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Water Softeners FAQs

Water Softening FAQs

What is a water softener?

The ion exchange water softener is the most common tool used in the removal of scale-forming calcium and magnesium ions (known as temporary hardness) from hard water. In many cases, a water softener can also be used to remove ferrous (soluble) iron from a supply. A typical water softener supplied from Derwent Water Services has four major components which are also available separately as spares from our website.

Typical components of a water softener:

  • a pressure vessel to contain the ion exchange resin
  • the ion exchange resin
  • a control valve (i.e. Siata, Fleck or Autotrol)
  • a brine bin

The size of water softener required varies according to the flow-rate and the hardness of the water. However, Derwent Water Services does stock a large range of industrial water softeners and iron-removal filters.

How does a water softener work?

A standard water softener works by allowing hard water to filter downwards through a bed of ion exchange resin. The ion exchange resin attracts the calcium and magnesium ions (hardness) and replaces them with sodium ions which are less problematic for water systems and will not cause scale build-up. Once the ion exchange resins are saturated with hardness, the regeneration sequence on the water softener begins.

The water softener's regeneration sequence begins with the backwash cycle. The backwash cycle reverses the flow of the water to pass upwards through the ion exchange resin bed. This operation frees the beads of the ion exchange resin ready for the next step in the regeneration sequence.

Step 2
in a water softener's regeneration sequence is to saturate the ion exchange resin with a brine solution. It is during step 2 that the ion exchange resin releases the calcium and magnesium ions and replaces them with sodium ions. Both the calcium and magnesium ions flow along with the water and excess brine solution to drain.

Step 3
in a water softener's regeneration cycle is a down-flow flush to drain. This removes any excess brine left on the ion exchange resin beds.

Step 4
returns the water softener back into service mode.

The frequency of a water softener's regeneration cycle is usually pre-set, using a timer or a counter-signal from a water meter.

How do I know what size of water softener I need?

Following is the information you need to size your water softener:

(i) The total hardness of the incoming water supply the required service flow rate

(ii)If you need any assistance regarding the sizing of any water treatment plant, including water softeners and iron removal, our technical support team is always happy to help.

What sizes of water softener are available

Derwent Water Services stocks various sizes of water softening equipment, including simplex water softeners, duplex water softeners and triplex water softeners - ranging from 10" diameter composite vessels to large diameter steel water softeners as shown on the home page.

Specific problem with existing water softener

If you have a specific problem with any existing water softener on site, you can contact us at Derwent Water Services where we will be more than happy to give advice or to send one of our service team to help.

Is softener water suitable for drinking?

Most water softeners use ion exchange resin which is suitable for potable use. However, the taste may be changed, and more important is that the level of sodium dissolved in the water will increase. There are recommended levels of sodium for drinking water so you should check that the level of hardness in the water, when replaced by sodium in the water softener, does not add to the base level of sodium so much that the sodium exceeds recommended limits. Usual practice is to have a take-off point for drinking before the inlet to the water softener.

How soft will the water be from my water softener?

A water softener will usually effectively reduce water hardness to zero. There will usually be a small leakage level of hardness. This can be reduced further by increasing the salt use when regenerating the water softener. Leakage will be worse if the level of dissolved solids is very high.

In very bad water, there is a threshold level of salt use on the ion exchange resin, below which the water softener cannot be used.

What is the maximum flow I can get through my water softener?

The maximum flow through a water softener is usually limited by the size of the pipework and the increasing loss of pressure as you try to put more water through the softener. There are recommended limits, though, for using ion exchange resin in a water softening application. Typically 40-50 bed volumes per hour are quoted by the manufacturers so, for 100 litres of ion exchange resin, you can soften up to 5,000 litres per hour. How long you can do this for will depend on the hardness of the feed water. Don't try to soften water at a very low rate; it may tend to find the easiest path through the ion exchange resin and exhaust these first, leaking hard water before the whole of the ion exchange resin in the water softener is exhausted.

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