Stage II Vapor Recovery

What is Vapor Recovery...

Vapor recovery is a general term describing methods for preventing the emission of volatile organic compounds (VOC) into the atmosphere. It is a process used during product delivery and fueling operations at vehicle fueling sites as a means of improving air quality. Control of emissions during deliveries from truck transports into facility storage tanks, referred to as Stage I Vapor Recovery, is accomplished by capturing the vapors in the transport and returning them to the bulk terminal for processing. Control of emissions from vehicle fueling operations, referred to as Stage II Vapor Recovery, is accomplished by capturing vapors at the vehicle fill pipe and returning them to the facility storage tanks. The vapors captured during vehicle fueling may also be disposed of by other methods, such as on-site incineration.

Stage II Vapor Recovery System Types...

Balance Systems:

Pressure that develops in the vehicle tank during fueling operations, and vacuum in the storage tank created when the fuel is removed, forces displaced vapors out of the vehicle tank and back into the storage tank. Stage II vapor recovery systems that operate on this principle, without vacuum pumps or aspirators, are referred to as Balance Systems. Balance systems require a tight seal between the vapor recovery nozzle and the vehicle fill pipe, to prevent escape of vapors. Balance vapor recovery nozzles utilize face seals, bellows, and interlocks to insure a tight seal at the fill pipe. Coaxial hoses provide a vapor path back to the underground vapor recovery piping system. Vapor check valves may be located in coaxial adapters, dispensers, or nozzles to prevent the escape of vapors from the vapor-return path between fueling operations.

Vacuum-Assist Systems:

Vacuum-Assist Systems employ vacuum pumps, located either at the dispenser or in the piping, which create a vacuum to assist the movement of vapors back into the storage tank. Since the vacuum is created by a pump, the amount of vacuum may be adjusted to meet performance requirements. Vacuum-assist systems employ specific nozzle designs for use with their equipment. Pressure/vacuum vent valves on the vent riser pipes are necessary to reduce vapor releases to the atmosphere.

Aspirated Systems

Aspirator-Assisted Systems create a vacuum in the vapor-return path that assists the movement of vapors from the vehicle tank to the storage tank. This vacuum is created through action of the motor fuel, flowing under pressure from the submersible pump. A portion of the motor fuel is diverted into the vapor-return path tHRough use of a venturi or jet pump; this, in turn, creates the vacuum. The aspirator device may be installed at the dispenser or submersible pump. Pressure/vacuum vent valves on the vent riser pipes are necessary to reduce vapor releases to the atmosphere.

Stage II Vapor Recovery System Testing...

Static Leak Test (Pressure Decay):

The integrity of the vapor recovery system must be proven to ensure its proper operation. A system which will not hold pressure may permit the release of liquids or vapors. Leaks may permit excessive emissions and decrease the efficiency of the vapor collection or processing system. A Static Leak test is a low pressure testing method which is performed with all components connected to the piping. The acceptable pressure decay is dependent on several factors, including ullage in the tanks and the number of associated nozzles.

Dynamic Pressure Test (Flow & Block):

The vapor-return path from the dispensers to the tanks must be sufficiently large and free of obstructions to ensure the efficient flow of vapors. The Dynamic Pressure test simulates the system operation and measures the restriction to flow of vapors from the dispensing nozzles to the storage tanks during normal vehicle fueling.

Air to Liquid (A/L) Ratio Test:

The Air to Liquid (A/L) Ratio test is designed to measure the efficiency of vacuum-assisted vapor recovery systems by comparing the volume of vapor (air) captured and returned to the storage tank to the volume of fuel dispensed. The A/L test is conducted after the system has passed the static leak test, by simultaneously measuring the volume of air collected by the nozzle and volume of gasoline dispensed. Air entering the vapor-return path is measured instead of actual vapors from the automobile tank because of the difficulty in accurately controlling and measuring gasoline vapors from the wide variety of automobile fill pipe configurations.

Stage II Vapor Recovery System Testing Requirements...

(Most states have the following testing requirements)

Static Leak Test (Pressure Decay):

Annual test for Vacuum-Assist & Aspirated and five year test for Balance systems.

Dynamic Pressure Test (Flow & Block):

Five year test for Balance & Vacuum-Assist systems.

Air to Liquid (A/L) Ratio Test:

Annual test for Vacuum-Assist & Aspirated systems.