Water control valve with pneumatic actuator

A pneumatically operated three-way pure water control valve for use in pure water piping system for semiconductor manufacturing plants, comprising:

• an air actuator, including an air cylinder and air piston ring disposed in said air cylinder for sliding reciprocal movement therein in response to air pressure applied thereto, and a piston shaft connected to said piston ring for movement with said air piston ring in said air cylinder;
• a valve portion, including valve cylinder, a first stationary valve seat having a through-hole therein, a second stationary valve seat opposing said first valve seat, an obturator between said first and second valve seats, reciprocally movable in opposite directions into sealing engagement with said first and second valve seats, and a lower valve shaft mounted to said obturator,
• an intermediate cylinder mounted between said air cylinder and said valve portion and having an opening communication with the atmosphere;
• an intermediate valve shaft serially connected at an upper end thereof to said piston shaft and at a lower end thereof to said lower valve shaft, for transmitting movement of said piston shaft to said obturator to alternatively move said obturator into sealing engagement with said first valve seat and said second valve seat;
• a first bellows formed of polytetrafluoroethylene having one end hermetically mounted to said lower end of said intermediate shaft and the other end hermetically mounted to said inner wall of said intermediate cylinder;
• a second bellows formed of polyetrafluoroethylene having one end hermetically mounted to the upper end of said intermediate shaft and the other end hermetically mounted at an inner wall of said intermediate cylinder, such that said first and second bellows defined a space therebetween isolating said piston shaft from said lower valve shaft;
• said valve portion including a valve base portion integral with said first valve seat and mounted to a bottom end of said lower valve cylinder, said valve base portion having a flow passage therein, said through-hole communicating with the exterior of said valve through said flow passage, said obturator having a guiding portion below said valve shaft slidably mounted for vertical movement in said through-hole, said guiding portion having a side surface in sliding contact with a vertically extending surface of said valve base portion defining said through-hole, said guiding portion having at least one hole therein communicating at one end of said flow passage and opening at another end in said surface of said guiding portion such that when said obturator is in sealing engagement with said second valve seat, said flow passage is in fluid communication with a space surrounding said obturator through said at least one hole.