When the maximum amount of water is flowing, what is the residual pressure?

The concept of residual pressure in a firefighting context refers to the pressure remaining in the system after water is flowing, particularly when a large amount of water is being discharged through hoses or nozzles. When water is flowing at maximum capacity, the system experiences increased demand, and the pressure can drop significantly due to the effects of friction loss in the hoses and fittings, as well as the impact of the flow on the water supply.

In a firefighting scenario, particularly when working with large diameter hoses or multiple lines, the pressure at the source (such as a fire hydrant or water tank) can indeed be affected to the point where the residual pressure becomes very low, and in some situations, it can approach zero. This drop in pressure occurs because the flow rate surpasses the delivery capability of the water supply, leading to inadequate pressure to maintain proper flow rates.

Thus, when evaluating the situation where the maximum amount of water is flowing, it is accurate to determine that the residual pressure can reach zero, indicating that the system is unable to maintain any pressure under those conditions. This understanding is crucial for firefighters to ensure they manage water supplies effectively during operations.