cFm ?

[red maples]

With only 1 year of vac under my belt, I was very happy with the relults of having a vacuum. If I didn't have the vacuum I would have made very little syrup last year!!!

I still have a question about cfm's. I know that new pumps are rated at a specific cfm per inch of Hg. Is there a direct formula for calulating cfm. or do you need to hook it up to a dyno or something to figure it out. Much like find the horse power of an engine of rpm's/ torque.

I am just curious. I have a little bb2 and it works great. Last year with the tight as I could get it system I had an average of 24"hg and could reach 28-29" hg with perfect atmospheric pressure conditions end to end. with 250 taps on 3/4" 900ft mainline. Is there some point that inches of mercury will level off after a certain inches of vac pressure or the higher you get better you are only at a smaller percentage per inch. if that makes sense.

[tuckermtn]

keep in mind that the maximum you can pull on earth in a normal setting is 29" of Hg.

[farmall h]

What if your tapping maples on the moon?:rolleyes:

[danno]

Don't blame me Bob, you're the one who asked ...

Outer space has very low density and pressure, and is the closest physical approximation of a perfect vacuum. It has effectively no friction, allowing stars, planets and moons to move freely along ideal gravitational trajectories. But no vacuum is truly perfect, not even in interstellar space, where there are still a few hydrogen atoms per cubic centimetre.

Stars, planets and moons keep their atmospheres by gravitational attraction, and as such, atmospheres have no clearly delineated boundary: the density of atmospheric gas simply decreases with distance from the object. The Earth's atmospheric pressure drops to about 1 Pa (10−3 Torr) at 100 km of altitude, the Kármán line which is a common definition of the boundary with outer space. Beyond this line, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the sun and the dynamic pressure of the solar wind, so the definition of pressure becomes difficult to interpret. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather. Astrophysicists prefer to use number density to describe these environments, in units of particles per cubic centimetre.

Bought to you by wikipedia

[802maple]

Bought to you by wikipedia
Danno,
You scared me for a minute, I thought you knew this stuff, I'm glad to see it was wikipedia though LOLOLOL

[Dennis H.]

I was going to say the same thing.
For a minute I thought someone else had more worthless knowledge stuff than I do!

[red maples]

SO let me get his staight. I have to take my vac pump to the moon to check my max ...cfm/"hg right :D

[DrTimPerkins]

SO let me get his staight. I have to take my vac pump to the moon to check my max ...cfm/"hg right :D

Better have a long extension cord. :)

The original poster asked....

I know that new pumps are rated at a specific cfm per inch of Hg. Is there a direct formula for calulating cfm. or do you need to hook it up to a dyno or something to figure it out. Much like find the horse power of an engine of rpm's/ torque.

No, there isn't a univeral formula for calculating CFM for a pump. Each pump design technology (diaphragm, rotary vane, flood, liquid ring, etc) and construction is somewhat different, so it isn't a simple matter of how much energy can create how much CFM. Rather, there are charts that show the amount of CFM versus vacuum level for each specific pump. The curves are (not surprisingly) very different depending upon the pump. Some pumps can pull a reasonably high vacuum, but will not move much CFM at that vacuum pressure. Often what you see for ratings on the pump or in the documentation are both the highest vacuum and the highest CFM the pump can manage, but you'll never get both at the same time. It's kind of like saying your car has 400 HP and will get 200 miles per gallon. What they don't say is that is only when you're coasting downhill. The only way to really know is to consult the charts and compare them (that is the manufacturers CFM vs vacuum charts, not your horoscope).

The best pumps (technology and design) will not drop off as fast at moderate-high vacuum and some will continue to pull an adequate CFM even at fairly substantial vacuum pressures. To manage that, better plan on pulling out your checkbook and crying a little.

Of course, these charts are usually constructed under optimal conditions. Your mileage will definitely vary unless you're operating under perfect conditions at sea level. As far as the elevational component goes, the maximum vacuum pressure you can achieve with your pump will drop off by about 2.4% per 1,000 ft in elevation. That is the same regardless of the pump. So if your pump could pull a maximum of 25" Hg under ideal conditions (sea level), and your bush is at 2,000 ft, you'll lose roughly 5% of it's maximum vacuum, so the best you ever could do with that pump in that location would be 23.75 "Hg. Unfortunately you can't break the laws of physics as easily as you can break the speed limit. :)

Barometric pressure plays a little role in the matter too, but we'll ignore that for now.

[red maples]

thank you!!! I figured as such, but I figured I'd ask just to make sure. So that is possibly why I get a bit more " of Hg beacuse I am closer to the seacoast and a lower altitude!!!

[adam1493]

So can I tap a maple on the Moon or not?

[DrTimPerkins]

So can I tap a maple on the Moon or not?

You could, if 1) there were maples there and 2) if you could get there. You wouldn't get much out of it though.

[red maples]

you would probably have to bring a maple tree with you. I don't think it would run very well because (now this is coming out of the forgotten file in the brain it doesn't work very well) the day temps for the moon are right around 240F something and night its the opposite. -200F something . So I don't think you would get much sap.

[farmall h]

phew...I guess that answers my question.:)

[Kirk]

When you have achieved high vacuum in your tubing system, how much does CFM play into the equation? If your system has no leaks at a nominal 22", what does it matter whether you have a 1 CFM pump vs. 100 CFM pump? Does the pump with the higher CFM across the curve compensate for some leakage?

[DrTimPerkins]

When you have achieved high vacuum in your tubing system, how much does CFM play into the equation? If your system has no leaks at a nominal 22", what does it matter whether you have a 1 CFM pump vs. 100 CFM pump?

No, CFM isn't terribly important in a leak-free system, EXCEPT for the fact that trees not only exude sap, but also gas (mostly atmospheric gas enriched somewhat in CO2). So some minimal amount of CFM is necessary. As long as you meet that need to evacuate the gas, the real important factor is vacuum pressure. It is the vacuum gradient (difference in pressure from the inside of the tree to the inside of the tubing system) that primarily determines the flow rate and yield of sap from trees. Think of it this way....if you have a big leak, you can have a lot of CFM movement, but lower vacuum pressure....and not a lot of sap.


Does the pump with the higher CFM across the curve compensate for some leakage?

Exactly....it will compensate for both minor leakage (to some degree) and gas exudation from the tree. Therefore, it can maintain a higher vacuum pressure (in Hg) even if there are leaks. What is even better....combine that pump with a VFD which indicates amperage. This pump/VFD system then compensates for minor leaks, but indicates via current draw how much leakage+gas generation you are experiencing, therefore telling you when it's time to get out there and chase after leaks.

[Haynes Forest Products]

Thanks so much Dr Perkins it always sounds better when you say it. Hopefully we can put the need for high CFMs verses a pump that can pull high HGs in perspective.

Now Im confused buy your statement "vacuum Pressure" If I put my hand over the intake or vacuum side of my vacuum pump I feel a sucking sensation on the inside of my hand because the vacuum is pulling on the inside. My hand is trying to GO to the low pressure. BUT I also feel the pressure of the atomsphere pushing on my hand. So when you say vacuum pressure what do you mean?

[PATheron]

Brad- This is my experiance with cfms. The Dr. is right for sure if you have a leak free system you dont need much of a pump. One problem that you can get into and maybe you wont but a lot of guys do is its hard to keep it that perfect once you get quite a few taps. I try to but its tough. So what I do is try to run 3 cfm's per hundred. That way even if you lose a few whole drops one day, say your at work and it happens, you still get most of your sap for that day. Your kind of doing wrong not keeping it perfect but in the real world or at least mine you stuggle with leaks. Other thing is a cold pump. You have to do that expecially with a ring pump. If it starts getting warm its over, the cfms drop right off and usually your vac level comes down. Could be inches just from the heat if theres leaks enough. You want a small line with cold water coming to the pump head or what you can do is put a sump pump in the cooling tank and pump the water out of the tank and through a pond to keep it cool or any source of cool water. Other thing is pipe size and Jerry and the Governor have been all through that. If your leak free you can run vac a long way with small pipe. In my world it seems to take bigger pipe. I ran one inch 3000' to a realeser with 600 and some taps couldnt get it over 15" ran a second one inch pipe with it and it instantly went to 23". So the theory stuff is fine but my experiance has been a bigger cool pump and a bit larger line and do the best you can with the leaks and you seem to get a lot of sap. Other thing is when its warm and there isnt any freezes you have to keep at least 23" or so to keep the sap running on pure vac alone indefinitely. If you dont have up around there I dont think it will keep going. Last trick, DONT TURN THE PUMP OFF TILL YOU SEE LEAVES!!! Theron

[Gary R]

Haynes, Let me take a stab at it. Someone please correct me if I'm wrong.

In a perfect vacuum there is no pressure. As you go up from there, pressure is felt. We live on earth that has an atmosphere. The pressure is about 30 in. Hg. So we dont feel the pressure differnce on a line that is at atmospheric. We call anything between 0 and 30 as vacuum. But it is still a pressure differrence when compared to absolute. Hope that's OK:rolleyes:

The CFM thing,

Cornell did a webinar a couple of months ago. It mostly dealt with check valves and gravity. However at the end of it, Stephen Childs covered pipe sizing. Some of it is available on there web site. It takes a big pipe to carry a lot of CFM's. The charts will show you that no matter how big of pump you have, you can only move a few CFM's at a few hundred feet from the pump using 3/4", 1" line. It all had to do with plumbing friction.

[DrTimPerkins]

Haynes, Let me take a stab at it. Someone please correct me if I'm wrong.

No need to correct your explanation at all. Pressure is pressure, it just depends where we start from. It is just sometimes easier to start at ZERO (absolute vacuum) than at standard air pressure. I've been working on a paper to describe all this, but it is hard given that we use PSI for pressure above standard air pressure and in Hg for below. This means that for vacuum, a higher (negative) value is better, even though we're actually trying to reach a very low pressure. Keep your eyes on the Maple Digest over the next year or so and hopefully I'll have something that can explain it simply.


Cornell did a webinar a couple of months ago....no matter how big of pump you have, you can only move a few CFM's at a few hundred feet from the pump using 3/4", 1" line. It all had to do with plumbing friction.

Correct. Various restriction factors in tubing systems result in friction resulting in losses in CFM over fairly short distances. While a big pump will still move a lot of CFM and keep the vacuum good at the pump, out in the woods, the vacuum will be low. Sorry if that stance offends anyone, but it's a false sense of security in some ways to put a monster pump on your system to overcome leaks. If I recall correctly (and there aren't a lot of good measurements of this), trees (under vacuum) only produce about 0.0015 CFM on a warm day.

[red maples]

There now we're getting some good stuff here. Thanks guys. Lots of clarity. I was getting worried in the begining about the whole moon thing!!!

So basically bottom line is if your pump is pulling sap and you have as little leaks as you could possibly have and take out stock in 3M from buying electrical tape and you're getting sap and your pulling good inches out in the woods. then all is well!!! Oh and don't turn off your pump until you see leaves:)

[Haynes Forest Products]

Dang this is getting good and it all does make sense to me. I also agree with the doc that having a monster pump just in case the mainline breaks is a bad way to go. Fighting heat caused by lack of cooling air because a line might break is alot of work and worry. Being one of the guys that will try most anything in a pinch and not believe everything some says because he has a friend that heard from a guy down the road from his Mother that a small vac pump wont work. Thanks for the explanation:)

[sweetwoodmaple]

Yes, indeed...great discussion here. To add some spice to the conversation, I'm with Theron the the Governor on this one. I agree with the 3 cfm per hundred taps, especially for us "hobby" operators. On balance, as he said, it requires larger pipes and potentially dry lines to help with flow transfer due to plumbing friction.

If I had more time to monitor my system, perhaps I could size things as the experts say to...but I have a day job and only a few hours in the evening to inspect and boil. I'm also not a perfect driller of holes, which also can lead to leaks.

Case in point, last year I had a 5/16" line come loose....if not for my monster pump, I would have lost hundreds of gallons of sap by the vacuum dropping during the day when I wasn't there. Yes, I understand that flow losses sometimes help this situation as the closer taps will still get some vacuum, but still...I had a 1 cfm/hundred tap outfit for the first year...never again. Not with a short amout of time to be in the woods during the season (unless I take vacation time). I need the extra buffer.

And I do also understand the economics of the situation...that few hundred gallons saved probably cost me a bundle in extra electric! ;)

[Brian Ryther]

[quote=DrTimPerkins;119299] [QUOTE]"we use PSI for pressure"[QUOTE]

I think PISG is more accurate. We in the general public use PISG (G=gauge) to measure pressure. Scientist and engineer use PSIA (A=absolute) where 0 = 0 atmosphere. PSIG of zero = 14.7 PSIA

[DrTimPerkins]

If I had more time to monitor my system, perhaps I could size things as the experts say to...but I have a day job and only a few hours in the evening to inspect and boil. I'm also not a perfect driller of holes, which also can lead to leaks.

Brian....in your situation with the severe time limitation, this approach is reasonable. However many people "think" that the best way to get better vacuum (and thus better production) is simply to throw a monster-sized pump on a leaky or poorly designed/installed tubing system. With an oversized pump you might never even see the drop in vacuum pressure at the pump when you have leaks, but it is real out in the woods. I'm sure the equipment suppliers are more than happy to sell those big pumps, however for most people, the better approach, if time and personnel permit, is to be very diligent about finding and fixing the leaks in the first place.

A good place to start dealing with leaks is to avoid them by using a sharp bit and some care when tapping.

[twofer]

If I had more time to monitor my system, perhaps I could size things as the experts say to...but I have a day job and only a few hours in the evening to inspect and boil. I'm also not a perfect driller of holes, which also can lead to leaks.

One of my plans for my (microcontroller based) sap handling control/monitor system is to install an Omega vacuum pressure gauge to monitor the amount of vacuum on the system. This will allow me to do two things: pseudo VFD and report vacuum measurements to a remote server.

The pseudo VFD will control whether one pump is on or both pumps are on. Right now I have a Gast 1023 & 0823. In normal operation the 1023 will constantly be running. If the system senses the vacuum level dropping past a threshold it can turn on the second pump. It is my intention to save as much electricity as I can instead of just running both pumps all the time when it might not be necessary.

The reporting of vacuum measurements will allow me to remotely view the vacuum level from my desk at work and in the event that the vacuum level drops off the cliff it can send an email and a text message to my phone to inform me. This allows me to immediately either try and get someone out there or see if I can get away from work myself.

Below is the same microcontroller I plan on using reporting live temperature measurements from my home's gasification boiler system to a web based reporting system I designed (not purty but works).

Many apologies in advance for the rambling. :)

[sweetwoodmaple]

Dr Perkins - Yes, and unfortunately my tubing system was designed originally for just gravity and has been converted, so your point is valid. Also, I have sap ladders-a-plenty. I'm up to 6 ladders for only 550 taps! The land I use is very rolling. If I was to do it again, I would change the location of my tanks and do one final pump/lift to drain the tanks back to the sugarhouse.

twofer - Ha....I have a spare small pump that I've been trying to think about a two stage approach myself, but not for the purpose you are doing (though it sounds neat). Mine was to use my 15 cfm pump on the good running days, and fall back to my 5 cfm pump on the off times just to help keep the tap holes open and prevent back flow.

Has anyone heard of doing this to help save $ in electric and keep the tap holes and lines clear?

[PATheron]

Theres a lot of different ways to look at the big pump versus the little pump deal. Haynes and the Dr. are right, if the system is right you dont need a lot of pump. Example- Last year I used a 130 cfm pump on roughly 4600 taps. I kind of struggle becouse Im a one man band and my system is not optimal. Its not all running into the sugarhouse from a nice side hill. Theres releasers all over the place and pockets of maples here there and yon. Thats the resource I have. Theres a lot of connections with this type of setup. I also have a lot of squirrell problems. Last year Scott Wheeler up in northern Maine ran almost 20,000 taps on the same sized pump basically and Im sure he had better vac than I did. So that proves that if your stuff is right you dont need a lot of pump. Im pretty posative though that the lions share of producers have systems that are closer to mine than Wheelers. Theres a lot of varyiables. He is a full time producer that does just that. Most guys I know do it on the side and that would make quite a difference. I use kind of an all of the above approach. I try to do my absolute best to have a good system. I run a good sized pump and try to keep it ice cold. I cut trees out in the off season that are dead and may fall on my lines. All that being said everyone is going to have leaks unless there only running a handfull of taps or they can afflord labor enough somehow to have someone constantly cruising the woods. The difference in the cost of running the pumps is kind of minimal. I figured it out once and Id say my 10 hp motor costs me maybe 15 bucks a day? I cant remember exactly but even last year on a horrable year Id make a drum of syrup a day? 1500$ You run a 5 hp, half the pump say it costs you 7$ a day Theres a difference of a couple hundred bucks a month. Thats very minimal when your making syrup on a commercial scale. So for a couple hundred bucks a month if you lose a drop here and there and you cant get right to it you still get most of your sap? Thats a good deal for me at least. If you hook a big pump to a piece of crap tubing system though you are kidding yourself becouse if that sap is slugging everywhere your not going to get much no matter how big a pump you use. Just some different thoughts. Theron

[802maple]

I am going to be a politician here and agree with everyone. If your job is maple, then you can most likely get away with a smaller pump as long as you are vigilant in keeping up with maintainence during the season and off season. If your income comes mostly from the outside world then a larger pump in my opinion isn't a necessity but it sure does help as Theron says. It is true a larger pump will sometimes give you a false reading at the sugarhouse as it has overcome leaks and by looking at the vacuum gauge you could assume that everything is all right. I personally never go by what a vacuum gauge is telling me, I go 95 percent as to what the exhaust from the pump is telling me as it doesn't lie. No matter what your vacuum gauge is telling you if your exhaust is coming slightly more turbulent then steam off a cup of coffee you are allright, but if it looks like the exhaust from a hopped deisel engine at full boost, you better be headed for the woods, no matter what your $10.99 vacuum gauge says.

[Haynes Forest Products]

802maple Im happy to say that my exhaust is as you describe it. This site with the help of Dr Perkins will have an impact on the way I look at my tubing system and treat it. I wont be back slamming my lines just for the joy of watching the releaser dump or pulling taps in the woods to see if I really do have vacuum. I didnt sugar last year but the year before was my best year ever. I did everything I could to screw it up. To one thing I always did was try and keep the pumps running and lines tight:)

[maple flats]

Going to the moon for sap, wow, look at the freeze thaw cycles, one every day, no exceptions.