Maple/Vacuum 101


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Posted by Paul(in NY) on Friday, March 05, 2004 at 7:47PM :

In Reply to: Re: Nothing new posted by Ken See on Friday, March 05, 2004 at 6:58PM :

Maple Trees when flowing sap have a true internal pressure. You can take a tap and short piece of tubing connected to a presure gauge, tap the tree and visually watch the internal presure. On good sap runs, an internal pressure of 15 psi is normal. Go to my web site and you will see on the first page a presure gauge directly connected to a tree showing 15 psi. No trick its real.

Maple trees flow sap when their internal presure is higher than atmospheric presure. This is one reason the old timers always had good flows into their buckets on rainy or snow days, the atmospheric presure was low.

So, many years ago research ( a lot done at Cornell at the Maple Research Station at Lake Placid, NY) showed that when vacuum was applied to a tap line, the tree would flow sap because it was sitting at a much higher presure than the tap hole at 18-20 hg. It has also been determined that pressure higher than 22hg is a waste of money running the vacuum pumps to that high level.

If you look at a typical vacuum system, you will see 18-20 hg vacuum on the vacuum pump. If you go to the most distant tap, you better see the same vacuum or you have a system with leaks. When you drive a tap into a tree, its a air tight seal....or you have not done it right. Further for a vacuum system or any tubing system to function, it MUST be designed as a gravity system. In other words sap must flow by gravity from the tap to the end use location, be it a collection tank or sugar house. I can increase your sap yield 20 to 50% by just adding vacuum. Vacuum can produce sap flows when gravity lines or buckets are dry. So the entire concept of vacuum on Maple trees is to make the inside of the tap hole at a MUCH lower presure than atmospheric. A tiny pin hole in a main line or latteral can cause a major drop in vacuum at the most distant tap and thus your flow will be cut way back. I monitor all mainlines for the same vacuum that I have set at the vacuum pump.

And when it gets cold at night and goes below freezing, the trees quit flowing, no matter how much vacuum you put on the thap holes. I have closed circuit TV to the Sugar House, and can see my vacuum, sugar house temperature, outside temperature a few hundred feet up in the sugar bush (via thermocouples, sap holding tank temperature.
and actual sap discharge from the releaser.
When I see the temperature drop below freezing, I can also see the sap stop flowing. I turn off the vacuum pumps. The releaser allows the sap to fill a tank, then when full dump into my holding tanks, and while dumping maintain full 18-21hg on all lines. They NEVER dip or drop.

In closing ( thats what the preacher says when he has talked to long)Ha!....Ohio State has producted a major research document titled the North American Maple Producers Handbook. It covers in boring details all this technical stuff.

Check my web site for pictures of the presure gauge on the tree, vacuum pumps, etc.

Paul



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