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SpectraPure®Inc.
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Membrane Output Calculation Example
What is the expected GPD from a 75 GPD System at 40 psi pressure and 60°F
water temperature?
PCF = 40 ÷ 60 = 0.666
TCF = 0.754 (from Table 1)
Expected GPD = 75 × 0.666 × 0.754 = 37.7 GPD ± 15%
37.7 GPD would be the Actual Production Rate
TESTING THE QUALITY OF THE MEMBRANE
The performance of a RO membrane is measured by its ability to reject salts
(or TDS (Total Dissolved Solids)).
Important: Test the quality of the membrane once every 6 months.
Note: This procedure will require a Conductivity Meter (TS-C61) or (TS-T71).
Procedure:
1. Measure tap water conductivity. (Call it X)
2. Run the system for 15-20 minutes.
3. Rinse test instrument cell 2-3 times with RO water.
4. Measure RO water conductivity directly from the blue product
water line. (Call it Y).
5. Subtract RO water conductivity from tap water conductivity. (X - Y)
6. Divide this quantity by tap water conductivity. (X - Y) ÷ X
7. Rejection = [(X - Y) ÷ X ] ×100
* Conductivity in the above procedure could be replaced by hardness, alkalinity,
nitrate, phosphate, silica etc. (Measured in ppm or mg/l).
Rejection of the RO Membrane Calculation Example
1. Tap water hardness = 150 ppm (X)
2. RO water hardness = 7 ppm (Y)
3. X - Y = 143 ppm
4. (X - Y) ÷ X = 143 ÷ 150 = 0.953
5. Rejection = [ ( X - Y) ÷ X ] ×100 = 0.953 ×100 = 95.3
Membrane Hardness Rejection = 95.3 % : Rejection rates less than 95% may
indicate that the membrane should be replaced.
