Ro Rejection Differences... Why The Different Ratings For The "same" Membrane???...

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There is some confusion on RO membrane GPD ratings we would like to explain.

We have been testing our RO membranes for over 20 years to the industry
standard of 60psi. This is a significant amount of data for us to draw upon
when we share performance characteristics with our customers, help them
troubleshoot production problems, or back up our ratings claims for that
matter.

For example, the Filmtec 75GPD membrane that is so popular is rated 75GPD at 50psi. When we test it at the industry standard of 60 psi, the rating is 90GPD. The production rate of RO membranes is directly proportional to the applied pressure, thus the rating difference; this is why we sell our membranes and systems as 90 GPD (at 60 psi and 77F).

As a note, there are many other membranes that we frequently use besides
Filmtec with as good or superior performance, and those manufacturers use
the 60psi standard.

Unfortunately, most customers in the USA have less than 60 psi (or even 50 psi) available, let alone the 77F water temp that is used in the rating
process (average water temp is more like 50F across most parts of the
country). In these cases a pressure boosting pump can obtain higher
production rates. If you live in Hades (Phoenix in the summer) the 77F is
not much of a limiting factor as far as production goes. But for our
customers in upstate New York in January, it is a huge factor. Perhaps to be more realistic we should all rate membranes production on systems at 40 psi and 50F, although I doubt our competitors would drop their rating convention in this highly competitive market seemingly driven by perceived cost per gallon production rate.

Even more astounding, is that with the membranes that we hand-select and
test to insure rejection greater than 98%, we typically see production rates
exceeding 100 GPD at 60 psi (and 77 F) !!

If you look back at their literature, Filmtec started the 50 psi rating as a
sales gimmick wherein they stated that FILMTEC membranes have the same production at 50 psi as the competitors membranes do at 60psi. Great way to snag customers, but it requires customers to look at the production rate charts and how they are derived to really compare membrane production rates.

Also, in our hand-selected and -tested Filmtec 75gpd membranes, we can make sure that you are purchasing greater than 98% rejection (look at their spec on the DOW website, 96% is the bottom range of the guarantee! They are not all 98% like many think!....
http://www.dow.com/liquidseps/prod/tw30_181275.htm

Why is 1 or 2% so important?? A 2 % increase in rejection from 96% to 98% can double your DI cartridge(s) life. Over the life of the membrane that can save you big $$$ in DI cartridges! That is why our hand selection and proprietary testing (we reject more than half that do not meet our SPEC of >98.0% rejection) is worth the extra cost. Who else labels their membranes with actual rejection rate on the so called "the same" membrane?

Hope this helps explain the different ratings that you see for what appears
to be the "same" membrane.

bruce
SpectraPure, Inc.