inches of vaccum

[howden86]

I can run about 20-22 iches of vaccum at the pump. I am thinking of a new pump but does anyone know the difference in production in running vaccum around 28 inches. Is it worh it for the cost of a new pump

Thanks.

[caseyssugarshack93]

Every inch of vac Past 20 is going to produce 5% more sap for every inch of vac, that is what i was told,not sure if its true or not

[PATheron]

Thats what it is. One of lapierres videos explain that. So if you run 25 instead of 20 your going to get 25% more sap. Theron

[DrTimPerkins]

The relationship between sap yield and vacuum level is nearly linear, which makes sense because sap flow is related strongly to the difference in pressure from the inside of the tree to the outside (or in the tubing system).

Although I've also heard the 5% number mentioned, I'd suggest that 3% per 1"Hg increase is a more conservative estimate.

Takes the right pump and a darn tight (leak-free) tubing system system to get to 27-28"Hg. Equipment maintenance becomes more critical with higher vacuum as well.

Tim P.
UVM PMRC

[Mark]

The first year I had only 1200 taps but had a 10 hp sihi pump so I had plenty of vacuum. To clean the lines I had the vacuum going and carried cleaner to each spout. On a 55 degree day when I pulled the spouts most were frozen and I would have to put them in the fluid for a few seconds to thaw them out.
At high vacuum there must have been a slight leak and pressure drop to freeze them. I wounder if that also happened during the season, have you ever heard of that happening with the high vacuum levels?

[OGDENS SUGAR BUSH]

The first year I had only 1200 taps but had a 10 hp sihi pump so I had plenty of vacuum. To clean the lines I had the vacuum going and carried cleaner to each spout. On a 55 degree day when I pulled the spouts most were frozen and I would have to put them in the fluid for a few seconds to thaw them out.
At high vacuum there must have been a slight leak and pressure drop to freeze them. I wounder if that also happened during the season, have you ever heard of that happening with the high vacuum levels?

this should be interesting, i can hardly wait for the responses

[DrTimPerkins]

At high vacuum there must have been a slight leak and pressure drop to freeze them. I wounder if that also happened during the season, have you ever heard of that happening with the high vacuum levels?

Absolutely ice can form in this way -- but most people don't think about it because they don't see it in the pipeline.

At reduced atmospheric pressure (vacuum), the vapor pressure is also reduced greatly due to the venturi effect (air being sucked through a restriction), and ice can form anywhere you have a leak....even at temperatures somewhat above freezing. It's basically the same thing as "carb icing" in airplanes and older vehicles.

When it happens, it can build up ice around the leaky joint (either a tee or saddle) and restrict flow somewhat. As long as the sap is flowing well through, the amount of sap moving through will melt it quickly enough, so the loss in vacuum and yield isn't huge except during certain brief periods. Very interesting phenomenon.

(As an aside....this is a pretty big issue for pilots of piston/carb planes. Most small planes have "carb heat" where intake air is pulled through a heat box before takeoff or whenever carb icing conditions are prevalent. Not a lot worse than having the engine cut out on you in a single engine plane. Carb heat isn't left on all the time though as the increased temperature reduces the air density and thus the amount of air the engine receives....resulting in slightly lower power).

Tim P.
UVM PMRC

[Mark]

I am going to a two stage 20 Hp SIHI this year and am hoping I don't have too many problems.
I have an electric releaser and I know I will have problems with the pump on the bottom of the releaser. At over 23 inches the seal gets lifted off the fixed seal face. The only fix I can come up with is a stronger spring or put a well pump inside the releaser.
I have had icing in airplanes before, I have about 13,000 hours, but it sure was a surprise to see it when I could not find any leaks.
I have had that happen on a pumped transfer line and lost the sap for an entire day on 6000 taps. The only way I could find it was to turn off the vacuum for a couple hours until it melted.