Abstract: An overfill preventing device in an underground liquid storage tank is characterized in that a window for extending outwardly or accommodating a float is provided on a peripheral wall of a cylindrical sleeve, that an upper end of the float is pivotally attached to the cylindrical sleeve at a position above the window, and that a closure valve is mounted on the upper end of the float to open or close the cylindrical sleeve at a position above the window. Since the window for extending the float outwardly or accommodating the float inwardly is formed inside the cylindrical sleeve, the float can be firmly stored. When the float is extended outwardly from the cylindrical sleeve after installing the device of the present invention, the window is closed by a lid and the lid forms a part of the cylindrical sleeve so that construction of the space within the cylindrical sleeve necessary for liquid flow is minimized, whereby liquid is smoothly supplied into the underground liquid storage tank.

Abstract: A lock system which prevents the mixing of different kinds of oil at a gasoline tank comprises: locks for different kinds of oils provided on each of couplings constituting oil filler ports of underground tanks of the gasoline stand and each of tank base valves of a tank truck, and keys separately provided for unlocking the locks for the different kinds of oil, wherein only the lock on the couplings of the oil filler ports which accepts a selected key which unlocks the corresponding tank base valve of the tank truck can be unlocked. When one of the tank base valves is opened and an oil filler hose is connected to the oil filler port of one of the underground tanks, only the oil filler port of the underground tank containing the same kind of oil as that in the corresponding tank of the tank truck can be opened, thereby ensuring that the same kind of oil is reliably poured into the underground tank from the tank truck.

Abstract: This invention provides an oil-feeding coupling consisting of male and female coupling members capable of being engaged with each other only when predetermined portions thereof are opposed to each other, a guide ring fitted around the male coupling member and adapted to set an engaging position thereof in accordance with the kind of an oil to be fed to an underground tank, and positioning portions formed in the female coupling member so as to engage the guide ring therewith, whereby the male and female coupling members can be engaged with each other only when the guide ring is set in a predetermined rotary position with respect to the male coupling member.

Abstract: In case where a cylindrical gasoline tank embedded in the underground of a gasoline station is of the horizontal type, a liquid level sensor for sensing the liquid level of the gasoline is disposed in the tank, the liquid level in the tank as sensed by the sensor is converted into an electric signal, the electric signal is converted into a signal expressive of the quantity of the gasoline received in the tank by utilizing a segmental function, and this signal is used to indicate the received quantity of the gasoline with electric-light numerals.