continuous flow pans.

[michael marrs]

I am very curious how these work. my set up is VERY simple. block arch, rest, pans. but looking at the CFP, in pics, I can't see how the sap works its way to the next pan. are they built on a pitch? My buddy told me about them and simply said the sap starts on one side , flows to the other where it become syrup. If you have a good SS welder, can they be made / I know a lot of questions , sorry , reminds me of a fish ladder in a way. The reason I ask is I just found a oil tank in the woods, and am thinking of making an arch out of it, thanks

[psparr]

It's simple really. The bottom of the pan is flat.
There's a hole in the divider that allows sap through into the next channel, which works its way down that channel to the next hole and so on.
Basically your feeding raw sap into the first channel and as sap evaporates it draws needed sap towards the draw off point to maintain sap level.

[Urban Sugarmaker]

They are not built with a pitch from high to low. As the water evaporates the fluid level in the pans will decrease. Fresh sap will be added at one end, usually with a float box to maintain consistent fluid level. Because the fresh sap is being added at one end, it is gently "pushing" the sap through each section like a winding river. When it gets the draw off point it is at a much higher concentration.

Once the pan is "sweetened" (search Big Eddy on here for an in depth explanation of this) you will almost always have sap that's near syrup at the draw off. My pan is a flat 2x4 pan with four sections. If you set up each section end-to-end you'd have a 16' long channel. Imagine raw sap going in at one end, and by the time it reaches the other, it's syrup.

This is also what you call gradient. After shutdown the gradient disappears and all the sap in the pan is the same concentration until my next boil, then the process repeats.

A larger rig of 2 or more pans works the same way. There's usually 2 sections in the flue pan where the sap goes in first, then it goes to the syrup pan(s).

Don't quote me but there may some osmotic effect as well that draws the lower concentration sap toward the higher. Kinda like the "water follows salt" saying in chemistry.

[RileySugarbush]

Think of a continuous flat pan like this:

Assume a 2x4 flat pan with (4) 6" channels. Rearrange them so they are four 6" by 4' channels end to end, with openings in the touching ends so there is free flow between them. That is what the opening in the channels are. Now you have a 16' long pan 6" wide.

Start trickling sap into one end and it will slowly flow along the length and fill to say one inch. If you have a float to regulate it, it stops and you are done, with a long skinny pan with one inch of sap.

Now add heat. Even fire along the length. All along the pan, water starts evaporating and as the level drops, the float lets a bit more in on that end and the new sap pushes the old along the pan. As this continues, the density gradient develops. Not really a depth gradient. The fresh sap doesn't mix along the full length because the pan is shallow and narrow. There is nothing stirring and mixing them together along that long length. The sap that is farther from the float has been in there longer and gets denser. Keep cooking and eventually the far end, which hasn't seen hardly any of the new sap, gets to syrup, so you draw a bit off that end. This does about the same thing as the new sap, it drops the level a bit, so it's neighbors have to move towards it to keep everything level. That drops the level at the inlet so the float lets in a bit more sap.

If the heat is even and constant, and you set the valve perfectly to draw syrup at a slow and constant rate, your float will replace it with sap at the same rate, a continuous process. Perfection!

That never happens for me, any variation in the fire, even opening the door to load wood, disturbs the delicate balance and the process surges and get out of whack. So you have to watch and regulate the flow all the time. If the heat is very unevenly distributed, you can get syrup somewhere other than the draw off valve. Small pans can be more difficult than bigger ones.

If it was easy, everyone would do it. As it is, it's just us dopes.


Sorry to duplicate the description. I got distracted while typing this and the New Yorker beat me to it!