riciculation location

[MapleCamp]

I am building a new 2 by 4 by 40 inch RO and just have the wiring of the 1 hp motor and plumbing of the recirculation line left. My question is where to put the ricirc , should it be in front of the pump ( feed side) which is a procon, or the discharge side . I have a single post now and its on the feed side, but I feel that it might flow to the feed tank with the stronger pump . What do ya think. TIA

[maple flats]

the output to be recirculated should be from a tee just before the main needle valve (where you create and adjust the pressure) pump. This needle valve is after the membranes, the recirculation line needs no extra pump, because where you are taking off the pressure is there from the high pressure pump it's own small needle valve, then it should tee into the feed line just before the high preesure pump.
On my commercially made 250 (2 membranes 4x40") the recirculation line is 5/16" with a small needle valve to control the flow, then it enters the main pressure pump feed line just before it enters the pump at another tee. The only valve is the needle valve.
On larger commercial RO's they do use a seperate pump but on units like you are building one is not needed. On those larger ones I can't tell you how they plumb them, my only experience is with my 250 gph unit (I've had 2 over the years,both wee the same design.)
I hope this helps

[DRoseum]

Agree with Dave. You will need a needle valve on the recirc line in this configuration and i believe the combination of needle valves will influence your operating pressure and how much is being recirculated.

Alternatively, you could split the output AFTER your final pressure needle valve: (1) feed some back to the inlet side of the pump and (2) your final concentrate output. A needle valve on the recirc line in this configuration is also encouraged so you can control the recirc flow and final concentrate output flow independent of the overall pressure (controlled by main needle valve).

This is how I built mine so I can tweak the recirc line without effecting pressure and match my RO output to my evaporation rate.

[MapleCamp]

Thanks, I have the needle valve in place . I will plumb to the inlet/feed side of pump. One more question, any reasons to not test the unit with say 45 psi of air to check for leaks?
Thanks

[maple flats]

I have no idea, I never tested either of my 2 RO's except with sap in season.

[Ryan1]

Recirculation is being able to increase flow across the membrane without increasing total flow of the system. This slows the sugar molecules from sticking to the membrane surface and slowing down concentration. Usually done with an internal pump like Lapierre or cdl, but h20 and mes use the externals. All they do is suck off one side of the membrane and dump it back in The other side to keep flow moving. This can be done with a grundfos fire suspension pump, I read people trying to do this with another procon……. Don’t waste your time the idea of it is to be able to flow some sap. I’ve been towing with the idea of tig welding some recirc kits for 4” membranes with deep well pumps but haven’t got there yet.

The idea of a needle valve to bleed it back to the intake side of a pressure pump is generally referred to as a pressure control loop not a recirc loop. It’s not there for performance, just there to have a way to regulate pressure as needed when membranes start to not flow as well on a concentration cycle with out changing the gpm on concentration leaving the system. Lapierre and cdl needle valve right of the hp pump before it even has a chance to see a membrane housing and dump it back to the intake side of the hp pump.

[DRoseum]

There are 2 forms of recirculation: high pressure and low pressure.

Low pressure recirculation takes part of the concentrate output after the main pressure controlling needle valve and feeds it back to the low pressure input side of the main feed pump. That low pressure loop can be assisted by a pump, or not, or be throttled by a needle valve or not.

Doing a recirculation loop after the main needle valve allows you to control how much recirculation vs. Output you want without effecting the pressure (to an extent - maximizing recirc could increase sugar concentration to a point that it does slightly drive up pressure), which ultimately effects the total concentration and final flow output/time.

This is what I described previously for my setup. I do not have a low pressure recirculation pump, but do have a 2nd needle valve on that recirc loop to fine tune my output to match evaporation rate (while holding optimum pressure for the membranes steady, set with the main needle valve).

[Ryan1]

There’s about 20 things wrong with your high/low pressure explanations that leads me to believe that there’s just not much experience in the field.

If someone is serious about building a sweet functioning ro that can concentrate some sap you are best off looking into a used vessel like this seaprotec from Lapierres used section. https://elapierre.com/en/classifier/vessel-lapierre-4/
This vessel is capable of running up to 500psi continuously and has a 1/2hp recirculation built onto the bottom. I had a turbo 250 that ran 2 of these vessels. Even when one vessel had a bad start capacitor and I had to Isolate that vessel it still outperformed my 3 vessel hombuilt ro since it ran at 450psi and it could do (proper recirculation) machine would do 14brix on a pass feeding it 1.8 raw sap. Then you can get into a 10gb series goulds pump that can get you into the low 300s but Lapierre also has used pressure pumps that they list for cheap!

[DRoseum]

There is tons of knowledge on this forum and in the maple field regarding RO systems, their design, and operating princples. I understand how a system with high pressure recirculation pump works - just don't have a need for that design or interest in building it for the scale of my operation.

The low pressure recirculation approach is very common (especially for smaller units) and 100% works to increase the the final concentration % output, reduce the volumetric flow of concentrate output, while maintaining the same flowrate locally across the membrane(s). In short, this approach helps increase system recovery rate without increasing the membrane(s) recovery rates.

I've built multiple of these and take 1.4% sap and push out 6% at 10gph on a "single pass" because of the low pressure recirc loop. The concept is pretty simple - you are incrementally feeding some concentrate back, and in turn increasing the system input sugar % over and over again. Fairly quickly the final output will assymptotically approach a max concentration % value and level off.

Your main feed pump has to be sized appropriately to provide low recovery rates for each membrane in the system.

"RO System with Concentrate Recycle"
https://puretecwater.com/resources/the-basics-of-reverse-osmosis/#:~:text=RO%20System%20with%20Concentrate%20Recycl e

https://puretecwater.com/wp-content/uploads/2024/05/RO-w-conc-recycle.png

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEipaceO7ZdRbH9wfbmXefyiRRS_PNK8307RTnbMT36AmS idu_r7uNGqbKkAK2GiNotsqflHqLraZ5eN-teVH9ajmrP2jnjF46MO3PKtcFypJNaqUsOosbdN6bQv5N86xF1 DPj2Lyv7KLqSOSu1ethyxtvLt2EQdaa1qBKmfAKPptlgCtnWx6 oMN-WClmx02/w400-h256/Roseum-RO-design.jpg

[Ryan1]

Right but why would you use a pump to send your concentrate back when you are taking off a vessel already pressurized? That’s where you have me questioning. High flow recirculation builds are easy if you understand it and there vitally important to dealing with high sugar and minerals. $100$ vevor stainless deep well pump and a extra vessel and a few fittings and you have a true recirculation setup that will greatly increase numbers

[Mean_Oscar]

Doing that has not hurt my systems. I am a micro-scale experimenter and can easily leave a big percentage of a batch of concentrate in the system. I disconnect between pump and 5 micron filter and either blow in compressed air or attach concentrate outlet to a vacuum. Vacuum seems to work a little better. I can get a 20 oz soaked 5 mic down to 10 oz using a 110 VAC. -28" Hg capable, double diaphragm pump. Nominal weight of the 5 mic is 5 oz dry so I am still leaving some.