US Patent 7125242 Decompression device for an injection molding apparatus

A sprue bushing includes a melt channel for receiving a melt stream of moldable material from a source. The melt channel includes a first portion, a second portion and a decompression cavity located between the first portion and the second portion. A manifold having a manifold channel receives the melt stream from the melt channel of the sprue bushing and delivers the melt stream through the nozzle channels of several hot runner nozzles towards at least one mold cavity. A decompression device, which includes a rod having an enlarged head, is movable by an actuator to reciprocate within the decompression cavity between a retracted position and an extended position. Movement of the enlarged head from the extended position to the retracted position causes the suck back of the molten material in the hot runner nozzle and causes a portion of the molten material to be drawn toward the decompression cavity.