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Abstract
The aim of this work is to model an air valve, recently introduced into the market, the Vent-O-Mat RBX 3-Stage air valve, and to study its characteristics. This 3-Stageair valve performs like a conventional air valve. That is, it performs like an Air Release Valve releasing air under normal pressurized conditions as well as an AirNacuum Valve during filling and drainage of pipelines. In addition, it acts like a surge alleviation mechanism by releasing the air in the pipeline through two stages when the velocity of the displaced liquid is high. Throughout this study, an understanding of the complex behavior of the entrapped air could also be gained.
The performance of the 3-Stage air valve is compared to that of conventional air valves to demonstrate its advantages and disadvantages. When applicable, it is also compared to the case in which no air vents were installed on the pipeline. Some of the parameters affecting the operation of the 3-Stage air valve, such as the residual volume and the switching pressure are also studied. Throughout this work, more understanding of the dynamic behavior of air valves during transient is achieved
Two numerical models have been developed. The first model is based on the Method of Characteristics with its abilities to simulate complex pipes systems, unsteady friction, viscoelastic pipes and column separation. The air vent is incorporated into the model as a boundary condition. Also, some specific numerical parameters were included in the model which can be used later to fine tune the numerical results. The second model is based on the Rigid Water Column Theory. Both elastic and inelastic models proved to have their ranges of applicability and their own advantages and disadvantages.
The results are compared with the numerical results of two well-known surge computer programs; ”Pipe2000” developed by the University of Kentucky and ”Wanda 3.0” developed by ”Delft Hydraulics”, the Netherlands.