Manifold Pressure is typically expressed in which unit?

Manifold Pressure is typically expressed in which unit?

• A. Inches of mercury
• B. Pounds per square inch
• C. Kilopascals
• D. Bars

Answer: (A)

Manifold pressure gauges reflect the absolute pressure inside the intake manifold, which indicates engine load. In small aircraft piston engines, this pressure is traditionally expressed in inches of mercury (inHg). This unit comes from the historical use of mercury barometers and provides a convenient range for the readings you see on the gauge—roughly from vacuum up toward ambient pressure. Higher manifold pressure means the throttle is open more and the engine is drawing more air, while lower readings indicate a larger vacuum in the manifold. Other units like pounds per square inch, kilopascals, or bars are not the standard display for this instrument in general aviation, even though they measure the same physical quantity.

Manifold pressure gauges reflect the absolute pressure inside the intake manifold, which indicates engine load. In small aircraft piston engines, this pressure is traditionally expressed in inches of mercury (inHg). This unit comes from the historical use of mercury barometers and provides a convenient range for the readings you see on the gauge—roughly from vacuum up toward ambient pressure. Higher manifold pressure means the throttle is open more and the engine is drawing more air, while lower readings indicate a larger vacuum in the manifold. Other units like pounds per square inch, kilopascals, or bars are not the standard display for this instrument in general aviation, even though they measure the same physical quantity.