time to remove TDS creep

[shifty51008]

I would like to get an idea on how long you flush your RO water for to remove TDS creep before letting it go into your DI, for me it takes about 4 min to drop my TDS from 534ppm to 4ppm.

[Bent]

I would like to get an idea on how long you flush your RO water for to remove TDS creep before letting it go into your DI, for me it takes about 4 min to drop my TDS from 534ppm to 4ppm.

Holy cow really?

[shifty51008]

yeah, why? does that seem like a long time?

[Bent]

yeah, why? does that seem like a long time?

Yeah it does dude. Mine will go from 100 or so down to 2 in a matter of seconds.

[shifty51008]

Yeah it does dude. Mine will go from 100 or so down to 2 in a matter of seconds.

wow, now that is fast, mine has always been at least a few min. to drop. I will open up the RO bypass and drain that water for about 4 min then run it though the DI, if I don't it deff kills my DI much faster

[MiddletoM]

i dont normally stand there timing it but i would say i probably leave it flushing for about 5 mins. Well 5 mins flushing the waste line then about 1-2 mins flushing the product line before it goes through the DI.

[Vinny Kreyling]

I run 2-1 & Spectrapure suggests a 30 second flush.
I have doubled that on finish & start up.

[Buckeye Hydro]

Guys - make sure you understand the difference between:
1. A flush valve on the waste water line, and
2. A DI bypass

They function very differently and are used for different purposes.

Russ

[Buckeye Hydro]

http://i224.photobucket.com/albums/dd293/BuckeyeFS/Graphs/TDSCreep_zps2523e7a5.png

[jjvanb]

Usually 4 to 5 minutes here. I let it flush until the tds is down to about 10, post membrane, close the flush valve, then it takes another minute or so to drop down to 4. Which is when I close the secondary waste line and open the product line to let water start to enter the resin. Yes it takes a little more time, but my resin never sees more than 4 tds.

[Buckeye Hydro]

When you open the FLUSH VALVE, think about what happens to the net driving pressure on the membrane, and how that relates to the LOCATION of the TDS Creep water.

FLUSH VALVES on the waste water line are a terrifically inefficient way to deal with TDS Creep folks.

[Johnseye]

When you open the FLUSH VALVE, think about what happens to the net driving pressure on the membrane, and how that relates to the LOCATION of the TDS Creep water.

FLUSH VALVES on the waste water line are a terrifically inefficient way to deal with TDS Creep folks.

So are you saying not to use a flush valve? Just let it run until the TDS reading on the meter is at 0 (or 1)?

[hann1bal]

So are you saying not to use a flush valve? Just let it run until the TDS reading on the meter is at 0 (or 1)?

I have this question also. Should we or shouldn't we, flush?

[ktownhero]

I have this question also. Should we or shouldn't we, flush?

He's saying using the flush valve is inefficient. And what you should be doing is running a DI bypass, thus allowing the RO membrane to work as normal until TDS creep is resolved, because the location of said TDS creep is in and around the membrane. A flush valve runs the RO membrane at a lower pressure, thus it ends up taking much longer to resolve TDS creep and you waste a bunch of water in the process.

Correct me if I'm wrong buckeye

[Buckeye Hydro]

He's saying using the flush valve is inefficient. And what you should be doing is running a DI bypass, thus allowing the RO membrane to work as normal until TDS creep is resolved, because the location of said TDS creep is in and around the membrane. A flush valve runs the RO membrane at a lower pressure, thus it ends up taking much longer to resolve TDS creep and you waste a bunch of water in the process.

Correct me if I'm wrong buckeye

Right.

Maybe this will help:

Think of two "sides" of the RO membrane.

The HIGH Pressure side includes the high pressure feedwater reaching the RO element, going through the element, through the flow restrictor, and out the waste water tube.

The LOW Pressure side of the membrane is the permeate - the "RO water."


TDS Creep results from high TDS water on the LOW pressure side of the membrane. To get rid of this water it has to be pushed out of the permeate port.

A Flush Valve is a Bypass of the flow restrictor on the HIGH pressure side of the system.

A DI Bypass Valve is a way to temporarily divert the LOW Pressure Permeate away from the DI resin.

When you open the Flush Valve, the pressure needed to move the TDS Creep water away from the membrane goes to nearly 0 psi.

Use a DI Bypass Valve if you want to efficiently address TDS Creep.
http://i224.photobucket.com/albums/dd293/BuckeyeFS/Fittings/valves/3-wayvalve_zps9e9fda10.png

This is all pretty detailed wonky RO info, so I hope I didn't confuse folks...

[jjvanb]

It all makes sense. Thanks for clarifying! I have been wasting water. one question then... what is the purpose of the flush valve??

[Buckeye Hydro]

Flush valve is to flush the membrane and membrane housing by allowing high flow water to rush through.

Not at all intended to address TDS creep issue.

[Johnseye]

Flush valve is to flush the membrane and membrane housing by allowing high flow water to rush through.

Not at all intended to address TDS creep issue.

What's the benefit of flushing the membrane and its housing?

[Buckeye Hydro]

"Waste water" is better thought of as "flush water." Its job is to remove from the RO element everything that doesn't go through the membrane. So flushing is a temporary boost in this flush water to clean the membrane and housing.

[Bpb]

4-5 minutes here to go from 200+ to 4-5 ppm as well


Sent from my iPhone using Tapatalk

[Marty.H]

I run a valve to bypass Di and send water to waste until TDS has dropped then switch the valve over it then goes through Di

[azjohnny]

I usually make about 2-5 gallons of RO water for drinking before RO/DI using the same 3 way valve that Buckeye posted

I also use an inline check valve between the membrane and the 1st DI to help with TDS creep

[CafeReef]

I generally flush mine for about 9 hours.

This has absolutely saved me from TDS creep while also single handidly destroying my wallet.

Why you ask? because I'm an idiot and never remember because I'm like a golden retriever... :furious:

squirrel!

[Buckeye Hydro]

We had a client with an RO system with two large commercial RO membranes they insisted on running at line pressure (meaning no high pressure pump). The combination of low feedwater pressure and lots of membrane surface yielded a TDS creep period that lasted over 5 minutes. Ugh.

[Misled]

I use my unit to make drinking water. This is taken off the DI bypass. I fill a few gallon jugs for drinking water then close the bypass to make tank water.

[TheFishGuy31]

Buckeye- Thanks for explaining the differences.

Would you recommend flushing the RO membrane? If so, how often and for how long would you recommend?

Do you happen to sell a 24v solenoid valve?


Sent from my iPhone using Tapatalk

[Buckeye Hydro]

Buckeye- Thanks for explaining the differences. Would you recommend flushing the RO membrane? If so, how often and for how long would you recommend?


Sure - especially in instances with hardwater, and where you have the recovery cranked up (meaning a low waste water to purified water ratio). You can do it anytime the system is running, AND do it just as you turn the system off. That way, until next use, the membrane is "marinating" in water with a lower TDS and hardness than the concentrate that normally fills the RO membrane housing south of the brine seal.

Do you happen to sell a 24v solenoid valve?
Sure do! http://www.buckeyehydro.com/water-solenoid-valves/

[sleepydoc]

I run a bypass valve for ~5 min or so. TDS rapidly drops down to about 5-10 in less than an minute; if I leave it on for a few minutes more it gets down to 2-3, then I switch it over to the DI resin. I figure it's using about ⅓ of the resin for that extra time I let it run.

The bypass/flush valve I use every 2-3 weeks or so (i.e. when I think of it ;)) to keep the RO membrane 'clean'

[yraveh]

Right.

Maybe this will help:

Think of two "sides" of the RO membrane.

The HIGH Pressure side includes the high pressure feedwater reaching the RO element, going through the element, through the flow restrictor, and out the waste water tube.

The LOW Pressure side of the membrane is the permeate - the "RO water."


TDS Creep results from high TDS water on the LOW pressure side of the membrane. To get rid of this water it has to be pushed out of the permeate port.

A Flush Valve is a Bypass of the flow restrictor on the HIGH pressure side of the system.

A DI Bypass Valve is a way to temporarily divert the LOW Pressure Permeate away from the DI resin.

When you open the Flush Valve, the pressure needed to move the TDS Creep water away from the membrane goes to nearly 0 psi.

Use a DI Bypass Valve if you want to efficiently address TDS Creep.
http://i224.photobucket.com/albums/dd293/BuckeyeFS/Fittings/valves/3-wayvalve_zps9e9fda10.png

This is all pretty detailed wonky RO info, so I hope I didn't confuse folks...

could you please provide a diagram of an RODI system with flash-, and DI-bypass valves . that would be very helpful.

thank you
Yehuda

[FirstContact]

I flush and run a DI bypass valve. Guess I learned it backwards. My unit goes from about 130 TDS to 1 TDS in a couple of minutes.

[pisanoal]

Never timed it, but I would guess less then a minute and i've leveled off at what ever TDS it levels off at. I use a conductivity/TDS meter that by default turns on reading conductivity. Drops from about 350 mmhos to 12.5.

[Buckeye Hydro]

I use a conductivity/TDS meter that by default turns on reading conductivity. Drops from about 350 mmhos to 12.5.

Divide those numbers by 2 to convert from conductivity to TDS in PPM

[Buckeye Hydro]

I flush and run a DI bypass valve. Guess I learned it backwards. My unit goes from about 130 TDS to 1 TDS in a couple of minutes.

Opening the flush valve WHILE you have the DI Bypass open sort of defeats the purpose of the DI Bypass. You want full pressure flow when the DI bypass is open to push the TDS Creep water out of the membrane and down the drain.

Russ

[FirstContact]

Sounds good Russ! I'll change that going forward.

[Buckeye Hydro]

:thumbsup:

[boxfishpooalot]

I have city well water and te tds is anout 900. It takes about 15 minutes to get it down to 10. 98% rejection rate.

[Buckeye Hydro]

I have city well water and te tds is anout 900. It takes about 15 minutes to get it down to 10. 98% rejection rate.
Are you opening a flush valve, or a DI Bypass Valve? 10 minutes is much longer than typical if you're using a DI Bypass.

Russ

[boxfishpooalot]

No i just let it run. Its a watts home depot ro system. Doesnt have a flush. I doont use deion resin because the co2 kills it in 20 gallons unfortunatley.

[HBtank]

No i just let it run. Its a watts home depot ro system. Doesnt have a flush. I doont use deion resin because the co2 kills it in 20 gallons unfortunatley.

That was a delayed response! :fish1:

[outy]

Never. I don't get TDS creep. Always 0 out of line before DI.

[Joshsmit56001]

I have city well water and te tds is anout 900. It takes about 15 minutes to get it down to 10. 98% rejection rate.



I thought my water was crappy. I'm at around 700 tds and i have a couple valves I open and close to send the bad RO water (high TDS) to the drain. It takes a couple minutes to get to 9 tds, then I switch the valves and allow it to hit my DI. This has saved me from DI resin consumption.


Sent from my iPad using Tapatalk

[outssider]

Never. I don't get TDS creep. Always 0 out of line before DI.

that's strange.....what's your tap/source water at ??

[outy]

that's strange.....what's your tap/source water at ??

27-29 TDS :cool:

I'm able to use 3 membranes in line, and still get 0

[Buckeye Hydro]

TDS creep is a phenomenon common to all RO membranes. There are ways to address it, but if you have an RO membrane, and you assess it's function carefully enough, you'll see TDS creep. Nature of the beast.

Russ