Question
In designig of watermains, how to decide usage of double air valves and single air valves?
Answer
Single air control device let squeezing air out of pipeline in automatic mode in high-pressure condition and are usually designed in high direct of watermain in that air voids are present. Double air valves essentially serve same purpose except that it has another important function-it can get air into or out of the pipeline during low-pressure condition.
In WSD practice, watermain are in general divided into sections by installation of sectional valves to ease maintenance. In a single isolated pipeline section bounded by two sectional valves, at smallest amount a double air valve should be installed. Throughout normal maintenance operation like cleansing of watermain, water inside pipelines is tired from washout valves. Though, as regular watermain is subject to very high force like 1.5MPa and sudden withdrawn of water will reason a transient vacuum condition and will damage watermain. So at least one twice air valve should be present to let air to squeeze in to equilibrium pressure and this defend pipeline from damaging.