Reverse Flow

[1badsapper]

I just finished reading some posts where people bought 2 x 4 pans with "Reverse Flow"
Can some one explain what reverse flow is & how it works?

[DrTimPerkins]

I just finished reading some posts where people bought 2 x 4 pans with "Reverse Flow"
Can some one explain what reverse flow is & how it works?

This type of question is best answered by getting a copy of the North American Maple Producer's Manual. You'll find that it answers most of these questions, and includes a lot of color photos to help illustrate the points being made.

In brief, there are two major ways to deal with the build-up of niter (sugar sand, scale) in continuous-flow evaporator pans. This doesn't pertain to undivided flat pans, or pans with only a couple of partitions.

Niter build-up can cause an off-flavor and lead to scorching of pans. In extreme cases, it will warp a pan. One method of dealing with it, used mainly in Canada but becoming more common in the U.S., is to use what is referred to as "Cross-flow Pans", which have the syrup (front) pans divided into 2-3 seperate pans (with two partition sections in each normally), connected by pipes. The sap in the partitions in these pans flows from side-to-side (standing at the front of the evaporator). When the front-most (draw-off pan) syrup pan builds up niter, the fire is allowed to die down a little (or shut down if oil), the frontmost syrup pan is removed, with the other front pan is slid forward and becomes the draw-off syrup pan, and a new clean syrup pan being put in behind it. This can be done fairly quickly with experience. You then clean the pan you've taken off.

"Reverse-flow" is the second types of pans, and is more common in U.S. maple equipment manufacturers. In this case, you have one front (syrup) pan, typically with several partitions dividing it, and the sap flows generally forward and backward (when standing at the front of the evaporator). Generally these are set up to draw-off on either side. After you boil and draw-off syrup from one side for a while, niter will build-up in the last partition nearest the draw-off. At that point, you change the plumbing a little to reverse the flow of sap coming into the front pan from the back (sap) pan to now go to the partition on the other side, and begin drawing off on the opposite side. The new sap that is coming in from the back pan will dissolve the niter from that section, and niter will begin to build up on the other side where you are now drawing off. Whenever the build up gets too bad again, you simply reverse the flow and change the draw-off side. Basically you're just chasing the niter back and forth in the front pan, which allows you to continue boiling longer. Eventually though you have to stop and clean the rig in some way.

There are some newer styles of pans (Leader Revolution) and some varients of the cross-flow style that allow you to reverse flow but keep drawing off from the same side.