Patent ID: 7678320

Claim:
An injection molding apparatus comprising: a sprue bushing having a bore extending there through with a downstream portion defining a melt channel for receiving a melt stream of moldable material under pressure; a manifold having a manifold channel for receiving the melt stream from said sprue bushing and delivering the melt stream to a nozzle; and a shut-off valve provided in an upstream portion of said sprue bushing bore, said shut-off valve having an inlet for receiving the melt stream from a melt source and a melt channel for delivering the melt stream downstream to said sprue bushing melt channel, said shut-off valve including a pin retaining assembly defining a chamber that accommodates sliding movement of a reciprocating member therein and that contains a biasing member for biasing the reciprocating member in an extended upstream position said pin retaining assembly prevents melt from entering said chamber, wherein said reciprocating member is movable between the extended upstream position in which said biasing member biases a head portion of said reciprocating member against said shut-off valve inlet to close said shut-off valve inlet and a retracted downstream position in which said reciprocating member compresses said biasing member and opens said shut-off valve inlet, and wherein the pressurized melt stream acting on said reciprocating member head portion moves said reciprocating member into the retracted downstream position to allow the melt stream to flow downstream around said reciprocating member head portion to thereby enter said sprue bushing melt channel.