What is the function of the aneroid capsule in a supercharged engine?

• A. It senses ambient temperature to adjust fuel.
• B. It controls the position of the throttle butterfly to maintain MAP.
• C. It measures exhaust gas pressure.
• D. It indicates altitude to the pilot but does not affect throttle.

Answer: (B)

An aneroid capsule in a supercharged engine is a pressure-sensing device that responds to ambient air pressure and uses that information to regulate the throttle, keeping the manifold pressure (MAP) at a set value as altitude changes. As you climb and ambient pressure falls, the capsule expands or contracts and moves the throttle linkage so the throttle opens appropriately to maintain the desired MAP. This automatic adjustment is essential because the booster (supercharger) can raise intake pressure, but without compensating for lower ambient pressure at altitude, MAP would drop. The other options don’t fit the function: it doesn’t sense ambient temperature to adjust fuel, it doesn’t measure exhaust gas pressure, and it isn’t merely an altitude indicator to the pilot without influencing throttle.