TDS 38 out of Membrane. Need Help

[tank41]

Hello guys. I have a question. I replaced my membrane just a little over a year ago. I noticed my DI resin was running out in just a matter of a couple of days. I have a 5 stage 75gpd RO/DI from Thefilterguz. My carbon filters are in need of replacement having approximately 8 months on them. The RO filter is turned on once per day utilizing inline leveloc ATO. I have it set to come on for a half hour a day and replaces about 2 gallons per day. I make about 50 gallons per month in additon to that for water changes and top off for a small tank. Im just curious what would cause the membrane to be exhausted that quickly. Water coming into the RO is about 450. My last membrane last almost 3 years. Any ideas would be much appreciated.
Thanks.

[Buckeye Hydro]

Based on the info in your post we don't know that the membrane is bad. What we need to know is the TDS of the RO (not DI) water. We can then compare that to your feedwater TDS and calculate your rejection rate - that will tell us how your membrane is working.

Also - your 75 gpd should be kicking out about 2 gallons per hour - yours is making water twice that fast. Do you have very high pressure/warm feedwater?

Russ

[tank41]

Thanks for the feedback. My tds is 38 coming from the Membrane.
Thanks.

[Buckeye Hydro]

So your membrane's rejection rate is:
(450-38)/450=
412/450=
92%

92% is too low for a 75 gpd membrane. Are you giving the membrane enough pressure? What is the pressure reaching the membrane?

Russ

[cham]

Did you replace your restrictor when you replaced your membrane??

I learned that lesson the hard way, 3 membranes in one year later...... :/

[Buckeye Hydro]

And why are you going to the expense of using two carbon blocks? Do you have chloramines?

Russ

[tank41]

Hey Russ. Thats how i have allways ran it because that is the way i recieved it when I purchased the unit. #1 would be the micron filter, 2 is the cto carbon block and 3 is another carbon block and finaly the DI stage. How should this be done in the correct order? I am pushing about 45 -50 psi into the unit. I did not replace the restricter when I changed the membrane. Should U allways do that?
Thanks again for all the help.

[Buckeye Hydro]

Assuming you are on city water - I checked for another customer in Sioux City this week and they don't add chloramines to your water. So you realy don't have a need for 2 carbon stages. You probably don't need two sediment filter either. So if I were you I'd use a 1 mic sediment filter and a 0.5 micron carbon block and leave the third prefilter housing empty.

regarding changing the flow restrictor - typically you don't need to unless you change the gpd capacity of your membrane. Check to make sure you have something close to a 4 to 1 waste to permeate ratio.

Russ

[tank41]

Thanks again appreciate the advice. What about the correct psi. Where should i be there for the unit to be operating the best for longevity of the membrane.

[Buckeye Hydro]

Within the range of acceptable pressures, the pressure doesn't really affect the life span of the membrane. Assuming you have a Filmtec membrane, the minimum you'd want is 40 psi and the max (given limits of other components in the system) is 80 to 90 psi.

Russ

[tank41]

So can i contribute my 92 percent regection rate from the membrane my leading factor to my rapid use of my DI resin? Also What if anything can i do to get more life then a year out of my membrane.
Thanks again.

[Buckeye Hydro]

With an RO TDS of 38, I'd expect you are getting about 150 gallons from a single DI cart. Are you? What was the rejection rate on that membrane when you installed it? It may be no different than when it was new.

Is your system configured to give you something near a 4:1 waste to permeate ratio? Measure it and see what you get. If its too low that could be killing your membrane prematurely.

[tank41]

I put new DI resin in and after two days of water making for evap with only a fe 3 or 4 gallons made and am getting a tds of 6. It was that way on my last Di change also. How to you test what ratio you are getting.
Appreciate your knowledge and help on this one.
Thanks again.

[Buckeye Hydro]

How about giving us a call - we'll get this straightened out in a 5 minute phone call faster than we will will a dozen posts back and forth.

Russ
513-312-2343