Check valves for fluids are a type of valves which allow fluids to flow in one direction, but automatically close when the flow reverses. They are also called non-return valves or one-way valves. They can prevent the backflow securely and open with small differential pressure. They are applied to piping systems where the backflow prevention is required, frequent open/close are expected, some restrictions exist around the pipings, etc. To install, there are screw-in connection type to screw in the check valve, and flangeless type that clamps the entire check valve with pipes. Furthermore, they are divided into small diameter valves or large diameter valves. Materials of the main body are copper alloy, stainless steel, fluoropolymer, plastic, etc. Sealing materials vary depending on the application; metal is used for places where the temperature becomes high due to steam, etc., and rubber is for places under low temperatures such as hot or cold water.