Running 2 ROs on same system?

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Floyd R Turbo

Aquarium Advice Addict
Joined
Feb 7, 2009
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West Des Moines, Iowa
I have an idea that I need some feedback or critique on. I have an existing 3 stage (+ taste) with a 4g holding tank in the basement that feeds the fridge and sink tap, with another 4g tank below the sink. The system is around 20 yrs old, the basement tank is original (and probably has a bad bladder) and the sink tank is about 8-10 yrs old. It has poor capacity and no shutoff valve, and probably a high dump ratio.

So here's what I'm thinking of doing, I'm going to buy this

http://cgi.ebay.com/150GPD-0ppm-Rev...emQQptZLH_DefaultDomain_0?hash=item19b8e266f9

and hybrid the 2 systems together. I'm going to throw the older 2-stage prefilters away and use the new 3 stage, then split the output to both RO membranes, like this

img_1063177_0_bc1dd5529ac297286612cef574716170.jpg


And add the auto-shutoff around the old filter/tank system.

My idea here was that I don't want to drain out the tank system on the household side when I fill up the Brute can (or when I empty it out to do a PWC). I figure this way, one system for the house, one system for aquarium water, and they both run off the same pre-filter block.

From my understanding of RO systems, you have high pressure on the supply side that would prevent backflow through the membrane, but if I connect 2 RO membranes feeding separate systems from the same supply line, is there any possibility of backflow? For instance, if the household tanks are full and that system is shut off via the auto-shutoff, and I drain the trash can so that the aquarium system is now in full-production, is there any possibility of the tank system backflowing through the household RO membrane? I figure it wouldn't and if it did, it would only be enough to lower the pressure to match and then it would stop. But I figured it was worth asking.

Any other observations or comments welcome.
 
I had another thought, could I run the house system off the same membrane as the aquarium system, but put a backflow preventer on it so that when the trash can/holding tank is filling, it will hold it's water in the tanks? Or even hybrid the shutoff valve somehow so that when the household side gets used, it will fill the holding tanks and not the trash can, until the tank it full then switch back over to the filling the trash can?
 
I was wondering what the water pressure will be after pre-filter. You might need a pump to push water through DI filters. And maybe up to house taste filter. I think it looks good. As far as running both on one, that might work. Draw it out if you dont mind.
 
Standard municipal water pressure, so that really shouldn't make a difference. As far as using a hybrid shutoff system, there's really no way to make that work that I can tell. A shutoff works on differential pressure, so you have the high pressure (before membrane) and low pressure (after membrane) and when the low side increases in pressure from the tanks filling, it pushes a plunger over to the high side and stops flow (before the membrane). There's no way to use one in the way I was thinking. You would have to have the household tank pressure side be the determining variable in controlling it's own flow on it's own side of the system, as well as the other side. It just won't work.
 
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