First Source Engineering offers various types of valves in desired conditions and working temperature. Patented Stem double sealing design provides a high cycle automatically adjusting stem seal. The spherical segment ring at the bottom of the stem, energized with Belleville washers provides constant pressure to the primary stem seal forcing it outward and upward against the bottom of the stem journal. All of the media will be contained by this seal under most conditions. A top journal set of three v-ring chevron packing acts as a secondary seal promoting a high cycle, self adjusting stem seal.