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Understanding the Impact of Mesh on Tank Overflow System Capacity
Citation:
Burkhardt, J., J. Goodrich, Jeff Szabo, J. Hall, S. Tourney, J. Crosby, AND R. Clement. Understanding the Impact of Mesh on Tank Overflow System Capacity . Presented at ORD/OW Small Systems Webinar Series, Cincinnati,OH, July 31, 2018.
Impact/Purpose:
The purpose of this presentation is to present results geared at understanding the impact of mesh on overflow system discharge capacities. This is relevant to water utilities, design engineers, and regulatory bodies (States, Regions or EPA offices) that wish to understand the impact of mesh on sizing overflow systems to ensure prolonged useful tank lives. Water storage tanks are an important component of most water distribution systems. Tanks are typically designed with decades of use in mind, with designs based on capacity predictions made at the time of installation. Through time a system’s needs change along with available technology and design or operation recommendations. One of the components of a tank that may not get significant attention is the tank overflow system—specifically, how changes to a tank or its overflow system might impact overflow system performance and design. Tank overflow systems are a vital component to a resilient water distribution network, ensuring that a tank will not become over-pressurized due to over filling. Understanding how changes made to the tank could impact the overflow capacity of a tank can help ensure that systems can count on having storage available. This work specifically set out to study the impact of a #24 mesh installed at the system outlet on overflow capacity. Experiments were conducted to test the overflow capacity of the upturned elbow style overflow configuration using three different pipe sizes (4”, 6” and 8”), two pipe configurations and including varying degrees of blocked mesh. The Francis formula, used to calculate flowrates in weir systems, conservatively predicted the overflow capacity for all tested configurations that included a single vertical pipe outside the tank, with mesh having been clogged at up to 25%. Introduction of a horizontal portion of pipe near the bottom of the overflow system resulted in consistently lower capacity than predicted. When the overflow system reached backpressure limited flow, small increases in flow resulted in large increases in required excess head. The presentation will discuss the results of the experiments as they relate to tank overflow system design to help water utilities ensure that an overflow system is appropriately sized even after making changes.
Description:
Water storage tanks are an important component of most water distribution systems. Tanks are typically designed with decades of use in mind, with designs based on capacity predictions made at the time of installation. Through time a system’s needs change along with available technology and design or operation recommendations. One of the components of a tank that may not get significant attention is the tank overflow system—specifically, how changes to a tank or its overflow system might impact overflow system performance and design. Tank overflow systems are a vital component to a resilient water distribution network, ensuring that a tank will not become over-pressurized due to over filling. Understanding how changes made to the tank could impact the overflow capacity of a tank can help ensure that systems can count on having storage available. This work specifically set out to study the impact of a #24 mesh installed at the system outlet on overflow capacity. Experiments were conducted to test the overflow capacity of the upturned elbow style overflow configuration using three different pipe sizes (4”, 6” and 8”), two pipe configurations and including varying degrees of blocked mesh. The Francis formula, used to calculate flowrates in weir systems, conservatively predicted the overflow capacity for all tested configurations that included a single vertical pipe outside the tank, with mesh having been clogged at up to 25%. Introduction of a horizontal portion of pipe near the bottom of the overflow system resulted in consistently lower capacity than predicted. When the overflow system reached backpressure limited flow, small increases in flow resulted in large increases in required excess head. The presentation will discuss the results of the experiments as they relate to tank overflow system design to help water utilities ensure that an overflow system is appropriately sized even after making changes.