Check valves are flow sensitive and rely on the line fluid to open and close. The
internal disc allows flow to pass forward, which opens the valve. The disc begins
closing the valve as forward flow decreases or is reversed, depending on the design.
The function or purpose of a check valve is to prevent reverse flow. Construction is
normally simple with only a few components such as the body, seat, disc, and cover.
Depending on design, there may be other items such as a stem, hinge pin, disc arm,
spring, ball, elastomers, and bearings