Abstract: A level indicator comprises a tubular probe immersed in the liquid to a depth defining the minimum liquid level in the reservoir. The probe communicates with a gas-filled chamber with a heating resistor therein. A warning member is connected to the gas-filled chamber to indicate that the level of the liquid reaches a minimum as indicated by no pressure increase occurring in said chamber.

Abstract: A level indicator for monitoring liquid contained in a reservoir. The indicator comprises a tubular probe which has one end immersed in the liquid and the other end connected to an inlet orifice to a gas-filled chamber in a housing. The gas-filled chamber is connected to a liquid column manometer and an external gas reserve. A valve is located in the inlet orifice to control communication between the gas filled chamber and the probe. A venting duct controls the development of a pressure drop in the gas-filled chamber to establish a permanent connection between the gas reserve and probe irrespective of the position occupied by the valve.