RODI setup

[sirclintler]

I guess GPD is 24 hours? Is it a problem to run 75 GPD thru a 90 GPD membrain?

 

[Entacmaea]

Hey there - not quite sure what you are asking - The Gallons Per Day (GPD) rating is how much good RODI water your particular membrane will make in one day, as you said. Most systems waste 2-4 gallons for one gallon of filtered water, so you'd have to run more gallons through than the membrane rating - 200-300 gallons from the faucet, to get 75 gallons of RODI water for example.

 

[sirclintler]

Thanks for the reply. I can produce a qt of good water in 5 min so doing the math I get about 72ish gallons in a 24hr period. However I am using a 90 gal per day membrain so am I just under using the membrain? the more water I force thru the worse the quality correct? So it would seem if I could go with less water production it is of better quality?

 

[Entacmaea]

You are totally fine - GPD is an estimate, and I doubt if any of us get precisely the quantity rated. Pressure and water temperature also effect the membrane's efficiency - so if pressure is low, you will get less finished water. Your unit should give a target water pressure - do you have a pressure gauge on the unit? They make booster pumps to boost pressure into the unit for better performance (closer to spec'd GPD). Usually, if you are under your ideal PSI for input, the membranes actually perform worse (have higher TDS water), so I'd shoot for the ideal range for your unit (usually 40-60PSI). If your pressure if crazy high, you could damage the membrane as well I suppose, but this is much more rare than low pressure.

 

[drillsar]

one way to tell is the waste to ro/di ratio. all systems are different in this regard. I think 3 to 1 ratio is ideal for most units unless you have a commercial unit which can be 1:1 ratio but very expensive

If the ratio isn't at least 3 to 1 than check your flow restrictor as it should match your membrane. If it does match your membrane you may have to cut it.

Optimum input pressure is in the 60-80 PSI range. 80 is ideal below 60 you need a booster pump

 

[Entacmaea]

Just read your particular unit's instructions, for PSI ratings - they should say. For instance, BRS units (75GPD) say 50 PSI above is good, below 35 PSI you need a booster. Dual membranes are a little higher. But don't take our word for it - we have no idea what unit you have - check your instructions, and if they don't say - call the retailer or manufacturer and find out.

 

[sirclintler]

it is a 5 stage that i have built myself, sediment, 5micron carbon, .5micron carbon, 90gpd ro, and di, all 10 inch filters, spectrapure parts, floe restrictor is a ball valve

 

[Entacmaea]

Nice! Well then, so much for "contact the manufacturer" : ) LOL. Maybe find an analogous unit and see what it says. Spectrapure's 90GPD membrane puts optimal pressure at 60PSI:

http://www.f3images.com/IMD/UserManuals/SP12291.pdf

 

[drillsar]

The flow restrictor must match your membrane in your case a 90gpd restrictor. Do a waste/water ratio test

 

[sirclintler]

Thanks folks

 

[Buckeye Hydro]

The membrane you're talking about is marketed at a 90 GPD membrane, but it is a re-labeled 75 gpd membrane that the vendor tells you to run at 10 psi higher (60 psi) than the manufacture's spec (50 psi).

Expect the full 90 gpd plus or minus 20% only if you feed it 77F water at 60 psi.

Russ

 

[Buckeye Hydro]

it is a 5 stage that i have built myself, sediment, 5micron carbon, .5micron carbon, 90gpd ro, and di, all 10 inch filters, spectrapure parts, floe restrictor is a ball valve

Assuming you have the correct pore size on your sediment filter, I'd change the order of your carbon blocks. Put the higher capacity block first in terms of water flow. Let it take the brunt of full chlorine exposure. The concept of having a decreasing pore size on successive filters is a good one, but it applies ONLY to the sediment filters.

If you want an adjustable flow restrictor, a standard BALL valve is really the wrong tool. Like trying to turn a screw with a hammer. Where precise flow control is the goal, think about a needle valve.

Russ

 

[Buckeye Hydro]

...below 60 you need a booster pump

Just so no one gets confused - this really isn't the case.

Realize that there are a variety of residential RO membrane brands on the market, and most are factory spec'ed at 65 psi or 60 psi. Only one brand, FILMTEC, is spec'ed at 50 psi.

So what is "low" pressure for one membrane, may meet the factory spec for another.

Membranes don't suddenly "stop working" if you feed them pressure below the specification. In general, the lower the pressure, you can expect:
*lower rejection (dirtier RO water)
*lower recovery (higher waste to permeate ratio)
*slower RO water production

These three items are also significantly affected by the temperature of the water.

Russ

 

[Buckeye Hydro]

If your pressure if crazy high, you could damage the membrane as well I suppose, but this is much more rare than low pressure.

Not really a concern in residential units. Your RO membrane housing, fittings, and or tubing would split before you'd get to a pressure that would damage the RO membrane.

Russ

 

[Buckeye Hydro]

I guess GPD is 24 hours? Is it a problem to run 75 GPD thru a 90 GPD membrain?

Back to the original post...

Yes - gpd = gallons per 24 hour day.

For your 75 ("90") gpd membrane - how much production should you expect? Plug in your water temperature and your water pressure into our calculator to find out.

You'll see that at the factory spec - 50 psi and 77F, a 75 gpd membrane will produce... 75 gallons per day.

Add 10 psi and what do you get? 93 gpd. That's why your membrane vendor tells you to run the re-labeled membrane at 60 rather than 50 psi.

Russ