描述了在地面固定顶储罐和可变蒸汽空间系统中，使用压力真空排气阀来减少在大气压力下储存的石油的蒸发排放损失。还介绍了选择排气阀时应考虑的因素。

Describes the use of pressure-vacuum vent valves to reduce evap loss of petroleum stored at atmospheric pressure in aboveground fixed-roof tanks and variable vapor-space systems. Also presents factors to be considered when selecting vent valves.