auto-filling top-off resevoir

[mark]

This might been the thread http://216.187.96.54/vbulletin/showthread.php?t=27193&page=1&highlight=float

Still have my ro/di direct to float in the sump. After more than a year of running my unit with no maintenance (yes, I over used the filters and resins) highest I seen my TDS was 20. Changed filters and resins back to low TDS.

btw, just went downstairs and ran a few oz into a cup from the float, got a TDS of 5.

[fishface]

Mark, your link seems to be broken...

[Delphinus]

I used to run my RO/DI directly into the sump (with the pressure cut off). I don't anymore because I went through 4 RO membranes in a year, each with premature failure.

Some background..

At my old house I had about 50' of line from my RO unit to my tank, because I mounted the unit in my laundry room where there was a water supply and a drain. I was concerned that the pressure dropoff over 50' would not be enough to clear an occasional blockage in the float valve so what I did was have it empty into a reservoir, and then use a little powerhead to pressure up a 6' line to the sump. Worked like a breeze for several years.

In my new house, my RO/DI unit is about 10' away from my tanks so I removed the intermediary reservoir and plumbed the output of my RO/DI to the float valves of my tanks.

The contant on/off cycling that this produced was too hard on the membranes and contributed to the early failures. It would be on for 30 seconds, then off for a few minutes. Then on again for 30 second, then off again. I tried slower membranes and I tried faster membranes (note - with the appropriate flow restrictors of course) in the hopes of just getting it "tuned just right." Neither made a difference, they all failed prematurely.

I'm sure bad luck was a factor as well, but I don't think it was luck alone. It occured to me that the reservoir idea I was using in my previous house, buffered the unit well enough that it's on and off cycles were much longer. I.e., it would run for a few minutes every hour. This was well enough to keep the membrane from failing.

The trick, they say, is that you want to run your membrane for about an hour a day. One method people suggest is using an irrigation valve on a timer on the input of your RO/DI so that it only runs for an hour every day.

This method that kwirky suggests is a reasonable looking DIY alternative. The nice thing is that it is self-regulating. Ie. It will only get the RO/DI to turn on as it is needed, it won't over- or under-produce over time, but it nicely buffers the unit from over-cycling.

Currently I run my RO/DI into a 50g drum and feed my float valves off that. Problem is with my evaporative rates I only need to fill it about once every 2 weeks, sometimes longer. In the meantime, my RO/DI sits idle and this is not good for a membrane either. I have to flush the membrane on every run and even then the TDS surge approaches 100 or more for a few seconds.