It started off as a MemTek 4x20...

[TuckerMike]

A few years ago I bought an older Memtek RO that originally had a 4x20 element with a 1.8gpm triplex plunger pump. The unit was upgraded to a 4x40 element at some point in its life. After I bought it the pump started leaking and I couldn't get parts for it, so last summer I undertook the project to totally rebuild the RO and upgrade it again. I'm now running a Procon 265 (4.7gpm) with two 4x40 elements in series. The unit also has recirc plumbed in. With the current setup I can get 3.5-4% on the first pass at 150psi with .75gpm concentrate and 1.25gpm permeate. If I raise the pressure to 225-250psi and drop the concentrate flow to 0.5gpm I can push the sugar content to around 5.5-6% with almost the same permeate flow.

Next year I'm thinking of adding a 3rd element and possibly upgrading the pump to either a 330 or taking the big leap to a 660. I've got a couple questions:

1) I've read several posts about using a recirculation pump. What is the advantage to that? I'm only dropping 10psi across each element, so wouldn't there still be plenty of pressure for the supply back to the HP pump suction?

2) When people are speaking of their HP pump...what pressures are they pushing? Higher than 300psi?

3) what sugar content can I expect to get on a single pass with 3 elements in series?

[wiam]

Biggest thing a recirculation pump does is keep flow up across membranes to keep fowling down.

[TuckerMike]

Over the summer I decided to take the big leap and upgrade from the Procon 265 to the 660. I also added a supply pump because of the positive suction pressure needs of the 660. I kept the everything else in the system the same, with two 4x40 membranes. I'm shocked at how little permeate flow I am getting. The 660 is rated at 11gpm. The Filmtec membranes are each rated at 14gpm at 100psi. When I start the system pressure builds to about 225psi with as much recirc as I can put back to the suctions >5gpm (recirc flow meter upper range is 5gpm). Permeate flow is only 2gpm with concentrate flow of 1.5-2.0gpm. I don't want to close down the recirc any more because the membrane housings are only rated for 300psi.

I had similar permeate flows last year but assumes it was because of the 265 pump was maxed out. I was expecting much higher permeate flows from the 660. My RO has the ability to run the membranes in parallel or series. It doesn't seem to matter the configuration, I still get about 2gpm of permeate. Other than plugged membranes, I am at a loss as to what could be causing the low permeate flow? The membranes were washed and acid soaked at the end of the season and stored in solution.

Any ideas on what I can check?