how does a water softener works

How does a water softener work? Everything you need to know.

What is a water softener?

A water softener is a device which will soften your household water, or you may say that it removes hard water. Water can be defined as hard when it contains minerals like magnesium and calcium.

Hard water leads to scale buildup, which will lessen the life of your appliances contrary to softened water which will increase it. Soft water also is better for your skin and hair and has more benefits.

See here why you need a water softener.

How does a water softener work?

how does a water softener work diagram

So, what’s the “magic” behind a water softener? What happens with the water after it gets inside?

First of all, a softener has three main components:

-The head valve is the control unit found at the top of your water softener and which controls all the cycles and the water flow.

-The resin tank in which the actual softening process happens through ion exchange.

-The Brine tank where the salt is stored, it’s used to mix a solution called brine that helps with the regeneration cycle.

There are four types of water softeners, they can work manual, semi-automatic or automatic and are rated by the amount of water hardness is removed before each required regeneration.

Semi-automatic:  this type requires an operator to start the regeneration cycle, the rest is done automatically by the machine.

Automatic: they come equipped with a timer which can be set by the user to automatically initiate the regeneration cycle and the required steps to finish it. You’ll only have to add salt and remember to set the timer, it is usually done during low water usage times, like between midnight and 5 am.

 Demand-initiated regeneration (DIR): as the name suggests this kind of water softener initiates and handles automatically the regeneration based on your soft water needs.

It determines how to activate it by measuring the change in electrical conductivity of the resin bed or by measuring how much water you consume in general or either by detecting a change in the hardness of the water.

They come equipped with two softening tanks and a brine tank, so one can work while the other one is recharging. With this type of water softener, you may save on salt and water usage since the regeneration starts only when it’s needed.

Off-site regeneration: Those can be rented and used at home for exchange and then regenerated at the central location.

Here’s a summary of how a water softener is working:

It all starts with your main water supply which is passed through the resin tank, inside it, are thousands of ionic beads. As the water flows down in resin tank, it removes all hard minerals like magnesium, calcium, iron and other contaminants then returns soft water.

Most water softeners use a process called ion exchange, also there are other methods used in the water softening process.

So, let’s explore this subject more than we’ll talk about others.

Ion exchange method

Ions are electrically charged particles which form when minerals dissolve in water.

Some synthetic and natural materials can exchange ions by removing minerals from water. Ion exchange materials are found in the form of small crystals or beads. They create a bed several deep feet so that water can be transferred.  

The beads are produced out of polymer which are attached to charged functional groups. In order to ensure charge neutrality, the functional groups lure and loosely attach counterions of adverse charge.

For example, let’s take calcium carbonite (CaCO3), it creates a carbonate ion with negative charges (an anion) and a calcium ion with a positive charge. (a cation)

At the same time, counterions may be transferred from resin to the solution, in exchange for alternative types of ions. Meaning that the ions can be exchanged.

E.g. Water passing through a simple cation exchange softener removes all magnesium and calcium ions and replace it with sodium ions.

For the interested here is the reaction which removes calcium from hard water.

water softener ion exchange formula

Resin beads become saturated with magnesium and calcium after enough water has moved through the bed of ion exchange resin. Meaning that the water flowing through the resin won’t be softened.

That’s when the column is regenerated by a strong sodium chlorite which passes through.  In order to surpass the inherent affinity of the resin for magnesium and calcium, a vast supply of sodium is needed.

If the resin requires regeneration, the softener is ignored, and while the regeneration happens your household will use some hard water.

There are four types of resin:

Strong Acid Cation Resins this is the ion exchange resin used by the majority of home water softeners, also in the demineralization process as well. This kind of resin needs a quite big amount of regenerant, especially when it’s being regenerated with an acid. But the pros are low cost, resistance and nonselective removal of all cations.

Strong Base Anion Resins are usually used in the demineralization process, alongside strong acid cation resins. The regeneration of strong base anion resins is usually inefficient and it needs a lot of regenerant.

Weak Acid Cation Resins not as popular as the strong base resins but can have particular applications due to the better selectivity for Ca 2+ and Mg 2+.  These resins can also be used for a two-bed system together with strong acid resins because they efficiently regenerate with acids. To improve the process economy and efficiency, the weak acid resin can be regenerated with depleted acid from the regeneration of strong acids.

Weak Base Anion Resins they can be used for the selective elimination of chlorides or sulfates, and for deacidification too. And can be regenerated with near – stoichiometric amounts of a strong base.

Water softener regeneration

It all starts with the service cycle, where the calcium and magnesium ions are exchanged for sodium ions. As the water gets softened, the exchange capacity is depleted and hardness starts to leak past the resin bed. At this point, the softener pauses the service cycle and starts to regenerate.

The next step is brine fill, in which salt gets added in the salt storage, then it dissolves and it creates a saturated or near-saturated brine solution. The exact amount of water added varies between systems, it can be controlled by a float control valve or by a flowmeter. The same thing goes for the brine fill too, some water softeners do it before regeneration and some after it. Though it is better to do it after the regeneration process has ended, the benefit is better reliable control of the salt concentration during regeneration.  Because by next time the regeneration cycle happens, the brine would be saturated.

Now we move to the next stage: brine draw.

In this stage, the brine is moved by a venturi system in the brine tank. The water flows through a specially constructed nozzle and draws the brine into the water system. This leads to the transfer of saturated brain in the brain tank to the ion exchange tank, at the same time diluted to the required concentration of 10-15% NaCl. 

The diluted brine gets distributed through a riser pipe in the ion exchange resin tank, and it’s introduced into the tank by a brine header. Then through the stratified resin bed, the brine flows up and then flows out of waste. The ion exchange resin gets regenerated by the flow of brine from the calcium and magnesium form back into the sodium form.

The composition of the waste brine will be different during regeneration. Frist will be abundant of CaCl 2 and MgCl 2 but this changes as the process complete. The concertation of sodium chlorite will be higher and the concertation of magnesium and calcium will be lower.

After the water softener completes the brine draw process than it moves to the next one called slow rinse.

In the same direction as in the brine draw process, the raw water is introduced into the resin bed. At the end of the process, the brine in the resin bed will be a mix of calcium, magnesium, and sodium chloride, which in the finished water product would be unwanted. By slowly displacing and diluting the brine the slow rinse process makes sure that the brine has entirely passed through the resin.

As the brine displacement happens, some further regeneration will occur too, because, at the brine draw sequence end, the resin bed brine will be rich in sodium chloride.

As the slow rinse process ends, the water softener enters in the backwash stage.

Same as in the slow rinse process, raw water gets in the pressure vessel via the riser pipe and is introduced to the resin bed through the header. But there’s a difference, in this process the flow of water is much higher in order to fluidize the bed of ion exchange resin.

The high-water flow is able to remove impurities and dirt that were filtered out of the water during the service cycle. Also, during the backwash stage precipitated iron oxides will be eliminated.

The resin fluidizing loosens and fluffs the bed to make sure that all the ion exchange beads will make contact with the flow of water.

Besides these two processes, the flow of water in the backwash stage decreases the amount of regeneration brine in the bed.

The backwash stage requires a high flow of water in order to be highly effective in fluidizing the bed of resin, unlike during the service cycle.

And finally, we move the final stage which is fast rinse.

Raw water during this process enters the pressure vessel the same way as in the service cycle and it gets out through the riser pipe. The water flow direction is the same as in the service cycle. Any regeneration brine left in the system gets removed and the water flow repacks the resin bed during the fast rinse process. When this process has ended, the regeneration sequence is complete and the system moves into the service cycle.

Conclusion:

You have enough information here to get familiar with how a water softener works. This is useful if you’re looking to buy one, knowing how it works will help you maintain it better and make sure it will last as long as possible without breaking.

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