wmick, to address your questions. My pump moves just over 4 gpm. I have no measure of how much is recirculating, it utilizes a small needle valve just ahead of the main needle valve that controls the pressure of the system and I have 2- 4x40 membranes in series. My pump is belt drive off a 2HP motor.
I only get my flow numbers from observing the flow meters.
On my RO with no recirculation I get barely over 4 gpm, adding the concentrate and permeate flows. With 2% sap I can adjust those ratios from well below 1 gpm of concentrate at about 285 PSI (about .6 gpm) up to about 1.8 gpm at between 240- 250 PSI, in each case the balance of just over 4 gpm is in permeate.
I run most of the time, when inputting about 2% sap at 270-275 PSI and get about 1.1-1.2 gpm of concentrate and 2.8-2.9 gpm permeate. That is with my recirculation needle valve open about 1/2-2/3 turn (I have no idea how much is recirculating when I do this.
Just an observation, when on wash cycle, as the cycle is nearly done I get readings of about 2.6-2.8 GPM on both flow meters and at that the pressure is about 60-70 psi. All during my wash cycles I try to balance both flow meters, Early in the cycle it is not achieved, but within a couple of minutes I can balance the meters. From then on I adjust the pressure to maintain equal flows, as the membranes get cleaner the pressure needs to be set slightly lower and the totals of the 2 flow meters slowly climb until I get to between the 2.6-2.8 GPM on each.
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.