Time for new filters?

[Guest beatle]

For my birthday this year I got a set of TDS meters that I attached inline with my AWI Typhoon 3. The "inlet" is after the membrane, the "outlet" is pure water after my DI. In is around 81, out is 1-2. I've had my system for about a year (got it last year as a birthday present) and I'm guessing I've made about 500-600 gallons or so.

[YBeNormal]

That is a very high reading to have after your RO membrane. I have a Typhoon III and I get 1 after my membrane and 0 after the DI with source water TDS of around 200+. I'm afraid your membrane may be worn out or defective. What is your input TDS?

[lancer99]

Beatle,

Did you mean 81 *before* your RO membrane and 1-2 after? If so, that's normal...an RO membrane should reject about 90-95% of TDS.

 

If you're getting 81 *after* your RO membrane, Bob is right...there's something seriously wrong.

 

-R

[YBeNormal]

The 75gpd membrane used in the Typhoon III has a 96% to 98% reject rating. That shoudl give you a TDS reading of between 1 and 3 after the membrane. The DI resin should be able to mop that up and easilly produce 0 TDS product.

 

I agree with Lance. Please confirm where the readings are bing taken. Also, TDS creep will result in higher TDS reading when the unit it first turned on. Let the unit produce a a few cups of water then take input and output readings and let us know what you find.

 

As far as replacing filters goes, I recommend changing the prefilters whenever you begin to see a pressure drop or every 6 months, whichever comes first. You may need to change the sediment filter even more often. It's only $30 for two sets of prefilters from AWI (2 of each sediment, 1 and 5 micron carbon) and that would last you a year with your usage rates. Keep in mind though that prefilters do not reduce TDS. If anything, they may actually increase TDS. They are simply there to remove sediment and some chemicals such as chlorine and chloramine that would damage your RO membrane. Your RO membrane should last for 2-3 years, maybe a little longer. Replace your DI resin when the mixed-bed color changing resin changes from blue to near colorless or when TDS of your product water begins to rise above previous levels.

[magnetic1]

Id make sure the membrane is seated correctly first. I was having similar issues a little while back and found out my membrane was not inserted all the way or the o-ring was not fully seated.

[Grav]

Have you tried flushing the membrane? If there isn't a flush kit mounted, turn off the unit, then remove the restrictor on the waste water line. Then making sure you don't get water all over the place, turn the unit back on for 10-15 min.

 

Even if installed correctly, those o-rings can get blown out. Especally if the membrane isn't flushed.

[Highland Reefer]

Have you tried flushing the membrane? If there isn't a flush kit mounted, turn off the unit, then remove the restrictor on the waste water line. Then making sure you don't get water all over the place, turn the unit back on for 10-15 min.

 

Even if installed correctly, those o-rings can get blown out. Especally if the membrane isn't flushed.

 

When I bought my unit, I bought the backflush kit. The manufacturer said to run it once a week for 30 seconds. Since I don't know the ins and outs of these units, is the 30 seconds long enough to really do a good job.

[Guest beatle]

Yes, the first reading is AFTER the membrane. As there are two lines coming out of the membrane at the top (one black, one white) I attached it to the white line before it enters the ASOV and then to the DI.

 

I looked this morning and the readings are 33/0. Unfortunately I really have no need to make water. I filled my ATO up and made water for a WC yesterday, so my reservoir is full.

 

I did flush the system last year when I was having problems with my RO/DI. It helped so I didn't bother to go through troubleshooting it further.

 

I don't know what my input TDS is. Maybe when I order new filters I should pick up a handheld TDS meter as well.

Edited March 22, 2008 by beatle

[lanman]

Are you all aware that AWI is a sponsoring member, and has a thread in the vendor section? I don't know if they are using it yet - but I'll bet they could answer all kinds of filter questions.

 

bob

[YBeNormal]

I still think it would be helpful to know what your readings are after you run off a few cups of water and it will be next to impossible to really say if there is a problem or not without also knowing the TDS of your source water. Also, RO membranes are not as effective for multiple, very small quantities of water or with very low water pressure and you can expect to see slightly higher TDS readings in those situations. (See "TDS Creep")

[stevearlen]

... (See "TDS Creep")

This is info & link is helpful. If I understand this correctly, it explains the reason why the instructions with my RO/DI unit mentions that "It is recommended that at least 2 gallons of purified water be discarded before collecting purified water for use. If the unit is not used for several days, run the system for at least 15 minutes before collecting water."

[davelin315]

If your readings are at around 33 and then 0, then I would say you need to replace something along the line, not sure what it is, though, as there are a variety of factors that can bring your TDS up. The rejection rates, I believe, are for optimal conditions - meaning that water temperature at the membrane is around 74 degrees or so and water pressure is at around 74 PSI as well (at least for the membrane I use). At optimal conditions, the rejection rate is supposed to be at 96% (I think that's what Bob said the rate is). So, if your initial TDS is around 280, which is what mine is at my house, then you should realistically be filtering your water down to around 10-12 TDS. Since yours is currently at 33, your filters are only getting rid of around 88% of your measurable TDS.

 

There are a number of things that might help this number come down without replacing the membrane. Could be pre-filters, could need a backflush, could need increased water pressure or water temperature, or, it could simply need to be replaced... the fact that the water is at 0 after the DI means that your DI is doing more work than it needs to do.

[YBeNormal]

Again, prefilters do not reduce TDS. They can cause it to be elevated going in to the RO membrane but they do not lower TDS. I'm leaning toward TDS creep being the issue here and allowing the unit to run for a few minutes before taking the reading will verify or disprove that theory.

 

This is info & link is helpful. If I understand this correctly, it explains the reason why the instructions with my RO/DI unit mentions that "It is recommended that at least 2 gallons of purified water be discarded before collecting purified water for use. If the unit is not used for several days, run the system for at least 15 minutes before collecting water."

 

 

Yep, that's right. My TDS reads up to 15 post-RO membrane for a few seconds when I first turn the unit on but then sinks down to 0 or 1.

[jason the filter freak]

1 to 2 out seems pretty darn good to me

[Guest beatle]

Well TDS creep strikes again. My ATO/kalk bucket finally emptied today and I could make more water. In less than a minute the TDS going into the DI dropped from 149 to 5. A few minutes later and I'm getting readings of 0-2. This seems pretty good to me, but how do I tell when to replace my 3 prefilters?

[YBeNormal]

Prefilters should be changed every 6 months or whenever you begin to see a pressure drop after the prefilters. I noticed the sediment filter in my unit gets real nasty long before the 6-month mark. It is the cheapest of the filters so I plan on changing it every 3 months now.