What is the purpose of a check valve?

What is the purpose of a check valve is to allow flow of fluid in one direction only and automatically prevent reverse flow or backflow, protecting equipment, maintaining prime, and preventing contamination without manual operation. In plumbing and pumping systems, check valve purpose includes preventing water from flowing backward when pump stops, which keeps pump primed so it does not need to be re-primed each time, important for well pumps and sump pumps. It prevents contaminated water from flowing back into clean water supply, protecting potable water from chemicals, sewage, or irrigation water, though for health hazard applications code requires more robust backflow preventer with multiple checks. It prevents water hammer damage by stopping reverse flow that could cause pressure surge, and prevents flooded basements by ensuring sump discharge does not flow back into pit. In heating systems, check valve prevents thermosiphoning and keeps hot water from migrating to cold lines. In sewage systems, check valve prevents sewage backup into home. Check valve operates automatically, with flap, ball, or spring loaded disc that opens with forward pressure and closes when pressure reverses, requiring no manual intervention. Overall purpose is to ensure one way flow, protect pumps, prevent contamination, and maintain system efficiency and safety in water, gas, and industrial fluid systems.