What does the overspeed governor in a hydromechanical fuel pump primarily sense?

The overspeed governor in a hydromechanical fuel pump primarily senses RPM (revolutions per minute) because its primary function is to monitor the rotational speed of the engine or turbine and prevent excessive speeds that could lead to mechanical failure. When the RPM exceeds a predetermined limit, the overspeed governor acts by reducing fuel flow to the engine, effectively limiting the speed and ensuring safe operation.

This device operates by using a mechanical linkage or electronic system that monitors the speed of the rotor or other components within the fuel pump system. If the rpm rises above acceptable levels, the governor will intervene to maintain control and prevent overspeed conditions, which could potentially damage engine components. Thus, the focus of the overspeed governor is specifically on RPM, making it the correct choice.