With sufficient slope, closed systems, such as we use, provide greater sap yields through the creation of natural or artificial vacuums. . . . A picture of a maple tree showing a tap and tubing One last feature of the tubing system worth noting is the use of drop lines. These are the vertical lines that connect the spiles to the branch line. These lines allow the spiles to be moved to new holes around the tree each spring without re-plumbing the line. These lines also allow for the separation of CO2 gas and sap.
All plants use carbon dioxide to live and maples are no exception.
A large part of what comes from the taphole is CO2 gas which, if not separated from the sap, can contribute to vapor locks, again inhibiting the flow of sap. This process alone takes several days. After the season, all the tubing must be washed so that the system is sterile at the beginning of the next season. This is done by forcing a disinfectant through the whole system and then rinsing. This process alone takes several weeks.