Structure characteristics: 1. attached with steam or air heat preservation mechanism and unaffected by the environmental humidity; with operation frequency decreased and service life prolonged 2. provided with filer screen and drainage valve 3. the valve runs flexibly and reliably with large displacement working principle: by taking advantage of thermodynamics characteristics, secondary evaporation will arise when the condensate water is discharged to the lower pressure zone and meanwhile when the viscosity and density of steam differ, the drain valve will open or close main functions: the valve is applicable in the steam pipeline and equipment to avoid steam leakage and eliminate steam leakage in order to conserve energy and keep from water hammer and other faults