Below is a list of Non Return Valve manufacturers from Chicago, Illinois. Non return valves are another name for check valves, or valves that regulate the directionality of gas or liquid process streams. Also known as one-way directional valves, these devices are employed in virtually every industrial, commercial and even domestic application that involves the unidirectional flow of materials. Water treatment, sewage, agricultural, indoor plumbing, medical, chemical processing, food processing, power generation and petrochemical facilities are all among those who utilize non return valves in their daily operations.