API RP 1639-2003 pdf download.Owner/Operator’s Guide to Operation and Maintenance of Vapor Recovery Systems at Gasoline Dispensing Facilities.
184.108.40.206 Two-point (Dual) System The delivery of product and recovery of vapors in a Stage I two-point system occurs through separate connections (see Figure 1). The product is delivered (dropped) by gravity through a full connection and the vapors are returned through a separate vapor connection. The fill connection is fastened to a submerged fill tube that must have its discharge opening entirely submerged when the liquid level is 12 inches above the bottom of the storage tank. (Local requirements may require the installation to be no higher than 6 inches.) The vapors are recovered through the second opening in the top of the storage tank and transferred to the tank truck through the vapor hose. 220.127.116.11 Coaxial System The delivery of product and recovery of vapors in a Stage I coaxial system occur through a single coaxial submerged fill tube, which is simply a tube inside a tube (see Figure 2). The product is delivered through the inner tube and the vapors are recovered through the annular space between the walls of the inner and outer tubes. As with the dual system, the inner product tube must be entirely submerged when the liquid level in the tank is 12 inches or more while the outer vapor tube is in the top of the tank. (Local requirements may allow the installation to be no higher than 6 inches.) The coaxial submerged fill tube may be either fixed in position or spring-loaded (moveable) with a vapor seal simi- lar to the dry break adapter seal in the dual system. Unlike the fixed version, the spring-loaded version has a flange around the edge of the inner tube. A gasket is seated on the top sur- face of the flange. In this position, the gasket makes contact with the inner surface of the adapter at the top of the sub- merged fill tube, thereby holding the entire assembly in place and creating a vapor seal. All current California Air Resources Board (CARB) Exec- utive Orders certifying vacuum assist vapor recovery systems prohibit the use of coaxial Stage I systems for stations con- structed after 1993. Many states refer to CARB Executive Orders for approved systems and components.
4.1.2 Stage II Vapor Recovery Stage II vapor recovery systems capture the vapors gener- ated during vehicle refueling. The vapors recovered from the vehicle tank are returned to the UST. Vapor recovery systems include all piping, nozzles, dispenser components, and other equipment necessary for the control of gasoline vapors during vehicle refueling (see Figure 3). There are two types of Stage II vapor recovery systems: balance systems, which use nozzles that make a tight fit with the vehicle fillneck during refueling, and vacuum assist sys- tems, which use nozzles that make a loose fit with the vehicle fillneck and use vacuum to recover displaced vapors. Nozzles are certified to work on specific vapor recovery systems and must meet minimum efficiency standards. 18.104.22.168 Balance System The balance type vapor recovery system operates on the principle of positive displacement during gasoline transfer operations. The system is designed to collect gasoline vapors displaced from the vehicle fuel tank during refueling and return them to UST. To contain vapors during refueling, a closed loop must be created between the vehicle fuel tank and the UST. The vapors are collected at the vehicle-fill pipe interface by a combination fuel-dispensing, vapor-collection nozzle. Typically, the nozzle contains a no-seal/no-flow fea- ture consisting of an interlock which prevents dispensing of gasoline unless the nozzle boot is compressed. This feature ensures the best possible seal between the nozzle boot and the fill pipe interface.