What are the two primary types of Stage II vapor recovery systems?

• A. Active and passive systems
• B. Assist and balance systems
• C. Mechanical and electronic systems
• D. Full and partial capture systems

Answer: (B)

Stage II vapor recovery systems are designed to capture gasoline vapors during the refueling of vehicles, preventing them from escaping into the atmosphere. The correct answer reflects the two primary configurations found within these systems: assist and balance systems.

Assist systems utilize a vacuum to draw vapors from the vehicle's fuel tank into the recovery system, often requiring a set of pumps and fans to facilitate this process. This method is particularly effective at ensuring a good capture rate of vapors, especially in high-flow situations.

Balance systems, on the other hand, work by equalizing the pressure between the fuel tank and the storage tank at the service station. As fuel is drawn from the storage tank, the vapors produced in the vehicle's tank are pushed back into the storage tank through a series of pipes, relying on the natural pressure dynamics between the two systems.

Understanding these two key types reveals the different technologies and methods employed to achieve vapor recovery, demonstrating their importance in reducing air pollution and complying with environmental regulations.