Ro/Di Dumb question

L

lmcnutt

I purchased a 60gpd unit from Kent. What physically keeps this unit at 60gpd? If I replace the RO membrane with a 100gpd, will I get 100gpd? Isn't everything else pretty much the same?

Larry
 
I have a 60 gpd Kent RO/DI unit as well. As I understand it, the membrane is what limits the maximum water production. It takes me about 14 hours to make 25 gallons of water using a booster pump. If you approach the max per day production let me know.
 
Again, I have the 60gpd (like you). I don't use a boost pump and get about 2 - 2.5 gallons per hour (summer time).
 
You would need to replace the membrane and the flow restrictor with the correct size and type.
 
Ok,

I have no idea where the flow restrictor goes, but I can find it. The flow restrictor is $6.00 at filterguys. That's a cheap upgrade on my next purchase or a membrane. The big difference I see is a 75gpd is 98% rejection and the 100gpd is 90% rejection.
 
I think you will have a higher rejection rate if your pressure is higher. I may be wrong. But, my thinking is, if you have more pressure, wouldn't that increase the rejection rate of the 100pgd?
-Chuck
 
Larry,

Here is a link to the 50 and 100GPD flow restrictors also.
http://www.aquariumwaterfilters.com/index.php?page=shop.browse&root=9&category_id=16&option=com_phpshop&Itemid=1

Additionally, if you talk with them I think they use the 100 GPD restrictor on the 75GPD membranes, but I could be wrong about that. I would highly recommend you stay with the 75GPD membrane due to the extra rejection capability that it has. Do a little math on some of your input water and you'll see that the difference is surprising.
400 TDS input *( 1.00-.98 ) = 8 TDS output before DI resin
400 TDS input *( 1.00-.90 ) = 40 TDS output before DI resin
The bad thing is that the extra stuff that the 100GPD *doesn't* remove from the water, will have to be removed with much more costly DI resin. Also, the rejection rates are 'ideal' and you will probably experience something even a bit less than that unless you have 'ideal' temperature and pressure on the input side. If you have very large water needs and don't mind spending the extra money on the DI resin just to get the projected extra 25 GPD, then go for it instead. On the other hand, if you really need the extra production, you can run 2 membranes in parallel (2*75GPD=150GPD) and still get good output quality (and probably pay for it in the DI resin costs you will save). I run 2 membranes in series rather than parallel to reduce waste, but I still get about 5 gal/40 minutes.
A higher input pressure will generate more output up to the limit of the membrane and the flow restrictor combination. Lower than ideal pressure will generate less production and each membrance is rated for it's GPD production at some 'ideal' pressure.
HTH
Doug
 
That does help Doug, Reading that the rejection % goes down SO MUCH with a 100gpd makes me shy away from it. However, I'd never considered running two membranes in parallel. Would you just put a 'T' on both sides of the RO and force it all through 1 DI chamber?

Thanks
 
Larry,
Yep, that's it. When I purchased mine, they offered to run them in parallel or series for me and I chose 'series' mode to help with waste water usage. The only problem that *might* arise is that it pushes too much water too fast for the DI resin to soak up the residue with a single cartridge. I also run double DI cartridges in series even though I run the membranes in series too, so I can't really say what would be *too* fast. It's just a consideration. If it were too fast for a single DI, you might have to add a second DI to get it all. I suspect that depends on the actual amount of water produced and how much contact time it needs with the resin. I've considered changing my membranes to parallel connection and double the output, but I'm satisfied with my production quantity at the moment and don't want to mess with what works for me (even with very high input TDS readings).
Doug
 
I've been looking at RO membranes lately as well, and I don't understand the differences really. It seems like every manufacturer has their own water parameters that they base their rejection rates on. For example, the applied membranes brand 100gpd membranehas a 96%rej. rate at these specs
Performance specifications based on 500 ppm tap water said:
They also sell the Filmtec membranes that are rated at 75gpd 98%rej rate with these specs: 250ppm, softened tapwater, 77F at 50psi, min rej is 96%, permeate flow may vary+/-20%.

Now from this info, it would seem to me that the generic membrane is the better one if you can get 65psi. Or are these basically equivalent membranes?

I'm way over-thinking this! :roll:
Click to expand...
 
These are my numbers

Water PSI = 85 (if my gauge is correct and outside faucet)
Water Temp = 75
Input TDS = 408ppm
After RO = 23ppm

Rejection = (input - output)/input (correct?)
which = 94.3%

It's all a crap shoot. My fish are lucky to be alive.
 
@lmcnutt wrote:
My fish are lucky to be alive. said:
:p I think that all the time!

I'm glad I'm not the only one with 400ppm! :shock:

I don't know what my psi is, but I'm on a well, so I imagine I need a booster pump even on an outside faucet. I'll have to get one and check before I buy an RO system.
Click to expand...
 
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