Simples vs Duplex Softeners

Simplex Water Softeners
Simplex water softeners are the cheapest configuration of water softener design. The problem with a simplex machine is that during regeneration it will deliver either hard water or no water at all - depending on the type of piston fitted to the valve.

Obviously this problem can be minimised if the regeneration is programmed when little or no soft water is being demanded. Most domestic water softeners are simplex machines and they are usuaally programmed to regenerate at 2am when it is assumed that little or no water is likely to be used. With industrial machines it can obviously be a bit more complicated - because demand may fluctuate.

Simplex water softeners always consist of a single column of ion exchange resin. The regeneration of this is usually controlled by an automatic valve (manual regeneration versions are sold by very few companies, but these days they are usually very small machines and the regeneration is messy and inaccurate).

Duplex Water Softeners
Duplex water softeners work on a slightly different principle - instead of a single tank or column of resin you have two, both controlled either a single valve or in the cases of larger plant, by independent valves which are linked together to communicate with each other.

Duplex softeners only ever use a single tank for softeneing, with the other tank essentially acting as a spare. When the media is exhausted in tank one, the valve head will trigger an immediate regeneration on that tank BUT importantly switch production of mains water over to the second, thereby ensuring soft water is continually produced. The second tank is used continuously until it's media is exhausted, at which point it is triggered for regeneration and the production of mains water diverts back to the original tank.

The biggest advantage with a duplex softener is that you should always get soft water assuming both resin beds are in good order. However, these softeners are more expensive because you require multiple or more complex valves and two resin chambers (with media - which represents a reasonably proportion of the cost of a softener). Typically you'd size these both chambers to be handle a days worth of production at a minimum to reduce the overall stress that regeneration causes to the media, so it's almost like putting in two complete softeners to prevent what in most cases is a dowmtime of less than an hour - however, in some environments (particular 24hr manufacturing plants) these are absolutely essential.