A pitot tube and gauge are used to:

• A. Measure gallonage
• B. Take residual pressure reading
• C. Take a flow reading
• D. Measure pressure loss

Answer: (C)

A pitot tube with a gauge is used to determine air flow by measuring velocity pressure. The tube faces the moving air to capture stagnation pressure and compares it to static pressure, giving you the velocity pressure. From that, you derive the air speed, and when you multiply that speed by the duct’s cross-sectional area you get the flow rate (typically in terms of CFM). This is why it’s used to take a flow reading. It doesn’t directly measure gallons, it doesn’t give residual system pressure, and it isn’t a direct measure of pressure loss across components.