What pressure measurement is crucial when assessing hydrant performance while in use?

When assessing hydrant performance while in use, the measurement of residual pressure is crucial. Residual pressure refers to the pressure that remains in the system after water is flowing through the hydrant. This measurement is essential for determining the availability of water for firefighting purposes.

In a firefighting context, understanding residual pressure helps firefighters gauge how much pressure is available to effectively fight a fire. If the residual pressure is too low, it indicates that the flow of water may be insufficient to meet the fire's demands. This can occur if multiple hydrants are opened simultaneously or if there are obstructions or limitations in the water supply system.

Static pressure, while important in the overall assessment of hydrant capabilities, does not provide insight into how much pressure is available while water is being drawn. Flow pressure is focused on the pressure at the point of flow but does not account for how much water can still be supplied once a demand is placed on the system. Input pressure typically relates to the pressure being supplied to the system, which is not directly useful for assessing the hydrant's operational performance during active use.