How is the pressure expressed when measuring flow from a hydrant under static conditions?

When measuring flow from a hydrant under static conditions, pressure is expressed as gauge pressure. This is because gauge pressure measures the pressure relative to atmospheric pressure, which is important in evaluating the potential for water flow from a hydrant. Under static conditions, the pressure reading obtained does not include atmospheric pressure, providing a clear indication of the water pressure available in the system. This is the most relevant form of pressure measurement for fire hydrant flow tests because it reflects the pressure that can be used to generate flow without the interference of additional atmospheric values.

In the context of fire protection systems, understanding gauge pressure is critical. It allows for proper calculations related to the performance of the water supply, ensuring that sufficient pressure is available for firefighting purposes.

Absolute pressure, while also a valid form of pressure measurement, differs in that it takes atmospheric pressure into account. This makes it less applicable in this specific context where gauge pressure gives a more straightforward understanding of available pressure for water flow.

Hydrostatic pressure generally refers to the pressure exerted by a fluid at equilibrium due to the force of gravity, often seen in scenarios involving depth measurements of a fluid, which is not the focus when measuring flow from hydrants.

Residual pressure refers to the pressure in the system while water