nonreturn

Nonreturn is a term used primarily in fluid handling and engineering to describe a device or provision that prevents reverse or backflow. In everyday language, it is synonymous with a check valve, one-way valve, or backflow prevention device. The term is used in plumbing, heating, gas distribution, automotive fuel systems, and various industrial processes. In British English, the term “non-return valve” is common; in American practice, “check valve” is often preferred; both terms describe the same function.

A nonreturn valve allows fluid to flow in a designated forward direction while automatically blocking flow in the opposite direction. It is passive, requiring no external control. Design choices include the mechanism (swing, tilting-disc, lift, or ball-type), seating, cracking pressure, material compatibility with the fluid, and the required pressure drop. Installation must consider orientation and upstream/downstream pressures to avoid unintended opening or chatter.

Common applications include protecting pumps and compressors from reverse flow, preventing contamination in water supplies, ensuring fuel system integrity, and maintaining proper operation in heating and cooling circuits. Potential issues include valve wear, clogging, corrosion, and backflow if the valve is damaged or installed incorrectly; regular maintenance and appropriate sizing reduce risk.

See also: check valve, backflow preventer, one-way valve.