The pressure remaining when water has begun flowing is known as what pressure?

• A. Residual
• B. Static
• C. Dynamic
• D. Atmospheric

Answer: (A)

When water is not moving, the pressure you read in the system is called static pressure. Once you open a valve or hydrant and water starts to flow, energy is consumed overcoming friction and creating velocity. The pressure that remains in the line during that flowing condition—the pressure you’d read on a gauge while flow is ongoing—is known as residual pressure. It’s typically lower than the static pressure because part of the system’s energy has been spent pushing water through the pipe. Dynamic pressure relates to the velocity of the moving water, and atmospheric pressure is outside the piping system, so neither describes the pressure remaining during flow.