The device that can be used to determine flow pressure at the opening of a smooth bore orifice is a:

• A. Venturi meter
• B. Pitot tube
• C. By-pass meter
• D. Compound gauge

Answer: (A)

A Pitot tube is used to determine flow pressure at the opening of a smooth bore orifice. It measures stagnation (total) pressure when placed facing the flow, and by comparing this with a static pressure reading you obtain the velocity pressure. From the velocity pressure you can compute the water velocity (v = sqrt(2 ΔP / ρ)) and then the flow through the nozzle (Q = v × A, with the appropriate discharge coefficient). A Venturi meter relies on a pressure drop across a constriction to infer flow and isn’t a direct single-point pressure measurement at the nozzle opening. A by-pass meter and a compound gauge don’t provide this direct flow-pressure-at-the-nozzle information.