Abstract: The characteristics of draining system of thermal power plants and the use of drain valve were introduced. The technical characteristics of metalsealed ball valve were compared with those of traditional cutoff valve, and the technical characteristics of new type metalsealed ball valve were compared with those of traditional metalsealed ball valve. The conclusion obtained by the comparisons is that in the power plant startup drain system, the traditional cutoff valve will be replaced by the metalsealed ball valve gradually.

Key words: draining system, drain valve, metal-sealed ball valve, cut-off valve