How does a check valve work

A check valve is designed to allow flow in one direction only. During forward flow, the valve disc should be open, and during reverse flow, it should close the passage.

In all types of check valves, opening occurs due to the pressure difference on the disc, and closing occurs:

• due to gravity force for valves with massive discs and lever-weight mechanisms
• due to spring force in spring-loaded check valves
• due to reverse pressure difference on the disc.

During forward flow, the pressure in the inlet port of the valve exceeds the pressure in the outlet port, and the disc, under the action of the pressure difference, is displaced, lifted, or rotated opening the passage for the flow.

During reverse flow, the pressure in the outlet port exceeds the pressure in the inlet port, and the higher the pressure difference, the stronger the disc is pressed against the seat, closing the passage.

The operation of a check valve does not require external sources of energy, so it is a protective direct-acting fitting.

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