What is the term for the part of the total available pressure not used to overcome friction loss or gravity?

The term that refers to the portion of the total available pressure that is not utilized for overcoming friction loss or gravity is known as residual pressure. This concept is essential in firefighting and water supply management, as it provides insight into the pressure available for effective firefighting operations after accounting for the pressure losses that occur within hoses, nozzles, and other components of the system.

In practical terms, when water is flowing through a fire hose, some of the available pressure is diminished due to friction between the water and the hose inner surface, as well as any elevation changes that occur. The leftover pressure, which can still be delivered to the firefighters at the nozzle, is referred to as residual pressure. It indicates how much pressure is available for effective firefighting once these losses are accounted for.

Understanding this concept is critical for fire captains and firefighters to ensure that they can effectively manage water supply and maintain adequate pressure at the nozzle, especially in high-demand situations. Knowing the residual pressure allows firefighters to make informed decisions about their operational tactics and resource allocation.