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|Stage I Vapor Recovery
"What is Stage I, Vapor Recovery?"
Stage I vapor recovery is used during the refueling of gasoline storage tanks to reduce hydrocarbon emissions. Vapors in the tank, which are displaced by the incoming gasoline, are routed through a hose into the cargo tanker, instead of being vented to the atmosphere. There are two types of Stage I systems, dual point and coaxial.
The North Carolina Division of Air Quality (DAQ), to help gasoline service stations comply with gasoline vapor regulations, is performing statewide inspections of Stage I Vapor Recovery equipment. Tank owners and equipment installers are reminded that a complete Stage I Vapor Recovery system, with the following specifications, is required on all gasoline storage tanks*(see exemptions below):
- Submerged fill tube extends to within 12 inches of the bottom of the tank (6" for exempt tanks), except for bottom filled above-ground storage tanks.
- A cap making a tight seal on the product fill tube.
- Poppet valve on the vapor recovery opening that remains closed when not in use (Dual Point System), or an unobstructed path in the coaxial opening allowing vapors to flow out of the tank (Coaxial System). Coaxial systems installed after June 30, 1994, require a poppeted coaxial fill tube. This type of coaxial tube seals off the vapor path when not in use.
- Cap on the poppet valve (optional, but preferred-protects the poppet valve and acts as a secondary seal).
- Pressure/Vacuum valve or flow restrictor on vent pipe.
Stage I Vapor Recovery was required on all gasoline storage tanks, both aboveground and underground, as of November 1, 1992, unless they meet one of the following exemptions:
- Tanks are 2,000 gallons or less and were installed before July 1, 1979 with submerged fill tubes extending to within 6 inches of the bottom of the tanks or;
- Tanks are 550 gallons or less and were installed after June 30, 1979 with submerged fill tubes extending to within 6 inches of the bottom of the tanks or;
- Tanks have a combined throughput of gasoline of less than 50,000 gallons per year and are equipped with submerged fill tubes extending to within 6 inches of the bottom of the tanks.
Dual point systems
Dual point configurations consist of two separate tank openings, one for delivery of the product and the other for the release of vapors. There are two types of dual point systems, dual point top filling systems ( fig. 1) and dual point bottom filling systems ( fig. 2)
Figure 1: Dual Point Top Filling System
Figure 2: Dual Point Bottom Filling System
Coaxial systems ( fig. 3) require only one tank opening. The tank opening is usually four inches in diameter with a three inch diameter product fill tube inserted into the opening. Fuel flows through the inner tube while vapors are displaced through the annular space between the inner and outer tubes.
Figure 3: Coaxial System