Vapor space pressure control system for underground gasoline storage tank

#This invention relates to underground gasoline storage tanks, and more particularly to systems for controlling escape of gasoline vapor from such tanks.

#During refueling of automobiles and other vehicles, liquid gasoline is delivered into the vehicle fuel tank, and a mixture of gasoline (or other fuel) vapor and air is displaced from the tank. To minimize escape of gasoline vapor into the atmosphere, gasoline dispenser nozzles are typically equipped (as often mandated by local environmental protection regulations) with vapor recovery vacuum systems to collect the displaced gasoline vapor, and air, and deliver it back into the ullage (i.e., vapor) space of the underground storage tank (“UST”). Preferably, a 1-to-1 ratio balance is sought between volume of liquid gasoline drawn from the underground storage tank, e.g. during vehicle refueling, to volume of gasoline vapor and air returned into the ullage space by the vapor recovery system. However, due to a variety of factors, including, e.g., differences in temperature, inefficiencies in the vapor recovery system, ingestion of excessive external air, etc., such a balance is difficult to achieve. As a result, some amount of gasoline vapor may be discharged, or air ingested, through the UST pressure/vacuum relief vent valve during any 24-hour period of operation.

#This problem has been addressed, in part, by design of ORVR (“onboard refueling vapor recovery”) equipped vehicles, in which gasoline vapor collecting in the ullage space of the vehicle tank is recovered onboard the vehicle, making it necessary for the fuel dispensing system to recover only a relatively smaller volume of gasoline vapor and air during refueling, e.g. as compared to non-ORVR vehicles. As a result of the differences between ORVR-equipped and non-ORVR-equipped vehicles, and the fact that both types of vehicles are in regular use, fuel dispensing systems must be designed to detect and accommodate different vapor recovery requirements.

#FIG. 1 is a somewhat diagrammatic representation of a typical prior art fuel storage and delivery system.

#FIG. 2 is a somewhat diagrammatic side section view of a passive pressure control system for temporary storage of vapor from the UST vapor space, e.g., during periods of increased pressure, including a tank containing a bladder; and

#FIG. 3 is a somewhat diagrammatic enlarged side section view of the bladder support assembly for the passive pressure control system of FIG. 2.

#Like reference symbols in the various drawings indicate like elements.

#Referring to FIG. 1, in a typical prior art fuel storage and delivery system 10, e.g. at a gasoline fueling station, S, an underground storage tank (“UST”) 12 contains a volume of volatile liquid fuel 14, e.g. gasoline, and a volume of a saturated or semi-saturated mixture of gaseous fuel vapor and/or air 16 in a vapor or ullage space, U, above the liquid fuel. The ullage space is connected to the atmosphere via conduit 20, controlled by a UST pressure/vacuum relief vent valve 22, which typically is set to open at −8.0 inches W.C. to permit intake of air into the ullage space and to open at +3.0 inches W.C. to permit release of gaseous vapor from the ullage space, thereby to avoid dangerous buildup of pressure or vacuum within the UST 12.

#During refueling of a vehicle, C, as liquid fuel, L, is delivered via conduit 27 from the UST 12 into the vehicle tank 28, fuel vapor, V, displaced from the vehicle tank by the liquid fuel is recovered (typically in a mixture with air) by vacuum drawn by pump 30 in the fuel dispenser 26 and returned to the ullage space, U, via conduit 32. If the vehicle, C, is an ORVR-equipped vehicle, the vacuum return is set at a relatively lower volume ratio of air ingested to liquid removed for delivery into the vehicle tank, e.g. at a volume ratio of about 0.26 to 1.00 (air to liquid).