auto-filling top-off resevoir

[Dave C]

Originally Posted by kwirky

Now I need to figure out if I can run a 50' hose from my ro/di to my tank, or if that's too long of a run.

Is this the thread? I don't see why you couldn't have a 50' run of RO hose.

[midgetwaiter]

I've got one of those pressure cut off switches for RO units I'm not using if anyone wants to try this. Seems like too much screwing around for me though, just flush your membrane once in a while.

[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.