By: Kristine Gali, Technical Program Manager, and Heidi Smith, Global Product Manager
The American Water Works Association nonprofit was founded in 1881 with a focus on providing education and training opportunities for drinking water professionals. Since its inception, the association has grown to roughly 50,000 members, multiple sections across the US, and multiple committee’s within each section. The California-Nevada Section of AWWA held its Summer Meeting and Workshop on August 20, 2019 with a focus on large meter testing, the importance of regular testing, methods of conducting field and bench tests, and a panel on how to develop a testing program.
With emerging water regulations across the US, utilities are becoming increasingly focused on annual water audits. Even more importantly, utilities are focusing on how to gather sufficient data to most accurately complete these water audits. The water that enters the water distribution system should equal the amount of water either consumed, lost, or exported. On the other hand, without accurate metering, it is impossible to confirm how much water is associated with each of these variables of the equation. Having a regular testing program for large meters helps utilities monitor not only production meters, but some of their highest revenue generating meters as well and ultimately hone in on accurate water audit inputs.
Reasons and consequences for large meter failures
Michael Simpson from M.E. Simpson Co. shared 7 reasons for large meter failures and their consequences:
- mechanical wear and tear,
- mineral buildup,
- fouling due to debris,
- misuse or operation outside of the meters range, and
- inadequate plumbing before and/or after the meter
The consequences of these potential failures include inaccurate billing of customers, lost revenue, over and under feeding of chemicals (in plant meters only), inaccurate annual reports and usage estimates, and an overall loss of control.
Meters will naturally age and experience wear and tear. Depending on water quality, other factors such as corrosion, mineral buildup, and fouling may ultimately affect meters as well. Finally, the installation configuration and operation of the meter itself can compromise the accuracy of meter reads. Due to the variety of issue types, the life expectancy of large meters can be difficult to predict without closely monitoring the meters as well as the quality of water running through them over their lifetime.
Simpson recommends that utilities test and calibrate their large meters annually. A survey of the largest US utilities also found that testing of large meters occurred on an annual basis (AWWA, M6, pg 58). Testing should be conducted using a certified test meter or a pitot rod. It should be noted that testing of the 4 to 20 mA signal between a meter head and the SCADA system is not considered a valid test.
What is a Pitot Test?
The pitot test is a common field testing method which measures differential flow pressure to determine flow velocity and ultimately flow volume (i.e. Q=VA) within a pipe. The pitot tube is inserted into the live pipe to determine the flow profile across the entire inner diameter of the pipe. Since the flow equation depends on the cross sectional area of flow, it is important to carefully measure the inner diameter of the pipe such as with a Polcon Pipe Caliper. It should also be noted that various pipe obstructions such as valves and elbows can alter the flow profile, therefore it is important to take pitot measurements on a straight line of pipe and at multiple depths within the pipe to ensure the most accurate flow volume can be determined. Furthermore, since flows may vary throughout the day, a 24-hour test is also recommended.
Ultrasonic strap-on test meter
Strap-on ultrasonic test meters can also be used to field testing large meters in-place. The meters are minimally intrusive and similar to a pitot tube, do not disrupt flow. Measurements are calculated based on the transit-time difference method. It should be noted that the test meter should be certified and calibrated prior to use and that the manufacturer specifications for installing the test meter are followed as most require a specified amount of straight pipe both up-stream and down-stream of the test location. Furthermore, it should be noted that “once the testing begins, the testing order is from the low flows to the higher flows. Experience has shown that when most meters begin to wear or lose accuracy, it occurs at the lower flows rather than the higher” (AWWA, M6 pg 85). An advantage of ultrasonic strap-on meters is their ability to measure low flows therefore covering most, if not all flow ranges within the large meter.
Utilities may opt to contract out services to companies such as Mars Company or to organizations such as Utah Water Research Laboratory (UWRL) for their testing and calibration of large meters. Mars Company has been offering water meter testing and technology services since 1986. At UWRL, meters and even volumes of water, can be shipped for testing in a laboratory which simulates the field piping installation.
Large Meter Testing Practices