A valve assembly (10), such as a tap for a liquefied gas cylinder, is disclosed having an overfill protection device (12) and a liquid level gauge (14) having an electrode assembly comprising a pair of lamellar electrodes mounted closely adjacent a housing member (28) of the overfill protection device and deflectable into close proximity with a float (30) of the overfill protection device for insertion into the gas cylinder (16). A circuit board (42) 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 (44) 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.