API BULL 2521-1966 PDF

Scope: Introduction This bulletin discusses venting of aboveground tanks used for the storage of petroleum and petroleum products at essentially atmospheric pressure (usually up to 12 in. of water pressure). Venting requirements for low-pressure (up to 15 psig) aboveground storage tanks are covered in API RP 2000: Guide for Venting Atmospheric and Low-Pressure Storage Tanks. The pressure-vacuum vent valve@ hereinafter referred to as a PV vent@ is a device which inhibits evaporation losses while protecting the tank from the possible damaging effects of overpressure or overvacuum. When the vapor-space pressure within a storage tank exceeds the pressure set point@ the PV vent opens to release vapors from the tank until the pressure is reduced below its set point when a vacuum is formed within the storage tank@ and exceeds the vacuum set point@ the PV vent opens to admit air into the storage tank until the vacuum is reduced below its set point. The use of PV vents on storage tanks will reduce certain evaporation losses from volatile liquids stored in fixed-roof tanks or in variable-vapor-space tanks and systems. It is a basic assumption that the tank and its accessories are in vaportight condition

API BULL 2521-1966 history

1966 API BULL 2521-1966 USE OF PRESSURE-VACUUM VENT VALVES FOR ATMOSPHERIC PRESSURE TANKS TO REDUCE EVAPORATION LOSS