Storage tank system having an internal overfill means

An underground storage tank system having an internal retained capacity area for receiving overflow of liquid resulting from a filling operation through a delivery hose of a transport tank truck, comprising:

• (a) a rigid storage tank having a storage capacity of at least about 1,000 gallons of liquid;
• (b) a fill pipe extending from near ground surface into the storage tank for delivering liquid therethrough;
• (c) a vapor recovery tube attached to the storage tank and a vapor recovery extension tube extending from the vapor recovery tube into the storage tank with a lower end of said extension tube terminating from about two inches to about eighteen inches from a top inside surface of the storage tank whereby said vapor recovery extension tube and vapor recovery tube receive vapors formed within the storage tank during the filling operation;
• (d) a vent line attached to the storage tank and a vent extension line extending from the vent line into the storage tank with a lower end of said vent extension line terminating from about two inches to about eighteen inches from the top inside surface of the storage tank, wherein the area within the storage tank which is above the vapor recovery extension tube termination and vent extension line termination which is uppermost represents the internal retained capacity area;
• (e) a dispensing line leading from within the storage tank to a dispenser at ground surface;
• (f) a single trapped vapor release valve in operable association with the internal retained capacity area so that when closed during a filling operation a build up of pressure occurs within the storage tank to prevent liquid from completely occupying the internal retained capacity area and when opened permits excess liquid in the fill pipe to freely flow into the retained capacity area;
• and
• (g) a by-pass vent line leading directly from the trapped vapor release valve to the vapor recovery tube so that upon the opening of the trapped vapor release valve trapped vapors in the internal retained capacity area exit the storage tank through the by-pass vent line and vapor recovery tube.