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Purpose: We need to make sure that our lever arm is able to adjust the alum dosage automatically for the entire flow range of the plant flow. Since alum dosage is ultimately set by the float moving up or down the entrance tank as plant flow changes, we need to make sure the lever arm can respond to minimum and maximum water height in the entrance tank, which corresponds to the minimum and maximum plant flow rate. Head loss in the plant determines the difference between minimum and maximum entrance tank water height. Greater The greater the head loss in the tank, the greater would be the difference between minimum and maximum water height for any given any plant flow rate. Even though we would design the lever arm based on analytically calculated head loss, there is bound to be a minor difference between calculated minimum and maximum water flow and the actual heights. Calibration will also minimize the sources of error mentioned above. These are the calibration steps:
Step 1. Confirm and/or adjust the total head loss in the plant : Either either through inspection of the plant or dialogue with the experts on the ground, we . We need to confirm the minimum and maximum water height possible in the plant. If there is too much difference between minimum and maximum water height and the lever arm would not be long enough to respond to the change, we must decrease the total head loss in the plant. If needed, we can make adjustments to the rapid mixer to increase or decrease the head loss in the plant. Mark the location of the maximum water height.
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