Valve device for an injection nozzle used in injection molding machine

A valve device for selectively opening and closing an injection nozzle connected between the cavity of a mold and a cylinder serving to feed a molten resin material to be injected into the cavity of the mold via a connector connected at an upper end thereof to a lower end of the cylinder and at a lower end thereof to an upper end of the injection nozzle, the connector having a resin channel for feeding the molten resin material from the cylinder to a vertical injection passage defined in the injection nozzle, the injection nozzle having an injection port formed at a lower end of the injection passage and connected to the cavity of the mold, the injection port being selectively opened and closed by a valve pin received in the injection passage and controlled by the valve device, comprising:

• a vertically-extending hollow cylindrical housing having a top plate mounted on an upper end of the housing and provided with an upper opening, and a bottom plate mounted on a lower end of the housing, the cylindrical housing being defined therein with a vertical cylindrical space completely receiving the connector in such a manner that the upper end of the connector, which is coupled to the cylinder, is positioned at the upper opening, while receiving at least an upper portion of the injection nozzle;
• a cylindrical piston reciprocatively disposed within the housing between the top and bottom plates, said piston having an axially upward extending unitarily formed annular first wall portion and an axially downward extending unitarily formed annular second wall portion which define therein a vertical cylindrical space partially receiving both the connector and the injection nozzle, the first wall portion having an external peripheral surface in sliding contact with a portion of the housing to define a first chamber, and the second wall portion, which is radially superior to the first wall portion, having an external peripheral surface in sliding contact with an external peripheral wall surface of the housing and an inner peripheral wall surface in sliding contact with an annular guide/shield extension which is unitarily formed with the bottom plate, to define a second chamber, said piston further having a peripheral piston portion selectively subjected at upper and lower surfaces thereof to a hydraulic or pneumatic pressure respectively prevailing in the first and second chambers;
• and
• valve pin connection arrangement adapted to connect the valve pin to said piston in such a manner that it reciprocates in accordance with the reciprocation of the piston.