A Purge Tee has a ball valve placed in between two closely separated tees, which allows for power purging of individual loops in a hydronic system. This is especially useful to remove build up air in a closed loop system. When the handle is turned on the fluid is forced through the secondary loop, purging excess air from the system through the drain. Nations WareHouse has a great selection of Webstone Purge Tees for your residential heating system.