Safety features of a salt chlorination system

Hi Mark,

Can you explain the underlined section below for me, does the water flow detection work because of the absence of water & the presence of gas, all off the back of a single sensor or detector?

Or are these two different detectors, i.e. one for water flow & one for gas?

Safety features include electronic water flow detection (NOT a mechanical flow switch/pressure switch) for gas detection & high current protective shutdown.

A/

Hi Paul

The gas sensing tang is on the side of the cell close to the top.  The power supply monitors it for voltage.  If it is covered with water, the power supply will see voltage when the cell is powered.  It will simply pick up the stray voltage from the electrodes in the water.  The gas sensing tang is simply a piece of titanium welded to a wire there are no moving parts so it is about as reliable as you can get.

In the cell, the electrodes are splitting the salt and at the same time they are splitting the water to produce hydrogen and oxygen.  It is this hydrogen/ oxygen gas that makes a salt water cell dangerous.  In a Watermaid, water flows up the cell between the clear outer tube with the mesh anode, and the inner titanium tube (cathode).  It rolls over the top of the inner tube and then down the centre of the titanium tube and ejects into the bypass water flow.  As the water rises a current is passed through the water to generate chlorine.  If you look, you can actually see the cloud of hydrogen/oxygen and chlorine coming off of the electrode.  It mixes with the water and flows out to the pool.  If the water flow slows down too much in the cell, you can get a bubble of hydrogen/oxygen at the top of the cell.  If the water flow is too slow, the bubble will start pushing the water down in the cell.  If the cell was mounted horizontally, the gas could find its way down to the pool and build under a solar cover or go back and fill the filter.  This can be an explosion hazard.  Other manufacturers address this concern by putting a paddle switch in the water flow to sense when flow slows too much and shut down the cell.  In Australia It is a code requirement to have a gas sensor (like the paddle switch, or our gas sensing tang) but it must also have a gas trap as well.  If you picture the Watermaid cell, it stands upright to meet this requirement.  The safeties in the Watermaid work like this.

-The chlorinator is wired with the pump.  If the pump is selected on the Watermaid unit will have power.  If the pool pump is selected off, the Watermaid unit is powered off no matter what the switch position of the unit is.

– The cell stands upright so if water flow isn’t sufficient to carry away the gases, the water will be forced down in the cell.  Once water pushes down past the gas sensing tang at the top of the cell, the tang will not be able to see stray voltage from the electrodes any more and the unit shuts down power to the cell.

– to meet the gas trap requirement is easy for the Watermaid cell.  If the pump to Watermaid electrical connection isn’t correct or if the water flow slows for any other reason than pump shut down,  the gas tang is there to shut things down.  If for some reason the gas tang doesn’t work, the gas will continue to build in the cell and force the water further and further down the cell until the water finally is pushed past the electrodes.  At this point no more gas can be generated by the cell.  This is the gas trap which is an Australian code requirement.  If you have a horizontal cell in Australia, you need to put an upside down u in the plumbing with the cell at the top.  The pipe would go up one foot turn and go through the cell and then go down a foot and turn to continue on to the pool.  It is a lot of plumbing and it takes up a lot of space.  The paddle switches used by other manufacturers are not as reliable.  They tend to calcify and stick or break rendering them useless as a safety device.

There is no code requirement to have a gas trap in North America.  When a filter explodes and it takes out half of a house and kills someone I am sure that we will see a requirement here as well.

 

 

Mark

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