... SS420/SS304/SS316 The seat material: PTFE Applicable medium:hydrofluoric acid, phosphoric acid, alkali chlorine,with the corrosive medium.Design Standard:API ... without pin connections. 2 disc outside line 3-5mm thick PTFE seat and disc, using ball seal. Smooth transition open, ... friction torque, reduced, more reliable seal. 3 all contact with the media part adopts the F4 materials, and guarantee and ...