Is there a formula or way to know the appropriate amount to set the flow restrictor?
I’m pretty sure there’s something, but I haven’t used it in at least a decade and can’t recall what/how I came to the numbers I did… I’ll think on that one!
In the meantime; I can tell you how my functionally similar RODI is set up:
my old
BRS 6-stage 150GPD water saver plus RODI system came with dual RO membranes; Dow Filmtech 99.5% TDS rejection (IIRC, May be 99% TDS rejection instead…)
This system has either 1.5:1 or 2:1 waste: product ratio from factory (info not available online readily anymore, and I’ve long since forgotten…)
It employs a flush valve with built in flow restrictor. Factory flow restrictor was 400 liters per-day; producing the aforementioned waste:product ratio…. — I switched to a 550LPD flow restrictor, increasing the RO membranes product water purity at the expense of extra water discarded as waste!
My city water is 200-220PPM TDS, my RO membrane product water is 1-2ppm TDS. — you want to get your RO product water as clean as possible before the DI stage(s), thereby reducing DI resin consumption!
I added a second RO membrane
Once you start trying to pressurize multiple RO membranes, city water pressure starts to be an issue, depending on the specific municipality! — dual membrane RO systems often list a minimum operating pressure of 65PSI, and perform even better at higher pressures (up to the safe operating limit of the tubing, fittings, and housings, of course)! — An RO water pressure booster pump is what I use here, running the system around 90-95PSI!
Reducing it would be great since I live in a desert climate, but I also want 0 TDS water.
Your RO membranes will get you CLOSE to 0PPM TDS, but aren’t intended to do that on their own; this is where DI resin comes in! — we just shoot for getting close to 0ppm RO product water so DI resin is consumed slower!
I recommend plumbing your RO waste line to an outdoor water feature or garden to use the waste water for something! — mine goes to my outdoor aquaponic system!
