Positive-displacement pumps proportioning

Flow. Nonintrusive sensors that can be maintained at the process temperature are ideally suited to measure the flow rate of feed and product streams. Magnetic flow meters are suitable and inexpensive choice for aqueous streams. Organic streams with low dielectric constants require a vibrating tube mass flow meter to satisfy these criteria. Although commonly installed, flow meters that operate by inducing a pressure drop proportional to the flow rate present restrictions for solids accumulation that may alter the calibration. An alternative approach is to monitor the rotational speed of a positive displacement pump. Accuracy of this method is subject to wear and tolerances in the pump. 

A system to add chemicals to cooling tower make-up water is needed. Currently, the process operator adds the chemicals intermittently by starting a positive displacement pump which delivers the chemicals to the make-up water. The exact application of the microprocessor control system would be to monitor the cooling tower make-up water rate and add a precise amount of chemical proportional to the make-up water rate. 

Dosing relates to the various methods of applying chemical product to the cooling system. Dosing is normally proportional to the makeup water demands or the system volume, and the most common method is via the use of positive displacement, diaphragm metering pumps. 

The metering pumps are precision-made positive-displacement gear pumps, especially designed for melt spinning. They are used to ensure that a precise proportion of the melt from the extruder is delivered to each thread line and that the thread line denier does not vary with time. Modern pressure-feedback-controlled extenders operate remarkably steadily, but not steady enough for multifilament spinning without meter pumps. 

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