The operational principle of sanitary expansion butterfly valve is: when the compress air pushing the valve seat to valve clack, the sealing function of valve developed, when valve operate to ON/OFF position, release the compress air, not any touchment of valve seat and valve clack happen(No friction caused).  The design of vavle will increase the life of seal material, also will reduce the worry about seal material fall of from engineers of food/pharmacy industry who concerning the media purity; all of control elements operated by compress air can meet the anti-explosion requirements of production. The valve widely used for fluid/power/pellet in food industry, biologicals industry, milk industry and sugaring industry.