These check valve taps are the latest in tap technology. When it gets cold at night your tree creates vacuum and sucks "dirty" sap back in through the tap hole. These taps prevent that from happening. By not allowing any contamination back into the tap hole, the hole does not heal over as fast and it allows you to get more sap over a longer period of time. These are scientifically proven (UVM & Cornell Univ.) to improve sap yield.