What is the role of motive flow in the operation of jet pumps?

The role of motive flow in the operation of jet pumps is primarily provided by fuel from engine driven pumps. In jet pump systems, motive flow is the high-velocity fuel that creates a pressure differential, which allows fuel to be drawn from a lower pressure area into the jet pump. This process is crucial for the efficient operation of the fuel system in a jet engine, as it helps to ensure proper fuel delivery to different components as needed.

This flow is not generated by the auxiliary fuel system, nor is it controlled directly by the pilot’s throttle input. While the throttle input can affect the engine’s overall performance, the motive flow itself operates predominantly through the engine driven pumps that maintain adequate fuel pressure to sustain jet pump functionality. Additionally, motive flow is not limited to engine starts; it is an ongoing requirement for the continual operation of the fuel system as the engine runs, especially during various phases of flight.