Disappointed in my homemade RO and need advice

[GoldyCon]

I finally made the plunge and purchased the supplies to make an RO which I was able to try out today. I’m running 2 400gpd membranes in parallel with an aquatec 8800 pump. I’m able to run around 100psi but I’m only making about 1.25 gal of ro water per hour. That rate seems very low to me, what are some factors that could be causing a slow rate like that? I do have a pair of drips to take care of but they don’t amount to much volume.

[carls47807]

Send a pic. Are you using a variable flow
Restrictor? When you say 1.25 gph permeate, do you mean 1.25 gph if concentrate as well (are you running it at 50/50). Those numbers are super low.


Sent from my iPhone using Tapatalk

[30AcreWoods]

How much is coming out your permeate line, and how much is coming out of your concentrate line (per hour)? Do you have a needle valve on your concentrate line after the membranes? If they are in parallel, are the membrane outflows combined before the needle valve so you are putting equal pressure across each? You should be able to process 10-15-gal per hour at 50/50 with that setup. I would suggest using them in series rather than parallel.

[blissville maples]

It's pretty simple you're not running enough pressure. In order for a membrane to work you have to force the water through a core of mesh and fibers and all kinds of stuff. That has a lot of resistance it takes pressure to overcome this resistance. The more pressure you apply the more flow you will get. Of course the more pressure you apply the more chances you get to foul up your membrane and must be vigilant about cleaning. most people run around 400 lb never over 500.

You're going to want to beef up your pump your lines in the whole system to handle more pressure

[30AcreWoods]

I wouldn't try putting 400psi across those 400gpd membranes or you'll have a disaster on your hands. Those are likely designed for 150psi. But everything needs to be balanced and your pumps need to match your membranes needs to match the housing max pressure needs to match your fittings, tubing, etc., etc.... Then crank it up and like Bliss said, wash your membranes often to keep 'em from fouling.

[blissville maples]

I guess I am not familiar with membranes other than 8" CDL, filmtec, hydronautics, I'm not so familiar with the small hobby machines.....these can all take 400 psi. You can usually find a cut sheet (spec sheet) that tells you max pressure, max pH, rejection rates etc....

[carls47807]

His pressure is fine, but being that he is running 2 membranes in parallel he is probably restricting to nearly no flow to achieve that pressure. The aquatec 8800
Can’t really handle 2 400’s in parallel. Not sure if OP is still around anyways!


Sent from my iPhone using Tapatalk

[DRoseum]

I run two 400 gpd membranes on the aquatec 8852 pump at 100 psi without a problem. I have those feeding into a 3rd membrane and was really happy with its performance this year. Was probably running around 15 or more gallons of raw saw per hour thru it to get around 4 gallons of concentrate depending upon sap temps. Some warmer days was able to get thru 50+ gallons in about 3 hours or so.

[GoldyCon]

Sorry guys! I got locked out of my account and got busy with COVID issues.

21312

There is an image of my set up. The system seems to be working better now but still not what I was hoping it would do. I think I'm up to 2-3 gallons of permeate per hour but I can't get a 50/50 split, its more like 25/75. I suspect the issue is running in parallel as many of you mentioned so I'll try and run them in series. My housing has 3/8 inlet at the top and two 1/4 outlets at the bottom. Should I find a fitting that goes from 1/4 to 3/8 so I can keep the 3/8 tubing to the second membrane?

Thanks for all the help so far.

[carls47807]

Sorry guys! I got locked out of my account and got busy with COVID issues.

21312

There is an image of my set up. The system seems to be working better now but still not what I was hoping it would do. I think I'm up to 2-3 gallons of permeate per hour but I can't get a 50/50 split, its more like 25/75. I suspect the issue is running in parallel as many of you mentioned so I'll try and run them in series. My housing has 3/8 inlet at the top and two 1/4 outlets at the bottom. Should I find a fitting that goes from 1/4 to 3/8 so I can keep the 3/8 tubing to the second membrane?

Thanks for all the help so far.

Before changing from parallel I would figure out why you can’t get a 50/50 split. You should be able to completely stop the flow of concentrate with the needle valve. That is how you build up more pressure and force more permeate out.


Sent from my iPhone using Tapatalk

[DRoseum]

I run two 400 gpd membranes on the aquatec 8852 pump at 100 psi without a problem.

Should have been more specific. My first 2 membranes are in parallel. I agree that you should be able to get this working.

[GoldyCon]

I can stop the flow of concentrate but when I do that the permeate is also reduced. For some reason I seem to get the best volume flow of the permeate when I run a 25/75 split. If I go higher than that the volume decreases from a weak stream to a steady fast drip.

The 50/50 split works for a bit but within 10 mins they are no longer matching and the permeate is back to a drip. At this point I usually open the needle valve all the way to try and flush the system out which seems to help.

[DRoseum]

Are you able to post a picture of the plumbing coming out of the membranes?

[30AcreWoods]

Something isn't adding up here...

This is a long shot and I'm virtually certain isn't the issue, but have you tried to move up to a 3/8" line where the two 1/4" permeate lines come off the bottom of the membranes? Use a 1/4"x1/4" x 3/8" wye.

Also, not all needle valves are created equal, I've learned. Some of them leak a bit at the valve assembly. Do you hear any hissing around the needle valve when it is cranked down to 50/50?

[carls47807]

Pull your two permeate outlets and measure their flow independently. Even at 100psi you should be running better than you are. At this point I would suspect your membranes are bad. Use 30acres suggestion and go to a 3/8” line as well.


Sent from my iPhone using Tapatalk

[GoldyCon]

Update

Things are running quite a bit smoother now after 2 days of use. Initially I was recirculating my concentrate but I found that running fresh sap in one pass was giving me 4% con and a much better permeate flow. Additionally, I also found out that my helper used a small amount of olive oil to lube the filter when putting it in the membrane. I’m guessing this oil caused some of the issues but is now flushed out. It also makes sense why I’m seeing improvements over time.

[30AcreWoods]

You might want to try an acid wash and then a soap wash/rinse. I bet you will see some really great improvements.

[MapleCamp]

I use the same pump with 4, 150 gpd membranes in series , I get up to 140 psi on freshly cleaned membranes , and 8% concentrate . I would think you should get better than 4%. I have .25 inch tubing on every thing. Check your prefilter I change after every run which might be 2-300 gallons. Try cleaning as described elsewhere on maple trader I bet it will help. My sap averages 2.2%