What device is used to control pressure surges by adjusting engine speed based on flow changes?

The pressure governor is the correct choice because it is responsible for managing and maintaining consistent water pressure in a fire apparatus during operation by automatically adjusting the engine speed in response to changes in water flow. When firefighters open or close nozzles, the flow of water changes, which can lead to pressure surges or drops. The pressure governor detects these changes and adjusts the engine's RPM accordingly, ensuring that the pressure remains stable, which is crucial for effective firefighting operations.

While the flow regulator also plays a role in managing water flow, it doesn't necessarily adjust engine speed to control pressure. The throttle controller regulates the engine's throttle position but may not directly respond to pressure changes in the same automated way that a pressure governor does. A flow meter measures the amount of water flow but does not actively manage pressure or adjust engine speed. Therefore, the pressure governor stands out as the specific device designed to maintain proper pressure by adjusting engine speed based on flow changes.