Järelvalve

Järelvalve is a valve installed downstream of another valve or device in a piping system to prevent reverse flow or unintended discharge, and to isolate a downstream section during shutdowns. In many contexts the term corresponds to what is commonly called a check valve. It is used to protect equipment, maintain system integrity, and prevent contamination or damage when pressures change or when upstream components are closed.

Operation and varieties depend on the application. A järelvalve can be spring-loaded, swing, ball, or piston type. It generally opens automatically with forward flow and closes if the flow reverses or pressure drops. Some designs are pilot-operated or designed to limit pressure surges and water hammer. The choice of valve depends on factors such as fluid, temperature, pressure, and required leak-tightness.

Applications are widespread across water supply, heating and cooling systems, power plants, chemical processing, and oil and gas pipelines. The valve helps protect pumps, meters, and sensors, prevents backflow into clean systems, and supports safe maintenance by isolating downstream equipment without shutting down the entire network.

Installation considerations include correct orientation and directional markings, material compatibility with the fluid, temperature and pressure ratings, and adequate downstream clearance for maintenance. Regular inspection and testing are advised to ensure reliable operation. In potable water systems, additional backflow prevention measures may be required by local codes to prevent contamination.