Abstract: A plastic extruder having a rotating helical screw within a cylindrical shell. An automatic shut-off valve is mounted at the forward end of the helical screw. The valve includes a unitary or integral valve body and a poppet which is axially movable and is rotatable relative to the valve body. A rearwardly extending axial bore is provided at the forward end of the screw and the valve body extends into and is secured to the screw within said bore. The poppet has an axial stem which extends through the valve body into the axial bore. A compression spring is mounted on the rearward end of the poppet stem to act cooperatively with respect to the poppet to urge the poppet against a seating surface of the valve body and maintain the valve in a normally closed position. Flow of plastic through the valve upon rotation of the screw causes the valve to open. However, the valve automtically closes upon cessation of screw rotation to prevent back-flow of plastic during the injection step.

Abstract: A nozzle shut-off valve for an injection molding machine has a plunger mounted to reciprocate in a bore so as to block the passageway of the plastic through the nozzle, a single-acting pneumatic piston and cylinder to reciprocate the plunger, to block said passageway, and a pilot passage connecting the underside of the plunger to a location upstream of the intersection of the bore and the passageway for plastic through the nozzle.

Abstract: A shuttle is mounted in a passage connecting ducts from injection barrels. An outlet in the passage wall connects to a common sprue channel. The shuttle isolates one duct from the opening at each end of its travel but at no time blocks the opening. The shuttle is preferably a ball and is preferably located in the spigot of a shut-off tap.