The valve used for the prevention of reversal of flow in a pipeline is a Check valve.

Check Valves, also known as Non-Return Valves (NRV) are self-activating safety valves that permit gases and liquids to flow in only one direction, thus preventing process flow from reversing.

When open and underflow pressure, the checking mechanism will move freely in the medium, offering very little resistance and minimal pressure drop. Check valves are classified as one-way directional valves; fluid flow in the desired direction opens the valve, while backflow forces the valve to close. A check valve is hence a unidirectional valve for fluid flow.

Some of the advantages of the Check valve is 

(I) Protection of equipment due to reverse flow.

(ii) Prevention of reverse flow in the system during system shutdown

(iii) Prevention of backflow under gravity