Image Number 2 for United States Patent #8162619.
A system for controlling the pressure output of an engine-driven centrifugal fire pump includes a discharge pressure sensor mounted in the discharge line of the pump. A governor varies the rpms of the engine in response to pressure changes detected by the discharge pressure sensor. If the pressure in the system is higher than the desired output pressure when the engine is running at its idle speed an electronically controlled hydraulic relief valve responsive to the discharge pressure sensor operates to relieve the excess pressure in over pressure situations. If the pressure in the system is lower than the desired output pressure when the relief valve is fully closed, the engine speed is increased.