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Old 04/03/2012, 03:54 PM   #3
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Join Date: Jun 2003
Posts: 4,658
Another perspective on Booster Pumps for RODI systems

We often are asked the questions, “If you operate your RODI system at less than optimum tap water pressures, what is the downside? Is there a negative?”

To help answer these questions, I have provided data (below) that shows the actual results of various pressures applied to a typical RO membrane.

Membrane Pressure GPD Measured % Rejection % Increase
35 39.3 97.5
45 55.2 98.2 0.7
55 67.9 98.3 0.8
65 81.8 98.3 0.8
75 97.7 98.5 1.0
85 111.5 98.7 1.2

Note: 80.8 F, .932 TCF, 950ppm TDS, 1150 uS,
OPCF 7 psi; corrected psi 67

Generally speaking, production rate is directly proportional to operating pressure. It can be seen in this example that raising the pressure by the use of a booster pump from 35 pounds (a commonly found pressure in many homes and offices, especially as demand fluctuates during busy periods) to 75 pounds increases production rate by a whopping 2.5 times! This is the primary and most common reason for adding a booster pump to your system (either an RO or an RODI system)
you want to make more water faster! In cold-water locations, a booster pump can also increase the production rate, as production rate is proportional to water temperature.

Another reason for booster pumps that is often over looked, is that in hard water locations (many places in the country) % rejection improves significantly with the increase in pressure provided by a booster pump. Our data above shows a rejection performance increase from 97.5% to 98.5%, or about 1%. How important is 1%? The rule of thumb for DI resin capacity is for every 1% RO membrane rejection improvement you get a 25% increase in DI cartridge life (due to the reduced ionic load). Thus, with this particular RO membrane as an example (they do vary somewhat), you can see that operating an RODI system at higher pressures (75 psi) will gain a 25% increase in cartridge life over lower pressures (35 psi). In other words, with a 25% gain, every fifth DI cartridge is free! As DI cartridge changes are a significant cost of producing DI water over the life of your system, a 25% increase in cartridge life can add up fairly quickly.


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