RO / DI System

[Caribbean Jake]

I currently have a 5 stage RO/ DI system I bought from Airwaterice.com over a year ago. It is specified to produce 70GPD although in the past year the most I been able to get is 12 to 14 GPD. Currently the system is slowing down to a mare 5 GPD. I thought maybe it is cloughed or needs new filters so I replaced all three Carbon Filters, but the output is the same. The DI filter is specified to be changed every 3 to 5 years. As I said the system is one (1) year old. Do you guys have any idea why production is so slow? I checked the lines, changed the filters (except DI) and cleaned the diaphragma but still output is the same.

 

Any ideas? Suggestions?

[flowerseller]

What kind of PSI are you getting prior to the RO membrane?

Have you noticed if the waste water ratio has increased?

No kinks in any tubes correct?

Do you have a backflow valve for your RO membrane and if so, did you use it every couple months?

 

I know it's all questions but.............

[Caribbean Jake]

Chip

I have no idea on the input psi, the RO/DI is connected directly to the cold water

pipe. The waste water has definetly increase in the last few month that is why I decided to change the filters. There are no kinks of any kind in any of the tubes or canisters. No, I do not have a backflow valve on my intake before the RO membrane. As matter of fact there is no backflow valve in the unit/system.

 

Still the throuput is low.

[ErikS]

Should you get the chance search for posts by az_desert_rat (I think) over @ RC - he's the RO/DI guru. He's tried several times to get it through my thick skull (bless his patience), I know a little.

 

#1 - Diagnosing filter/membrane changes is tough w/o a TDS meter.

 

#2 - A pressure guage is a "real nice" item, as water pressure fluctuates & this changes the effectiveness of the unit.

 

Two things jump out - I've never heard of a DI unit that lasts 3-5 years. Usually the resin lasts a few months, but that depends on the amount of TDS that come out of the membrane. Number 2 is that I'm not familiar with a 70gpd unit, even AWI doesn't list it. Maybe it's the 75gpd unit? That is, IMHO, the best Filmtec membrane (90% of home RO membranes sold are DOW Filmtec - I forget the other brand). The rejection rate on that unit is 98%. This is where the TDS meter comes in handy - take the TDS of the water on the way into the membrane -> the membrane should remove 98% (i.e. input is 100 then output should be 2). If this is the case then the membrane is functioning correctly. Where a pressure meter comes in handy is determining the PSI @ the membrane, the membrane in question runs with as little as 50psi. You can use a pressure guage to compensate for lower pressure by using an adjustable flow restrictor.

 

A rough gauge of pressure is to calculate the waste -> good ratio, it should be on the order of 5:1 (for every gallon of good water made you should have 5 gallons of waste). If you're in the area of 10:1 or even 15:1 (sounds like you might be) then most likely pressure is the culprit. You can solve this with either a booster pump os an adjustable flow restrictor (about $5). Just be careful with the restrictor & stay on the safe side (go with 6:1) - going over 90psi can cause the membrane to rupture = bad news (you'll cruise through DI resin as it will be removing most of the TDS). Personally I run my membrane hard, in the area of 80psi - this gives me a low good:bad water ratio.......but.........I replace my membrane annually (or if I see the DI being used up fast)

 

The DI is the final stage & as I said doesn't last more than a few months (depending on amount of water made) - the membrane can last a few years given care (flushing).

 

No, I do not have a backflow valve on my intake before the RO membrane. As matter of fact there is no backflow valve in the unit/system.

A dumb term if you ask me, why they call it backflow when it's a just a flush I have no idea. They're simple to make with some RO tubing & a trip to Lowes.

 

Goes like this (on the waste line from the RO membrane):

 

(one leg) line -> "T" -> restrictor -> "T" -> waste line

(other leg, makes a U shape) "T" -> ball valve -> "T"

 

You just open the ball valve & let the water flow for about 5 - 10 minutes, this rinses out the inside of the RO membrane = it's cleaned up & ready to go.

[Caribbean Jake]

Erik

Great, that shares some light in the matter. My unit is the one called COMAPCT at airwaterice.com and you are right it is specified for 75GPD. The ratio is currently 6 to 1, and the pressure more likely is the culprit. Now, on the web site as well as the documents I received from airwaterice.com it calls for a DI to be replaced every 3 to 5 month depending on usage. (or is it the membrane?), now you got me confused.

[jwildman]

Jacob,

 

I have a TDS meter and a PSI meter. Would be happy to lend you for diagnosis purposes. Just let me know.

 

Regards,

 

John

 

 

Erik

Great, that shares some light in the matter.  My unit is the one called COMAPCT at airwaterice.com and you are right it is specified for 75GPD.  The ratio is currently 6 to 1, and the pressure more likely is the culprit.  Now, on the web site as well as the documents I received from airwaterice.com it calls for a DI to be replaced every 3 to 5 month depending on usage.  (or is it the membrane?), now you got me confused.

40948[/snapback]

[Caribbean Jake]

John

I will love to borrow it for few minutes. LMK when I can pick it up, or perhaps come over to your place and on the same trip take a look at your new stand.

[ErikS]

Here's a link to the bypass @ Buckeye Field Supply (this one has an adjustable flow restrictor in the middle)

 

Buckeye's Bypass

 

Simple to make, but if you're ordering something else it's cost effective (darn & we could have made one the other day from spare parts too )

 

Yep, that's about right, 4-5 months for the DI cartridge (it all depends on how much water you make). Up to 3 years for the membrane (I'm just anal about it ).

 

If I had to guess the lack of rain has had an impact on the water pressure in our area (either that or the level of new housing -> more houses = less pressure on the same line).

 

Yep, that's a 75gpd filmtec (good membrane). All the units are pretty standard, does that DI cartridge come apart? If it does you can re-fill it with bulk DI resin from BuckeyeFieldSupply. Given that the DI unit isn't clear (color change won't help) I'd definately invest in a TDS meter - check the water every couple of months so you'll know when to change out the resin.

[Caribbean Jake]

how will the bypass increase the flow of water? you are actually diverting the flow into two streams this in fact will slow the flow, wouldn't it?

[davelin315]

Hi Jake, I also have a TDS pen you can borrow, as well as a pressure gauge that you can attach to a spigot on the outside of your house. This will give you the pressure reading for the whole house. My house is at 80 PSI which should mean you have about the same since you're close.

 

Anyway, the life of a membrane is rated for when people use it for drinking water. Since we typically will use it a lot more in the marine hobby, none of the filters last as long. They will clog more quickly, and yes, the more waste water there is, the less effective the RO membrane is becoming. It's rejecting more because it's clogged, and I don't think (could be wrong) that simply flushing it will make a big difference. I need to replace all of my filters as my TDS reading has skyrocketed of late to over 60ppm, not good!

 

Like I said, if you'd like to borrow my stuff, you're welcome to it as well. I happen to have it with me this weekend as I brought it home from school to take care of some stuff at home.

[flowerseller]

Hey Dave,

 

Have you noticed a real change in the tank with the higher TDS?

I have never found a reading basis to make the change of filters.

Prior to my RO/DI unit I used a straight DI unit. My readings form it were 75+

and my tank seemed fine so I don't know when to make a PF or membrane or both switch.

[Caribbean Jake]

I just got the meter from John. Thanks John for letting me borrow it. The first read said 115 ppm. WOW, and I been using this water for top off and salt mixing. Now I used the meter to test the salt water than I condition with ALK, Marine Salt and the same water tested at 115, and the salt water is at 001 ppm. WOW, what a difference. I wne ahead and change all the filters and DI unit, just to be save, but the throughput is still the same mear drip of water.

[davelin315]

I have noticed an increase in nuisance algae, although the introduction of a couple of fighting conchs has solved that problem in the larger tank. In my smaller home tank, however, it is overgrowing it since the last wholesale water change, so it's time to do it again after I replace filters.

 

Jake, you shouldn't get a reading of 001ppm for saltwater. Instead, it should fly off the scale for a TDS meter. TDS meters use conductivity to determine how many foreign elements are in water. The more stuff there is in water, the more conductive it is. When I tested water around the house, my tap was at around 200+, the RO/DI was in the 60s, bottled water was at around 3 ppm, and the salt water didn't even register because of all the dissolved solids in it (in reality it's above 3000 ppm I believe).

[Caribbean Jake]

Dave

Thank you. Please allow me to correct my post. The saltware read was OFF the scale... it read 1001. sorry for the missprint.

[Caribbean Jake]

I did a water test again after flushing the RO/DI unit. The water is at 004 ppm. WOW :o that is awesom. Now, the funny part of the story. :D I did a test before doing any changes and the water tested at 234 ppm. Well I just added baking soda to the fresh made water to pump ALK since I use Oceanic Salt and is normal low in ALK. What a scare ! :pumpkin: but I was able to go back to records and remember the water treatment. Now that I know the effect of baking soda in raw water, I ca use the information to improve the quality of DI water.

 

Dave

Thank you for lending me a hand and teaching me how to flush an RO/DI system.

 

John

I willl come by your house tomorrow morning to return the meter.

[flowerseller]

after flushing the RO/DI unit.

I'm glad you tried this since now you are allowing more water to pass though the membrane. Do that every couple months. I say this because the more you push on stuck particles, the harder it is to push them back out the other way.(back flow-flush)

On my unit, I get 2 waste and 1 collect with a TDS of 002 but our pressure is 70-80 PSI.

[Caribbean Jake]

thanks Chip, now that Dave showed me how to back flush I will keep it in mind and incorporate into maintenance schedule

[Caribbean Jake]

the pressure is around 70 - 60 psi, but the troughput is still at 10 GPD. I read a little and found that when incorporating a membrane, two carbon filters and one .5 micron filter, the system goes from 75 to 10 GPD. So there is where I am so far. I tested the water again this morning and read 003ppm.