 3ft per second.