What is the residual pressure in a water flow test using two hydrants?

In a water flow test using two hydrants, the residual pressure refers to the pressure that remains in the water supply system when water is flowing from the hydrants. This pressure is crucial for understanding the effectiveness of the water supply, especially in fire protection systems, as it indicates how much pressure is available once the flow has started.

When conducting flow tests, the residual pressure is measured alongside the static pressure (the pressure without flow) and the dynamic pressure (the pressure with flow). Specifically, the residual pressure is the pressure retained at the hydrant not being used for flow measurement, while the other hydrant is allowing water to flow. Assessing this pressure helps in evaluating the performance of the water supply under operational conditions and ensures that adequate pressure is available for firefighting and sprinkler systems.

Understanding residual pressure is essential for system design and for ensuring that fire protection systems will function properly in case of an emergency.