Greensboro, NC--Vapor recovery systems installed at the gas pump contribute to the better health of all. Estimates indicate that, in California alone, such systems reduce hydrocarbon emissions by 48,000 tons annually. Economically, they also save some 15 million gallons of gasoline.

Many of these new systems, however, could stand improvement, particularly with regard to accuracy. Over-collection of vapor requires a post processor, typically a burner. Under-collection continues to expose customers and service station attendants to gas vapors that contain benzene, xylene, ether, and other potentially toxic compounds.

Designed by electrical engineer Edward Payne of Gilbarco Inc., the VaporVac(R) vacuum assist vapor recovery system avoids under- or over-collection. Chief components include flow meters, a variable speed vacuum pump, an electronic control system, and coaxial hose.

During system operation, pulser signals from the flow meters indicate the gasoline's real-time flow rate. The controller combines this input with a decaying exponential term that accurately models mixing and turbulence as the fill progresses. The result is an accurate prediction of instantaneous vapor volume at the fill adapter.

Vacuum pump velocity feedback simultaneously tells the controller the instantaneous volume, or the rate at which the pump is removing vapor. The controller subtracts this value from that produced by the prediction algorithm to derive system error.

Deriving a forcing function whose input is system error, in turn, helps the controller model and compensate for the vacuum pump's inertial characteristic. Employing inertial compensation mitigates pump velocity slewing delay, as well as the undershoot/overshoot of instantaneous pump velocity. In this manner, the variable speed pump creates a vacuum that removes vapors from the vehicle tank with a very high degree of accuracy, thereby meeting California's tough 95% efficiency requirement without needing bellows on the nozzle.

Because the VaporVac vapor recovery system creates a vacuum, its nozzle doesn't need the spring-loaded elephant trunk boot used by competing systems. This design difference makes pumping gas easier for the customer. Fueling is quicker, too. Competing vapor recovery systems pump at about 8 gal/min. Flow rates for the VaporVac system average 10 to 12 gal/min.

Designed for the company's Advantage(TM) gas pumps, the vapor recovery system can be factory installed, or retrofit. "The new system more than meets the requirements of the 1990 Clean Air Act," says Payne.

Additional details...Contact Gilbarco Inc., 7300 West Friendly Ave., Greensboro, NC 27420, (910) 547-5184.