Changing from 3 4 inch membranes to single 8 inch membrane?

[markct]

I have a cdl hobby 250 ro that currently has 3 of the 4 inch membranes in series, I am considering changing it out to a single 8 inch membrane. My thoughts are that for one thing its more permeate flow area, a single 8 inch membrane is cheaper to buy than 3 of the 4 inch ones, and also its cheaper to have it cleaned than 3 separate ones. Aside from having to buy a new vessel is there anything I am missing here?

[Flat Lander Sugaring]

Iv been told one 8 is equal to 4 or 5 4" membranes so yea less maintenance

[bowhunter]

The active area on an 8 inch is about 4 times the size of the 4 inch, but the problem is the 8 inch has a minimum concentrate flow of 10-12 gpm vs about 2-3 gpm for the 4 inch. This means you need a pump with 4 times more capacity.

[markct]

So im thinkin i might be ok with this as my recirculation pump is 15.5 gpm so thats above the 10 to 12 min, maybe not as effective as it would be if the membrane had near its max feed rate of 40 gpm i believe i read. Yet i think the increase of surface are may help make up for a slight decrease in performance. Also this is a relatively low pressure ro as well so that may help the matter as far as early fouling

[bowhunter]

Sounds like the pump should be fine. Did you say the 4 inch membranes are in series now? Was just curious.

[markct]

Yes they are in series. The Cdl hobby 250 is setup a little dif than many ro it has a procon pump that basicly pressurizes the system then the recirculation within that loop is done entirely by a seperate pump that just circulates it within that loop

[bowhunter]

That's interesting...so you use the concentrate needle valve to control the pressure or is there still a valve on the recycle and a separate valve on the concentrate?

[markct]

Yep the only adjustment is the needle valve for concentrate, simple to run and works well for the most part

[bowhunter]

Thanks. Just one more question. What kind of pump did they use for the recycle pump? That might be good way to expand my unit.

[markct]

Its a grundufos pump thats rated like 250 case pressure and 15.4 gpm flow, all stainless impeller and all. Has a 1/3hp motor. Expensive tho around 1800 i hear. If you look in the catalog at hobby 250 you can see it to the left of the flowmeter panel

[bowhunter]

Thanks. I believe Springtech uses the same pump.

[markct]

yea i been lookin at building a 2nd ro gota find a grundufos dealer and get some real numbers on one maybe a lil bigger