Water Column Separation and Cavity Collapse for Pipelines Protected with Air Vacuum Valves: Understanding the Essential Wave Processes

Abstract

Elevated high points along a pipeline profile are the most common places where air vacuum valves (AVVs) are installed. This paper uses basic water hammer theory to semianalytically explore the effects of such AVVs. A simple frictionless reservoir-pipe-reservoir system with an exaggerated intermediate high point is considered with a sudden flow curtailment assumed upstream. Key design parameters such as the maximum air pocket volume, the duration of air pocket growth and collapse, and the maximum magnitude of the pressure spike resulting from water column rejoinder are semianalytically developed for various high point locations. The magnitude of the reduced pressure wave created by the refraction at the high point, and both its vertical and horizontal position, are demonstrated to crucially determine system performance. Numerical examples are compared with the semianalytical expressions to highlight the accuracy of the derived expressions. The effect of friction is later introduced to help reveal friction's influence on air valve performance.

The Crucial Importance of Air Valve Characterization to the Transient Response of Pipeline Systems

“…As a result of the secondary pressure wave phase, a substantial increase in head occurs at the upstream end of the pipeline, which is typically the maximum head experienced by the system during the transient event. After this first water hammer cycle, subsequent cycles, with the four described phases, usually occur with the progressive attenuation of the transient oscillations [15,26].…”

Study on water hammer protection of the siphon breaking structure in the water supply system

“…The vacuum breaking valve (VBV) is a special air valve, which is characterized in such a way that the operated pressure of the VBV can be set below the atmospheric pressure to ensure that it does not work under a certain negative pressure. According to the influence of transient response in the system, the location and its characteristics are analyzed (Ramezani & Karney 2017). A combination of vacuum relief and air release valve is studied in order to avoid column separation and rejoinder water hammer.…”

Hydraulic modeling during filling and emptying processes in pressurized pipelines: a literature review

“…However, entrapped air could also enter through air valves, joints and valves, during the stopping and failure of hydraulic systems, during the release of dissolved air, and by vortex generation at pump inlets. High points along pipelines are likely locations for the accumulation of air pockets (AWWA 2001;Ramezani and Karney 2017), which can experience pressure surges during a filling process (Zhou, Liu, and Karney 2013b;Fontana, Galdiero, and Giugni 2016;Martins et al 2016;Covas et al 2010) or drops of sub-atmospheric pressure during an emptying process (Fuertes-Miquel et al 2019;Tijsseling et al 2016;Coronado-Hernández et al 2018c). Air valves are used as protective devices to avoid these situations (AWWA 2001).…”