RO/DI upgrade flow restrictor question

[Reefiez]

Hey guys, I'm about to add a second 75 gpd RO membrane to my RO/DI system, totalling 150 gpd. (non BRS ro/di system).

I will be installing them in series, ie, waste water from first RO membrane feeds into the second RO.

My current flow restrictor is 450ml.

I've been looking around, and Amazon flow restrictors seem to suggest 550/650 for 100-200 gpd systems.

BRS site recommends 800 for 75-100gpd systems (barrel style).

does anyone have any experience which is more appropriate? In terms of increasing membrane life, and decreasing waste water. Or is 450ml ok since i'm running them in series?

Thanks!

 

[homer1475]

I would give the guys over at spectrapure a call. Always willing to help out a fellow hobbyist, and they will hook you up with what you need.

On my 150GPD(BRS dual membranes) system, it uses a 550.

 

[fixingstill]

I just had this question this morning and I would like to share my findings (and so that I can come back to it).
A 75 GPD membrane normally has a 3:1 waste to production ratio. If you add 2nd 75 GPD membrane in series (reusing the waste water from the 1st), then you have 1.5:1 ratio. Two 75 membranes will produce 150 gallon good water and reject 225 gallon of waste water.
A 591 ML flow restrictor gives 591ML per min which is 851040 ML per day which is 224.8 Gallon per day.
But they don't make 591 ML flow restrictor. The closest is 600ML but I see 550ML is quite popular.
If you run the 75GPD membranes in parallel, then you need one 600ML/550ML flow restrictor for each membrane.

If you have 100GPD, you need 800ML / 750ML restrictor.

I suggest getting those flow restrictor + flush valve combo. Save you a lot of push-connect connectiosn (less risk of leaking.)

Oh, make sure you have check valve for your auto shut off valve.