Valve gate system

Abstract

A valve gate assembly comprises a piston that is actuable between a forward position and a rear position and has a piston stop surface and a forward pressure surface. A cylinder has a cylinder stop surface that is disposed to contact the piston stop surface when the piston is in the forward position. The cylinder stop surface is radially outward of at least a portion of the forward pressure surface and a shutoff pin is substantially aligned with the axis.

I claim: 
     
         1 . A valve gate assembly for injection molding, comprising:
 a clamp plate having
 a first bore having an axis and a first diameter; 
 a second bore adjacent to and forward of the first bore, aligned with the axis, and having a second diameter larger than the first diameter; 
   a cylinder having a third diameter larger than the first diameter but smaller than the second diameter, the cylinder being insertable into the second bore;   a piston being insertable into the cylinder through the first bore and actuable along the axis between a forward position and a rear position, the piston having a rear piston stop surface, a gate shutoff pin aligned with the axis and affixed to the piston; and   a cover plate disposed rearwardly of the rear piston stop surface and having a cover plate stop surface disposed to contact the rear piston stop surface with the piston in the rear position.   
     
     
         2 . The apparatus of  claim 1 , further comprising
 a cylindrical wall of the cylinder formed to be parallel to the axis;   a forward opening communicating with a hot manifold pin hole;   the shutoff pin having an elongated shaft with a front end forward of the cylinder and a rear end affixed to the piston, the shaft passable through the forward opening and the front end of the shutoff pin operable to open and close the gate.   
     
     
         3 . A method of adjusting the stroke of a piston of a valve gate assembly comprising the steps of:
 providing a valve gate assembly including a cylinder and a piston actuable along an axis within the cylinder between a forward position and a rear position, the piston having a rear piston stop surface;   providing a plurality of cover plates, each cover plate having at least one leg, said at least one leg having with a predetermined length and a cover plate stop surface, the cover plate stop surface contacting the rear piston stop surface with the piston in the rear position; and   adjusting the stroke of the piston by replacing a first cover plate having a leg of a first predetermined length with a second cover plate having a leg of a second, different predetermined length.   
     
     
         4 . The method of  claim 3 , wherein the second length is longer than the first length. 
     
     
         5 . The method of  claim 3 , wherein the second length is shorter than the first length.