Mechanism for valve gated injection molding with resilient retaining ring

In a valve gated injection molding system having at least one heated nozzle seated in a cavity plate, the nozzle having a central bore in alignment with a gate leading to a cavity, an elongated valve pin having an enlarged driven end and a tip end, the valve pin extending through the central bore of the nozzle with the driven end being operatively connected to a hydraullic valve pin actuating mechanism mounted on a mold back plate whereby the valve pin is reciprocated between a retracted open position and a closed position wherein the tip end of the valve pin is seated in the gate, and a melt passage extends to convey melt around the valve pin through the central bore of the nozzle to the gate, the improvement wherein;

• the valve pin actuating mechanism comprises a piston with a body and a cap, said piston seated in a cylinder with hydraulic fluid lines connected to apply hydraulic pressure to opposite sides of the piston to reciprocate the piston according to a predetermined cycle, the driven end of the valve pin having an enlarged head, the body of the piston having a well with an inner wall and an open mouth to receive the cap therein, the well having a shoulder at the bottom thereof forming a cup leading to a central bore extending through the body of the piston to receive the valve pin therethrough with the head of the valve pin seated in the cup, the inner wall of the well having a groove to receive an inwardly compressible resilient retaining ring which expands into the groove to removably retain the cap between the retaining ring and a compressible circumferential sealing means compressed between the shoulder and the cap, whereby the cap retains the head of the valve pin in the cup to removably connect the driven end of the valve pin to the piston and the compressible sealing means seals against leakage of hydraulic fluid.