The acceptable difference between measured flow and pitot readings is commonly no more than:

The acceptable difference between measured flow and pitot readings is commonly no more than:

• A. 10%
• B. 5%
• C. 15%
• D. 20%

Answer: (A)

When you compare a measured flow to what the pitot-derived calculation says, you’re looking at accuracy and tolerance in flow verification. A pitot tube measures velocity pressure; by knowing the pipe cross-sectional area, you convert that velocity to a flow rate. Real systems, however, have several sources of variation—turbulent flow around fittings, nonuniform velocity profiles, calibration drift, and instrumentation limits. All of these cause small differences between the actual flow and the flow you’d calculate from the pitot reading. Because of these practical uncertainties, a commonly accepted tolerance is about 10%. That means if your target flow is, say, 1000 gpm, readings within ±10% (roughly 900–1100 gpm) are considered acceptable. A tighter tolerance (like 5%) would be hard to achieve in field conditions, while looser tolerances (15–20%) could hide meaningful discrepancies. This 10% range provides a practical balance, ensuring reliable verification without demanding impossible precision.

When you compare a measured flow to what the pitot-derived calculation says, you’re looking at accuracy and tolerance in flow verification. A pitot tube measures velocity pressure; by knowing the pipe cross-sectional area, you convert that velocity to a flow rate. Real systems, however, have several sources of variation—turbulent flow around fittings, nonuniform velocity profiles, calibration drift, and instrumentation limits. All of these cause small differences between the actual flow and the flow you’d calculate from the pitot reading. Because of these practical uncertainties, a commonly accepted tolerance is about 10%. That means if your target flow is, say, 1000 gpm, readings within ±10% (roughly 900–1100 gpm) are considered acceptable. A tighter tolerance (like 5%) would be hard to achieve in field conditions, while looser tolerances (15–20%) could hide meaningful discrepancies. This 10% range provides a practical balance, ensuring reliable verification without demanding impossible precision.