What is the primary function of the manual primer in an aircraft?

The primary function of the manual primer in an aircraft is to assist in starting the engine. The manual primer achieves this by drawing fuel from the fuel system and priming the engine's cylinders with a rich fuel-air mixture, which is essential during the initial start-up phase. This ensures that there is enough fuel available for combustion, making it easier to start the engine, especially in cold conditions or after the aircraft has been sitting for a while.

The other functions listed are not accurate representations of what the manual primer does. While fuel pressure and flow management are important in the overall fuel system of an aircraft, these are typically managed by other components such as fuel pumps and regulators. Similarly, filtering out fuel impurities is handled by fuel filters, not the primer. Thus, focusing on the role of the manual primer highlights its critical importance in facilitating engine starts efficiently.