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Water Softeners - How They Work
All ion-exchange water softeners operate on the same principle regardless of the brand. There is a mineral tank, which contains 'cation resin', and a second tank (or bin), which contains salt (common sodium chloride, NaCl). The resin is actually millions of tiny beads about the size of the period at the end of this sentence. The tanks may be from six to ten inches in diameter and from 12 inches to five feet in height for domestic use. A multi-cycle valve on the mineral tank with a metering or timing mechanism automatically controls the equipment. The ions of the molecules of the principle substances that make up limescale; calcium and magnesium, are attracted to the resin as mains water flows through the mineral tank. The water exits the mineral tank into the household mains as soft water.
After a certain volume of water has passed through the mineral tank the resin is eventually overloaded and ineffective. For the average household this takes approximately 3 days at average consumption rates. At this point (in the middle of the night) the valve will carry out basic functions. First of all, the system will backwash itself in order to clean out any substances which may have accumulated. It then transfers saltwater from the salt bin to the mineral tank. Minerals which have been removed from the water and accumulated on the ion-exchange resin are washed off from the effects of the salt water. The water softener will then go into another backwash cycle draining off the mineral and salt laden water while rinsing with fresh water. This procedure may vary depending on the model and manufacturer. Fresh water is automatically put back into the salt bin and the process is completed.
The method by which the cycles are controlled and the resin capacity and price are the main differences between different brands of water softeners. The principle remains the same with all brands. The size of mineral tanks vary. An 8x35 or 10x23 mineral tank (with valve) is typical for a one family home. Salt tank sizes vary in capacity from 25 litres to 75 litres and larger. The system will use, on average, one bag (25Kg) of salt per month. A 'Volumetric' or 'metered' model is water meter controlled therefore will use less salt.
An ion-exchange water softener installed under the right conditions and properly maintained may be expected to give 12 to 15 years of good service. Owner maintenance basically involves adding a bag of salt once a month.
Bacteria: Water softeners do not remove bacteria. See Drinking Water Filters for more information about dealing with bacteria.
Other related information
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