FAA Powerplant Written Practice Test

What feature of pressure injection carburetors distinguishes them from float-type models?

1. Use of multiple fuel tanks

2. Absence of a float chamber

3. Regulation through mechanical valves

4. Use of electronic control systems

The correct answer is: Absence of a float chamber

Pressure injection carburetors are specifically designed to deliver fuel under pressure, which eliminates the need for a float chamber that is characteristic of float-type carburetors. In a float-type carburetor, fuel is drawn into the float chamber where a float mechanism maintains a certain level of fuel, allowing for the regulation of fuel flow through various openings. In contrast, pressure injection carburetors operate by using a pump to inject fuel directly into the air stream, relying on pressure rather than gravity to facilitate the fuel delivery process. This design allows for more precise control over the amount of fuel introduced into the engine, enhancing performance, especially in high-demand situations such as during takeoff. The absence of a float chamber in pressure injection carburetors contributes to their ability to function effectively across a wider range of conditions, including higher altitudes where float operation may be less effective. The other options, while they may relate to different types of systems or components in aviation, do not define the fundamental distinction between pressure injection and float-type carburetors.