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Unread 01/27/2007, 01:02 PM   #1
Kayadad
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rodi help

My new to me kent 35gpd hi-s rodi is making water really really slow. It has been running for about 2 hours and has just covered the bottom of a 32 gallon rubbermaid. It has a used ro membrane and di cartidge and new carbon and sedimate filters.

I currently do not have a tds meter, but will get one soon as $ permits. I also will get a flush kit.

My water is cold but very clean as we have some of the best water in the nation (many of the major bottled water componies, mt shasta and crystel geyser, bottle from around here). Water company report says water is around 60 tds and they only use chlorine twice a year for a one week period.

How much water should I expect? Is there anything I can do?

thanks,

michael


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Unread 01/27/2007, 02:03 PM   #2
AZDesertRat
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A 35 GPD is only going to give you 1.5 gallons per hour in the vetry best of conditions and that would be at 65 psi and 77 degree water temperature. Colder water hasa huge effect on out put so you will probably see less than half of that in the winter. As an example my Spectrapure MaxCap 90 GPD sives me 102 GPD in the summer with a pressure of 64 psi and water temperature of 82 degrees but right now with the same 64 psi but only 60 for the water temp I am getting 62 GPD.
This graph from Dow Filmtec will give you an idea of how pressure and temperature affect output. Your membrane is equal to their TW-3--1812-24 or the bottom line as they rate theirs to produce 24 GPD at 50 psi and 35 GPD at 65 like yours.
http://www.dow.com/PublishedLiteratu...romPage=GetDoc

If it were me when it comes time for a new membrane get a Dow 75 GPD and new flow restrictor to go with it so you can make water 300% faster.


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Unread 01/29/2007, 12:04 AM   #3
Kayadad
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AZDR - Thanks!

I am guessing my water temp is a big part of the problem. I just did a freshwater leak test and checked the temp (from the outside spigot but should be about the same) and it was just a hair above 40 degrees.

I have made about 10 gallons of clean water in over 24 hrs with a lot of waste.

Should I just buy a new membrane?

Pressure booster?

I know I need a tds meter. What is a good value for my money (I am a public school teacher so $$ is always a issue)?


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Unread 01/29/2007, 08:57 AM   #4
AZDesertRat
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With 40 degree water you really need either a dual membrane setup or a booster pump or both. I would call someone like Spectrapure as ask their advice. They sell both and could steer you in the right direction. They have a new 150 GPD RO membrane that might just be the ticket for you.


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Unread 01/29/2007, 11:42 PM   #5
Kayadad
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well it looks like to get decent amount of water (35 gpd), I may need a higher gpd membrane and a booster pump. Both start becoming expensive options, especially since we are on metered water and they base our sewer fees of meter usage.

Since I have decently clean water, is running a DI filter a good option? By DI filter, I mean using the prefilters (and perhaps even adding additional prefiltration) and using bulk di resin with no RO in the mix. Some DI resins can be recharged correct?


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Unread 01/30/2007, 09:31 AM   #6
AZDesertRat
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DI resin if kept in seperate cation and anion canisters can be recharged. It will never be quite the same quality as RO/DI but close. You can expect about 3000 total TDS per pound of resin so if your tap water has a TDS of 150 ands you had a 24 oz cartridge each or cation and anion you could expect to make about 60 gallons before recharging. Its a little more complicated than that though as normal mixed beds are not 50/50 cation anion but a little more of one than the other.
I am not a fan of recharging just because of the chemicals involved, lye and acid plus you can never recharge resin to a full 100% of its original capacity at home. For you though it might be viable option. I would still look into a higher capacity membrane or dual membranes as I think it is a safer option.


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Unread 01/30/2007, 10:24 AM   #7
RandyStacyE
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Quick question AZDesertRat ... I have some extra bagged DI resin in my garage. It's not kept in freezing temps, but it's very low temp. Will this harm the resin that you know of?

Let's just say that it did freeze ... would that destroy it?


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Unread 01/30/2007, 11:05 AM   #8
AZDesertRat
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I honestly don't know. I do know it needs to be stored damp since when it drys out it loses its electrical charge other than that I can't help you. Let me ask this question of Purolite and see what they say.


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Unread 01/30/2007, 11:56 AM   #9
Moloch_0
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Here is something from Melev's site:

"When your source water is very cold, RO units tend to slow down in production rate. They are designed to run with water that is closer to 78° F, which just happens to match our aquariums. Here's a neat trick that will get things back up to speed during the colder months:

Replace the tubing that leads from your cold water pipe to the unit with a 25' long piece. Coil as much of that tubing inside a 5 gallon bucket and fill the bucket up with water so the coils are submerged. Put an aquarium heater in the bucket and set it to 78° F (or hotter if necessary). The heater will keep the bucket water at that temperature, and that water will warm up the water traveling through the tubing to your RO/DI unit. Production rates will jump back to normal."

http://www.melevsreef.com/ro_di.html


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Unread 01/30/2007, 12:39 PM   #10
AZDesertRat
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Here is a file from Purolites library on resin storage. Go to the section titled " Storage and Transport....". It appears low temperatures do not affect it but higher temperatures and UV/Sunlight do.

http://www.puroliteusa.com/fr_library.htm


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