How did James Watt's flyball governor regulate the speed of a steam engine?

James Watt’s flyball governor is a classic example of a negative feedback control system used to maintain a constant engine speed despite varying loads.12

The device functions through the following mechanical process:

• Connection: The governor consists of a pair of weighted balls attached to a vertical spindle by hinged arms, which is mechanically coupled to the engine's output shaft.32
• Centrifugal Action: As the engine's rotational speed increases, centrifugal force causes the weighted balls to move outward.32
• Regulation: This outward movement is transmitted to a valve that regulates the supply of steam to the engine. As the balls move outward, the valve closes to reduce the steam flow, thereby slowing the engine.32
• Correction: Conversely, if the engine load increases and the speed drops, the balls move inward, allowing the valve to open and increase steam flow to restore the desired speed.3

By using the system's output to automatically adjust its input, the governor eliminated the need for manual human intervention to regulate steam engine speed.12