After testing, why should hydrants be shut down slowly?

Shutting down hydrants slowly is essential primarily to prevent surges in pressure within the water distribution system. When a hydrant is closed rapidly, it can create a sudden change in water flow velocity, leading to pressure fluctuations. These surges can cause water hammer effects, where pressure waves travel through the system and can potentially damage pipes, fittings, and other components. By shutting down the hydrant slowly, the flow can be gradually reduced, allowing the pressure to stabilize and minimizing the risk of damage caused by these pressure surges. This practice ensures the integrity of the entire water system and promotes overall safety and reliability.