Rodi/Tds - question/help

[AquaJunkie]

I hooked my new rodi unit up today and it only gives me a pressure of 30 psi lol

Booster pumps cost to much considering what I've already blown on the rodi unit it self.

I know I will get less water which don't bother me and also membrane life will probably be shorter but my question is would this low pressure effect my Tds levels in any way?
Would my water still come out ok? Thanks

 

[Roachant]

No, it won't affect your tds levels.

 

[AquaJunkie]

Great! Forgot to say it only 50gpd and il only be using it for 1 day every 2 months so il only of used it 3 times in 6 months.

 

[robbrouse]

I'd get a TDS meeting and check for yourself. I have heard lower PSI will cut the filter life in as much as 2/3.. I have know way of knowing this.. I bought the booster pump.

 

[Isletime]

If you're only using your RO-DI once every couple of months you might consider getting either a manual or automatic flush kit as well. You can use it before and after running the unit to wash any impurities off of the membrane. This will help with membranes lifespan.


Sent from my iPad using Tapatalk HD

 

[AquaJunkie]

Thanks for the replys.

Think I might consider buying an inline Tds meter, the unit already has a manual flush kit on it but I'm using the rodi as a portable with shut off taps.

If I flush it after won't that dry out the membrane?

 

[Buckeye Field Supply]

Let's back up a little guys.

Will low pressure affect the TDS of your RO water? Yes. See the graph below from a couple of tests with a 75 gpd membrane as an example.



So in this example if your feedwater is 250 ppm, at 80 psi (with a pump) your RO water would be about 6 ppm. At 30 psi your RO water would be about 8 ppm. Your cost savings in what you spend on DI resin will depend upon how much water you process.



In terms of saving money, your bigger issue may be the extra $ you spend on water. At 30 psi, you'll be no where near a 4 to 1 ratio of waste water to purified water. You'll be sending a lot more water down the drain. You'll want to spend $4 and get a different flow restrictor that gives you something closer to a 4 to 1.

The issue I'd be most concerned with is what you said about how often you use your RODI system. Membrane manufacturers tell us that if the membrane isn't used at least once a week the membrane should be removed and stored in a preservative solution. I don't think you want to mess around with that, so you might want to think about changing how much DI water you make at a time - and only make enough to last you 7 days at the most.

Russ

 

[russo36]

The pressure does not affect your tds reading... I have an 8 stage ro/dI unit rated for 100 gpd.
I'm lucky if I get 50.... But I adjust the water ratio and I get my tds readings down to zero!!! However
I'm impatient waiting for my water to be made so I order a 100psi booster pump. I don't know what your
Budget is ... But my booster pump only cost me $80.... By the way... Like other stated... Don't have your unit
Sitting around so long w out being used... Get a cup of water out of it at least once or twice a week... That
Shouldn't take long at all to do. Hope this helps.

 

[AquaJunkie]

Ok so il just use it once a week, I can make some topoff water out of it. It has shut off taps so I just switch them off after use and pack away. If I half closed a ball valve on the waste pipe to slow the waste coming out, would this be more effective for the membrane?
After spend over $200 on an rodi there's no chance of me spending another $80 on a booster pump.

 

[russo36]

I don't know if it affects the membrane... But one thing I can tell you is that it will affect your tds readings for sure!!! So unless u have a tds meter I wouldn't mess w it.... Another q is how you know your tds are ok w out a meter? We can't say water is good bc you have an ro/di unit.... Remember they need to be twicked and adjusted to get the tds down or as close to zero as possible. I notice in mine that my tds go up depending how much water I have coming out to the waste pipe... (This is the good to bad ratio) I use my meter and test it until I get it down to zero. Other wise I would have my tds in the 20-30 range... Which is a great improvement considering my tap comes in at about 200 but zero is best for me and I'm sure for many others.

 

[AquaJunkie]

Thanks man I'm defo gonna invest in a Tds meter to see what my levels are.

I may have a little Tds in the water still but it's my first rodi and my tank has been running on tap water for the last year so it's gotta be some improvement right? Lol

 

[Hampton]

My first membrane lasted 5 years. I have 50 psi, and was making about 20 - 30 gallons per week. I started using a long of DI cartridges. Changed the membrane, and back in business.

 

[AZDesertRat]

Yes pressure affects the TDS the membrane produces which in turn shortens the DI life driving the cost of ownership up.

Check your waste ratio, you are probably sending way too much to waste. If you adjust the waste ratio your pressure at the membrane will go up and your efficiency will also rise making your DI last longer. Don't just close a valve, actually measure the waste versus treated using a measuring cup andclock or watch for one minute from each and calculate the true ratio.

Russ stated a very valid concern, membranes need to be used every 10-14 days maximum to keep the flushed and operable. It is not good to let a system sit dormant for longer than that.

 

[russo36]

What AZDesertRat pointed out is correct and can be done using two cups one for waste and one for clean water... This way u can tell if your ratio is as close to the ratio is supposed to be or not.... However I did this step w my unit and my water was still at about 7-9ppm... I twicked a lil more and got it down to Zero... I believe if you own an RO/DI unit is important to have a tds meter!!! Is the only way to know how clean and pure the water really is.

 

[AZDesertRat]

Adjusting the waste ratio doesn't have a huge effect on the TDS, it is more to ensure the membrane stays well flushed while in use and that it lasts as long as it should. You could stop the waste all together but the membrane will soon fail, or you could raise the waste to 8 or 10 to 1 and flush the heck out of it but the resulting loss in pressure available to the membrane would reduce the rejection rate and eat your DI quicker. Many people confuse rejection rate and waste ratio when they are completely different, the rejection rate is the removal efficiency(98+/-% rejection) while the waste ratio is how much you send to the drain to keep the membranes surface clean(4:1 ratio is optimal).

It only takes on measuring cup to check the waste ratio. You place the empty cup under the waste line for exactly one minute and record the amount in ounces or m/L then do the same with the treated line for exactly one minute and compare the two amounts, the waste should be approximately 4 times as much as the treated in the same given amount of time, it does not have to be one minute as long as both are the same amount of time. The TDS could be the same either way, you are not changing it much by adjusting the waste, only how long it will stay at that level until the membrane plugs and fails. At 3:1 or 4:1 waste to good the membrane will last as designed. Add head on the treated side of the membrane and you increase the waste and slightly raise the TDS, reduce the waste and the TDS goes down slightly, for awhile anyway, and the membrane does not last as long.