The effects of air and vacuum pockets present in a liquid piping system can negatively impact not only pump, meter, and control valve operation but can also be responsible for pipeline breaks and collapses. Choosing and installing the correct air valve is critical to all liquid piping systems. This manual of practice provides essential information for selecting, sizing, locating, and installing air valves in water, wastewater and reclaimed water pipeline systems. This revised second edition includes information pertaining to wastewater applications including scouring velocities for larger piping systems, and information on an inflow preventer device installed to protect from malicious tampering, freeze and flood, and to prevent the entry of contaminated water into the potable water distribution system. Operators, technicians, and engineers will use this manual to understand the design, use, application and maintenance of air valves. The air valve types listed in both ANSI/AWWA Standard C512, Air Release Valves, Air/Vacuum, and Combination Air Valves for Water and Wastewater Service and ANSI/AWWA C514, Air Valve and Vent Inflow Preventer Assemblies for Potable Water Distribution System and Storage Facilities are covered. Chapter topics include: locating air valves along a pipeline; design of valve orifice size; water hammer effects; and installation, operation, maintenance, and safety.