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What is it
Stage two vapor recovery is the process of trapping and recovering gasoline vapors during vehicle refueling. Stage two vapor recovery systems can be used anywhere vehicles are refueled but are required by law to be used in almost all gas stations nationwide to reduce the amount of emissions produced at the pump.
Why is it Required
Gasoline is made up of hundreds of hydrocarbon compounds and additional additives. These hydrocarbons and additives may be blended in any number of ways to produced certain performance levels. Gasoline is extremely toxic, and its vapors are chock full of volatile organic compounds, or VOCs, and hazardous air pollutants, or HAPs. In the sunlight VOCS and nitrogen oxides released into the atmosphere react to form smog. This heavy vapor burns eyes, damages lungs, causes breathing difficulty, can be fatal to asthmatics, and destroys crops and rubber products.
Gas stations and other high-output gas dispensing facilities are required by law to limit the amount of toxic emissions that they produce. The use of stage two vapor recovery at the vehicle and stage one vapor recovery at the tank help to drastically reduce the amount of VOCs and HAPs that are released into the atmosphere.
How it Works
Stage two vapor recovery captures gasoline vapor that would otherwise be absorbed into the atmosphere during refueling. Specialized nozzles use vapor return lines to direct the vapor from the vehicle fueling receptacle to the storage tank. This design allows the vapor that is displaced while fueling to replace the volume space formed by the dispensed fuel. The collected vapor then condenses back into liquid gasoline for later use.
Stage two vapor recovery works like this. As fuel is dispensed into a tank, it froths and churns, producing vapor. This vapor is forced out of the tank by the pressure of the incoming liquid. If no recovery method were in place, this vapor would escape into the atmosphere. During stage two vapor recovery, specialized nozzles collect the vapor forced out of the vehicle tank and route it back to the storage tank for later use.
There are two gasoline vapor recovery systems used today – vapor balance and vacuum assist. The two systems use completely different nozzles and methods of vapor capture and rerouting, but achieve about the same level of vapor capture.
Vapor Balance Stage Two Vapor Recovery
Vapor balance recovery systems use direct displacement to reroute vapor from the vehicle tank back to the storage tank during fueling. Vapor balance nozzles use bellows and a faceplate. These systems generally use standard coaxial hoses.
During the vapor balance recovery process fuel is dispensed into the vehicle tank through the main tube. At the same time, bellows collect the displaced vapor within the vehicle tank as it is pushed out of the tank. The bellows connect to a line that transfers the collected vapor back into the storage tank where it will condense back into liquid gas for later use.
Vacuum Assist Stage Two Vapor Recovery
Vacuum assist stage two vapor recovery utilizes a vacuum-inducing device to capture vapors and route them back into the storage tank’s ullage space. Vacuum assist nozzles use either a vapor escape guard or a mini-boot. Commonly, vapor collection holes are found near the end of the dispensing spout.
A Vacuum Assist System is a gasoline vapor recovery system that uses a vacuum-inducing
device to collect vapor from the vehicle fuel tank and direct it back into the gas storage tank’s ullage space. Holes in the spout or at the spout’s base allow vapors to be pulled into the return line by the vacuum device. Vapors are actively suctioned from the vehicle tank using a vacuum, therefore the fit is kept intentionally loose to allow for airflow and to prevent vehicle tank damage.
It just makes sense to use a stage two vapor recovery system, even if the law does not require it – as in the case of facilities with a 400,000 gallon or less per year output. Stage two vapor recovery systems are better for the environment and better for a business’ pocketbook in the long run. The recovered vapor condenses back into liquid gas, reducing the number of tank fills required.