Abstract: A liquid overfill protection system uses an arrangement for delivering a fluid, such as air, to first and second outlets with a pressure difference that is indicative of the extent to which the tank has been filled with liquid. The system includes a control arrangement for closing a valve when the difference in fluid pressure between the first and second outlets exceeds a predetermined level. In this manner, liquid flow into the tank may be blocked when the tank has been filled to a desired extent. In a preferred embodiment, a diaphragm mounted in the valve assembly is used to trigger release of the valve into a closed position when a sufficient pressure differential exists.