equalizing air pressure in sap collection jar

[emu742]

I was reading an article entitled 'plastic tubing and maple syrup quality' by Yawney and they mention a set up with a tube going into an air tight jar which collects the sap.

However, they outfitted the jar with a glass 'u-tube' plugged with cotton at one end, to equalize the air pressure (or so they say).

It got me to thinking, is a closed tube to jar/bucket system a bit of a natural vaccuum? Would one want to do as they did - and for what purpose?

[DrTimPerkins]

I was reading an article entitled 'plastic tubing and maple syrup quality' by Yawney and they mention a set up with a tube going into an air tight jar which collects the sap.

However, they outfitted the jar with a glass 'u-tube' plugged with cotton at one end, to equalize the air pressure (or so they say).

It got me to thinking, is a closed tube to jar/bucket system a bit of a natural vaccuum? Would one want to do as they did - and for what purpose?

The U-shaped tube with cotten was done so they could collect sap aseptically. It is not a technique to be used for production.

[emu742]

Hmm yeah they were aiming for aseptic but they did say the purpose for that was to equalize the air pressure. Not sure it's making sense yet to me.

[DrTimPerkins]

Hmm yeah they were aiming for aseptic but they did say the purpose for that was to equalize the air pressure. Not sure it's making sense yet to me.

If the jar were completely sealed with no vent....only a very small amount of sap would make it to the jar before the gases coming from the tree pressurized the jar and stopped the sap from flowing out of the taphole. Kind of like if you took a jar with a hose connected to it and tried to get air out of your tire. The jar would quickly fill with air then stop due to the pressure equalization, and air would stop coming out of the tire.

[emu742]

ah ok makes perfect sense. I wonder, I have a setup almost the same, but I don't think there has been anytime I've noticed sap flow being restricted, I've even had 4 gallons a day a few times out of the one tap. I guess it must not be completely air tight even though it seems to be (tube was put through puncture in lid, but hotglued around to seal it, so no air leaks that I'm aware of, unless the spile connection is a bit loose/generous in letting built up air escape).

There was a point at the beginning of the season where sap seemed to backup in the tubing (empty jar though) and fizz out where the spile connected to the tubing. But I think it was windchill freezing the sap in the tube, which stopped it up and created a bit of a vacuum too.

At this point well as they say if it aint broken don't fix it. But I like to understand how it all works regardless.

[DrTimPerkins]

At this point well as they say if it aint broken don't fix it. But I like to understand how it all works regardless.

If sap was fizzing out the spile, you may have had too much backpressure for the sap to flow.

Simplest thing to do would be to drill a small (1/8") hole in the bucket just below the lid.

[emu742]

I am now leaving the lid screwed on just a bit loose for any air pressure to escape (glass jar, so can't drill).