Pipeline Engineering

Valve Orifice Sizing - Releasing Gases Under Pressure

The air and other gases are vented through the orifice of the air-release valve or combination air valve at the liquid piping system working pressure for each valve location. Since high pressures are involved, the applicable flow equation for air flow through an orifice is based on compressible flow. This tool was developed using AWWA M51 method for sizing gas releasing valve orifice.



The orifice size for releasing air and wastewater gases under pressure is generally between 1/16 inch (1.6 mm) and 1 inch (25 mm) in diameter or equivalent area of other shapes; however, the size of the air-release valve inlet connection can range from ½ inch (13 mm) to 6 inch (150 mm) in diameter with the smaller orifices found in the smaller-sized inlet port and higher-pressure valves. Consult the available orifice sizes from suppliers and select the valve that meets both the capacity and pressure requirements of the application.