3rd RO Membrane in series

[Sidius]

Hello!

I have done some searching and haven't found the answers that I'm looking for so I figured I would ask what the collective thinks about running a 3rd RO membrane in series with my RO/DI system.

Background info... I currently have a 4 stage 100g per day AquaFX RO/DI system. I'm pretty lucky in that the water in my area is very low TDS to begin with (9 - 11 TDS coming from the garden hose supplying my RO system).

I've been wanting to install an upgrade kit to increase the output and waste less water but instead was recently given a free 200gpd Aquafx system that someone no longer used. After a good cleaning it's in decent shape. Since it cost me nothing, I figured I would combine the two to make an even better system by adding additional carbon and DI resin stages. That gives me a total of 3 RO membranes at my disposal. I was thinking that since I have them and my TDS is low to begin with, adding a 3rd RO membrane in series would up my output even more, further reducing waste water. If I start with 9 TDS in the first stage, 2nd stage would be around 12-13 and 3rd stage around 16-17 TDS, I would not be worried about taxing the membranes... am I crazy or throwing money away with the extra cost of resin, filters, etc?

 

[Sidius]

I should add that I'm a bit of a hoarder of equipment so I doubt I'd sell it. It's much easier to store it somewhere than convince my wife that I need a new RO/DI system if something ever needed replacing. Free stuff is gold to me lol

The other option is that I keep stuff for parts until they've collected enough dust that I can convince myself I no longer need it lol..

 

[Salacious Crumb]

I run 3 membranes. Works great as long as you have enough pressure. Go for it. I get a 1:1 waste to product ratio.

 

[Sidius]

Great to hear!! I have just a hair under 80 PSI currently.. Is there a recommended PSI for extra membranes?

 

[Sidius]

Also... @Salacious Crumb , If you could post a pic of how you plumbed all 3 membranes into one output to your DI resin, that would be great. I see there are cross style 4 way fittings or I could use a couple Y's somehow... thanks in advance!!

 

[kyleinpdx]

Great to hear!! I have just a hair under 80 PSI currently.. Is there a recommended PSI for extra membranes?

80psi will do just fine, I have to run a booster pump and run it closer to 90psi but it would be a heck of a waste to use a booster pump for an extra 5 or so psi. You dont want to go higher than 90 or so regardless of the number of membranes you have.

 

[Salacious Crumb]

Also... @Salacious Crumb , If you could post a pic of how you plumbed all 3 membranes into one output to your DI resin, that would be great. I see there are cross style 4 way fittings or I could use a couple Y's somehow... thanks in advance!!

I have separate 3 stage di resin for each membrane output. But yes yes can combine them easily with y fittings. I just prefer longer contact time with the resin.

 

[Sidius]

@Salacious Crumb I guess when you're running 3 membranes into 1 output, it pushes water through the DI resin a lot faster. Are there flowrates for resin that I need to worry about exceeding?