Powell Valves manufactures non return check valves for various applications. Non-returnable valves received their name from what they do. These values allow fluid, whether in the form of liquid or gas, to flow in only one direction. There are different types of non-return valves such as: spring-loaded, clapper and swing type. These specific valves are used mainly in heating and cooling systems but can also be seen in water systems and boilers. Boiler non-return valves automatically prevent steam backflow. View Powell Valves checklist for Non-Return Valves.