How does vacuum work?

[Lance]

May be a dumb question but I never was very strong in physics. What is/are the process(es) by which we get so much more sap with vacuum than without? I know (or so I've been told) that vacuum doesn't actually suck the sap from the tree. And the huge difference between vacuum and gravity seems to be way more than should be expected by eliminating friction loss from the gravity system. So what is the physical/mechanical process of vacuum that results in more sap? Does vacuum actually cause the tree to run more sap than without? How? Or is vacuum just a much more efficient system of sap transport? Inquiring minds want to know!!

[maplehound]

Vacuum is not for transporting sap through your lines ( unsless of course you are using sap ladders.) Tubing should always be set up for gravity flow, as much as possible. The benifit comes by lowering the ambient pressure at the tap hole there by allowing the sap to flow more freely from the tree. To me that is the same as sucking it out of the tree but to the college professors that tell us how it works it is an all together diffrent thing.

[wdchuck]

Basically it just gives you more of what naturally occurs any way-pressure differential. And it works!

[ennismaple]

15" Hg of vacuum will double your sap production versus gravity tubing. We've recently put two bushes on vacuum that were previously on gravity and we get more than double the sap! It's pretty easy to justify the additional expense!

[brookledge]

Like maplehound said the ambient pressure is what its all about. By lowering the presure in the tubing the pressure in the tree is higher so the sap flows out of the tap hole easier. Especially on days where the temperatures have not frozen so the next day the trees won't run that good on there own. There are many days in the season where it hasn't froze and consiquently the tree hasn't "recharged" itself so to speak.
Keith

[Russell Lampron]

Sap flow depends on the pressure that is created when the trees thaw after a freeze. This pressure in the tree forces the sap out. When you add vacuum it creates a negative pressure that lets the tree push the sap out easier. The sap is still there on days when there is no freeze but the is pressure isn't. With the negative pressure from adding vacuum you can/will get that sap.

Even a little bit is better than none. If you are thinking of adding vacuum stop thinking and do it. Other than adding an RO machine it will be the best thing you can do and it will pay for itself really fast.

Russ

[802maple]

The best thing you can do is add the vacuum and make your life living h#ll with to much sap to take care of and then you can add the r.o. to make life easier.

[markcasper]

It does make your life a living h?ll with the maintenance of it to.

[mapleman3]

for me its a matter of sucking the sap !! my 100 trees in the back woods are low and flat... so I slope as best I can but the furthest tap is about eight friggin feet off the ground... I use 2 6' sap ladders to get the sap up to the sugarhouse... without the vac I wouldnt get sap from those trees....

if the pump wasnt free to me I wouldn't have done it for only 100 taps... if it was 300-400 definately!!

[Lance]

Thanks for all the info from all.

I did, in fact, decide to go with vacuum this year so I got a Sap Puller. It's the smaller model, 200E. Glenn Goodrich says it's perfect for 800 taps which is what we've got this year. I'll try to make a long and frustrating story shorter. I ran the Sap Puller last week when we had our first run. The needle on the vac gauge didn't budge off zero. Having read all the horror stories about tending a vacuum system on this board, I walked all our lines, checked every tap, tee, fitting, saddle, and other connections from top to bottom.

I found several no-nos: a few taps hanging in the wind, a saddle or two pulled away from the mainline, some critter chews, some less than perfect fitting connections, etc. I mended everything, redid the connections that were even slightly questionable, everything I could think of. Two days ago (Wed.) when it began to warm up, I fired up the Sap Puller even though the sap was running real slow. To my amazement, the vac gauge was bouncing between 8-10 in. Hg. No question I was getting some suction but it was a far cry from the 18" Glenn said it would realistically do.

Got to the sugarhouse this morning (Thurs.), sap was running about 60 gph, I fired up the Puller expecting considerably more vac 'cause the flow of sap was quite a bit more than yesterday. The needle bounced between only 0-2 in. Hg. Mind you, this was only about 12 hrs. after the 8-10 in. reading and, as far as I know, nothing had changed.

I walked some of the lines again, didn't find any pigtails (the loop from the hook connector to the saddle) where the sap or bubbles were moving faster than an ant walks (Thanks, Kevin!). In some of the pigtails though, the liquid/bubbles were kinda bouncing, almost vibrating back and forth. A bubble would head toward the saddle, then head back the other way, back and forth slowly. I don't know what to make of the whole thing.

If I had forever to figure it out, I probably would eventually. But we all know how short our sugaring season is and I jsut don't have the luxury of time to figure out how to get it running the way it should. Any help would be greatly appreciated!!

[Pete33Vt]

First thing to do is check your belt tension. If they are not tight you won't get very much vacuum. Trust me I know. If they are good, its a matter of walking the lines. I know it takes time to do but its a have to do thing with vacuum.Also check your regulator. If all else fails, disconect your lines from your vacuum to your releaser. Startup your pump then plug them your vacuum should jump right up. That would tell you if its the pump or in the woods. If its in the woods, just walk the lines and check everything over. With that little vacuum you have you should have a serious leak some where.

[Russell Lampron]

I have 2 mainlines coming into my releaser and each one has a shut off valve. If I suspect that I have a leak I close one of the valves and watch the vacuum gauge, the vacuum gauge will tell which line I have to search for leaks on first. It is also a good idea to have some shut valves and gauges at branch points in the woods so that you can do the same thing there.

The sap pulsing back and forth in the lines is normal. When everything is working correctly the flapper valve in the releaser will be vibrating open and closed with the pulses from the pump. This is what you are seeing at the trees.

Russ

[brookledge]

Lance
For starters if the sap puller is new(I think from your post it is) then it should be working ok. But you might want to run it and plug the mainline and see if it will pull 18". If it does then you have leaks in the bush. You descibed some of your laterals bouncing back and forth when it gets close to the mainline saddle.
That is a definate sign of a leak further up the mainline.
As the sap is flowing down the main andgoes by a latteral it will temporarily pull harder on the lateral and then as the gush of sap goes by the sap in the laterals will look like it bouncing back.
Usually the easiest way to check your laterals is walk the main line look and listen. The lateral should have a solid flow and not have the sap flying by. You can also bend a little sag in the lateral with both of your hands to see if there is a leak.
Another easy and cheap way of testing your vacuum system is to buy a vac. gauge(should be able to get one for less than $20) and set it up with a piece of vacuum tubing the size of your taps either 5/15 or 7/16.
Pull a tap and push on the vacuum gauge on the spout and look at the reading.Start at the releaser and pull a tap here and there.
Make sure you check the mainline to for leaks some time they split or animals chew them also.
Keep working with it and it will pay off.
Keith

[Lance]

Thanks for all the advice and suggestions, guys. The Sap Puller is a different critter than the more sophisticated systems you've described. It's a very simple rig - a diaphram pump. There are no releasers, no vac boosters, etc. It's just a small electric pump that sits on top of my gathering tank with a quick connect manifold into which the two mainlines run. At the other end of the machine is an outlet through which the sap flows right into my gathering tank. And that's the extent of the Sap Puller vacuum system. It's supposed to realistically pull 18" Hg. When I bought it, Glenn told me it's more susceptible to leaks than a ring pump like the rest of you guys have. After God knows how many hours traipsing my lines looking for leaks, I can see what he meant. Even one tap out of a tree will supposedly drop your vac to 5" Hg. I spent today walking about 1/3 of my taps, running every inch of every lateral through my hands. I'm resigned now to the fact that the only way to get it working right is to keep trudging those lines 'til I get it tight. I'll keep y'all posted as to the trials and tribulations yet to come. Again, many thanks!!