ro/di question

[riche]

I have a brand new set of filters on my ro/di unit and I am making water but the tds is starting out high in the 30's and then going down to 0. But only if I turn the waste water valve wide open but then the good water trickles out,

Is there were a booster comes into play?

 

[jabx1]

Do you have a flush valve? This helps when you first turn the water on it will bypass the RO membrane extending its life.
My TDS is usually in the 80-100 range when I first turn it on. I let it flush for 3-5 min until the TDS is below 5 then close the flush valve.

Also what is your pressure before the membrane? I have a BRS system and they recommend 60 psi or greater. If you don't have the recommended pressure then you need a booster

 

[Water Dog]

You are experiencing TDS creep. Install a 3 way valve between the RO membrane and the DI stage. Upon start up, open up the DI bypass, diverting flow from the DI stage to the drain. Run it until water exiting the membrane reads whatever it normally should read post RO, then direct water back through the DI stage. This will drastically preserve your DI resin life.

Here is an explanation that I wrote up about the differences between a DI bypass and a manual flush valve on a flow restrictor.

RO/DI - Are all equal?

Quite frankly, the only thing you need is the vertical DI kit. You already have everything else. Based on your numbers though, I do think you need a new RO membrane.

www.reef2reef.com

* Note - I have a dual TDS meter that reads my post RO TDS as well as my post DI TDS. This is important to monitor TDS creep as well as keeping an eve on the efficiency of your RO membrane.

 

[riche]

You are experiencing TDS creep. Install a 3 way valve between the RO membrane and the DI stage. Upon start up, open up the DI bypass, diverting flow from the DI stage to the drain. Run it until water exiting the membrane reads whatever it normally should read post RO, then direct water back through the DI stage. This will drastically preserve your DI resin life.

Here is an explanation that I wrote up about the differences between a DI bypass and a manual flush valve on a flow restrictor.

RO/DI - Are all equal?

Quite frankly, the only thing you need is the vertical DI kit. You already have everything else. Based on your numbers though, I do think you need a new RO membrane.

www.reef2reef.com

* Note - I have a dual TDS meter that reads my post RO TDS as well as my post DI TDS. This is important to monitor TDS creep as well as keeping an eve on the efficiency of your RO membrane.

Do you happen to have a picture? I see where you are talking about the 3 way between the ro and di but do i need 2 3 ways?

 

[Water Dog]

Do you happen to have a picture? I see where you are talking about the 3 way between the ro and di but do i need 2 3 ways?

Use one of these to divert flow from your RO membrane to either the drain or through your DI resin... hence a 3 way valve.

3-Way Ball Valve with 1/4" Push Connect

Control Your Water Flow with Ease Versatile 3-Way Design Effortless Flow Direction Control Ideal for Freshwater and Saltwater Systems The 3-way ball valve is a versatile and essential fitting for any saltwater mixing station. With a simple swing of the handle, you can easily turn the water...

www.bulkreefsupply.com

 

[Jekyl]

What size tank is this for? After using a small RoDi to start with I upgraded to the BRS 5 stage. In the long run it will be cheaper for me. Comes with a built in flush valve and TDS meter. Just a thought before spending money on your current unit.

 

[KingTideCorals]

What size tank is this for? After using a small RoDi to start with I upgraded to the BRS 5 stage. In the long run it will be cheaper for me. Comes with a built in flush valve and TDS meter. Just a thought before spending money on your current unit.

I agree with this! Invest in the bigger and badder system if you can so that you dont have to continue to upgrade your own! Totally feasible though and lots of good information getting sent your way on this thread!

Best of luck!

 

[Water Dog]

Regardless of what unit you have, it’s a wise idea to add a DI bypass valve to address tds creep to preserve DI resin life.”. A flush valve does not address this. I have a top of the line Spectrapure MaxCap unit and still added a 3 way valve for DI bypass to address tds creep..

 

[Jekyl]

Regardless of what unit you have, it’s a wise idea to add a DI bypass valve to address tds creep to preserve DI resin life.”. A flush valve does not address this. I have a top of the line Spectrapure MaxCap unit and still added a 3 way valve for DI bypass to address tds creep..

This is exactly what the valve on my BRS unit does as far as I know. I can switch my TDS meter from pre and post DI and watch the TDS drop before I start making my finished product.

 

[Reef.]

You could need a booster pump for low water pressure.

Not sure why you are running the system with the waste water valve not fully open?

 

[Gtinnel]

As far as I know there is tds creep on every rodi filter, so I don't see how upgrading to a bigger filter will help with this issue. All the OP would need is a tee and a couple of valves or the 3 way valve that @Water Dog posted.

The important part is to not let the initial water coming out of the membrane to go into the di resin because it will deplete your resin quickly. My system is setup to run for 3 minutes before it allows water to enter into the di resin.

 

[Gtinnel]

Not sure why you are running the system with the waste water valve not fully open?

Some of the systems I have seen the waste water "valve" is actually the restrictor and it just allows you to open it up to flush the membrane. In which case you would run with it closed most of the time.

 

[Water Dog]

This is exactly what the valve on my BRS unit does as far as I know. I can switch my TDS meter from pre and post DI and watch the TDS drop before I start making my finished product.

Your RODI unit has a manual flush valve on the flow restrictor. This does nothing to reduce tds creep. The reason you’re seeing the TDS go down is because you’re forcing it through your DI resin... although slowly because your flush valve is open so there’s no pressure going through the system. Next time you start up, keep the flush valve closed. You’ll see the TDS go down faster as it’s being pushed through your DI resin faster because it’s under pressure. Either way, the DI resin is getting depleted exponentially faster because it’s processing this high TDS creep water.

 

[KStatefan]

Your TDS unit has a manual flush valve on the flow restrictor. This does nothing to reduce tds creep. The reason you’re seeing the TDS go down is because you’re forcing it through your DI resin... although slowly because your flush valve is open so there’s no pressure going through the system. Next time you start up, keep the flush valve closed. You’ll see the TDS go down faster as it’s being pushed through your DI resin faster because it’s under pressure. Either way, the DI resin is getting depleted exponentially faster because it’s processing this high TDS creep water.

Flush valve and tds creep seems to be one of the most misunderstood parts of a RODI system

 

[Gtinnel]

Flush valve and tds creep seems to be one of the most misunderstood parts of a RODI system

I agree and I was going to say it's not that complicated, other than I have no clue why the water that initially passes through the membrane has higher than normal tds. Does anyone know what causes tds creep?

 

[KStatefan]

I agree and I was going to say it's not that complicated, other than I have no clue why the water that initially passes through the membrane has higher than normal tds. Does anyone know what causes tds creep?

When you shut your system off there is going to be water on both sides of the membrane on side is going to be high tds and the other low. The tds is going to move to low from high until they are equal

 

[Water Dog]

I agree and I was going to say it's not that complicated, other than I have no clue why the water that initially passes through the membrane has higher than normal tds. Does anyone know what causes tds creep?

RO systems work efficiently under high pressure. When you shut down a system, you have high TDS water on the waste side of the membrane and extremely low TDS water on the permeate side. When it sits idle under no pressure, the low TDS water aggressively seeks to reach equilibrium. So through “osmosis” the two sides reach equilibrium as it sits in this no pressure state. Hence TDS creep that now sits on the permeate side that no flow restrictor flush valve will remove.

 

[Gtinnel]

I've always wondered what causes it but never bothered to ask anyone.

So through “osmosis” the two sides reach equilibrium as it sits in this no pressure state.

I'm mostly familiar with osmosis in terms of the biological process but I though that it was only the solvent part of of a solution that would pass through the membrane and the solute wouldnt. If the tds on the permeate side is high then doesn't that mean that the solute passed through the membrane, and in which case as my understanding goes it isn't truly osmosis? Of course I am sure there is a reason it's called "reverse" osmosis.

Either way understanding what each of those 2 things are is simple. One is that the initial water coming through the membrane has a high tds, and the other is that there should be no resistance on the waste water side of the membrane periodically to flush it off and increase its lifespan.

 

[Water Dog]

That‘s a different discussion altogether... Manual flush valves don’t really do anything IMO precisely because all they’re doing is passing water over the waste water side of the membrane under no pressure. That doesn’t really accomplish anything. True RO membrane flushing happens when you maintain a proper 3 or 4 to 1 waste to product water ratio.

 

[Gtinnel]

That‘s a different discussion altogether... Manual flush valves don’t really do anything IMO precisely because all they’re doing is passing water over the waste water side of the membrane under no pressure. That doesn’t really accomplish anything. True RO membrane flushing happens when you maintain a proper 3 or 4 to 1 waste to product water ratio.

While I agree that having a proper waste: product ratio helps extend the life of the membrane, my understanding was always that it is the increased volume and flow rate of the manual flush that makes a difference in "cleaning" the membrane. Although I've never seen any specific recommendation on how often or how long to manually flush the membrane. Ive set my system is set to flush it for 1 minute every half hour and then at the beginning and end of running, but I just arbitrarily set those numbers.

I suspect it's a combination of those 2 things (among other factors) that help increase the life of the membrane.