Why must a dry barrel hydrant be completely opened when operating?

A dry barrel hydrant must be completely opened during operation primarily to maximize flow from the hydrant. When the hydrant is fully opened, the valve allows the maximum amount of water to flow through, facilitating efficient firefighting efforts or any other need for water. If the hydrant is only partially opened, it could restrict the water flow, reducing the effectiveness of using the hydrant in an emergency situation.

Additionally, completely opening the hydrant ensures that the water flow is at optimal pressure, which is critical during firefighting operations. Maintaining the right flow and pressure is essential for achieving the desired reach and force of water, which can make a significant difference in controlling a blaze. While other considerations, such as conservation of water or minimizing noise, might be of some relevance, they are secondary to the primary function of ensuring adequate flow during critical operations.