How to prevent TDS creep?

S

silicon_dt

I recently bought a 6 stage RO/DI unit.
Since my wife wouldn't just let me get one for my tank, I got the one with DI and Drinking water spout. The drinking water goes through a (taste filter) and the Di goes through a Di filter.

I am the type that has to PERFECT everything I do, and learn EVERYTHING about anything new I get. It's a curse sometimes...

Anyways I noticed I was getting bad TDS creep. Mostly cause my wife is getting one glass at a time. This would cause the ro membrane to kick in and top off my pressure tank. The back pressure of the tank would cause the membrane to output high tds water. I fixed this issue with a permiate pump.

NEXT issue. It seems that I STILL get TDS creep when my wife gets glasses of water at a time. I have tracked it down to another form of TDS creep. This is caused by the shut off valve turning off. The left over water in the membrane still tries to push the low pressure water through a little bit. Causing high TDS water.

Is the ANY way to get around this? I read about an auto flush valve that will flush the water for 18 seconds everytime the RO is active. Any ideas???
 
Do you have a link to the auto-flush valve thingy? I'd be interested in this as well. My ATO is in line between the RODI and the sump. The problem is the float switch only needs about 1/16" to activate and causes the unit to kick on and off about every 15 minutes. I'm blowing through DI resin :shock:

Options are to put the ATO on a timer to shut it off for several hours at a time and only let it back on for about 10 mintes to top it off. The flush valve would be great.

You might want to check the auto shut-off valve on yours. I only get a glass at a time from my inside unit and only hear my unit kick on every other day or so. It is also hooked up to the icemaker in the freezer. It sounds like the valve may be running a little on the low pressure side.
 
I added a Permeatic Pump to my RO system and it has seemed to help with TDS creep. The permeatic pump also helps when you have the pressurized storage tank for the drinking water and it helps with more water output and less waste water. Also the membrane flush option is nice to have and will help with TDS creep.
 
Here is the link to the auto flush valve.

http://www.waterfiltersonline.com/detail.asp?product_id=aquatec-aft

You will have to buy some special transformer for it though. - Another $15

It says it will purge the water for 18 seconds upon system startup (Getting rid of the crappy water thats sitting in the membrane) then it will do it every hour after that. (only if the system is making water)

For your setup, this still might not be the best thing, cause if your topoff is always turning on, this auto flush is going to waste 18 seconds of FULL pressure water before it gives your tank just a little bit. Thats alot of wasted water! BUT it would fix the tds creep problem :)
 
I think I'm just going to set my ATO on a timer to be off for say 6 hours then on for 1. That should at least let it avap. more than the 0.1 gal it does now before coming back on. I'd like to get it up to about 1 gallon prior to coming back on.
 
One question though... The brine water auto flush just cleans the membrane right? Like an auto flush kit.

Isn't the tds creep caused from the idle water bleeding into the permiate side at very low pressure.

Would a brine flush suck/purge that bleed water out of the permiate side? Thus sucking cleaner water back into it from the pressure tank or something?
 
@silicon_dt wrote:
How do you turn float valve off? said:
I've got an oceanus system with dual float switches. I just shut the power off to the unit entirely using the AC Jr. The solenoid is a normally off unit so the water will not go through without power. I set it this morning to be off for 3 hours then on for 15 minutes. As it was, it was coming on every 30 minutes and running for about a minute.

Hmmm, lets see here. 100 gpd unit = 4.1667 gph = 0.069 gallons every 15 minutes

Now, it should be taking the sum of what it was doing every 30 minutes or so and doing that every 3 hours = 0.4 gallons. that should equate to about 1/2" drop in the return section before it comes on. I'll see when I get home this evening around 5:30 and the unit should be coming on at 6:01
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