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Next fill the plant entrance tank to its height for maximum flow rate, halfway up the top row of holes in the linear flow orifice meter. The lever arm should be at the top end of its range (20 cm). Double check that the dosing tube system stays in place by moving the dosing ring up and down the lever arm. Make sure it does not slip out of the notches as this would cause improper dosing. Take an alum flow rate measurement at different locations along the lever arm. Check to make sure the CD is delivering the correct multiple of 2 mg alum per L plant flow at the respective notch. Expected alum flow rates at each notch are listed in the table below.
Notch from pivot | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Alum Dosing (mg alum/L plant flow) | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 | 24 | 26 | 28 | 30 | 32 | 34 | 36 | 38 | 40 | 42 | 44 | 46 | 48 | 50 |
Expected alum flow rate (mL/min) at full plant flow | (2 mg/L * 700L/min)/120 g/L = 11.67 mL/min | 23 | 35 | 47 | 58 | 70 | 82 | 93 | 105 | 117 |
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128 | 140 | 152 | 163 | 175 | 187 | 198 | 210 | 222 | 233 | 245 | 256 | 268 | 280 | 292 |
If the CD is not dosing as much alum as expected, the FC outflow tubing may need to be shortened. Cut off small pieces of the tubing and re-check flow rate. Conversely, a high flow rate would mean that longer tubing is needed. Also make sure to double-check that the tubing is in fact 3/16" inner diameter. The table above is designed for 3/16"ID tubing that is 3.25 m long.