Actuating mechanism for gate valve of injection nozzle

In an injection-molding machine including a hot-runner structure with a sprue channel for conveying liquefied plastic material from a pressure chamber to an injection gate,

• the combination therewith of valve means for alternately blocking and unblocking said injection gate, said valve means comprising:
• a rod having a free end located at said injection gate for selectively obstructing same;
• a cylinder remote from said injection gate provided with an end wall and a peripheral wall bounding an internal space, said end wall having an opening slidably receiving said rod;
• a cover plate separated by said cylinder from said structure with formation of an air space surrounding said peripheral wall;
• a piston head in said internal space connected with the other end of said rod, said peripheral wall being centered on an axis perpendicular to said cover plate and terminating at a face of said cylinder opposite said end wall in contact with said cover plate, said face having an aperture giving access to said internal space, said peripheral wall being divided into a thickened wall portion proximal to said face and a reduced wall portion proximal to said end wall, said wall portions meeting at an internal shoulder between said end wall and said face, said piston head being guided by said thickened wall portion and being provided with stop means limiting its stroke to less than the axial length of said thickened wall portion, the latter having at least one bore generally parallel to said axis extending from said face to said shoulder and communicating at said shoulder with said internal space;
• conduit means including passages in said cover plate communicating with said bore and with said aperture;
• and
• control means connected to said conduit means for alternately admitting a pressure fluid to said aperture and to said bore with resulting reciprocation of said piston head and said rod.