Auto-Shut Valve

Excessive soak time can cause a problem if the material is heat sensitive. If extra caution is necessary, a heat probe can be inserted into the nozzle, or the endcap can be removed for checking the melt directly. Once the endcap is removed, insert a temperature probe inside the non-retum valve. The material within a non-retum valve is generally the last to reach operating temperature. The Auto-Shut valve can be checked by using pliers to gently pull open the poppet. 

The Auto-Shut Valve requires more soak time than conventional non-retum valves. This valve has a spring loaded poppet that rides in the body of the valve. There is a pool of plastic contained inside the valve by the poppet. The pool of plastic in the center of the valve, and the poppet shaft, are the last front end components to reach operating temperature. The plastic around the screw will reach operating temperature before the internals of the Auto-Shut Valve. If screw rotation occurs too soon, the plastic from the screw will ftow into the valve, and either the poppet will resist opening, or the cold slug of plastic in the valve will block the flow. If the screw continues to rotale, the Auto-Shut valve may become damaged. 

A pump was being dismantled for repair. When the cover was removed, hot oil, above its auto-ignition temperature, came out and caught fire. Three men were killed, and the plant was destroyed. Examination of the wreckage after the fire showed that the pump suction valve v/as open and the drain valve shut [3]. 

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