Maple Sap Preheater and Transfer Device

Karl J. Buter

Summary:

Many families make maple syrup during the spring just as the snow is melting and the days are creeping above freezing while the nights are still below. Commercial maple syrup boilers are available for the home boiler but they are very expensive, beginning at $1000. Due to this steep price many of these families set about to create their own maple syrup boiler. The one used for this project consists of an old sheet steel, wood fired area heater with a square hole cut into the top. However due to the use of the area heater two significant problems arise: the amount of heat lost through the uninsulated sides of the firebox and the inability to preheat the fresh sap. From this it is determined that three things are necessary for this project; a way to preheat the sap, a way to reduce or use the heat loss from the sides, and a way to transfer the preheated sap into the main boiler pan.
The commercial boiling systems that are available to hobbyists have a method of preheating the sap; this is commonly done by placing a deep pan covering about 1/8 the total area on top of the boiling pan. This design uses the steam and air heated by the boiling sap to warm the fresh sap which is then gravity-fed into the main boiler pan through a valve to adjust flow rate. Another method of preheating that is currently used with the homemade boiling system is to stack clean coffee cans filled with fresh sap against the uninsulated sides of the firebox. The radiant and convective heat transfer from the sides warms the sap and it is transferred by pouring the can into the main boiler pan. Neither method met the three project necessities therefore another method to preheat the sap was needed.
Many concepts were considered as solutions to this project though they are classified easily into their methods of preheating and their methods of transfer. The main designs either called for tanks to be hung on the sides of the firebox thus capturing the lost heat and using it to preheat the sap or to use a coil of copper tube inside the firebox itself through with sap would be moved in order to heat it up. The different transfer methods evaluated were a peristaltic or centrifugal pump, a gravity feed, or a manual transfer method.
Upon consideration of the necessary flow rates, ease of use and cleaning, and the fulfillment of the three main problems a side tank preheater with a peristaltic transfer pump was chosen as the final design. The tanks are constructed out of 1/16” stainless steel sheet that are welded together and hang on brackets off the sides of the firebox. The tanks each contain a bulkhead fitting from which a 1/8” ID silicone tube leaves and connect at the peristaltic pump. The pump consists of a 12V DC motor geared down to 152 RPM that is connected via an aluminum shaft to the actual pump mechanism. The pump mechanism is also constructed aluminum but uses Delrin rollers on stainless steel shafts spaced 120o apart with a final pumping diameter of 6 inches. The tube track is cut out of Delrin and uses 1/8” side walls to hold the tubing into place. The pump then transfers the preheated sap through more silicone tubing into the main boiling pan.
The final design performs admirably and actually beats expectations because it will self prime. Due to imperfect placement of the pump roller shaft holes the rollers needed to be custom sized but otherwise the pump fit together exactly as drawn up. The tanks are still being built at this time but because of their lack of complexity the most difficult part was designing and building the pump. The pump cost around $55 for the purchased parts which is right in line with what was expected, though $26.50 of that was for expedited shipping. The pump will work well with the tanks and the entire setup satisfies all three major requirements as well as all of the minor requirements set forth in the development of the project.