System and process requirements:Supply and demand controlled systems

Supply and demand controlled systems

When designing a pumping system the process requirements of flow and pressure have to be well defined. These requirements will dictate the selection of pumps and the way the pumps are controlled. The need to control pump operation varies depending on whether the pumping system is supply controlled or demand controlled.

Supply controlled systems pump away incoming flows. They may need to match the rate of variable inflow, and hence they may require variable pump operation. If the inflow varies, one or several constant speed pumps can usually accommodate these variations if some storage volume is provided, however this may not always be the most cost effective approach, an infinitely variable flow may sometimes be more appropriate. Examples of supply-controlled systems are pumping sewage, storm water, discharges of process liquids, and de-watering or flood protection schemes.

Demand controlled systems pump liquids into a process or to recipients at a constant or variable rate, as required. Examples of demand-controlled systems are those pumping drinking water, cooling liquid and process liquid. Again, variations in demand can be handled by variable speed pumps or by using storage in combination with constant speed pumps.

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