VERIFYING FLOW METER ACCURACY: A COMPARISON OF APPROACHES, LESSONS LEARNED, AND BENEFITS BASED ON EIGHT YEARS OF FLOW METER ACCURACY TESTING

Flow meter accuracy is an important part of any utility's ability to manage its system. Even though a meter may test as being accurate under one set of conditions, it may have significant error under another set. This paper summarizes seven different techniques available to verify the installed accuracy of collection system flow meters, the lessons learned on the sources and effects of typical flow meter error, and the benefits of performing routine accuracy verification. It is based on eight years of meter verification work performed in Detroit, Ann Arbor, Genesee County, Oakland County, and the South Huron Valley Utilities Authority systems in Michigan; and the Pittsburgh and Philadelphia systems in Pennsylvania, including more than 600 independent flow meter accuracy tests on more than 150 collection system flow meters.The seven techniques evaluated for flow meter accuracy verification are summarized in Figure 3. For each technique, the level of effort and costs required to perform each one, flexibility of use, expected accuracy, and objectivity information is indicated based on experience. Drawdown testing offers the greatest potential accuracy and most reasonable cost, but is limited to very few locations. Other commonly used techniques such as velocity profiling and use of a reference meter are not highly accurate or objective. Dye and trace dilution method ultimately offer the greatest flexibility and objectivity, and can be used in most cases where high meter accuracy is required.