Improving RO performance

[maple flats]

I have a Deer Run 250 RO. I'm looking to get more out of it. Adding 2 more membranes likely needs more HP pump or the trade off will be far too little concentrate flow to gain permeate flow. How much HP pump do I need, If I run 4- 4x40 membranes in series at 275 PSI? I have plenty of power at the sugarhouse but I don't want to build it with trial and ERROR engineering.

[mkoehler79]

The limitation in the case of 4 membranes in series is the max flow through the membrane, typically 13-15 GPM for most 4" membranes​.

[maple flats]

I was told 13, it may be 15. However I'd need new ends for larger ports in the caps if all in series, mine now have 1/2" pipe thread in the ends. I could get them drilled and tapped for 3/4" for the permeate, but I'd also need 3/4" (or larger) for the permeate flow. That's why I'm now thinking I'll assemble another 250 and use 1 or 2 units based on the sap quantity.

[BreezyHill]

Dave talk to a DOW tech. I did and he was very helpful when I was trying to figure why I was passing sugar on the xle 4040s.

He said, 13 gph is the max flow to be working efficiently and not passing sugar.

There is a drop in pressure of 10 psi after each membrane. So your pump will still work you will just be down to 235 psi out of the last one. This is still plenty for an xle that will function well at 100 psi.

RO is a game of numbers. get any one of them below or above a desired point and you have an issue. To much circulation and you pass sugar. To low of flow out of the concentrate and you can pass sugar. To high pressure you pass sugar.

Do factor in how you will be rinsing and washing the unit when doing the plumbing. Rinse and wash wants to have all vessels parallel so that you don't rinse from #1 and law into the following membrane.

3 way valves will be the ticket for the design.

[maple flats]

My current understanding using 4 membranes at 40" each is that at the 240-260 gph my pump will move is that I'd still get more permeate removed but that the concentrate would be near half what I get now. Using the existing pump would thus be very poor at best. That is why I've tentatively decided to make a second 250 gph RO and build an insulated room as an addition to my sugarhouse to house it. My sugarhouse is too crowded now and adding something new in the existing space is not practical. I may make enough addition to also house my current RO too and insulate it even better than it is now (I have a well insulated room except for the door which is nearly impossible to improve because of clearance issues).
Ray Gingerich says he has tried as have several owners of his RO's to add more membranes using the existing pump but none have been successful.
Thus, rather than swap the pump to an 11-13 GPM pump at 300 PSI, then change the end caps to 3/4" fitting instead of the 1/2" they now are, and add all new 3/4" HP lines, larger valves, a bigger low pressure supply pump and larger fittings all around, it seems to make better sense to make a second 250 unit. Then run 1 if sap supply is low and run 2 when called for. I'm now shopping around for all of the components. Ray has some, others must be ordered from other suppliers I think.