Improved Air Valve Selection through Better Device Characterization and Modeling

Employing a set of well-chosen and maintained air valves is a widely recommended strategy for air management in pressurized pipelines. However, precisely characterizing, modeling, and sizing air valves for the various functions they serve can be a demanding task. This paper considers the key challenges of air valve characterization in light of several potential complications. The paper summarizes and gives context to location criteria for air valves and discusses some of the common pitfalls in selecting such devices. Moreover, the effectiveness of four air flow models in representing data from characterization tests is evaluated. Not surprisingly, the most complex model with an adjustable polytropic exponent is found to have the best curve fitting capability, although the simpler isentropic model fits experimental data reasonably well. However, employing a fixed polytropic exponent of 1.20 tends to underestimate air flows for relatively intense differential pressures, while the incompressible model poorly represents air inflow. The paper also shows how representative air flow curves may be constructed even if only scant characterization data are available.