3. Valves

3.1 Check valves (CNR)

The role of dampers is generally to perform one or more of the following functions:

• allow fluid to flow in one direction, with minimum pressure drop;

• prevent fluid from flowing in the opposite direction;

• provide a seal against fluid backflow (e.g. a check valve to prevent a centrifugal pump mounted on the suction or discharge side of a stationary pump arranged in parallel with another pump at low flow, and itself fitted with a CNR on the discharge side to prevent "ducking").

We distinguish :

• linear displacement dampers (diagram 1, figure