In a normal sap flow event, trees exude sap during the above freezing period and replenish that lost water by ÒsuckingÓ it up from the roots during the below freezing period. If on a tubing system, during this negative pressure period they tend to draw sap back into the tree from the dropline. Sap, once it enters the droplines, is quickly contaminated with microbes. When they are drawn back into the tree, tap hole closure is initiated. The problem is compounded in 3/16- inch tubing because, unlike 5/16-inch tubing, the smaller diameter collection tube remains full of sap. A Cornell study found that up to 12 feet of sap in a 3/16-inch tube can be drawn back into the tree during this recharge time. CV spouts are one proven method of limiting this drawback with 5/16 inch tubing. The question was: will they also be effective with 3/16-inch tubing that is full of sap?
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Since check valve adaptors and spouts reduce sap backflow, this research studied whether or not dropline replacement is as important to improving sap yield when using these taps.