A flow meter should be installed on every recirculation line as well as on the filter backwash lines.
Flow meter shall consist of a sensor and a display/transmitter. The sensor is a Signet insertion style magnetic flow sensor (GF Signet 2551) that has no moving parts. It is capable of measuring flow accurately (+/- 1%) even in dirty liquids. Sensor can be mounted upstream of filter if necessary but downstream of filter is preferred location.
Sensor shall have a frequency output to a display/transmitter device. The display/transmitter device may be part of the chemical controller or as a separate unit (Signet GF Signet 8550) normally mounted next to the controller. With either option, there shall be the ability to output a 4 – 20 mA signal to variable frequency drive. Signet GF Signet 8550 requires 24 VAC power. Coordination with electrical is important to confirm that the VFD is ready to receive this 4-20 mA flow signal.
The impact flow meter should be installed on the filter backwash piping. CH specifies around the F-3000 series flow meter by Blue-White Industries. If installed in Schedule 80 PVC pipe, the F-3000 impact flow meter will have a 12% variance in the reading. If this variance is unacceptable (which it is in Illinois), Schedule 40 PVC should be substituted for the backwash waste piping.
For magnetic flow sensor, install with at least ten pipe diameters downstream and five pipe diameters upstream on a straight run of piping. According to manufacturer these guidelines will achieve accurate readings even though their literature sometimes recommends more separation from fittings.
The magnetic flow sensor is acceptable for installation in vertical pipe as long as water is rising and not falling.
Ohio and Georgia require one flow meter for every pump.
LA County Dept. of Environmental Health and many other CA DEH offices require location and model numbers of flow meters shown on the drawings. The flow meters should be selected and model numbers from LACDEH approved equipment list.
On CA projects, the equipment schedule needs to be included as a standard item on the mechanical room drawing.
In Gwinnett County (Georgia), each pump system must have a separate flow meter.
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