R/O, di then IBC storage tank. We did it that way as there were 2 of us then later a third cleaner all drawing water. If we didn't then we would have to have invested in another 2 di vessels for the remaining vans in those days. (The 2 of us remaining mainly work off my van these days.)
We have never had an issue with the tds of the water in the van's tank. Our rejection rate from the r/o is between 2 and 3 and the resin in the 7 liter di vessel lasts about a year.
Toward the end of the year the water tds from the di vessel reads 1ppm on the inline tds meter, but my hand held tds meter still has it at zero from the van's tank. I'm guessing my hand held tds meter is accurate as it was recalibrated to 34ppm calibration fluid. Either way, I'm not going to loose sleep over 1ppm difference between tds meters.
Resin change time is usually around September/October. Being this time of the year the windows dry quicker and we do take the opportunity to do visual window inspections from time to time to ensure the job is right.
Had the di vessel been on the van it won't necessarily mean that water was being filtered slower. I would estimate that we draw more water through our pumps per minute than the 4040 produces at the same time. My gut tells me we draw about 3lpm through the pumps (not continously) where the r/o produces 2lpm of pure (continously). I appreciate that this statement can be argued convincingly either way. If having a di vessel on the van makes better use of the resin, then I believe in my case the difference is negligible. I would also have to make provision for properly securing it if it was on the van.
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