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Section 4.7.1.9.1 of the MAHC covers opens with:
Over 22% (approximately 20,000) of the POOL inspections that led to POOL closures in the state of Florida in 2012 were caused by non-functioning flow meters (State of Florida, unpublished data).
Flow meters are an extremely important tool in the pump room, and are routinely referenced by operators, inspectors, installers. Equipment is sized by them; operational calculations reference them. As such, the MAHC dedicates nearly an entire page to this topic.
Different flow meters will require different install methods. As an example, if a top mount flow meter is installed horizontally, it will not read accurately. Flow meters should not be installed immediately after bends in the plumbing as this will also cause inaccurate readings of the flow. Always read all manufacturer’s guidelines before install. Failure to do so may lead to inaccurate readings, causing many headaches further on. Accuracy concerns need to be addressed immediately. Ideally, there should be more than one flow meter on a system, and more than one type of flow meter.
Flow meters should have a measurement capacity of at least 150% of the design recirculation flow rate through each filter, and each flow meter should be accurate within +/-5% of the actual design recirculation flow rate.
Having at least 150% of the designed flow rate will allow you to read flow even during changes. If a flow meter is maxed out, it’s less than useless: it may deceive operators into believing the flow rate is whatever the max of that meter may be. Inaccurate flow meters will cause the same problem.
Flow meters should be inspected annually, and accuracy evaluated. Certain types of meters, such as paddle wheels, may foul up and need to be cleaned more often. If using the paddle wheel meters, keep in mind they should be installed after the filter to avoid more fouling. All flow meters should be positioned so they can be easily read and maintained. Flow rates should be logged daily, maintained with the other readings.
Different equipment requires different flow rates and is often installed on a bypass. The manufacturer may recommend installing a flow meter so the installation manuals should be consulted.
Finally, the MAHC recommends using magnetic or ultrasonic flow meters, as they are much more accurate than most flow meters (+/-1%). The downside to that is they are expensive. There are clamp-on ultrasonic flow meter that can be moved around to confirm flow through a system and can be used to evaluate other meters for accuracy.
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