An Electrical Solution to TDS Creep

After building my auto top off I eliminated the constant cycling that the RO/DI did with a float valve. This was a major improvement and has reduced how often I had to replace the DI resin. Yet looking at my TDS meter I have seen TDS creep as high as 250. It takes 5 minutes to remove the saturated water from the membrane, then it is sent to my DI canisters and they take care of the remaining TDS. The DI resin taking care of the creep shortens the life of the resin as most of you know.
My solution is a simple device. It uses a relay, two solenoids and a delay to make switch. The schematic should explain the electrical side of the assembly. The run solenoid is placed after the DI canisters and the flush solenoid is placed before the canisters on a tee and its drain line is tee'ed into the waste water line on the ro.
The way the thing works, the auto top off sends 120vac to the flush assembly. 120vac hits the Delay to Make switch and the naturally closed contact on the relay then off to the flush solenoid. The flush solenoid opens and water flows from the ro to drain. After 6 minutes the delay to make switch closes and the relay is energized. 120vac moves to the energized contact and voltage removed from the flush solenoid and sent to the run solenoid. Water now flows through the DI canisters then through the run solenoid and off to my display.
Here is my hand drawn schematic.

The actual device works great but looks terrible. I built is with stuff that I had lying around. The relay is way over kill, it is one left over for my MH setup. The solenoid was used on my calcium reactor for a bit, I replaced it with a better one. The delay to make switch came from a friend, thanks David. Normally I would have put this on a project board and in a project box, like my auto top off, seen on the left but, like I mentioned it was built from stuff left over from other projects and is hidden in the basement.


This thing feeds from my electric auto top off. Here is a link to its build

DIY Auto Top Off - Wi****a Aquarium Club Forums

 

you should patent that one and sell it to air/water/ice!

 

TDS creep sucks...so is Dow...K5 rules!

K5 has a self cleaning reverse osmosis membrane through which pure water is used to rinse the membrane immediately after water is drawn from the system. This water stays in the r.o. chamber so when the first glass of water is drawn, NO TDS CREEP no matter how long the unit stays in the off state.

Now I don't know how Kinetico did it, but DNGSPOT, if you can figure out a way to emulate that - without using electricity and not wasting more than a glassful of water - I'll make you a Nobel Prize winner and you will be a legend in the reef community.

Keep up the good work and keep thinking while Dow is doing xword puzzle.

 

I would continue developing but, the solution I posted is working for me, so I have no drive to continue.

 

Good information, where did you source your solenoid valve for the ATO from?

 

Thanks,

The solenoid valves came from McMaster-Carr
http://www.mcmaster.com/#7877k23/=2tvjsx

 

I am not sure of how any water being flushed would effect the D.I resin ?

I think you have created a problem that does not exist if unit is plumbed correctly ? I thin k I get from this you are not running waste water and maybe you are backwashing the r/o unit ? The D.I if a auto cut off is used is piped in line between the R/O outlet and the float valve you are using in a sump and then the water can only go in and out of R/O to D.I then to sump . there should be no connection of your D.O to any flushing or backwashing waste mechanism. Or maybe I'm just missing somthing ? But this would not be the first time my simple brain did not catch on ..

 

The solenoids work like this during startup; start up is when TDS creep is the highest. RO water, the water that is from the membranes only, is sent to the first solenoid and then sent to drain. This is held for 6 minutes. Then the second solenoid is opened and the first solenoid to drain is closed. Water then flows to the DI. This water is at the lowest TDS that the membranes can send.

My system uses an auto shut off valve. There is no back flushing in my system TDS creep is a normal side effect of pressure held on the pure water side of a RO. This is how a auto shut off valve works, It senses pressure on the line to the DI or whatever, water then pushes down on a diaphragm which closes a valve that feeds the RO membrane. It is that pressure against the membrane that creates TDS Creep.
The line to the drain is under pressure until the solenoid is shut down. I cannot see how any back flushing is possible here.
The system has a waste line that goes to drain also.
The plumbing of my auto top off is as such. First the membrane, then the auto shut off, then the solenoids and last the DI.
I am not sure what you mean by D.O. I do not see problem with this system as it is not open to drain unless it is the line is the high pressure. Then the solenoids close and then the line to drain is closed.

I read the TDS from the Water feed line, both membranes and after the DI. From those readings one can verify if there are any negative effects. Nothing has been noted yet and I do not expect any problems. This unit has been running for 4 months without any ill effects also.

 

Question: During your 6 minute flush, how high do you see the TDS (ppm) creep up before coming back down to its running level, and what is that level?

 

I have seen the tds up to 250 ppm, after the flush the tds is at 30 ppm. Each membrane is at 15 ppm. My incoming water is 520 ppm.