Untangling the Mysteries of Air Valves

Abstract

Air valves are required for water and wastewater pipeline systems. However, the purpose and intended use of air valves must be identified to properly select type, location, size and specify the proper air valve. This paper will help identify the various uses of air valves within a pipeline system. Once the designer has identified the primary, secondary and potentially tertiary purposes of the air valve, the interrelationships of the various design parameters can be refined. Many times a designer will specify a vacuum, air release and/or a combination air valve for multiple intended uses (i.e. normal operating air release and surge control) without considering the sometimes conflicting design approaches employed when sizing for multiple uses. The paper will also introduce refinements to the existing air release valve design procedure. The percent volume of air in water can fluctuate dramatically by the amount of energy and turbulence imparted to the water. At a steady, atmospheric pressure condition water has approximately 2% of air by volume. The primary purpose of an air release valve is to release this air as it builds-up over time within a pipeline. This build up of air over time will introduce excessive head loss and/or reduced capacity in an operating system. However, sizing the air release valve using the 2% rule of thumb, which is utilized in the AWWA M51 guideline, has become a “known” rather than a variable in the sizing of air release valves. This paper introduces a design approach that allows the designer to independently consider the volumetric flow rate of air for a better sizing technique for air release valves as well as the secondary usage (i.e. surge control) of air valves for a more comprehensive sizing and/or location.