Double DI-lemma

[DeLaCruz]

Wanted some advice on the cost efficiency of a DI system which i use. My water TDS for my location is 70ppm, I recently had a van system installed with single DI onboard.

When i purchased this van system  i was told: "i could achieve a double DI filtration by adding another DI vessel next to the tap i fill from."

I am unsure if this was incorrect? I have to run 15m from tap to van.

Recently i was told (ironically by the techy who fitted the van) for a true double DI system i would need to go straight from DI vessel to DI vessel with no chamber between, otherwise it would be an inefficient use of resin. I am considering adding the second vessel to the van if it makes a big difference on resin cost. 

Fwiw the water coming from the first DI vessel is TDS 0-1 so its pure water going into the van to be re-filtered by the van vessel, which seems illogical.

Thanks in advance for any advice ?

 

[spruce]

Wanted some advice on the cost efficiency of a DI system which i use. My water TDS for my location is 70ppm, I recently had a van system installed with single DI onboard.

When i purchased this van system  i was told: "i could achieve a double DI filtration by adding another DI vessel next to the tap i fill from."

I am unsure if this was incorrect? I have to run 15m from tap to van.

Recently i was told (ironically by the techy who fitted the van) for a true double DI system i would need to go straight from DI vessel to DI vessel with no chamber between, otherwise it would be an inefficient use of resin. I am considering adding the second vessel to the van if it makes a big difference on resin cost. 

Fwiw the water coming from the first DI vessel is TDS 0-1 so its pure water going into the van to be re-filtered by the van vessel, which seems illogical.

Thanks in advance for any advice ?

You need to understand the principle behind double di.

Your resin is working when your tap water comes out of the di at 000. But there will come a time when the water comes out at 1, then 2, then 3 and slowly increases until the point where the resin is completely spent.

If you decide that you don't want to be cleaning windows with pure above 4 say, then when your pure reaches 4 you replace the resin in your di vessel to get back to zero. There is still some life left in the resin at 4, but you throw it away and replace it with new. If you add a second di vessel after the first at 4ppm the second vessel will mop up those 4ppm. Your resin in the first di vessel will still be removing the majority of the dissolved solids in the water, so you will be using your resin more efficiently.

There will come a time when you decide that the resin in the first di vessel is spent. So you refill that with new resin and swap the vessels around. In time the resin in the leading vessel will loose its efficiency and the cycle will be repeated.

You could put a di vessel at the tap and have one in the van with a length of hose inbetween. You could also have the 2 di vessels after the pump and filter water on demand. I would do this as it would be easier to fill my van's tank from the tap directly. Water will go through the vessels slower so allow more time for the resin beeds to work.