A check valve is a backflow prevention device, designed to control direction of flow and protect against contamination. It will allow a fluid (liquid or gas) to flow through it in one direction only, automatically preventing flow in the other direction.
Reverse flow can be harmful to some components in a system, such as flowmeters, strainers and control valves. In sanitary and manufacturing applications, backflow can cause problems with water or product quality.
Check valves can support a number of different mediums such as water, air, other gases, steam and in some cases liquids with fine particles and slurries. Typical applications for Check Valves include Water, HVAC, Pump Systems, Steam Lines, Injector Lines, Oil & Gas, Shipbuilding, Pharmaceuticals and Manufacturing.
Types of Check Valves
The most common and oldest type of Check Valve is the Swing Check Valve. This uses a disc to block the or allow flow by swinging on a hinge either away from the seat to allow flow or the flow pushes the disc against the seat to block further flow. A Spring Check Valve works in a similar fashion, except the disc sits on a spring which will open when the flow is sufficient enough to compress the spring and thus open the valve.
Other types include Ball Check Valves and Diaphragm Check Valves. Ball check valves use a ball as a moveable part to either block or allow flow depending on the direction, whereas diaphragm check vales use a flexible rubber disc instead. Lift Check Valves are similar to swing check valves, except a disc is lifted up with the flow instead of swinging open.
Check valves are often used on pumps systems to prevent the discharging liquid returning to the original source should the pump fail. Check valves can also be used when multiple mediums are mixed into one stream. In this instance, a check valve will be installed on each of the incoming streams to prevent mixing of the original sources.
Check valves will always be provided with an arrow on the side. This dictates the expected flow of the medium and therefore should always be placed with the direction of flow to ensure that the check valve works as expected.
You must also check how the valve operates and how this might affect other components nearby. Some check valves have components which extend outside of the valve when fully open, which could affect the performance of nearby components.
Furthermore, turbulence generated by other components can interfere with the performance of a check valve. For this reason, sufficient distance should be allowed between check valves and other components.
Whilst check valves can shut off reverse flow, they are not suitable to used in place of an isolation valve.