Does flushing membrane also flush TDS creep and carbon dust (RO/DI)

[Miami Reef]

I’m a little confused about something.



In an RO/DI system, there is a flush kit (where you open the valve so the waste water can bypass the flow restrictor).



This flush kit is placed AFTER the membrane.

Question #1

If I want to flush out the TDS creep (initial high TDS from diffusion), is flushing via the flush kit the correct way to do it?



Question #2:

If I change out my carbon blocks and want to flush out the carbon dust, do I also turn on the flush kit, or am I supposed to make a T right after the carbon blocks to flush it before it enters the membrane?



I hope my way of explaining makes sense.

 

[blaxsun]

1. Yes, after the membrane - correct. The flush kit bypasses the flow restrictor so that you can essentially flush the membrane out by manually turning the valve. And yes, flushing your membrane every few months can help prolong its lifespan.

2. No. You'll want to use flush caps and temporarily remove both your membrane and (optional) resin cartridges when adding new sediment and carbon cartridges to flush both (otherwise you needlessly clog and shorten the lifespan of your membrane).

I run the AquaticLife twist system with auto-shutoff, TDS meter, flush bypass, etc. If you'd like me to take a detailed picture of how it's configured let me know.

 

[Miami Reef]

Thanks, Blaxsun.

I understand. Instead of removing the membrane and DI every time I need to change the carbon blocks, I’ll just make a T with a ball valve and I’ll drain the water right after the carbon.

 

[mfinn]

Thanks, Blaxsun.

I understand. Instead of removing the membrane and DI every time I need to change the carbon blocks, I’ll just make a T with a ball valve and I’ll drain the water right after the carbon.

I just direct the line just before it goes into the membrane to my sink when I replace carbon cartridges.
I let it run into a white bucket and as soon as it runs clear I replace the line.

 

[Mr. Malawi]

Thanks, Blaxsun.

I understand. Instead of removing the membrane and DI every time I need to change the carbon blocks, I’ll just make a T with a ball valve and I’ll drain the water right after the carbon.

Just take off the output of the carbon block or gac filter you want to flush and put it in a bucket and turn on the water. It will only take a minute or two to flush the fines out then reconnect the line , this is what I do

 

[spawn79]

Just take off the output of the carbon block or gac filter you want to flush and put it in a bucket and turn on the water. It will only take a minute or two to flush the fines out then reconnect the line , this is what I do

Be careful when doing this. After so many connects/disconnects the fitting will wear out and spring a leak. They aren't meant to be disconnected all the time. Not all are created equal though of course so some might fail tomorrow while some will 5 years from now.
The best option in my opinion is put a 3 way valve inline after the filters. I bought several 3 way's so it's super simple to just redirect whatever flow I want directly to the drain. Much easier than replacing a fitting later down the road.
You might also want to add a check valve to the membrane waste line to make sure nothing gets damaged by flow going the wrong way.

 

[Randy Holmes-Farley]

I'm a little confused about the answers relating to TDS creep and the flush valve.

TDS creep is the slow diffusion of salts across the membrane when the membrane is not pressurized, putting salty water on the post membrane side of the membrane. Then when you start up, that salt will pass to the DI and help deplete it faster.

If the flush valve is on the premembrane side of the membrane, then I do not see how water flushing out the premembrane side will do anything about the salts on the post membrane side. A flush valve on the post membrane side will also accomplish nothing about TDS creep since the flushing water is likely at least as salty as the TDS creep water.

 

[Miami Reef]

A flush valve on the post membrane side will also accomplish nothing about TDS creep since the flushing water is likely at least as salty as the TDS creep water.

This was my experience with flush valves. It didn‘t do much for lowering the TDS creep.

So, what’s the purpose of the flush valve?

 

[Randy Holmes-Farley]

This was my experience with flush valves. It didn‘t do much for lowering the TDS creep.

So, what’s the purpose of the flush valve?

To keep crap from collecting on the upstream side of the membrane, potentially clogging it.

FWIW, I never used a flush valve and my membranes lasted many years, so the need/benefit varies.

 

[Miami Reef]

To keep crap from collecting on the upstream side of the membrane, potentially clogging it.

FWIW, I never used a flush valve and my membranes lasted many years, so the need/benefit varies.

Thanks, Randy.

 

[Miami Reef]

This is the membrane I bought from my

 

[Opus]

To keep crap from collecting on the upstream side of the membrane, potentially clogging it.

FWIW, I never used a flush valve and my membranes lasted many years, so the need/benefit varies.

I'm in the same boat and have posted this on many RODI threads that mention it is best done to prolong the life of the membrane. In my 25+ years of using a RO unit, I've never done it and my membranes last 5+ years. I personally think it is something that seems logical so it is pushed as working more from a marketing perspective to sell flush kits. I won't ever have one unless I can find a scientific study that proves it does prolong the membrane life and by more than a couple of months.

 

[thatmanMIKEson]

I’m a little confused about something.



In an RO/DI system, there is a flush kit (where you open the valve so the waste water can bypass the flow restrictor).



This flush kit is placed AFTER the membrane.

Question #1

If I want to flush out the TDS creep (initial high TDS from diffusion), is flushing via the flush kit the correct way to do it?



Question #2:

If I change out my carbon blocks and want to flush out the carbon dust, do I also turn on the flush kit, or am I supposed to make a T right after the carbon blocks to flush it before it enters the membrane?



I hope my way of explaining makes sense.

I never ever flush new carbon blocks into the membrane, you should flush new blocks into a bucket or waste water ,after flushed hook up to membrane. Use the flush valve every time prior to and after collecting water.

 

[Opus]

I never ever flush new carbon blocks into the membrane, you should flush new blocks into a bucket or waste water ,after flushed hook up to membrane. Use the flush valve every time prior to and after collecting water.

Honestly up until the last membrane, I've never flushed my pre-filters and I've had a RO unit for 25+ years. I always get 5+ years out of my membranes so I have no idea how much longer flushing actually adds to the life of the membrane.

 

[thatmanMIKEson]

Honestly up until the last membrane, I've never flushed my pre-filters and I've had a RO unit for 25+ years. I always get 5+ years out of my membranes so I have no idea how much longer flushing actually adds to the life of the membrane.

Ewww 5 years no thank you! Lol yeah I never go past a year but it's probably less than that, but different water requires different maintenance.

 

[BeanAnimal]

I'm a little confused about the answers relating to TDS creep and the flush valve.

TDS creep is the slow diffusion of salts across the membrane when the membrane is not pressurized, putting salty water on the post membrane side of the membrane. Then when you start up, that salt will pass to the DI and help deplete it faster.

If the flush valve is on the premembrane side of the membrane, then I do not see how water flushing out the premembrane side will do anything about the salts on the post membrane side. A flush valve on the post membrane side will also accomplish nothing about TDS creep since the flushing water is likely at least as salty as the TDS creep water.

Hi Randy - Removing the flow restrictor from the equation allows a high volume of water to rinse the membrane layers directly into the waste side, clearing residue.

Ideally, on startup the DI is bypassed, the membrane is flushed (restrictor bypassed) and then the restrictor put back inline and further flushed until the TDS clears. Then during operation, the restrictor is bypassed at some interval to prevent buildup (and extend membrane life). You can greatly increase product to waste ratio if you actively flush the membrane during operation. I run 1:1.

 

[Opus]

Ewww 5 years no thank you! Lol yeah I never go past a year but it's probably less than that, but different water requires different maintenance.

You must have some very dirty water or you make a lot of RO water. My tds averages 400 to 450 out of the tap and my membranes have no issue with cleaning that up. I get 4 to 5 tds right now after the membrane and it is a couple of years old.

 

[Opus]

Hi Randy - Removing the flow restrictor from the equation allows a high volume of water to rinse the membrane layers directly into the waste side, clearing residue.

Ideally, on startup the DI is bypassed, the membrane is flushed (restrictor bypassed) and then the restrictor put back inline and further flushed until the TDS clears. Then during operation, the restrictor is bypassed at some interval to prevent buildup (and extend membrane life). You can greatly increase product to waste ratio if you actively flush the membrane during operation. I run 1:1.

But there is no proof that flushing the membrane actually extends the life of the membrane. If you know of a study that backs this up I would love to read it.

 

[I never finish anythi]

Yea I will change membrane every 12 to 18 months . My Water source TDS between 40 and 60.

 

[BeanAnimal]

But there is no proof that flushing the membrane actually extends the life of the membrane. If you know of a study that backs this up I would love to read it.

You don’t need a scientific study and there is no great flush kit sales conspiracy.

Waste gets trapped in the membrane pores, mostly in the form of scaling. Frequent flushes reduce this. A partially clogged membrane is less efficient than a clean membrane and TDS rejection and output rate decline as a result.

Many factors contribute to membrane life, not just the ‘TDS’ number of the input water. Your 400 TDS water and mine may be very different. If you really feel the need to dig in, GE has volumes of information on membrane design and data.

Don’t want to flush you membrane, by all means don’t.