What term is used for the pressure that remains in the system when water is flowing?

The term that refers to the pressure remaining in the system while water is flowing is "residual pressure." This pressure measurement is essential because it indicates the amount of pressure available to deliver water to the sprinkler heads during operation.

Residual pressure is particularly significant in fire protection systems, as it helps determine whether the system can deliver adequate water flow to the designated fire suppression areas. It reflects the pressure present after accounting for losses due to friction and other factors as the water moves through the piping.

Understanding residual pressure allows system designers and assessors to ensure that a fire sprinkler system can function effectively under actual conditions of flow, which is critical for safety and compliance with the NFPA standards. The other terms, while related to pressure in different contexts, do not specifically denote this scenario of pressure during water flow.