Which instrument is best used to measure air inlet restrictions?

• A. Water manometer
• B. Differential pressure sensor
• C. Thermometer
• D. Barometer

Answer: (A)

Measuring air inlet restrictions hinges on detecting the pressure drop across the inlet. The water manometer provides a direct readout of this differential pressure: the height difference of the water column translates straight into pressure using the hydrostatic equation. For the typically small pressure changes associated with air inlet restrictions, a manometer offers high sensitivity, simplicity, and a clear, immediate measurement without needing power or complex electronics. That direct measurement of the pressure difference across the inlet is exactly what you need to evaluate how restricted the inlet is.

A thermometer only measures temperature, which doesn’t tell you anything about pressure or flow restriction. A barometer measures atmospheric pressure at one location, not the pressure difference across the inlet. A differential pressure sensor can measure pressure differences and is common in modern setups, but the water manometer remains the straightforward, dependable method for obtaining a clear, direct reading of the restriction-induced drop, especially in basic testing or educational contexts.