Which instrument measures flow pressure at the opening of a smooth bore orifice?

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

Answer: (B)

At the opening of a smooth bore nozzle you want the energy in motion of the water, i.e., the velocity (flow) pressure. A Pitot tube is designed to face into the flow and capture the stagnation (total) pressure from the moving water. From that stagnation pressure, you can determine the velocity pressure and, with the nozzle size, convert that to discharge. This makes the Pitot tube the tool that directly measures the flow pressure at the nozzle opening.

The other instruments aren’t suited for this specific measurement: a Venturi meter relies on a pressure difference across a constriction to infer flow, not the pressure at the nozzle opening; a compound gauge measures static pressure and another pressure range (often vacuum) but not the dynamic flow pressure of the moving stream; a by-pass meter diverts part of the flow through a separate measuring path, which isn’t the direct measurement at the nozzle opening.