Is there a formula or rule of thumb for how much higher your loop condo or TDS should be than your RO output?

Henry,

Since what is circulating in your loop is what came from the RO, they should be the same. If they are significantly different you have a calibration issue.

Chuck

Why do you test conductivity after the RO? Do you check at the end of the loop?

I check loop condo near end of loop. Why? I had a holding tank installed a few years ago (after being direct feed for years and years)and just at the time thought it was standard procedure to compare the RO with loop. Maybe it's not. In any event, my loop condo has always been higher than RO out. That's with using a Hydra for both.

Henry,
Do you have a Product Divert Valve on your RO? If your answer is no, then that is the reason for having higher TDS readings in your distribution loop

pato

Is it possible there is some metal in your holding tank or loop?

Good one Pato, you are correct. I forgot about that. I'll point it out to the boss. Thanks

I thought a product divert valve was mandatory on in-center RO's?

Pato, why would a product divert valve cause a change in your TDS?

Joe, it's because when the RO first starts up, it has a higher TDS. A divert system puts water the RO makes down the drain when it first starts up.

Guest,

It's all about the money man. A lot of things are mandatory.

Thanks, so stagnant water in the line going from the RO membrane output to the storage tank has a higher TDS than when the product is flowing. So you should wait until the flush is over and the RO is actually making water to the storage tank. So the TDS of the RO should eventually get close to what is in your loop. Makes sense.

joebiomed, what happens is when the R.O. fills the tanks and shuts down, the water inside the membrane housing will flow in the opposite direction (osmosis vs. reverse osmosis), so the tds of the permiate water increases signifigantly when the R.O. is not running. Then when the R.O. starts up again, that high TDS water will be pushed into the storage tank. It takes a little while for the permiate water to get back down to normal a TDS range when the R.O. starts back up. Thats what the divert valve is for. It will shoot the permiate to drain until the TDS drops down to a normal range, thus safeguarding the water that is delivered to the patients. Hope this helped.

Considering that the AAMI standards are all "recommendations" and the state usually goes by their "recommendations" then you should defiantly have a divert valve. ANSI?AAMI RD62:2006 States that it is "Recommended" that if an RO is the last process in the water treatment system the it includes some type of diversion to drain in the event that the TDS or rejection alarms engage it will divert to drain. Seems like only good sense! Are you going to trust that the patient care staff will do anything about an alarm other than mute it?