What are direct speed drive and variable speed drive pumps?
Direct or fixed speed drives on centrifugal pumps are the most common choice for the pumps for reverse osmosis (RO) systems. This is because the operation is simple and once the required flow rate and total head (i.e., pressure) has been specified, the pump only operates on that pump curve. The direct speed drive type of design is well suited to applications where the feed water temperature is relatively constant or the variability of temperature is low, probably less than 5°C between high and low temperatures. Variable speed drives on centrifugal pumps have been used when the temperature variation on the feed water is high. The use of variable speed drives allows you to use less energy because you operate on more than one pump curve depending on the feed pressure required.
