RO-DI unit not behaving

rickyb

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I need some assistance with my RO-DI unit. I'm unable to get it to produce the rated amount of water or close to, I get about 1.5-2 gallons of water per hour.


The system consists of a 5 stage:
Sediment filter
Matrix Carbon 5micron
Matrix Carbon 1 micron
Color changing DI resin
DOW membrane 100gpd (new)

The ASOV and check valve was tested and are good. The flow restrictor is rated for the 100g membrane -1000ml, I also switched to a 550ml flow restrictor to see if I see any measurable difference.

I get the following psi:
58 psi before sediment filter
58 psi after the last carbon filter
42 psi after membrane and before DI
I have not measured the psi after the DI.

I recently replace the pressure gauge and found that my old one was reporting about 10 psi more than the new one. I'm assuming that my issue is with the water pressure but would like to hear your recommendations.
 
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webmanny

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Can you take a few pictures of the setup for us with some focus on the connections from and to?

The reason I ask is because your list looks out of order, but that may not be intentional on your part. Also, you mentioned that the DOW membrane is new. I wonder if you replaced one that was 50gpd before it. If so, did you also change the flow restriction valve?

These are the ones in charge of the gpd rating for each system. If you get a 100gpd membrane, but use a 50gpd flow valve, you still accomplish only 50gpd.

You should also change the order of your stages below.
Your list
Sediment filter
Matrix Carbon 5micron
Matrix Carbon 1 micron
Color changing DI resin
DOW membrane 100gpd (new)

Should be
Sediment filter
Matrix Carbon 5micron
Matrix Carbon 1 micron
DOW membrane 100gpd (new)
Color changing DI resin

This is what the flow valve/restrictor looks like.

1568919401192.png
 
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rickyb

rickyb

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Thanks for the reply.
The order you listed is how it is connected. I can take pictures later tonight if needed.
Sediment filter>Matrix Carbon 5>Matrix Carbon 1>ASOV>Membrane>ASOV>DI
and waste line - membrane>flow restrictor>drain

The current flow restrictor is 1000ml which was provided with the membrane, I found out that the flow to match the 100gpd membrane should be 800ml. However, to test, I installed my previous 550ml flow restrictor and had the same output of water. So regardless of the flow restrictor size I use, I get the same output.

I have the other type of flow restrictor (barrel style)
 

lyscer

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If the flow restrictor is >= your membrane output you should be good on that front. The next thing I would test would be the membrane rejection to see if it is producing where you're expecting.

Are you able to measure the TDS and the temperature of your water before it goes into the RO unit, then the TDS of the RO water (right out of the membrane before it goes through the DI? (This will help calculate the expected RO Membrane Rejection expected range. ).
 
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rickyb

rickyb

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I really appreciate the feedback. Unfortunately is not. The flush valve is in the close position, if I open it I can fill a 5 gallon bucket quickly, lol.
 

theMeat

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The membrane alone should have at least 95% rejection rate. If you have 171 tds coming out of it you need a new membrane. Unless your water is so off the charts dirty that 171 tds is only 5% of your tap source. In that case i’d move
 

lyscer

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can you disconnect the DI, let the water from the membrane run for like 5 minutes to flush out all of the built up TDS at the membrane and then test the tds after the membrane (and before DI) after it has been running for 5-10 minutes? 171 tds at that point is really high which would suggest a fouled membrane (which is what I am suspecting).

Someone years ago referred me to the spectrapure membrane document because it breaks down mathematically how to figure this stuff out otherwise it is all guessing.
https://www.spectrapure.com/wp-content/uploads/2019/05/MEGAMAXCAP_MANUAL_web.pdf (page 15 is where it starts if you're interested).

Since I enjoy looking at this, I ran the numbers for you based on the input you gave me:

Water Pressure in: 58psi
Tap TDS: 206ppm
RO TDS: 171ppm
Temp: 78f
Membrane GPD: 100
(TCF) Temp Correction Factor: 1.031
(PCF)Pressure correction Factor (Pressure/60): 0.967
Tap - RO: 35
[(Tap-RO)/Tap]*100: 16.99% (This is your rejection rate. Should be 98% but RO TDS of 171 is bad)

Based on all of your other numbers you should see a max of 99.66 GPD production which is pretty amazing but that rejection rate is WAY too low so I would see if running the unit longer and then testing TDS brings it down or you could have a bad membrane or possibly a mismatched flow restriction valve.

To give you something to compare to, here are MY RO UNIT NUMBERS.
Water Pressure in: 50psi
Tap TDS: 230ppm
RO TDS: 7ppm
Temp: 63f
Membrane GPD: 90
(TCF) Temp Correction Factor: .779
(PCF)Pressure correction Factor (Pressure/60): 0.833
Tap - RO: 223
[(Tap-RO)/Tap]*100: 96.96% Rejection Rate
 

theMeat

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Yes you should let unit run for a few minutes before you test, or collect product water for that matter. When you first turn it on tds might even be higher than tap source.
If that membrane is putting out 171 from 206 tds it is toast. Flushing it will not repair it. A flush valve is a good way to prolong the membrane lifespan, and best to flush before you shut it off. Would suspect the membrane got burned/melted from chlorine or fluoride because carbon blocks are done.
 
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rickyb

rickyb

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Thank you for the feedback. I flushed the membrane and installed new batteries in the dual tds meters, test, swap and test again, I'm still getting around the same numbers, so the membrane is probably shot. As a last attempt, I have a manual TDS pen, I'll collect some water at each step and test TDS to see if matches the inline dual TDS meters, and if it does I'll get a replacement membrane.

More to come, Thank you guys.
 

lyscer

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Another thing to check out would be that it seems like most membranes have a warranty so if you reach out to the manufacturer they should hook you up with a new membrane or at least pro-rate it for you.
 

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