Continuous Vacuum Releaser

[Dave Y]

I have a question about the continuous vacuum releaser. If they work the way I understand ,vacuum is maintained when they dump sap. It is my understanding that a flapper closes on the vacuum side of the releaser when it dumps sap. As I understand , there will be no drop off in vacuum. there fore no sap will travel back up the line into the tree. If this is all true then why did so much go in to developing a check valve spout, when you can achieve the same thing with your releaser? The extra cost of the CV releaser would pay for its self in a couple of years. Then you could buy the less expensive spout adapters or even new standard spouts each year. After all we are putting new in the tree and not allowing sap to back up the line and contaminate the tap hole. would this give us better production? Same scenario as the check valve spout, just a different way of getting there. Please let me know if I am full of it or if this argument holds water.

[Brent]

Hmmmm.. seems pretty logical. It should be ok IF there are no leaks in the system anywhere. Overnight, however, a small leak would let the vacuum bleed off and the sap would get sucked back into the tree.
And I think all systems have some leaks.

[brookledge]

Dave
There are a few things that I will comment on.
Many releasers out there do keep constant vaccum on the lines. The issue is when you turn off the vacuum pump. The vacuum that has been applied to the tree acts like a vaccum tank and the tree pulls sap back up into the tap hole.
Now I know there are some who will say just let the vac. pump run 24/7 but when sugarbushes freeze up they don't all freeze equally and at the same time. You can have some lines that will freeze while others have not and those taps can then pull sap back into the hole even though the pump is still on.
Then there is the case where a line gets knocked down from a branchor an animal chews a hole etc and sap can flow back into the tap hole.
So I feel it is best to stop the back flow at the tap while still doing it at the releaser so when it dumps it doesn't lose the vac only to build it back up
Keith

[PATheron]

Dave- This is how I do it. I run the pump whenever it may be above freezing. Basically my rule is if it might go above 32 tomarrow the pump stays on. If its going to freeze for a week wait till its good and froze and then turn it off. Last year I used new adapters on all my taps. I started tapping the second week of January. Took two weekends to tap my main bush so by Feb 1st that bush was all in. That bush ran well untill april. Once we got into April it was down to 750 gallons a day on 2500 taps. But untill that it ran well. By the second week of February the bush across the road was in. Bout a thousand taps. When I quit in April I was still getting a gallon a tap on that bush when I turned the pump off. I just couldnt keep the sap in the evaporator pans anyway so I had to quit. My sugar last year was terrable and I still did pretty close to 4 tenths. So my main trick is new plastic in the trees and I try to always have vac on thawed lines. The other thing with the bush freezing up unevenly is the lats freeze first anyway. One minute theyre flowing and the next minute theyre solid. Anyhow thats been my experiance here and it seems to work ok for me. Ill have to watch this year but I have two releasers running on the same pump and I dont think Ive ever seen the sap go backwards when they dump. Im not saying it isnt but Ive never noticed it and I spend a lot of time in my woods. This year there will be four releasers running all the time on the pump so I should see it if its happening. Anyhow I think the only way I can make a lot of syrup in my area is to tap early and get every single run. I also think the only way Im getting away with that is the new plastic in the trees. Theron

[Thad Blaisdell]

I would find it hard to believe that sap can go back up the main line and jump up into the multi-fittings and then up the laterals anyway.

[Dave Y]

Thad,
I don't believe that anyone has said that it could. It is the sap in the dropline that has been suggested to flow backward when trees go to negitive pressure.
I am asking if that happens when you releaser dumps and if a continuous vacuum releaser keeps that from happening.

[DrTimPerkins]

It is the sap in the dropline that has been suggested to flow backward when trees go to negitive pressure.
I am asking if that happens when you releaser dumps and if a continuous vacuum releaser keeps that from happening.

Yes, sap in laterals and drop can backflow when vacuum is interrupted. The amount that flows back and the distance is related to the size of the leak and how it forms, or the type of releaser. A sudden large break in vacuum is worst. A small pinhole leak isn't terribly bad except locally (affecting only a few taps on that lateral perhaps). When a mechanical releaser dumps, there will be a short-duration pulse backward in the system. Not large, but it happens many times over the course of a day when the sap is running. An electric releaser doesn't work the same way, so doesn't have this problem (that style of releaser can present other issues for those using high vacuum though).

Tim P.
UVM PMRC

[Russell Lampron]

Just as the laterals were starting to freeze one evening last spring I watched the unfrozen sap stop and then flow backwards. At the same time I watched as it traveled back up a drop and into the tree. The vacuum pump was on and pulling 21" the whole time. The laterals froze at the mainline end first and still had liquid in them at the trees. It was pretty amazing to see and gave me "saw it with my own eyes" proof that a check valve at the tap hole would prevent that.

[DrTimPerkins]

[QUOTE=Russell Lampron;85581]Just as the laterals were starting to freeze one evening last spring I watched the unfrozen sap stop and then flow backwards. At the same time I watched as it traveled back up a drop and into the tree. The vacuum pump was on and pulling 21" the whole time. /QUOTE]

Seeing is believing.

This is just ONE of many reasons why the check-valve was designed to be in the adapter, not at the vacuum pump or the mainline or the lateral line or any other of many possible places. To ensure that sap doesn't get back into the taphole at any time, it needs to be as close to the taphole as possible....thus it was incorporated into the adapter.

Tim Perkins
UVM PMRC

[maple flats]

Another reason to check valve the spout adapter is because the vacuum is being contained by plastic which expands and contracts as the vacuum varies. This live tubing can give up sap into the tree regardless of what you have at the pump. The same as in reverse if you have a long garden hose with a spray valve (nozzle) on the end. When you pressureize the hose and then shut off the supply the nozzle will still spray for a while if opened. With vacuum a similar thing can and does happen, even if you have zero leaks which is unlikely in and of itself.