RO/DI Q's & membranes

my membrane is a 50 gpd membrane. I wana increase its output. is it as simple as switching the membrane to a bigger one ? would like to kick it up to 100. how much di resin do you think itll burn through ? Im guessing a decent amount in a short amount of time.
I know the tds of water coming in is gona have alot to do with it as well


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another consideration is the pressure. If you are only running normal residential pressure (40-80 psi) then you might consider a small booster pump(around 100PSI - check your RO/DI manuf. recommendations!!!!) as this will ensure you reach the total rated output of the membrane. If the pressure drops, so does output and efficiency of the RO/DI unit.

Switching the membrane to a 100GPD unit will use more Resin, but I can not quantify for you how much more than your 50 GPD unit runs.

I currently run a 50 GPD unit and plan ahead with usage - it has proven to be plenty water for now to service 4 tanks (3 salt, 1 fresh for a total of about 200 gallons of tanks combined).

 

If your water pressure is below 50, a booster pump is a good idea.

For a membrane, you need to buy a new membrane, along with a new flow restrictor, I believe. As long as you get one with the same rejection rate, you won't burn through more DI per gallon.

 

just talked with a friend and he says I need to change the flow restrictor on the discharge side as diff membranes use different sizes and that would lead to burning massive amounts of di resin.

once a membrane has been used is there a way to take it out and store it for reuse ?

 

exactly ! I have no idea where to get a new flow restrictor from... and the membrane doesnt have the manufacturer on it...

 

If you store it, it'll likely need to be stored wet. I would wait for an opinion of someone who knows more about this *hinthint* to do anything.

You can get both a membrane and a flow restrictor (and even a booster pump too) from spectrapure.

 

I believe each manufacturer will have their own directions but it looks like the general rule of thumb is that if they are going to be inactive for more than 30 days the membrane is in danger of drying out and becoming useless and will require some sort of longer term storage with controlled moisture.

 

New membrane

 

I would hold off on replacing it, until the resident filtration expert shows up. He (AZDesertRat) knows more about this than anyone else on the site lol.

 

Switching the membrane can be as easy as a new membrane and matched flow restrictor depending on which brand you have today. Some membranes are not the standard TW-1812-XXX configuration such as some Watts Premier, Sears and Whirlpool units and a few others. Their membranes have a different nipple and O ring configuration and a standard Dow Filmtec 1812 series will not fit. No big deal though as a new housing is not that expensive either.
Not all membranes are equal, stating a 100 GPD will eat more DI resin is not accurate. The Dow Filmtec 100 GPD in particular is not a good choice since it is really a 90% rejection rate nano filter membrane and not a 96-98% rejection rate RO membrane like their 50 and 75 GPD varieties are.
A 100 GPD GE Water or Applied Membranes RO membrane on the other hand is a 96-98% device but is not really a 100 GPD membrane in most situations.

Different manufacturers rate their membranes differently, there is no one standard. Dow says their 75 GPD membranes will produce 75 GPD at 77 degrees F and 50 psi. GE and Applied say theirs will produce 100 GPD but require a whopping 65 psi and 77 degree water to do so. If you take the graphs from all three and lay them on top of each other you see they all three do 75 GPD at 50 psi, 90 GPD at 60 psi and 100 GPD at 65 psi. So in effect the 75 GPD Dow Filmtec and the 100 GPD GE and Applied are essentially the same thing. They all do 96-98% rejection and the same flows at the same pressures and temperatures, they just advertise differently.

That being said, I would go with a Spectrapure 90GPD SpectraSelect series RO membrane and here is why.
Spectrapure starts with a 75 GPD Dow Filmtec RO membrane then treats all their membranes with a special proprietary process to improve both the GPD and the rejection rate or removal efficiency. They then bench test their membranes, the normal ones get a random or batch testing for quality control and for the most part are better than 98% rejection and 90 GPD at 60 psi. With the SpectraSelect series they bench test each and every membrane individually then write the test results on the membrane and package and guarantee its efficiency in writing at better than 98% rejection unlike any other manufacturere or vendor. By comparison years of testing dry off the shelf 75 GPD Dow Filmtec membranes has shown an average rejection rate of 97% after break in.

This can be very important when you consider for every 2% you increase the membranes rejection rate or removal efficiency you DOUBLE the life of your DI resin. It does not take many resin replacements to pay for a new membrane. My personal MaxCap UHE system is averaging 99.35% rejection rate with RO only and thats in Phoenix with a tap water TDS between 650 and 850 most times. My TDS is usually around 3 with RO only.

Increasing the pressure does improve rejection rates but the cost of a booster pump if you don't absolutely need it exceeds the cost of a more efficient membrane if you still have maybe 50 psi available at the tap.

You can find everything in the sales flyer here including the SpectraSelect membranes and booster pumps:
SpectraPure Customer Appreciation SALE! 20% - 50% off

The thread grew while I was typing! Once a membrane has been wet it needs to stay that way. They should be used every 10-14 days to stay fressh or should be removed and stored wet in a zip loc bag in the back of the refrigerator. Same with DI resin.