A valve assembly, such as a tap for a liquefied gas cylinder, includes an overfill protection device and a liquid level gauge having an electrode assembly comprising a pair of lamellar electrodes mounted closely adjacent a housing member of the overfill protection device and deflectable into close proximity with a float of the overfill protection device for insertion into the gas cylinder. A circuit board is provided, preferably mounted on the electrode assembly, and has an electronic converter circuit for measuring the electrical capacitance between the electrodes and producing in response to the measured capacitance an output signal representative of the liquid level in the container. A display means is mounted on a body of the valve assembly or remote therefrom, to indicate the liquid level in the container in response to the output signal from the electronic converter circuit.