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RO/DI Output

L

lawman

I just hooked up a 6 stage ro/di unit I purchased on an auction site. Although I dont know what my water pressure is, I assume it's sufficient because I'm getting water both from the good end as well as the rejection hose. My question is, on average what is the ratio between rejected and clean water? Just estimates would be fine not looking to break it down to ozs or anything.
Thanks,
Tom
 
C

captnmorgan02

it will depend a lot on your water pressure. The manufacturer of my unit says 4:1. At my old house with city water it was about 3 or 4:1 now at my girlfriends with a well I can't even use it till I get my booster pump in.
 
C

Carlo

IMHO, forget what the "manufacture" tells you. Find out what membrane you have and then go look up the specs for the membrane. The only reason you need this ratio is because of the membrane so if in doubt ask the people who make the membrane.

3:1 is the normal standard for our size membranes.

With that said, the whole idea for the waste water is to keep water moving across the membrane which keeps it clean. I've always cut mine back to 2:1 and run them in manual mode and then I manually flush the membrane at the end of each can fill (using a flush kit - cheap). I flush for 20 seconds or so and turn off power. I also flush as soon as I start the unit too. You can't do this with a float valve where you leave the unit constantly on however as the unit can turn on/off at will.

In my current system I'm using 2 membranes. The waste of the first feeds the second membrane. The effluent of both are joined back again and fed into the DI canisters. My overall system setup this way runs at 1:1.

Carlo
 
B

Boomer

Yes Carlo this is staring to catch on a lot

In my current system I'm using 2 membranes. The waste of the first feeds the second membrane. The effluent of both are joined back again and fed into the DI canisters. My overall system setup this way runs at 1:1.

Tom who's system do you have ? Feel free to call Jim at the filterguys he will answer your questions with no BS, no matter who's RO/DI unit you have. All RO's are not treated equal. Some of them out there are "flyby night specials" And as pointed out line pressure is important.
 
K

ken6217

My manufacturer states 4:1. I also think they are assuming that your water pressure is at 60psi. By the way, the temperature of your water will influence how much good water you will get. The warmer the water, the more output.
Ken
 
C

Carlo

But you really don't want to mess with the water temperature a lot. By this I mean running a mixture of hot/cold water through it from a faucet if you use the screw on type connector. Most membranes have a spec calling for temperature to run roughly between 40 & 93F. Actually the colder the water the less throughput you'll get but the better the membrane will perform filtering wise. This is easy to understand because the membrane itself does most of the work and have a pour size around the size of a water molecule. Water molecules get bigger when cold (better filtering) and get smaller when heated (goes through membrane easier). Most membranes are rated at 77F.

If the temperature of the water is to high you'll damage the membrane. This is the reason you don't want to add hot water directly even if mixed with cold water. If you have the RO/DI unit set up in an automated fashion and don't have any issues with the amount of time it takes to make your water, you're better off letting it run colder directly from the pipes.

Here's a Temperature Correct Factor chart from Spectrapure that shows the affect of temp on efficiency:
TCF.jpg


Now there are a couple of tricks you can do to help warm up the input water a few degrees in a safe manner, which you can see from the chart above helps. If your sump or salt water container are nearby the RO/DI unit, you can run a 50 foot section of hose coiled and put this in the heated salt water. The water from your plumbing will have to pass through this coil before it gets to the RO/DI unit which brings up the temps. The opposite affect is that it helps cool the other water a bit. This can be a good thing in the summer if you have temperature issues. You can also run the waste line as a coil in the sump also to cool down the temps in the sump during the summer (free cooling).

You can also coil up a bunch of hose in a 5 gallon bucket filled with tap water with a heater in it too. You can kick the temp of the bucket up pretty high this way which will warm up the RO/DI input water pretty decently in a safe manner.

http://www.spectrapure.com/faq_p0.htm has some interesting stuff regarding temperature and water pressure and how they relate to your final GPD. The information in that page is pretty good regardless of manufacture as all RO/DI units work pretty much the same in principle. There are also a lot of specific SpectraPure stuff there also but it's a good read to understand how everything affects production rates.

Carlo

PS ken what brand RO/DI unit do you have?
 
K

ken6217

I didn't mean altering the water temperature. I meant that the ratings are based on a given temperature. Mt unit is hooked up to a faucet right where it comes into the house. I get much more good water (quicker) in the summer than the winter.
Ken
 
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