kent membrane for RO/DI doesnt last why?


New member
ok ...... my embrane on my ro/di unit is rated for 50 gallons per day.. works great for mont or so.... then bam.. it slow down to 15 gallons per day... i have done the math and it should be lasting much longer.

i have now gone through an extra half dozen which i now believe i shuld nt have had to.

the systems is as follows..

goes through....carbon block, sediment twine, ro membrane, to di one and then to di two...

thoughts please... water pressure is not the issue..... it truely is the membrane clogging...

i have a flushing kit installed.... did not solve problem... it has been suggested to send the used membranes to kent....

thoughts thanks
many things might slow down flow:

-sediment filter is gummed up.
-carbon filter is gummed up.
-pressure difference due to other people using the water supply.

I find in my apartment, durring the day the ro is very slow, but at night its 10x faster due to more pressure.
going in is 137 out is 001 sometimes 000... actually i think i do have it set up that way ..goes first to the sediment .. then carbon block...then membrane ..then first di then second di...

any thoughts...
Sad possibility.

Sad possibility.

Sounds like you are setup right so other than a very low pressure input; it could be that your water has something in it that is clogging the RO unit quickly.

Have you tried changing just the RO cartridge to see if it is the one that is clogging?

Anyways, I'm no water tech, but having had similar problems I just thought I'd try to help.

FWIW, I ended up buying a second unit and ganging it up with the first then I added a pressure booster to make my system last longer between filter changes.


My brother and i just picked one of these up. I hope we dont go through the same problem.
its not the pressure..... for some reasone the membrane does not last as long as it should...... ..... will post after kent gives me some answers... when i get a new one tommorrow i am sure ut will be back up to par
You keep saying its not the pressure. Do you know what both the incoming pressure and pressure after the pre and carbon filters are? If you don't have them, you need inline pressure gauges on the incoming line and after the carbon, just before the membrane like so:


There will be a pressure drop across the filters and if any plugging is going on its should be the pre and carbon and not the membrane. I have a 0.5 micron prefilter and a 0.5 micron Chlorine Guzzler Carbon block and my drop is 5 lbs when new.
thanks.. will check it out.... how much water do you get out of a spectra pure membrane... is it the same as used by kent.. the huosing for the di carbon and sediment loooks the same ...
75 GPD at 50 psi and 90 GPD at 60 psi. I have 69 psi incoming and 64 to 65 on the membrane and pretty warm water, 82 at times so I get over 100 GPD easily at 98.96% rejection with the Select series hand tested membrane.
I assume you are on city water. How often are you changing the carbon block filter? If chlorine is getting through to the membrane it will destroy the membrane, although I don't know if that will show up as decreased output or as increased output with high tds.
just un screwed some of the fittings... water from the house past the sediment... fine... water throgh the sediment and then through the carbon block... still strong.. i am now attaching a gauage and will see what the pressure is... some thing is definetly up here.... will report back.. i just checked my log and this memebrane has onlly been in use for about 8 weeks...
my psi from the faucet is 52.... out of the sediment is 52... out of the carbon block is 52... out after the membrane is 48... to get that reading i used a valve to close it while the waste water still ran..... over a period of a few minuites it went from 0 pressure to 48..

i just put in a new membrane... and the clean water is flowing as it did before.... ... i will be getting the towns water report soon to see how hard the water is....
well... it was definetly the membrane..... new 60hisi,,,gallons per day... is doing 500 ml in five minuites which equates..

63gallons per day...

so what went wrong with the membrane in just six weeks...

who makes them... are these companies simply relabeling them...
There are only three major manufacturers of household sized RO membranes, Dow Filmtec, Applied Membranes and GE Water/ Desal. There are a slew of Chinese and Taiwanese knock offs aswell as a few who actually make a pretty good membrane but the major three sell 98% of all them out there.