How to Rate the RO/DI

[fishjinx]

Does anyone know what determines the rate on these types of units.

By rates "I mean GPD" is it the membrane only, or is it the actual units that you can purchase.

[Mitchell]

The amount is determined by the membrane I believe.

Mabey a real R/O guru can answer better, but I think that is the concept.

[ajx22]

Mitchell is correct.

The TFC membrane (RO stage) is what actually determines the GPD rating...all other stages can handle any flow rate.

Once you know what flow rate your membrane is...you then install a matched Flow Restrictor to actually produce the restricted flow rate.

If you bought a RO unit that had a 25 GPD membrane - you could replace that membrane (and the associated flow restrictor) with a 100GPD (or any other flow rate) membrane - and have a faster producing filter without any problems.

HTH,

[fishjinx]

Are These TFC Membranes more expensive than the slower rated ones.

What is the flow restrictor and where is it located, what happens if you only replace the TFC Membrane and not the flow restrictor.

Is 130 Cdn. dollars a good price for a TFC Membrane that does 300GPD ( if that is possible or if there is such a membrane ) this is what i was told from some supplier that i know

[Mckitrick]

300GPD seems really high for an RO membrane and that's a cheap price too.
The most I ever see is about 100GPD. Past that you get into multiple membrane commercial-type units which are lots of dinero.

Generally, there are two things about a membrane to look for:
1. Flow Rate - The higer the better, usually expressed in Gallons per day.
2. Rejection rate - How much water gets through the filter versus how much is thrown away as waste water. In general, better membranes have better ratios.
Filtered:Wasted 1:4 is worse than 1:2.

[Lukan]

HI AJ,

You might be able to help me. I've heard that the bigger units of ro/di are not as effecient as the slower units. I've heard the ideal one are the 60 gpd.

I've got 3 different units. I've got one that is 200 gpd and two that are 60 gpd. I find that my two 60 gpd units which are the older units are more realiable. I constantly test all my units with my TDS meters.

I'm gettting a higher reading on my 200 gpd unit which is less than a year old.

Thanks

[ajx22]

There really shouldn't be any difference between them - as they all have the same amount of water passing over them - only the higher-flow rated membrane produces more filtered water.

In theory...I would say that a lower-flow rated membrane 'should' have a little better filtration rate...but I have never noticed a difference myself (I have used 25, 50, 60, 75, 100, 200 & 300 GPD units). I currently have a 200GPD unit - and have 0.00 - 0.01 reading of TDS always.

Technically...a higher rated membrane is MORE cost efficient as the same amount of water will pass through the filter whether it's a 25GPD or a 300GPD. The 25GPD unit will ONLY produce 25Gal (at best) of filtered water...yet the prefilters (sediment and carbon) will have filtered ALL the water passing through the filter...thus wasting a good portion of the prefilters life on waste water. If you were to get 300Gal out of the higher-rated filter - then you would have more good water (obviously) - and would have wasted a lesser % of the filters on the waste water.

Make sense?? :)

[ajx22]

Originally posted by fishjinx
Are These TFC Membranes more expensive than the slower rated ones.

What is the flow restrictor and where is it located, what happens if you only replace the TFC Membrane and not the flow restrictor.

Is 130 Cdn. dollars a good price for a TFC Membrane that does 300GPD ( if that is possible or if there is such a membrane ) this is what i was told from some supplier that i know

The higher the flow rate...the higher the cost for the membrane (only makes sense as you're getting more out of it).

HOWEVER...when you get into the 300GPD membranes, you're loosing effectiveness too. We only deal with the DOW Filmtec membranes, and like on my personal 200GPD unit...I have x2 100GPD DOW Filmtec membranes inline to be able to produce the desired 200GPD. This way I still get high quality water...and fast production too.

The flow restrictor can be in a number of places...depending on the manufacturer. If it's a custom-made unit...then it should be placed INTO the output tube (yellow line). If it's a prefab unit (SpectraPure, Kent, etc.), then it MAY be just about anywhere - and harder to find. It will either look like a little black tube connected to a small plastic fitting that is INSERTED into the tube - or will look like a small (about 1" diameter) cylinder connected to the tubing.

HTH

[Mckitrick]

AJ - Are the two membranes in parallel or actually in-line?

[bertcmg]

I think AJ's set-up would have em parallel otherwise there would not be any benefit in having two inline because you are again limited by the slowest membrane

Bert

[venkiw]

The make of the filter matters too. DOW makes the best RO filters.

[ajx22]

Originally posted by Paul_BB_Guy
AJ - Are the two membranes in parallel or actually in-line?

The way I have mine set-up is:

Source water into Booster Pump -
Booster Pump into Sediment (20") -
Sediment into Carbon (20") -
Carbon into 1st 100GPD rated TFC Membrane (good water from this membrane is connected to the DI stage, Rejected water connectes to the 2nd 100GPD TFC Membrane - good water is "T" connected to the DI stage and the rejected water goes to the drain) -
I have x2 DI stages...so once through the first, then into the second - and then out to the auto refill of storage vats & sumps.

HTH