XTV-40 - Standing Diaphragm Hydronic Expansion Tank - 21 GallonElbi XTV 40 Standing Diaphragm Hydronic Expansion Tank 21 Gallon The Elbi XTV 30 is a 21 gallon diaphragm expansion tank designed for use in hydronic heating, solar thermal, and closed loop cooling systems. Part of Elbis XT XTV Series, this tank features a durable steel shell with welded construction and a heavy duty Butyl diaphragm that permanently separates air and water to prevent waterlogging and ensure reliable pressure control. Designed for non