View Full Version : RO membrane clogged? Help...

07/19/2006, 05:01 PM
The RO membrane on my 4 month old RO / DI unit appears to be clogged. I went to make some water this morning, and despite adequate water pressure, nothing came out. After some troubleshooting, the problem is in the RO membrane. There's no good water coming out of the membrane, only water coming out the waste line. I opened up the membrane housing and tried to remove the membrane, but it will not budge. Should it be difficult to remove from the housing? Is there a trick to it? I even made a handle out of a couple of plastic ties, feeding them through a pair of holes in the center post of the membrane, with no success -- the plastic ties strectched and broke.

I make water at least once a week, usually twice, and I make 3 - 15 gallons of RO / DI at a time. The filters before the membrane are a 5 micron sediment followed by two 10 micron carbon blocks (original to the unit). (I'm planning on a slightly different configuration when I replace the cartridges.)

Can I reverse the flow through the membrane to back-flush whatever's clogging it? Other suggestions?

Edit: I've only made a total of < 400 gallons of RO / DI with this unit.

07/19/2006, 05:38 PM
Did you try disconnecting from the last carbon to the membrane first to see if you have pressure there? The membrane going bad like that is not common at all. I am much more inclined to believe your prefilter and/or carbons are clogged and causing enough head loss there is not sufficient pressure to force it through the membrane. Do you have a pressure gauge that can be iinserted after the last carbon to see what the pressure is at that point? I would replace the pre and carbons before blaming the membrane. A quick test would be to remove the prefilter and first carbon, reassemble the housings and see if it works. The last carbon should not be plugged and should give sufficient pressure to operate correctly. I would also contact the manufacturer as it should still be under warranty.
If you must remove the membrane use a soft rag around the nipple and grasp it with a pair of channel locks or pliers twisting slightly as you pull. If you have it a very slight dab of silicone grease on the sealing surfaces will help in sealing and removing it next time.

07/19/2006, 05:58 PM
I had similar problems with short life. I installed a booster pump and keep my pressure abouve 70lbs and it works great now.

I do not think there is anything you can do except buy a new membrane.

What is the input pressure? What is your waste ratio.

07/20/2006, 02:09 AM
Ok, here's what I found out...
input water pressure (before the sediment filter): 65 psi (varies, and has recently been as high as 90 - 95, normally around 75 - 80)
We have city water and live less than a mile from a water tower, so we've never had problems with low water pressure. But, could the input pressure getting that high damage the membrane? If so, is there something I can do to keep the pressure from reaching into the 90s?
I moved the pressure gauge so it's after the last carbon block but before the RO membrane...
pressure just before the RO membrane (with only the 2nd carbon block in place): 20 psi
The auto-shutoff isn't closing, despite several minutes of tilting and shaking, and water is just running out the waste line (not enough pressure building up for the valve to close?). I'll replace the filters today, see if there's any improvement, and post the results.
I decided to not remove the membrane from the housing at this point, thinking that until I replace the filters I don't want to potentially create another problem.

07/20/2006, 03:26 AM
IMO, 65 is too low and 90 psi will not hurt, but a booster pump will make the pressure more consistant.

20psi after the sediment and carbon is way to low. there is a problem somewhere. Max drop should be around 10psi, and you are dropping about 40.

07/20/2006, 08:14 AM
You have a clogged prefilter or carbon, a 40 psi drop is evidence of that. An incoming pressure of 60 psi is fine if you have a Dow Filmtec RO membrane and will work with an Applied or GE membrane though not as well. 90 psi isn't going to hurt the membrane at all, Dows are pressure rated up to 200 psi. The thing you will find with higher pressure is lower rejection rate though but not significantly lower. What micron rating pre and carbons are you using? What is your cities water source, is it wells or treated surface water or both? Well water tends to have higher suspended solids and silt so if that the case you may want to use a larger 10 or no less than 5 micron prefilter along with a 5 and 1 micron carbon block. If its surface water you should be able to get by with all 1 microns or even a 0.6 for the last carbon. It all depends on the incoming water quality.

07/20/2006, 09:21 AM
We are on a well so the pressuer varrys a lot. after it runs for a while the pressuer drops to 40 psi and then the well kick on to re-fill the water storage tank and then it goes up to 70 psi but then it drops again. while its at 70 psi the good water comes out pretty fast but after it drops then it comes out much more slowly.

07/20/2006, 03:08 PM
Evan, you could adjust the pressure switch for less swing. Or, a plumber could, if you can't

07/20/2006, 04:02 PM
You don't want to adjust the well pressure switch. You will cause short cycling of the well pump and an expensive failure if you do so.

07/20/2006, 05:20 PM
I guess I rushed to the worst case scenerio... I bought some 5 micron sediment and carbon blocks locally, replaced all of the cartridges, and now have 60 psi just before the RO membrane (after the filter cartridges). I'm ordering some better quality cartridges and a catalytic carbon cartridge to better remove chloramine, but these will do well enough until the new ones arrive next week (no rush for new water, still have some in reserve), and at least allowed me to figure out the RO membrane is ok afterall (it's a 100 gpd GE Osmonic TFC membrane, btw, but I've already decided to get a 75 gpd DOW Filmtec when it comes time for replacement).

Having only been 4 months and 400 gallons, I thought the original 5 micron sediment and 10 micron carbon blocks (kind of strange configuration, IMO, but that's what it came with) would last another 2 months, but I guess not with our water. Our city water comes out of the river, but we live in a 40+ year old house with copper pipes, so I'm not real confident about how good the water quality is coming straight out of our tap, no matter what the city's water quality report says. I still haven't bought a TDS meter, but it's on the list. I guess I need to bump it up a few spots...

Thanks for the help!