Simply, the Non-return function for a valve is to prevent the fluid from backflow. Such function valves is called check valve commonly. Basically, Non-return or check valves control the direction of flow. Flow in the desired direction opens the valve, while flow in the opposite direction forces the valve closed, So it is also call one-way valve or Reflux valve.

Check valves generally are very small, simple, and inexpensive, they work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. These valves are important for preventing backflow to systems in applications such as wastewater management and in process systems that have varying pressures and must be kept separate.

Flanged Swing Check Valve

Non Return Swing-Check Valve

Wafer Check Valve