Check Valves / Non-Return Valves

swing type check valve with counter weight

A check valves is a valve designed to automatically permit flow in one direction while preventing reverse flow in the opposite direction. Check valves, which can also be called non-return valves, are typically used in suction lines of pumps to keep pumps primed or in discharge lines to prevent reverse flow, which can cause serious damage for pumps, motors and other system components. In other words, the basic function of check valves (NRV) is to protect mechanical components in a piping system by preventing fluid from moving the wrong direction.

Since check valves automatically open with forward flow and close against back flow, it required a moving element. The moving element, which can be a disc or a diffuser or a plunger, normally rests on the seat to form a seal. In some types, springs are used to control the opening and closing and in others, the check valves rely on gravity.

For gravity-powered swing type check valves, the force needed to keep the valve open increases as the valve opens. If the balance between disc mass and fluid-dynamic forces is not achieved the valve will open partially only which can lead to premature damage of the check valve. On the other hand, increased fluid velocities can lead to unexpected wear or erosion damage. Therefore selecting the right NRV type and design that matching your system operating conditions is crucial to achieve durability and to avoid unnecessarily shutdown and/or damages.