Portable Meters Help Troubleshoot Flow Discrepancies

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An Ontario municipality deployed portable flowmeters to solve flow rate discrepancies between sewage pump station effluent and lagoon influent flowmeters. The project involved use of portable doppler flow meters using an ultrasonic transducer and a level-velocity logger with a submerged ultrasonic sensor to monitor level and flow at both ends of the sewage pipe.

An Ontario municipality deployed portable flowmeters to solve flow rate discrepancies between sewage pump station effluent and lagoon influent flowmeters. The forcemain meter at the pump station read five times higher than the open channel flowmeter at the lagoon two kilometers away. The township needed to determine which of the two flow meters was reading incorrectly.

Faced with suspension of construction permits due to flow rate uncertainty, the Township of North Glengarry called on Greyline Instruments to help troubleshoot two permanently installed flow meters.

The first step was to evaluate performance of the 12” magmeter at the sewage pump station. The cost to remove the magmeter for calibration was prohibitive so Greyline supplied a clamp-on PDFM 5.0 portable doppler flow meter to verify readings. The battery-powered unit displays, totalizes and data logs flow in any size pipe with a single-head ultrasonic transducer.

The forcemain is fed by four pumps. In normal operation only two pumps run at the same time. The two pumps located closest to the wall of the wet well create severe turbulence at the ultrasonic sensor mounting location and flowmeter readings were erratic. But results were conclusive when the two more distant pumps were operated. The readings from the portable meter corresponded exactly with the 30-32 gpm rate displayed by the magmeter.

Greyline Stingray level-velocity logger temporarily installed at the North Glengarry sewage lagoon.

The investigation then shifted to the site where the forcemain discharged to an open channel and then to a sewage lagoon. The existing open channel flowmeter had been installed for several months measuring flow to the lagoon through a 24” rectangular weir. The open channel flowmeter was reading much lower than the magmeter back at the pump station.

To compare readings from the pump station magmeter and the open channel flowmeter the Township of North Glengarry needed a data logging flow monitor for temporary installation. Dean McDonald, the Waterworks Manager, and Jose Castro, Greyline engineer, installed a portable Greyline Stingray level-velocity logger in the 16” pipe between the rectangular weir and discharge to the sewage lagoon.

The Stingray uses a submerged ultrasonic sensor mounted at the invert of the partially filled pipe to measure water level, velocity and temperature for flow calculation. They installed a stainless steel bracket in the invert of the pipe to secure the sealed ultrasonic sensor in position. The logger was operated for one month and logged data was downloaded to a computer and opened in the Greyline Logger software program. Flow cycles from the pump station were clearly illustrated in the log file and totals from the Stingray and magmeter corresponded within 1 gpm.

Conclusion

The results were clear. The portable doppler flow meter and level-velocity logger both corresponded exactly with the magmeter. By process of elimination the township was able to conclude and document that the permanent open channel flow meter at the lagoon site was malfunctioning. It has since been repaired and put back in service.

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