Abstract: An automatic operating system for a pump driven by an internal combustion engine is disclosed in which the engine is kept in operation at a low and economical speed automatically disconnecting the pump from the engine when delivery pressure from the pump is not required and connecting the pump automatically when delivery pressure from the pump is required. Such automatic control is effected by a valve block in which a safety valve is incorporated, the movement of the valve body of which is utilized to control the connection and disconnection of the pump, the movement of the valve body being dependent on the pressure in the discharge line of the pump.