What Is a Check Valve?
A check valve, also called a non-return valve or one-way valve, allows a fluid to flow in one direction only and prevents it from flowing back. By stopping reverse flow, it protects pumps, compressors and other equipment from damage and helps the system operate efficiently and safely. In many cases a check valve can replace more complex arrangements of fittings.
Working Principle
Check valves operate automatically on the pressure difference across the valve. When the upstream (inlet) pressure is higher than the downstream (outlet) pressure, the closing element, a disc, flap, ball or piston, is pushed open and the medium flows through. When the flow stops or the downstream pressure becomes higher, the closing element returns to its seat, either by gravity, by a spring or by the reverse flow itself, and blocks the passage.
Check Valve Types
- Swing check valve: a hinged disc swings open with the flow and closes under its own weight; long-lasting and simple, widely used on pump systems.
- Spring-loaded check valve: a compression spring closes the valve quickly; suitable for vertical installation, as gravity and back pressure do not affect its operation.
- Dual plate (double flap) check valve: two spring-loaded plates close automatically; lightweight and compact, used at pump outlets and in refinery, petrochemical, gas and water systems.
- Disc check valve: a compact disc design for liquids, gases and steam.
- Wafer check valve: installed between two flanges; commonly used in fire-fighting and HVAC systems.
- Flanged check valve: for high-flow lines, pressure tanks and pump discharge points.
- Threaded check valve: for smaller lines with threaded connections.
- Fire check valve: prevents reverse water flow in fire-fighting systems and can also serve as an alarm valve at fire pump filling ports.
- Stainless steel check valve: for corrosive media.
Technical Range
Luna Flow Control supplies check valves in steel, stainless steel, bronze, aluminium, plastic and other materials, with flanged, SW/BW or threaded connections. The range covers DN 50 – 1200 (½″ – 32″), pressure ratings from PN 6 – 320 and CL150 – CL2500 (150LB – 2500LB), and operating temperatures from -50 °C to +560 °C.
Application Areas
- Pump discharge lines and booster systems
- Fire-fighting installations
- Refineries, petrochemical and gas systems
- Water supply and wastewater networks
- Steam lines, cooling and HVAC systems
- Heating and irrigation systems
Advantages
- Automatic operation without external power or an operator
- Protects pumps and equipment from backflow
- Prevents contamination of the medium by reverse flow
- Available for a wide range of media, including liquids, gases and steam
Selection Tips
When choosing a check valve, consider the installation orientation, the flow rate, the risk of water hammer and the properties of the medium. Spring-loaded and dual plate designs close quickly and are well suited to vertical lines and pump outlets, while swing check valves offer low pressure loss in horizontal lines. Always confirm that the pressure rating and temperature range match the operating conditions of the system.
