Quote:
|
Originally Posted by Andy CWS
A membrane flush is the only way you can prevent this. I know of one RO for residiential applications that has it. Everytime the tank fills up, 140-200ml of RO water flushes the membrane. So the water can sit there for extended periods of time and the creep stays away.
I don't think your can be modified to do that. Stagnant water is a major reason for membrane failure.
Since the water to the fridge (as well as the faucet) comes from the tank, why does the TDS go up for that only? How long has the fridge been hooked up to the RO?
Andy Christensen, CWS-II
|
Thanks for responding on a Sunday, Andy. I really appreciate it.
Basically, the r.o. in the house is always on a short cycle mode - only a glassful is drawn at a time and most of the time in the afternoon and at nights when nobody is around, only the fridge ice maker draws water from it. The problem I've discovered is when the system just sits there for maybe 15 minutes or more, tds starts to creep in. I know because I had a 2-probe tds meter hooked up to the unit. The reading at the pure water line after the membrane canister normally would be in the low to mid 20s ppm, but when it sits there for 30 minutes and longer AFTER it shuts off (tank already full and no draw), the creep would spike up to the 100s and and even higher the longer the inactivity drags on. Worse, the rate of the creep would increase if there is pressure on the feed line to the membrane unit. What I did to stop this was to shut off the valve on the feed line to the unit because mine is only equipped with a permeate pump which only stops the pure water and brine lines not the feed water. But before shutting the feed line off, I had to purge the unit of the contaminated water that has accumulated in the membrane housing up to the portion of the pure water line with the tds sensor on it, and let it fill up the tank and shut itself down. When it did, I turned the feed water valve off and let the water just sit there inside the membrane housing. I checked the tds reading at the pure water line just outside of the housing and it stayed at 30 ppm. I didn't let this fool me because I know that the pure water side of the membrane inside the casing is slowly being invaded by tds. After waiting for about an hour, I opened the r.o. faucet full as soon as water came out the tds count surged from 30 to 200+ ppm - not a surprise there. I waited until the count went back down to the mid 20s and stabilized then I shut the faucet off. What I have learned from this experience is, with or without pressure, when water is not flowing inside the chamber there is always TDS creep. All reverse osmosis out there has this problem and only a small percentage of r.o. owners know this.
Flushes are good for cleaning the membrane surface of contaminants. If it is done with non-ro water (e.g. unpurified, before-membrane water), TDS will always be present. The only exception to this that makes sense would be if you flush the membrane with RO-filtered water or you let RO-filtered water sit inside the chamber i.e. both sides of the membrane filled with ro-filtered water, no matter how long you wait for the creep to happen, there will be no creep because ALL the water inside is already purified. I've heard that the Kinetico K5 does this. Can you confirm?