Which statement about residual pressure is true?

Which statement about residual pressure is true?

• A. Residual pressure is the pressure when water is flowing.
• B. Residual pressure is the pressure with no flow.
• C. Residual pressure is the maximum pressure during testing.
• D. Residual pressure is the pressure in the air line.

Answer: (A)

Residual pressure is the pressure in the water-based system while water is flowing. This matters because it shows how much pressure remains once the flow has started, accounting for friction losses in pipes, fittings, and elevation as water moves through the system. It’s different from static pressure, which is the pressure when no water is moving. The other statements describe conditions not related to residual pressure—static pressure (no flow), maximum pressure during testing (not the same as pressure under flow), and air-line pressure (a separate air-side measurement).

Residual pressure is the pressure in the water-based system while water is flowing. This matters because it shows how much pressure remains once the flow has started, accounting for friction losses in pipes, fittings, and elevation as water moves through the system. It’s different from static pressure, which is the pressure when no water is moving. The other statements describe conditions not related to residual pressure—static pressure (no flow), maximum pressure during testing (not the same as pressure under flow), and air-line pressure (a separate air-side measurement).