Disc Bottom outlet valves are compact and ensure a tight shut-off. Their design can incorporate bellows or diaphragm seals to guarantee zero leakage to atmosphere. The sealing to the vessel is always a positive seal and can be metal to metal, stellited or with a sealing ring. The material for the sealing ring on the disc depends on pressures and temperatures inside the vessel. SchuF disc bottom outlet valves are fire-safe tested under the rigorous procedures specified in the BS standard 6755 Pt.2.