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. These one-way valves only restrict the flow in one direction, while allowing full and unimpeded flow in the opposite 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.