Help RODI issue

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Japoy013

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Hey Guys, looking for some help with my RODI system.

I have a 5 stage RODI system. I have had this system for about 3 years. I just did a plug and play initially when I installed it.
Now, I’ve start playing around with it because my DI gets used up fast.

1st stage - 5 Micron sediment
2nd stage - 5 Micron granular Activated Carbon
3rd stage - 1 Micron Coconut Carbon block
4th stage - RO Membrane
5th stage - DI resin

This system comes with an auto shut off valve. The TDS of the tap water is 180ppm and the TDS coming out of DI is 0ppm. I have an inline TDS meter with dual sensors connected to the system. First sensor is after the RO membrane and the second after the DI resin.

So here’s my issue and I don’t know if this is normal. When I take water or use the water from the storage tank, the system starts making RO water. But whenever this happens, the TDS coming out of the membrane jumps 5ppm to 100ppm initially. This goes down back to 5ppm after a while and the TDS after the DI remains at 0ppm. I initially thought its a membrane issue so I have changed the actual membrane but even with the new membrane, this still happens. I think this is why my DI resin gets used up fast.

Does anyone know why the TDS coming after the membrane would jump from 5ppm to 100 ppm initially them drop back down to 5ppm? Would it be the membrane orings are letting prefiltered water through the output of the membrane?

Thanks in advance!
 

Gtinnel

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What you are describing is called tds creep. On my rodi system I have it setup to put the first water that comes out of the membrane to waste for the first several minutes so it doesn't go through my di. It's best to not allow the system to make small amount of water frequently. You're better of making large amounts less often.
 
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Japoy013

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What you are describing is called tds creep. On my rodi system I have it setup to put the first water that comes out of the membrane to waste for the first several minutes so it doesn't go through my di. It's best to not allow the system to make small amount of water frequently. You're better of making large amounts less often.
Good to know! Thanks! That is what I’m doing now ever since I found that this is happenning. I installed several shut off valves along the lines and a drain tube after the membrane. I will run the system only when the storage tank is empty now and I now direct water from the membrane to waste until the TDS reads 2-5ppm and then redirect it to the DI.
 
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Gtinnel

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Good to know! Thanks! That is what I’m doing now ever since I found that this is happenning. I installed several shut off valves along the lines and a drain tube after the membrane. I will run the system only when the storage tank is empty now and I now direct water from the membrane to waste until the TDS reads 2-5ppm and then redirect it to the DI.
That's the best way to do it. I've asked others why it happens because it didn't make sense to me either, but it apparently has something to do with the filter sitting under low pressure the tds raises on the permeate side of the membrane. I believe it was because of the tds equalizing across the membrane.
 

Gtinnel

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Does your RO system have a flush valve?
Unless I've misunderstood how the membrane works the flush valve has nothing to do with tds creep. Tds creep happens when the filter is sitting with no pressure on it. Flush valve is to remove the restriction on the waste side to clean of the concemtrate side to extend the life of the membrane.
 
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Japoy013

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Unless I've misunderstood how the membrane works the flush valve has nothing to do with tds creep. Tds creep happens when the filter is sitting with no pressure on it. Flush valve is to remove the restriction on the waste side to clean of the concemtrate side to extend the life of the membrane.
Yeah thats what I know about the flush valve. It’s to get rid of debris and build up inside the membrane housing to extend the membrane life. I usually flush before making RO water now
 
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Gtinnel

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Yeah thats what I know about the flush valve. It’s to get rid of debris and build up inside the membrane housing to extend the membrane life. I usually flush before making RO water now
I flush for a few minutes when the system kicks on, and then my system opens up the flush solenoid for 2 minutes (I think it was 2 minutes at least) every 30 minutes that the system runs. My system is completely automated and works with a micro controller that controls an outlet to kick on the booster pump and it turns on and off a series of solenoid valves. From the time it kicks on my system doesn't start making water for about 5 minutes.
 
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Japoy013

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I flush for a few minutes when the system kicks on, and then my system opens up the flush solenoid for 2 minutes (I think it was 2 minutes at least) every 30 minutes that the system runs. My system is completely automated and works with a micro controller that controls an outlet to kick on the booster pump and it turns on and off a series of solenoid valves. From the time it kicks on my system doesn't start making water for about 5 minutes.
Nice! I was looking at the solenoid stuff but just settled to doing it manually haha
 

Gtinnel

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Nice! I was looking at the solenoid stuff but just settled to doing it manually haha
Mines a diy solution. Well sorta, I'm lucky enough to have a dad who is an electrical engineer so he does all the fancy electronics parts (lol) and my brother is a computer programmer, so I just tell them what I want it to do and between the two of them they make it. Sometimes I feel like the moron of the family.

My rodi, ato, and skimmate container are all diy.
 
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Japoy013

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Mines a diy solution. Well sorta, I'm lucky enough to have a dad who is an electrical engineer so he does all the fancy electronics parts (lol) and my brother is a computer programmer, so I just tell them what I want it to do and between the two of them they make it. Sometimes I feel like the moron of the family.

My rodi, ato, and skimmate container are all diy.
Haha nice! Im a mechanical eng so I usually just hammer anything broken
 
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dadnjesse

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I use this valve to dump the high TDS water down the drain until the TDS comes back down then switch it back to your storage tank.
 
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Japoy013

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I use this valve to dump the high TDS water down the drain until the TDS comes back down then switch it back to your storage tank.
Cool! Might need to get me one of those
 
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