HOW DO WATER SOFTENERS WORK?
The job of a water softener is to extract calcium and magnesium from water and replace it for (exchange it for) either sodium from the softener salt or potassium from a salt substitute called potassium chloride. The medium used to do this is called ion exchange resin, resin, or synthetic zeolite. The medium is also reasonably effective in removing clear water (ferrous) iron, manganese, copper, radium, aluminum and some other trace metals.
The resin is made from two materials: styrene and divinylbenzine. This material is impervious to most chemicals, can be operated at temperatures up to 212 F, pH from 1 to 14 and has a normal service life measured in decades if properly maintained. About the only thing that shortens the resin’s life are strong oxidizing agents such as chlorine or repeated freeze/thaw cycles. Removal of chlorine before a softener with activated carbon, KDF or a feed of sodium bisulfite will significantly enhance the resin’s life.
Once calcium and magnesium is exchanged for sodium or potassium through the softening process the water is referred to as softened water (not soft water, which is nature’s water before it has dissolved minerals into it). Water before softening is called hard water. The level of hardness is usually expressed in grains per gallon as calcium bicarbonate. A grain weighs 65 milligrams. A grain per gallon can also be expressed as 17.1 milligrams per liter. For domestic purposes, a remaining hardness of 1 or 2 grains per gallon is acceptable, commercial applications normally require 1 grain or less and high temperature boilers will need 1 mg/l or less of residual hardness.
The math required to properly soften water for boiler applications is quite extensive and requires the results of a complete water analysis to properly calculate. The technical staff at Dime Water, Inc. is prepared to do all of the calculations and recommend the proper equipment.
The calcium, magnesium, sodium and potassium all exist in the water as ions, which by definition are dissolved and cannot be seen. The hardness ions cause scale in pipes, soap curd, water heater failure, poor soap use, etc. Sodium and potassium do not cause these problems so there are aesthetic and financial benefits to softening water.
Standard beads of resin are about 1/64? in diameter and the color varies from almost white to black depending on the manufacturer. Made of a blend of 92% styrene and 8% divinyl benzene it is durable from just above freezing to boiling temperatures. The benzene compound is mildly soluble in water with free chlorine, so pre-treatment with activated carbon extends the life measurably. Plan on a resin life of 15 years + with proper care. The resin used is the same for commercial water softeners as well as residential.
Running water across the resin is called the service cycle. When all of the sodium is gone, the water softener is said to be exhausted. At that point sodium or potassium mixed with water called brine must be introduced in a process called regeneration where the calcium and magnesium is run to drain and is replaced with the sodium or potassium.
The resin capacity is considered used up when exhaustion is reached. Water hardness is expressed as grains or grains per gallon (GPG) or as mg/l and 1 GPG+17.1 mg/l. The capacity of resin is expressed as kilo (thousands) of grains per cubic foot. The normal capacity of resin is 30 kilo grains/30,000 grains per cubic foot.
As an example: Water containing 10 grains of hardness and a 1 cubic foot commercial or residential softener. 30,000/10=3,000 gallons.
This is the frequency or regeneration. Commercial water softeners should always be sized by a professional!
KEY NUMBERS USED TO SIZE AND OPERATE A WATER SOFTENER
- To get 30,000 grains from a cu. ft. of resin, salt with 15 pounds of salt
- To get 20,000 grains from a cu. ft. of resin, salt with 8 pounds of salt
- One gallon of water added to salt will dissolve 3 pounds of salt and produce brine for regeneration
- Intermittent max. flow ranges from 5 to 15 GPM/cu. ft of resin
- People within a home in the US consume 60-75 gallons per day per person