Valve gated injection molding apparatus with a spring in the piston

In a valve gated injection molding apparatus having a melt passage extending to a gate leading to a cavity, a valve member having a front end, a rear end and an elongated shaft between said front and rear ends said valve member extending through the melt passage in alignment with the gate, the valve member having an enlarged head at the rear end, the enlarged head of the valve member being engaged by a piston having a cap removably attached to a main body of said piston, said piston having a bore through which the elongated shaft of the valve member extends forwardly, the piston being driven in a cylinder to reciprocate the valve member between a retracted open position and a forward closed position in which the front end of the valve member is seated in the gate, having the improvement wherein;

• the main body of the piston has a spring chamber extending in alignment with the valve member, the spring chamber having a rear end which is closed by the removable cap and a front end from which the valve member bore extends, the head of the valve member being received in the spring chamber with the elongated shaft of the valve member extending forwardly therefrom through the valve member bore, the head of the valve member being larger than the valve member bore whereby a stop is provided by the front end of the spring chamber, and compressible spring means mounted in the spring chamber rearwardly adjacent the head of the valve member, whereby in the closed position the head of the valve member retracts somewhat into the spring chamber against a predetermined force applied forwardly against the head of the valve member by the spring means.