RO topoff & TDS creep

Dave C · #1 09-23-2006, 12:31 PM

I've had my RO unit going directly to my sump through a solenoid/float switch thingy. It works great. But the tds out of my RO unit is brutal with so much start/stop etc. If I go & test it at any time it's about 50ppm. If I let it run for a bit it gets down to 0. But with an automatic topoff it will always be cycling for very short periods so the average tds out of the RO will suck. It won't be good for the membrane in the long run either. I know some people use other methods & would like to hear what you're doing. This won't be an issue when I get my larger tank going as I'll use a low & high water float so the RO will start supplying water when the level gets about 2" below normal and will cut off when it gets back to normal. But for the 65g tank there is no controller. Ideas?

littlesilvermax · #2 09-23-2006, 12:58 PM

I use my RO for drinking water as well so I have a storage container (RO tank w/ bladder). My RO unit cycles maybe 2 to 3 times per day.

Dave C · #3 09-23-2006, 01:52 PM

I have the same thing for drinking water and use it throughout the day. But my RO cycles much more often then that. I plugged the solenoid in this morning to catch up with the evaporation during the night and then unplugged it. I just tried it again & if I plug it in it would open the valve again. So it's cycling on & off very frequently. And that's not so good. But neither is plugging in the solenoid twice a day (or putting it on a timer) as then the fresh water is hitting the tank all at once rather then throughout the day. I've been reading on RC and there are ways to have the best of both worlds... constant replenishment of evaporated water and batch replenishment of topoff water. Ben, I thought you had something like that with the tupperware container that holds your replenishment water. Does is cycle on & off as it's used? Or batch replacement?

mark · #4 09-23-2006, 02:10 PM

My ro/di is direct to my sump as well but simply using a float valve for a furnace humidifier. Water level in the sump probably varies less than a 1/4" so flow is fairly constant. Just measured the TDS by only putting enough water in a glass so I could get a meter reading and had 7ppm.

Dave C · #5 09-23-2006, 02:59 PM

I'm not arguing with you mark, but if you watch the flow I'm betting it won't be constant. At least it isn't with my unit. It starts, tops up and then stops, 20 minutes later it starts again, drips a bit, then stops, and does this throughout the day. Maybe your tank is much larger and has more evaporation.

Here's an idea I got from RC.

The idea is that the entire container holds 4 gallons, it fills all at one time. The left side has an airline that has a check valve so as it fills it forces the air out, but the check valve prevents air from entering so a vacuum is created and the water level will hold up as the float valve is lifted & the water will turn off. At that point the entire container will be full. The right side will slowly lower as the water goes to the sump on the basis of the float switch in the sump. But the left side will remain topped up so the RO unit will stay off. When the right side gets low enough it will break the siphon and the left side will empty, the RO unit will turn on and start to refill the entire container. The siphon break probably won't empty the entire left side but hopefully most of it will drop from the sheer weight of the water.

The advantages of this design (again, it's not my design) are as follows:

- it doesn't rely on any electrical devices that can break down
- it uses your RO unit all at one time for 4 gallons of water
- TDS creep won't be much of a factor
- your tank gets evaporated water replenished immediately throughout the day

It could be supplemented with another float switch on the right side that connects to a solenoid that is inline on the RO line. If the water level rises too much to trip this float switch (i.e. if the left side malfunctions and the water level keeps rising) this solenoid will shut off, otherwise it will always be open.

mark · #6 09-23-2006, 04:42 PM

Yes it does start and stop hence the FAIRLY constant comment but my TDS are low. RO/DI been up for quite awhile with the same filters and believe that's the reason for the 7ppm as up to a few months ago a lower TDS was more common.

As for the RC idea seems complicated to me just to add some water. Had at one time planned similiar that would just fill a large vessel every few days (by timer and float, or just manually opening a valve but with the float in the holding vessel in case I forgot to turn off) then gravity feed sump through the float valve thats in the sump. Until that was setup I put the ro/di direct to the float. Ended up it's working fine as is so jut left as is.

Getting back to the range I have (1/4" variance) perhaps thats the reason for my low TDS as opposed to waiting (time between cycles) to drop 2 inches.

picture of the valve I'm using in this thread http://216.187.96.54/vbulletin/showt...ighlight=float

Dave C · #7 09-23-2006, 04:48 PM

Quote:

Originally Posted by mark

Getting back to the range I have (1/4" variance) perhaps thats the reason for my low TDS as opposed to waiting (time between cycles) to drop 2 inches.

Could be. I doubt my water level fluctuates by 1/4"... much less then that. I'm going to leave my float/solenoid on for the day and test the tds of the water entering the sump throughout the day and see what it measures. Could be making something out of nothing. And right now it's only servicing about 100g of water in my 65g tank/35g sump system. Once I add a 225g tank with sump it might really not be an issue as it will probably be running much more often & for a longer period of time. That's especially true since I'll have a high/low float on the 225g tank so the water will drop 1 or 2" before the RO will kick in and then it will run for awhile to top up.

littlesilvermax · #8 09-23-2006, 06:37 PM

I have an RO storage tank that holds 14 gallons of water. The valve the automatically turns on the RO has a pressure switch that turns it on at 60% of line pressure, so after maybe 4 or 5 gallons is used it will turn on.

My tuperware container is there to first aerate my top-off water, and provide a clean environment for my float valve to work and not get plugged (seeing it is at up to 60 psi). From the container I have aline that feeds the main tank via another float valve. This valve can get much more crap in it and still work becasue it is at only about 6 feet of pressure or 2.5 psi.

Railskinner · #9 09-23-2006, 07:16 PM

Pictures of top up systems that people use would be a gr8 addition to the thread.
I have a ro/di unit hooked up to a 10 gallon container operated with a humidfier float valve ( bought at HD). Thats as far as i got so far, still taking water from container by hand (syphon)to top up sump.I loose about 1 gallon a day due to evaporation.Ro/di unit starts and doesn't run long replaces what i use, I was thinking of putting another float in sump, hasitante as thinking this would just be a trickle system then from ro/di to 10 gal.container to sump.Might as well went straight from ro/di unit to float valve in sump then.How does one rig container to drop 3 to 4 gallons then kick in ro./di unit.So this then would cause my ro/di unit to kick in about every 4 days creating new water.

Dave C · #10 09-30-2006, 01:28 PM

I've been testing the water from my RO unit throughout the day for a week or so now. I do it when I notice that my topoff unit kicks in. When it does kick in it puts water into the sump for about 5 seconds and then shuts off. The TDS of the water coming into the tank ranges from 65 to 150ppm. Not good. If it were to run for a good minute or two it would be great as after running for 15 seconds it gets back down to 0ppm. But the way it's going right now it's adding crappy water to my sump.