To prevent water hammer, how should valves, nozzles, and hydrants be closed?

Closing valves, nozzles, and hydrants slowly is essential to prevent water hammer, a phenomenon characterized by a pressure surge when the flow of water is suddenly stopped or changed direction. When these components are closed quickly or forcefully, it creates a rapid change in water velocity and can cause a shock wave within the piping system. This shock wave results in significant pressure surges, potentially leading to damage in the water supply system, including ruptured pipes, fittings, or connections.

By closing them slowly, operators allow the water flow to decrease gradually, which mitigates the abrupt pressure changes and reduces the risk of water hammer. This practice not only protects the integrity of the infrastructure but also enhances the overall safety and reliability of the firefighting water supply system.