Side-by-Side Comparison of Swing Check Valves and Resulting Mechanical Shock Caused by Reverse Flow

Swing check valve mechanical shock (slam) is caused by the sudden build-up of reverse flow after a pump has stopped, being followed by the sudden stoppage of that reverse flow by the check valve. The faster the check valve closes the less reverse flow, and hence the smaller slam. This video (courtesy of Val-Matic) demonstrates this phenomenon  under real operating conditions.

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