Which instrument is used to measure pressure drop across an inlet restriction?

• A. Manometer
• B. Dial indicator
• C. Vernier caliper
• D. Thermometer

Answer: (A)

Measuring pressure drop across an inlet restriction requires comparing the pressure on two points in the flow. A manometer uses a column of liquid to balance these pressures. When there’s a difference between upstream and downstream pressures, the liquid moves in the U-tube, and the height difference translates directly to the pressure difference, usually read in inches of water or pascals. This makes it ideal for detecting how severely an inlet is restricting flow, which is exactly what pressure drop measures.

Devices like a dial indicator, vernier caliper, or thermometer do not measure pressure. A dial indicator measures tiny mechanical displacements, a vernier caliper measures dimensions, and a thermometer measures temperature. They don’t provide a direct reading of pressure drop across a restriction.