What I'll say about it is that Deer Run RO's (by Ray Gingerich) have a recirculation line. It starts just before the high pressure needle valve, Tees in and goes to just before the high pressure pump inlet. It has it's own needle valve. On a 250 gph RO it uses about a 1/2" inlet hose feeding the high pressure pump and a 5/16 braided hose for the recirculation. On other size units I don't know the sizes.
In use it works well, but certainly not as well as recirculation on it's own pump like the better RO's, but it works well. You first get circulation going with the recirculation needle valve closed, then each time you open the recirculation needle you need to adjust the main needle valve to get up to a good pressure.
I ran my 250 at 270-275PSI, as I started recirculation I would open the smaller needle maybe 1/3 turn, then bring the main pressure back up to 270-275, I repeated 2 or 3 times, adjusting each time. I think about 1.25 -1.5 turns on the little needle was about the most recirculation I did, but that, while reducing the concentrate flow, gave me a higher sugar %.
There were no back flow issues.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.
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