At what rate should a hydrant or valve be opened to prevent water hammer?

To prevent water hammer, which is a shock wave caused by the sudden stopping or changing of water flow, it is important to open a hydrant or valve at a controlled and gradual rate. Opening the valve at a rate of 1/4 turn per second is optimal because it helps to maintain a steady flow of water, allowing the pressure within the system to stabilize as the flow increases.

When valves are opened too quickly, it can lead to rapid changes in pressure within the piping system, resulting in water hammer, which can cause damage to pipes and fittings. A rate of 1/4 turn per second strikes a balance between efficiency and caution, enabling operators to effectively manage pressure fluctuations and enhance the longevity of the water distribution system.

Slower rates, such as 1/8 turn per second, may be overly cautious and inefficient for regular operation, while faster rates, such as 1/2 turn or 1 turn per second, increase the risk of pressure surges that contribute to water hammer incidents. Thus, the recommended rate of 1/4 turn per second effectively mitigates the risk of water hammer while allowing for smooth operation of the hydrant or valve.