Really stupid question on RO/DI

B

Baltimore Bryan

New member
I'm sure this is a stupid question, but it has really been annoying me. I bought an RO/DI system so I wouldn't have to use tapwater awhile ago (I guess it's been 1.5-2 years or so, can't remember exactly) from Air, Water & Ice. It was the mini Mighty-something model, 50 gpd which would be more than enough for a 2.5 gallon weekly water change and topoff.
Here's the problem: The unit only puts out about 2.5 gallons per day at most. I'm not sure why? I have the unit attached to a spare sink with the faucet adapter that comes with it. I have no idea what the water pressure is in terms of PSI or anything, but I can tell you that it is not a weak trickle... it is just as strong as any in my house. I leave it on full force hot and cold water.
The other thing is that with the waste water hose that comes out of it, sometimes I leave it open all the way so it's a steady stream but usually I close it so that it just drips out slightly faster than the RO unit because it hasn't seemed to make a difference in production.
It just seems that it should be putting out more than one drop every 2-3 seconds. Is there any (relatively) easy, inexpensive fix or test I can do to see how to get more out of it? If I could actually get 10 gallons per day even that would more than enough.
Thanks for your help,
Bryan
 
Hot water trashes the RO membrane.

You should be getting a 4:1 or 5:1 ratio. There is a restrictor on the waste side that should be adjusted so you get that ratio.

You should probably change all of the pre filters and the RO membrane. It is beyond time for the prefilters and the hot water along with closing the waste has probably damaged the membrane.
 
Thanks for the response.
Just to clarify, I didn't leave the hot water on by itself, it was both hot and cold so the water coming from the faucet was in the middle. Even when I first got it, I never had any better production. It was always about 2 gallons per day at best. I can't figure out how to get a 4:1 or 5:1 ration since like I said the output of good water is only about one drop every 2-3 seconds... so I cannot make the waste water too slow- it's either the same as the good water or none at all, the valve isn't precise enough to get that little coming out.
Before I invest all the money to get new filters, I just want to know if that would really help. Like I said, right out of the box I was getting the same production now, so I am just unsure about how new filters will dramatically increase productions.
Thanks for the advice, I appreciate it.
Bryan
 
Pull the

- Input line to pre-filters
- Input line to membrane
- waste water from membrane with restrictor removed.

and see what type of flow is coming from each one.

Stop using warm water.
 
I just took apart the various connections and checked what you said. The first was very strong for going into such a small tube from the faucet. The other two got progressively weaker, but barely, it was still a good strong stream that could probably (just guessing here-) shoot water about 10 feet across a room. Even the last thing I checked was a goof bit stronger than the waste water with restrictor attached.
I will stop using warm water.
Now does this give any indication of what I could do to increase production? Sorry if my response is too vague, I'm having a hard time quantifying how "strong" the water flow is, if you have any other specific ways or suggestions I'm willing to give them a try.
Thanks again,
Bryan
 
tkeracer619 said:
Hot water trashes the RO membrane.

You should be getting a 4:1 or 5:1 ratio. There is a restrictor on the waste side that should be adjusted so you get that ratio.

You should probably change all of the pre filters and the RO membrane. It is beyond time for the prefilters and the hot water along with closing the waste has probably damaged the membrane.
Click to expand...

+1. I found out the hard way also about that. The R/O membrane seems sensitive with temp.
 
Flippers4pups said:
Sounds like you need a new RO membrane. Back flushing, IMHO, just makes sense. What's your water pressure at?
Click to expand...

Ok, so the membrane could be the problem it sounds like. I will look into what it costs to replace it. Sorry for my ignorance, but what is back flushing?
I do not know the water pressure in the unit, is there any easy way to find out or can I get some sort of cheap PSI gauge that can be installed inline with the unit without too much hassle? Aside from that, is there any other thing I can do to give you some idea of the water pressure?
Thanks,
Bryan

*Edit*- I just went on the website, and a replacement 50 gpd membrane is $40. Would I also need replacement filters, or just the membrane? And I'm guessing it wouldn't work, but if I instead replaced the membrane with a 75 gpd or 100 gpd membrane, would that give me more output or is the unit limited to 50 gpd?
 
Do you have an adjustable flow restrictor? Whenever I get a new membrane I always get a new flow restrictor and I have never seen or used an adjustable one. Backflushing is when you take off the flow restrictor and let the water wash out the membrane.
 
b442adams said:
Do you have an adjustable flow restrictor? Whenever I get a new membrane I always get a new flow restrictor and I have never seen or used an adjustable one. Backflushing is when you take off the flow restrictor and let the water wash out the membrane.
Click to expand...

The only flow restrictor I see is the one coming from the membrane in the waste line. I don't know if it is adjustable but I don't think it is because I don't see any way for it to turn or twist or anything.
The unit goes in-line cartridge filter --> in line filter --> membrane --> DI --> clean water. To backflush it, should I just take off the tube connecting the filter to the membrane so it can drain out?
Also, just because I wanted to see, I took off the tube from the membrane to the DI so that just RO water would come out. It came out still very slow, maybe 1.5-2 times as fast as the RO/DI.
Bryan
 
Yea you should change the filters as well.

If you can shoot water 10 feet then I think your pressure is ok. I was mainly concerned about clogs or obvious points of restriction.

You can get an adjustable needle valve to use as an adjustable restrictor. Not a ball valve but a needle valve.
 
Ok so it sounds like the issue may be the membrane and hopefully replacing it will help with increased output. If I were to put in a 75 or 100 gpd membrane, would that produce more water compared to the 50 gpd membrane in there now or no?
And out of curiosity, what kind of pressure do people have that get good output from RO/DI units? 30 psi? 50? 100?
Thanks,
Bryan
 
They recommend you change your prefers every 6 months. CAT membranes can hold up to chlorine but most of us TFC membranes. You prefilters contain carbon that removes the chlorine. It's hard to tell when the carbon runs out so 6 months is a safe option. If you don't replace you prefilters your new membrane will not last.
 
Also, buy a cheap pressure gauge. I think 50-90 PSI is optimal. You should be getting WAY more than 2.5 per day. Where is your water going? Do you have a reservoir with a float valve or something? It doesn't sound like your pressure so obviously something else is wrong. I agree about the membrane. You really need to replace that and your pre filters.
 
Thanks for all of the replies.
I don't know if this changes anything, but I have well water so there is no chlorine or chemicals to be removed by the prefilters. The incoming water has a TDS of about 105-115, and after the RO/DI it is 0-1.
I will look into getting a pressure gauge if I can find one, and I was told the water pressure in the house is about 45 psi. I am really hoping a don't need a booster pump...
I have no idea where the water is going. No reservoir or float valve, good water goes into a bucket and waste water goes into another bucket. After leaving the unit on all day at full force cold water, I get about 4 gallons worth of water between the good and waste bucket combined.
Still have this one question about the membrane though:
Can I replace it with a 75 or 100 gpd membrane to get better output, or will only a 50 gpd work?
Bryan
 
Baltimore Bryan said:
Thanks for all of the replies.
I don't know if this changes anything, but I have well water so there is no chlorine or chemicals to be removed by the prefilters. The incoming water has a TDS of about 105-115, and after the RO/DI it is 0-1.
I will look into getting a pressure gauge if I can find one, and I was told the water pressure in the house is about 45 psi. I am really hoping a don't need a booster pump...
I have no idea where the water is going. No reservoir or float valve, good water goes into a bucket and waste water goes into another bucket. After leaving the unit on all day at full force cold water, I get about 4 gallons worth of water between the good and waste bucket combined.
Still have this one question about the membrane though:
Can I replace it with a 75 or 100 gpd membrane to get better output, or will only a 50 gpd work?
Bryan
Click to expand...

You can replace it with any flow rate as long as you replace the flow restrictor also. I would not get a 100 gpd membrane they are only have a 90% rejection rate.
 
I started with 48 psi out of my house. I found out that most RODI units need about 75 psi to really "sing". I got a booster and everything is great.
 
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