AWWA JAW60137 PDF

Much of the literature on air valves emphasizes the installation of air valves at high points along transmission mains, with little or no discussion of the effects of their sizes on transient pressures. Larger air-valve sizes may work well for expelling trapped air quickly but may lead to pipe-bursting pressure surges resulting from a phenomenon called "air slam." This article explores different techniques to size air valves and, through two example applications, examines the positive impact of smaller outflow sizes on pressure surges following the expulsion of air. The study also presents a simplified equation to estimate the magnitude of pressure surges based on the pipe characteristics, the air-valve characteristics, and the pressure inside the valve just before the final release of air. Altering the way in which valves are sized could result in cost savings (using pipes of lower pressure ratings) and might also alleviate low-pressure situations that can result in pathogen intrusion.