Question for Dr Tim (Vacuum setting)

[jfroe939]

Dr Tim, a few years ago in the maple syrup digest (Oct 07), you did a study on various levels of vacuum and the sap analysis and/or volume... The graph of brix against vacuum showed a steady trend up from 15 to 18Hg and then a slight dip down in brix at 21 before really heading higher at 23Hg on its way to 25Hg... My question is, is the brix reading at 21 the anomaly or is the reading at 23? In other words, why might brix drop off in the first place at 21 and then why does adding two notches to the mercury not only re-start an upward trend in brix but blast right through it and regain that spot on the trendline on it's way to 25Hg? A producer's follow-up question might then be: Is it a fair statement to say that you'd really be screwing yourself to set your pump at 21Hg when all along it's 23Hg that is something closer to the golden goose?
Further, it's a known fact that more vacuum = more sap... if there's essentially no change in sap nutrient levels and syrup flavor and no harm to trees, then under what circumstance is there any viability to running vacuum on your lines less than what is physically possible to achieve? I suppose one could say that in practical terms there is essentially no cost-point at which higher vacuum isn't desired (short of 29Hg or 30Hg which borders the max)?
Last question... If you were Joe Syrup Producer and you currently had all gravity/pails, but you had ideas of making the switch to vacuum, but you live on an income that's more like Donald Duck than Donald Trump, how would you go about piecing together the critical components of vacuum for say 250 trees on a budget? The easy way without a budget is just to go online and whip out the credit card and take it up the backside. I guess the question is, is there a poorman's way to do it - a way to cobble together vacuum? If so (or not), what components do you not want to skimp on and what stuff can you "get by" with on the cheap? Open to anyone who wants to comment, certainly.
Thanks!!! Jason

[Haynes Forest Products]

Ill jump in. First great thread I like the way you put it. I will only speak about the last part of the Question. HOW TO BE A SYRUP MAKER ON THE CHEAP. One of the reasons it was easy for me and alot of others on this site to move up and to expand into higher tech methods is because we share our stories. Most of the stories are about the simple finds that we all love. A free pump, motor off a washing machine, some scrap SS for the sides of the arch. If you learn to work the grape vine and Craigs list or just put out the word you will get and have all you need on the cheap. You dont need a $1000.00 vacuum pump for 250 taps. I use a $50.00 pump for 1150 taps. Use your talents and things will start happening. I have 2 boys and 3 Go Carts I spent $50.00 for all 3 and I wasnt even looking for them. Its a matter of speaking up and out and letting everyone know what you need and want and are willing to DO not spend BUT DO the get there.

[Dennis H.]

One of the cheapest ways to start a vac setup is to goto farm auctions and look for old milk vac pumps. It may take a while but they are out there. I picked up 3 pumps at the same auction for alittle over $100. The tougher thing to find are the milk receiver jars you can use as a releaser.

What I found out in my 3 years making syrup though is that it usally ends up taking money to make syrup for a small operation. Now if you stick to buckets you can do that on the cheap. Really Cheap.

But who really wants to stay there!:D

[lmathews]

I am interested in the original question that was asked about the diff. vac levels.I would also like to ask at what level of vac does it become the most productive? Looking forward to his response.

[DrTimPerkins]

The graph of brix against vacuum showed a steady trend up from 15 to 18Hg and then a slight dip down in brix at 21 before really heading higher at 23Hg on its way to 25Hg... My question is, is the brix reading at 21 the anomaly or is the reading at 23?

None of those measurements are anomolies. With every measurement there is a range of error. Essentially what that graph shows is that sugar content does not go up or down with increasing vacuum....it is essentially flat across the entire range. Now the one exception to that rule (not discussed in that paper) is during extended thaw periods, when sap flow is entirely dominated by vacuum-induced flow. Under those conditions, with gravity you'd get no sap at all. With vacuum, when you have no freezes with extended thaws (week or longer), you start to dilute the sap because all the sap is essentially from water being pulled directly from the soil up through the trunk of the tree. But in that case the result is gravity = no sap and no sugar, vacuum = some sap and slightly lower sap sugar. Under normal conditions (occasionally freezes), there is no difference in sap sugar concentration as a function of vacuum. That graph is described in the text as:

There was no significant trend in the relationship between sap sugar content and vacuum level (Figure 3);


A producer's follow-up question might then be: Is it a fair statement to say that you'd really be screwing yourself to set your pump at 21Hg when all along it's 23Hg that is something closer to the golden goose?

No. Essentially the higher the vacuum you can pull the better (in terms of total SUGAR yield), given the limitations of your tubing system and vacuum setup. Please note that this doesn't mean to run your vacuum pump full bore. Not all pumps can deal with that well.


Further, it's a known fact that more vacuum = more sap... if there's essentially no change in sap nutrient levels and syrup flavor and no harm to trees, then under what circumstance is there any viability to running vacuum on your lines less than what is physically possible to achieve?

The only current limitations are time (spent chasing leaks) and money (to set up a good tubing system and have a great vacuum system). There are, however, several inherent weaknesses in current tubing systems, pumps (far better in the last 5 yrs), and releasers (getting somewhat better) that we are investigating and devising improvements to. More about that in the future.


I suppose one could say that in practical terms there is essentially no cost-point at which higher vacuum isn't desired (short of 29Hg or 30Hg which borders the max)?

That is true, although achieving higher and higher vacuum levels gets harder and harder as you approach the maximum possible for your elevation and barometric pressure. What that means is that to get an improvement of vacuum of 0.5" Hg is far easier and less costly at 15" Hg than it is at 25" Hg. What that boils down to is that an expenditure of $100 might mean an increase in vacuum from -15" to -16" Hg, whereas it might take $1,000 to go from -23" to -24" Hg.


Last question... If you were Joe Syrup Producer and you currently had all gravity/pails, but you had ideas of making the switch to vacuum, but you live on an income that's more like Donald Duck than Donald Trump, how would you go about piecing together the critical components of vacuum for say 250 trees on a budget?

I think Haynes addressed this question well. It is possible, but it takes more time and energy scrounging around. You can do it fast with more money or you can do it slow with less money. With 250 taps, there aren't a lot of inexpensive commercial options out there. Another possible option if you simply want to increase your total syrup produced would be to find more trees. It all depends upon what resources you have available. If you have more trees, and more buckets....go with that. If you have time and a little money, go Hayne's way and assemble the parts you need through careful looking and limited purchases.

[TRAILGUY]

LOTS OF GOOD POINTS. i WAS PUSHING TOWARDS VACUUM AND I STILL HAVE MORE UNTAPED TREES

[red maples]

that explains alot of last season. toward the 3rd quarter of 2010 season I was sure I was just pulling water out of the ground. the sap was running (under vac)but had several days(more like a week) without a freeze/thaw sap went from about 2%,or just under, to .5% in a matter of days!!!

[farmall h]

Dr. T. Two questions. One: Is it true that the highest hg's of vacuum is 29" on planet Earth? I'm thinking I read that somewhere, Number two: If I were to be running lets say 25" of vacuum at the releaser does that mean that with a tight set-up I should see possibly 20" of vacuum at the end of each mainline if I were to install vacuum gauges? Or is that the reading only at the releaser....1400-2000 taps hypothetically w/1" mainlines and 3/4" spurred mainlines.

[DrTimPerkins]

Dr. T. Two questions. One: Is it true that the highest hg's of vacuum is 29" on planet Earth? I'm thinking I read that somewhere, Number two: If I were to be running lets say 25" of vacuum at the releaser does that mean that with a tight set-up I should see possibly 20" of vacuum at the end of each mainline if I were to install vacuum gauges? Or is that the reading only at the releaser....1400-2000 taps hypothetically w/1" mainlines and 3/4" spurred mainlines.

Standard air pressure at sea level at 20 deg C is 29.92" Hg absolute. However our gauges are devised to indicate 0" Hg under those conditions, and anything lower as negative pressure. Normal convention in the maple industry is to ignore the negative sign, and simply give vacuum as gauge pressure from zero. So, under "normal" circumstances, -29.92" Hg is the maximum you could theoretically get. In general you'll see less than this, the most common reasons being elevation (air pressure decreases about 1" Hg for every 1000 ft elevation, so max vacuum at 1000 ft would be 28.9" Hg, at 2000' would be 27.8" Hg).

Again theoretically, if you have a vacuum pump running 25" Hg on a mainline system that is well installed (tight, straight, downhill) and no leaks, you should see fairly close to that at the end of the mainline, minus some minor amount for frictional losses. In a well designed mainline system, and especially with a dual-line mainline system, you should get reasonably close to the vacuum pump level (assuming you aren't really far away and don't change elevation to any great extent).

This is not the case in lateral lines however, as these are full of sap and have air in them (from leaks and from gases from the tree). Gases and liquid normally move at far different rates in a vacuum. Gases will move about a hundred times faster than liquid. Because the sap is there, the gases aren't able to move that fast, therefore there can be significant vacuum losses in the 5/16" lateral and dropline system under certain conditions (peak flows, long lateral lines, too many taps on a lateral). Now before somebody jumps up and says, "I've measured it and there is no difference in vacuum between the mainline and lateral line." That is true....under the conditions it is normally measured. How do people measure vacuum at the end of a lateral line? They would normally pull a drop to connect the vacuum gauge. When you do that, air rushes into the "leak" and pushes all the sap from that line into the mainline, leaving just air. You connect your vacuum gauge and what do you know....great vacuum at the end of that line....because there is no sap in the line. However that is an artifact of the way you've done your measurement and not representative of the line under operating conditions with sap and gases in it. Under those conditions, some vacuum will be lost dependant upon many factors....liquid flow rate (# of taps on the line and how well they are producing), gas flow rate (leaks and temperature), length of line, etc.

Finally, the gauges most people use in maple operations are +/- 2% of mid-scale (FS) accuracy. That means that if you have a normal type of vacuum gauge that is 0-30" Hg, the reading you see can be off by up to 0.6" Hg in either direction in the middle of the range (15" Hg) and probably worse as it gets in the high vacuum range. So if you did see a reading that is 1-2" Hg off, you might not think anything of it....or you might not even see that difference if it is actually there. In our research work, we try to use gauges that are +/- 0.25% full-scale accuracy. That means that we can detect changes down to 0.075"Hg across the entire range of the gauge. We also sometimes will use vacuum gauges that record measurements at up to 1-sec intervals, so we can use them when the system is actually working (with sap and gas in the lines) without having to take them out. When you do this, you see some interesting patterns.

Some work going on right now at UVM PMRC is aimed at trying to build a lab model system that simulates a tubing system so that we can determine the factors that are important in vacuum transfer in current tubing systems in order to identify, and more importantly, correct the flaws in the current mainline/lateral line tubing system. We are also at the stage of testing some of our ideas in large scale field tests. Hopefully more on those in May 2011.

[802maple]

mid-scale [/I](FS) accuracy. That means that if you have a normal type of vacuum gauge that is 0-30" Hg, the reading you see can be off by up to 0.6" Hg in either direction in the middle of the range (15" Hg) and probably worse as it gets in the high vacuum range. So if you did see a reading that is 1-2" Hg off, you might not think anything of it....or you might not even see that difference if it is actually there. In our research work, we try to use gauges that are +/- 0.25% full-scale accuracy. That means that we can detect changes down to 0.075"Hg across the entire range of the gauge. We also sometimes will use vacuum gauges that record measurements at up to 1-sec intervals, so we can use them when the system is actually working (with sap and gas in the lines) without having to take them out. When you do this, you see some interesting patterns.

.

I glad you touched on this as I have seen many a sugarmaker that has asked me why some of there gauges that they have installed throughout their woods are showing more vacuum then they are at the releaser. This why I tell them also not to rely totally on what a guage is telling them.
I have said before my first indication of leaks occur right at the end of the exhaust from the vaccuum pump. If the exhaust is lazy light steam like coming off a cup of coffee there isn't much more that can be done, or if the exhaust is billowing out like a modified diesel pulling tractor you better be headed for the woods.

[Parker]

HHMMM- That explains why I have 22" at the releaser and 23" up through the woods at the lateral main lines once we get things tight...After reading this I think I will plumb a gauge in at the last tap on the end of a long overloaded lateral line and see what that read during the season,,,I allways just yank out a spile and put my vac. gauge on that to see what I am pulling....I dont think I have ever seen the exhaust from my sp-22's "lazily riseing"....interesting points...

[Haynes Forest Products]

802Maple I like the way you put the steam off a coffee cup versus a diesel exhaust Except when your using a vacuum regulator.

[DrTimPerkins]

If the exhaust is lazy light steam like coming off a cup of coffee there isn't much more that can be done, or if the exhaust is billowing out like a modified diesel pulling tractor you better be headed for the woods.

Excellent indicator. With a variable speed pump you can tell by the RPM or amperage.

[Brian Ryther]

If the system is tight and straight how is fricton loss a factor? Once the pump is on and the ambient air is evacuated from the system you have un compressed air that wants to travel from the low pressure to the high pressure to reach equilibrem. But since the system is closed it has no place to go. Therefore no fricton due to no molecure movement.

[DrTimPerkins]

If the system is tight and straight how is fricton loss a factor? Once the pump is on and the ambient air is evacuated from the system you have un compressed air that wants to travel from the low pressure to the high pressure to reach equilibrem. But since the system is closed it has no place to go. Therefore no fricton due to no molecure movement.

That is true only if you have a perfect leak-free system and there is no gas being produced by the trees. These conditions are extraordinarily rare, especially when the sap is running. If sap is running, the trees are also producing gas.

[802maple]

802Maple I like the way you put the steam off a coffee cup versus a diesel exhaust Ecept when your using a vacuum regulator.

You are right Haynes with the older dairy pumps and such as they will most likely overheat unless you can find a way to cool them. Alot of the newer pumps have no need for a regulator as they are cooled better at the higher vacuum we put to them.

Excellent indicator. With a variable speed pump you can tell by the RPM or amperage.
Today 02:19 AM

How true

[TapME]

doc. can you fill me in on hg's vs sap increases at what levels? For us small guys some numbers may make a difference.
examples; 0-5 , 5-12 , 12-18. and the increase that can be expected in sap flow. Thanks

[jfroe939]

here's the link from
http://www.uvm.edu/~pmrc/vacsap.pdf

image attached of the graph

VACUUM SAP
COLLECTION: HOW
HIGH OR LOW
SHOULD YOU GO?
T.R. Wilmot, T.D. Perkins
and A.K. van den Berg
Proctor Maple Research Center
The University of Vermont
Maple Syrup Digest oct 2007

[ennismaple]

When looking at that graph you have to recognize that the data is from 5 trees for each vacuum level. A larger sample set of say 500 trees should produce a trendline with less variation. What it does is give those of us still running dairy pumps at 18" (or those not running vacuum at all) a sense of how their production levels will increase when you're calculating the payback period for a liquid ring or dry ring pump.

[DrTimPerkins]

When looking at that graph you have to recognize that the data is from 5 trees for each vacuum level. A larger sample set of say 500 trees should produce a trendline with less variation. What it does is give those of us still running dairy pumps at 18" (or those not running vacuum at all) a sense of how their production levels will increase when you're calculating the payback period for a liquid ring or dry ring pump.

That is correct, however with an r^2 value of 0.98 (perfectly straight line = 1.0), those results are quite good. In any case, you should pay more attention to the regression LINE than to the individual points, as that shows the pattern of increasing yield with increasing vacuum. As I said in response to an earlier question, there is some variation in any measurement.

You may also note that the trees in that study were fairly small (avg 7.5" dbh). We do not endorse tapping trees this small. We did it because we cut them down afterward to look at the staining pattern in response to vacuum level (no difference....higher vacuum does NOT cause more internal stain....staining is caused by a different process that is not affected by vacuum level). We don't like to cut down all our big trees, so we will use smaller trees as appropriate. Smaller trees are also a lot easier to cut down and dissect to measure staining. For our regular production bush however, our cut-off is 12" dbh before we tap. We are conservative because we're at fairly high elevation and the trees are under a fair amount of natural stress -- partly why we also only do 1 tap per tree regardless of size. Additionally, I believe the spouts and drops were new in that study.

Finally, please don't interpret this to mean that if you have a tree that is 7.5" dbh and you use new drops and run 23" Hg vacuum that you will get exactly the same amount of sap as we did. Yields vary for a lot of reasons. The main take home message is that increasing vacuum has a strong linear effect on yield (the more vacuum you pull the more sap you get), and that high vacuum has no effect on chemistry of sap or internal tree damage.

[farmall h]

Thank you Dr. Tim. Very good info.