Insights and Challenges Associated with Air in Pressurized Water Conveyance Systems

Air is present in pressurized water systems for a variety of reasons, including incomplete removal during filling, air entrainment at intakes or entrances, air admission during draining operations, or air exchanges due to transient events such as power failure or pipe burst. Each of these sources or events creates specific design and operational challenges, issues that often require thoughtful and sometimes expensive approaches to avoid serious upsets or accidents. Indeed, the design and operational challenges must collectively be blended to produce a robust and economical design that is valid for all foreseeable operational and emergency actions that might involve the presence of air, whether the air is admitted, expelled, or merely present in the flow system. This paper summarizes the key findings that relate to the presence of air in pressurized flow systems. The focus is on the available research and operational experience regarding the challenges and strategies for coping with residual air, for removing air, or for admitting air into the conveyance system. The emphasis is on practical recommendations but also highlights some of the key uncertainties that remain when dealing with the full range of design and operational challenges confronting those seeking to safeguard the long-term performance of pressurized water conveyance systems. One of the persistent challenges is to select suitable design events since the conditions a pipeline will experience over life are inevitably both highly varied and somewhat uncertain.