1. seat the seal structure for elastic preload, sealing and sealing structure of upstream and downstream. Always face to face seal between the valve seat and seals. 2. seat has a self cleaning feature, and not in the valve opening or closing process directly by air washing. Seating should be staffed by lubrication, do not wear material. 3. valve actuation failure will not affect the other parts of the valve, repair and replacement work can be carried out without removing the valve. (1) the yoke sleeve: aluminium bronze needle thrust bearing yoke sleeve configuration, minimizing the operating torque. (2) stem: length of thread until the tray; pin and spot welding; with stability. (3) pressure seal: simple structure, segmented retaining ring and silver-coated low carbon steel washers to aid disassembly and achieve the best bonnet seal. (4) the seat rings: welded seat rings are perpendicular to the flow path, easy to maintain.