Do I need to allow air into my small gravity flow tube system?

I am a novice at this point, 10 taps last year...looking for 40 this year, have 30 in now. Concerning the vacuum in the line....I live in a mountainous region and placed 11 taps on a ridge behind my house. I have 300' of 1/2" OD tubing going up an estimated 100' + of elevation. I have 3 taps going directly into the 1/2" tube (via 3' sections of 5/16" drop lines) and the remaining 8 taps going into 3/8" OD tubing that connects to the 1/2" line. I left the upper end of the 1/2" line open, fearing that sap on that long of a run may get air locked if there was not a way for air to enter the line. After reading some other posts on here I am wondering if I should plug the upper end of the 1/2" line? Any other input to make this system better would be appreciated as I plan two additional separate small runs of 3/8" line connecting 4 to 5 taps each.

First. Close the line. There's actually a negative effect on sap yield if it's open.
Second. Seems like your a perfect candidate for 3-16 tubing. Free vacuum is the best.

I agree. With that kind of drop, read up on 3/16 lines. Many on here are drooling already, just reading what your situation is.

Absolutely do NOT vent the lines unless your goal truly is to get less sap.

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Originally Posted by DrTimPerkins

Absolutely do NOT vent the lines unless your goal truly is to get more sap.

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Did you state that correct or should it have ended "...to get less sap."?

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Originally Posted by themidnightsapper

Did you state that correct or should it have ended "...to get less sap."?

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You are correct. I've fixed it. Serves me right trying to work while on vacation.

You will be better off with 3/16 laterals. Put 20-25 taps on each lateral and then run it downhill without a mainline. With what you describe you will get high vacuum without a pump. Now you need a bigger evaporator to keep up. You may need to sell some sap to another producer and save that money for a bigger evaporator. 40 taps on high vac. can give you 20+ gallons of syrup and if your sap is at 2% sugar that can be over 860 gal of sap to boil. Are you ready?

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Originally Posted by maple flats

You will be better off with 3/16 laterals. Put 20-25 taps on each lateral and then run it downhill without a mainline. With what you describe you will get high vacuum without a pump. Now you need a bigger evaporator to keep up. You may need to sell some sap to another producer and save that money for a bigger evaporator. 40 taps on high vac. can give you 20+ gallons of syrup and if your sap is at 2% sugar that can be over 860 gal of sap to boil. Are you ready?

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Thanks for the input and no, I am not ready for that kind of volume. My current evaporator in layman's terms is referred to as a "turkey fryer", however my son and I are in the process of constructing a small evaporator. We are tapping mostly red maples and had hopes the best taps would give us 10 gallons of sap each, but on average would be looking at 5 gallons per tap. Looks like we need to upgrade our system and our expectations. Thanks again and thanks to all for the input!

I tap mostly reds too. On buckets they were really hit and miss. Some wouldn't give a drop. On 3/16 I make the reds produce and have about a third of the taps and a lot less work.

An update and a thank you to the folks who provided advise. Through this site, our state CDL rep (WESTVIRGINIAMAPLER) sent me a note that he lived 5 miles from us. He came out to our bush and showed us how to run 3/16 line, tap with a proper bit, and many other helpful suggestions. I am happy to say my son (themoonlighttapper) and I completed our third run last night and we now have one run with 160' of drop from the top tree to the collection point and 2 runs with 60' of drop. Total of 65 taps, 59 on 3/16, however our tap holes on the first 40 or so trees are probably not the best for vacuum. Here's hoping for a good season, but certainly a much better season than we would have had without the help that came from this site. Expansion planned for next year with another 5 acres of unsearched trees further up the mountain.