More Info - How it works - Watermaid SA, Suppliers of Salt Water Chlorinator for Swimming Pools and Spas

Button Gif Images by Vista-Buttons.com v3.05

How It Works

The Cell The Power Supply Maintenance

Watermaid salt water chlorinators have been manufactured since 1971 and are designed to convert salt in the home swimming pool to liquid chlorine (sodium hypochlorite) in an electrolysis Cell.

The Cell

In theory most metals can be used as a cell material to produce the sodium hypochlorite reaction but again most metals break down in the presence of chlorine very quickly. For the past 200 years carbon was the metal of choice. Today 99% of coatings contain a baked coating of the platinum metals group . Current is allowed to flow from a titanium anode to the positive coated titanium electrode and the reaction proceeds.

Coatings appear to be destroyed by:

High acid concentrations.
The presence of high copper and tin concentrations.
Normal copper/tin algaecides in the pool have little effect. Placing copper/tin algaecide blocks in the skimmer boxes provides the very high concentration needed and observations suggest that the ruthenium oxide coatings break down in a short period of time.
Operating the electrodes in water temperature above 70°C also appears to dramatically shorten electrode life to a few days.
Such situations occur where water does not flow freely through the cell such as diverting water to a heater, pool cleaner, spa, or waterfall. In such cases the cell may see little or no waterflow and overheat.
Operating the electrodes in pH conditions below 6.0.
It is important to thoroughly wash electrodes after acid washing with clean water before putting a cell back into the line.
Operating the electrodes with an AC voltage.
Occasionally rectifiers fail and the DC becomes AC. The AC current does destroy the titanium metal.
Scale, particularly calcium carbonate, if allowed to cover or touch the coated electrode will block the release of sodium hypochlorite and chlorine gas will form. Chlorine gas will dissolve all-platinum metals especially ruthenium oxides and titanium and destroy the electrodes.

The Power Supply

A power supply must deliver the required voltage and current sufficient to make enough chlorine to do the job. Most units on the market today use between 6.2 and 9.2 Volts DC and operate between 10 and 30 amps DC. The power supply is fitted with the safety devices needed to cope with any hydrogen gas build-up that may occur as well as provide timers and underwater light transformer housing.
[As a general guide 20 bathers need 1 Kg of chlorine and most private swimming pools need a minimum of 80 grams of hypochlorite (OCl) equivalent per day with 8 hours filtration to remain clean, clear and disinfected.]

Vary the chlorine and one can vary the filtration but one without the other will not clear a pool. The smaller the transformer means a higher operating temperature within the power supply. The current output is also limited. Higher temperatures mean greater wear-and-tear on wires, circuitry and components which then become prone to break down and failure.

Maintenance

Low Maintenance Advantages:

	Salt top ups are generally only every 6 months to a year
	With marblite pools the cell needs cleaning only every 4-8 weeks
	With fibreglass, paint or vinyl pool cell cleaning is every 2-6 months

All brands of Cells will require cleaning periodically to remove scale deposits which form on the electrodes during normal operation. Scale occurs from the calcium and magnesium levels that are in the pool water or are added from powdered chlorine, calcium chloride additions or leaching from pebble or marblesheen surfaces.

Method of cleaning:

Prepare a solution of 1 part Hydrochloric acid and 10 parts of warm water in a separate container.

Pour it into the cell until the scale deposits have been removed.

Some deposits dissolve in a few minutes while others may take 30 minutes to an hour.

Repeat the process if the effervescence subsides and the cell is still not clean.

[Acid solutions with a hydrochloric acid strength greater than 5% will slowly damage and dissolve titanium. Concentrated hydrochloric acid is 33%.]

Other maintenance is usually limited to correcting the salt level and water chemistry balance in the pool - ie: pH, total alkalinity, Cyanuric acid and servicing the filtration system so that adequate water flow is maintained.

Sand filters in addition to normal backwashing require prolonged and adequate backwashing at least once a year as debris permeates from top to bottom of the sand bed.

[Remember, the slower the water flows through the chlorinator cell the slower the rate of scale build-up. Scale build-up is a direct result of calcium levels in the water and will build up more quickly in warm water, high pH and cells that see more water across their surface.]

Cyanuric acid (chlorine stabiliser) should also be added to all pools which experience strong sunlight in order to minimise loss of chlorine due to sunlight. Recommended level is in the range of 30 to 50 parts per million (ppm). Below 25 ppm cyanuric acid has no stabilising effect on chlorine. Chlorine has a half life of 35 minutes in strong sunlight. i.e. 1 ppm chlorine is reduced to .06ppm in just 140 minutes! Cyanuric acid can slow this loss to .4ppm in 140 minutes.

[For your information]

The equation for the process where salt is converted to sodium hypochlorite, or, as it is commonly known 'liquid chlorine' by electrolysis with a DC voltage is:

Salt + Water + DC current = Sodium hypochlorite + Hydrogen
NaCl + H2O = NaOCl + H2 (g)

The reaction is valid for water temperatures 5°C to 30°C. Below 5°C some Sodium Chlorate (NaClO3) may be formed and above 30°C some Sodium Perchlorate (NaClO4) may be formed. These two insoluble substances form part of the scale which builds up on the negative (titanium) electrode in the cell. Other base metallic elements such as calcium, magnesium, copper, iron and a variety of positive metallic ions will plate out or scale the negative titanium electrode. This build-up can stop the current flow of water and slow the reaction down. Therefore it is essential to de-scale the electrode from time to time.