A measure of the available line pressure prior to flowing the hydrant is __________

Static pressure is defined as the pressure in the water system when water is not flowing, providing a measurement of the available line pressure at rest. This pressure represents the potential energy of the water in the system and is crucial for understanding how much pressure is available to push water through the system when needed.

In the context of fire hydrants, measuring the static pressure allows contractors to evaluate the water supply's capability before any demand is placed on it—such as when a hydrant is opened and water starts to flow. This baseline measurement is a critical component in planning and designing effective sprinkler systems, ensuring that adequate pressure is available to deliver water for fire suppression when needed.

The other terms have distinct meanings: residual pressure refers to the pressure remaining in the system when water is flowing, flow pressure is the pressure measured while water is being discharged from a hydrant or sprinkler system, and relief pressure deals with pressure management in systems equipped with pressure relief valves. Each of these plays a role in the broader context of fire protection engineering, but only static pressure reflects the available line pressure under non-flow conditions.