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05-13-2004, 01:11 AM
|  | Member | | Join Date: Apr 2003 Location: Warren
Posts: 589 Zip Code: 48093
| | Quote: Originally posted by Jimbob
Also, buy the entire case of DI cartridges from him and each new DI cartridge works out to $25. Another fantastic deal! | I get the Bulk DI Resin from Buckeye. Four refills + shipping works out to $14 each.
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05-13-2004, 07:14 AM
|  | Member | | Join Date: Jun 2003 Location: Rochester Hills, MI
Posts: 861 Zip Code: 48307
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I saw those bulk refills from Buckeye too... I just don't feel like messing around with the bulk resins, getting the little beads all over the house, etc., etc. Although the $14 is a great deal, changing my DI cartridge take about 40 seconds and creates very little mess.
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05-13-2004, 10:21 AM
|  | Member | | Join Date: Feb 2004 Location: Da U.P. eh
Posts: 75
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Can someone please explain to me why I'd have a higher rejection rate if I hate higher psi? I have a 100gpd ro/di aquasafe unit, but I just can't get Ed to explain how this works. If the water passes through the system, it should be at 1 TDS, right? Why would having more water pressure lower the TDS rating? I normaly have 800TDS, but after my unit, I get 400TDS. I have low pressure, but I also have a 3 stage Kinetico RO unit and it gives me 50TDS.
Thanks for the help!
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05-13-2004, 11:28 AM
|  | Member | | Join Date: Jul 2003
Posts: 103
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ok...
Osmosis is the process by which a substance moves from an area of high concentration to an area of low concentration through a membrane. This process happens naturally.
Reverse osmosis takes energy. you are forcing something (water in this case) to go against what it would like to do naturally.
The energy for this process comes from pressure. Through pressure, water can be forced through little bitty holes, leaving the large junk on the other side of the membrane.
The greater the pressure the easier it is to move water accross the membrane.
The greater the TDS, the more stuff can block the holes, and the more difficult it is to move water.
Cold things contract. The colder the water, the more the membrane contracts. The smaller the holes, the harder it is to get the water to move throught the membrane.
Thus the membranes are rated at 5075/100 GPD under 'ideal' conditions. In general, a typical membrane working at someones home will probably produce half the water that it should. How many people have 70 degree water coming out of their cold tap?
-Scott
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05-13-2004, 11:35 AM
| | Member | | Join Date: Apr 2003 Location: Walled Lake, Mich.
Posts: 1,774 Zip Code: 48390
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That is right, I believe membrans are rated @ 60psi water @ 70*temp constant conditions. I have a 60gpd RO/DI, but only get maybe15 to 20gpd. I have well water and my pump runs between 40(pump kicks on) and 65 psi(pump off).
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05-13-2004, 12:20 PM
| | Member | | Join Date: Feb 2004 Location: Da U.P. eh
Posts: 75
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Thanks!
But I have one more question. If I have low TDS and low pressure, I could end up getting like 10 gallons a day. So that 10 gallons is the only water that passed through the membrane. Thus it should be 1TDS. Not 400 like I have. What do you think is making my RO/DI unit not work properly? It's hooked up to the cold tap. Been running for a month.
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05-13-2004, 12:49 PM
| | Member | | Join Date: Jun 2003 Location: Rochester Hills, MI
Posts: 861 Zip Code: 48307
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Something is definitely not right with that system... my 100g.p.d. aquasafe unit takes my ~350 TDS inbound house water and reduces it to ~7 TDS after the RO membrane and 0-1 TDS after the DI. My house water pressure is ~55 p.s.i. (sometimes a little higher, sometimes a little lower)
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05-13-2004, 12:57 PM
| | Member | | Join Date: Jul 2003
Posts: 103
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Sorry, forgot to address that issue.
If you have an RO that is giving you 50 ppm and another fiving you 400 ppm, I would assume that you have a bad membrane.
the 75 GPD membranes are good for about 95% rejection. This means that under ideal working conditions, 95% of the particles will be rejected. a 100 GPD has about a 90% rejection rate.
The trade off is more gallons per day, and extra cost on your DI filter to pull out the remaining impurities.
To be honest, I have studied how the RO units function. Until Friday I won't have any first hand experience on the functioning of an RO unit.
Consider, however, what an RO membrain looks like. Imagine something like a funnel filled with holes on the sides. Water goes in the big side, and out the bottom. Since the bottom hole is smaller, water backs up, increases in pressure and is forced out the holes in the sides. The holes in the sides are only large enough for particles that are the size of water or smaller.
A DI tank purifies all the water that passes through it. The water goes in one side and out the other. The water that goes into an RO membrane has two routes to take, one clean and one brine (waste).
So to answer your second question. It is not possible to have 100% of the water pass through the RO membrane. If the membrane is only lowering the water's TDS by 50%, I must assume that there is something wrong with the membrane.
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05-13-2004, 01:04 PM
| | Member | | Join Date: Feb 2004 Location: Da U.P. eh
Posts: 75
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GR! That makes me pretty angry! I put the membrane in and let the tank fill up. I emptied it and let it fill up again. I then tested the water and it was at 400TDS.  I'll have to bug Ed some more. This wasn't the first problem I've encountered...
Thanks for clearing that up for me. He's been telling me I'm getting crappy water out the unit because I have bad pressure. Well even if the water is dripping out the other end of the unit, it should still be 1TDS! Just wanted someone else to verify my thoughts. Thanks again!
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05-13-2004, 01:05 PM
| | Member | | Join Date: Jun 2003 Location: Rochester Hills, MI
Posts: 861 Zip Code: 48307
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I guess I'm fortunate with my 100 g.p.d. unit averaging a 98% rejection then... makes me even more happy with my purchase :-)
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05-13-2004, 01:09 PM
| | Member | | Join Date: Jul 2003
Posts: 103
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The higher the TDS, the greater chance you have that your membrane will become clogged.
Having talked to some people about RO, I asked if I could run an RO membrane by itself.
My thinking is this. If you use a membrane and the prefilters at school. And school is going to be out in a few weeks. I am concerned that I will get bacteria growing in my filters over the summer. I am also concerned that hard water, setting on one side of the RO membrane wolud deposit 'stuff' onto the membrane (thus fouling it).
So...it is possible that your membrane has been fouled due to the high TDS and possibly a bad prefilter allowing a large quantity of 'bad' water to come in direct contact with the membrane.
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05-13-2004, 01:12 PM
| | Member | | Join Date: Jul 2003
Posts: 103
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AquaFilly, how long have you had the unit?
I would need to talk to Ed or Dave and see if there is a way to test the RO unit.
I think I've come up to the limit of my knowledge about membranes. Now I have to research some more (THANKS). I'm not quite sure what would cause a membrane to let 'bad' water through the membrane if it was fouled. Maybe it gets a hole in it. It is true, like the filters in your car, when they have particles stuck in them, they work better. Apparently the RO membrane does not opperate the same way.
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05-13-2004, 01:21 PM
| | Member | | Join Date: Dec 2003 Location: Westland
Posts: 532
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Dumb question but did you hook it up correctly? Your not using the waste line for fresh water are you.
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05-13-2004, 02:39 PM
|  | Member | | Join Date: Feb 2004 Location: Battle Creek
Posts: 3,151 Zip Code: 49015
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Not a dumb question, I have seen a system hooked up that way!
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