9. Calibrating Chemical Feed Pumps

9. Calibrating Chemical Feed Pumps

CALIBRATION OF CHEMICAL FEED PUMPS:

The chemical feed pumps actual flow rates can differ from the calculated flow rate by as much as 2 times depending on the amount of back pressure provided by the process fluid.  The pumps must be calibrated to ensure that the correct dose of chemical is being injected.  Once the pump has been calibrated and the multiplier is known it won’t change over the entire % speed range provided the % stroke remains the same.
  1. If the pump is supplied with a calibration column on the suction side of the pump:  Fill the calibration column with chemical and switch the valving, so the pump is drawing from the calibration column only.  With a stop watch, time how long the pump takes to empty a metered volume of chemical out of the calibration column.  Divide the volume pumped by the time it took and correct the units to GPH and compare to the settings on the pump.  i.e.  A chemical pump pumps 200mL out of a calibration column in 30 seconds.  Flow Rate = 200mL / 30 secs = 6.6667 mL/sec * (60 sec/min * 60 min/hr.)/1000 mL/L / 3.78L/gallon = 6.35 GPH.
  2. If the pump isn’t supplied with a calibration column, then the chemical injection point must be removed from the process piping and a graduated container would be used to capture the chemical being pumped while timing how long it takes to fill a specific volume.  The pump flow rate is calculated in the same method as above.
  3. To calculate the multiplier, divide the actual flow rate by the calculated flow rate of the pump.  To use the example above, if the calculated flow rate was 5.25 GPH and the calibrated flow rate was 6.35 GPH, the multiplier would be equal to 6.35 GPH / 5.25 GPH = 1.21.

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