Check-valve spouts vs. standard clear spouts
Leader Evaporator Co. Check-Valve (CV) spouts and adapters incorporate a small, free-floating ball which is designed to reduce or prevent backflow of sap into the taphole during freezing, when leaks in the tubing system occurs, and when mechanical releasers dump and introduce air into the system. Several studies over nearly a decade have compared sap yields from CV adapters and spouts to various non-CV spouts and adapters.