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United States Patent 5258158
Douris , ê et al. November 2, 1993

Positive-type non-return valve and method of using valve

Dray November 2, 1993

Abstract

A positive-type, non-return valve primarily for use with an injection molding machine utilizes a frame which surrounds a first bore and a second bore. The second bore is accessed by inlets. Outlet passages are located downstream of said inlet and connect second bore with an accumulation area. A piston is dimensioned to slidably fit within the first bore and extend into the second bore. In a downstream position, the piston allows positive flow of material from the inlet to the outlet. In an upstream position, the piston positively blocks flow of material from the inlet to the outlet. The piston can be forced to its upstream position at the beginning of the injection step or can be preclosed by maintaining back pressure on the screw prior to injection.