Feed Rate Adjustment and Equipment Accuracy

Calibrated chemical feed equipment ensures that a specific equipment setting will deliver the expected amount of chemical to the application point. Adjusting the chemical feed equipment is necessary to maintain a consistent dosage as treatment plant 

Liquid sodium hypochlorite can lose strength over time. 

Plants with system control and data acquisition (SCADA) systems may adjust chemical dosage automatically. The SCADA system communicates the feed setting to the feed equipment to achieve the needed chemical dosage. These systems also offer manual feed equipment control to achieve needed dosage changes. In either case, the dosage is determined first, and then the equipment is adjusted to dehver the correct amount of chemical to match the volume of water being treated (fiow). 

Although the feed equipment is calibrated and set to deliver the correct amount of chemical, each system has its own accuracy limits. Every chemical feeder has a quantifiable error range. This is usually expressed as a percent (%) error. The equipment may deliver an amount above or below the set point (needed amount) equivalent to this percentage. Equipment dehvering chemical with the needed accuracy should be selected. 

The feed equipment is not the only source of error. The strength of the chemical may vary, thus introducing an error. When measuring the chemical strength, a percent error should be included, depending on the method used. Other parameters, such as temperature, altitude, pressure, and vacuum variability, may cause errors as well. All of these errors can combine in unpredictable ways to result in an amount delivered that is different from the intended amount. 

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