SpectraPure
®
Inc
.
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[email protected] www.spectrapure.com
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SpectraPure
®
Rejection of the RO Membrane Calculation Example
1. Tap water TDS = 150 ppm (X)
2. RO water TDS = 15 ppm (Y)
3. X - Y = 135 ppm
4. (X - Y) ÷ X = 135 ÷ 150 = 0.90
5. Rejection = [ ( X - Y) ÷ X ] ×100 = 0.90 ×100 = 90%
NOTE: Rejection rates less than 95% may indicate that the membrane should be
replaced.
MEMBRANE PRODUCTION CALCULATION:
Membranes produce the rated gallons per day (GPD) at 60 psi (4.1 bars)
operating pressure, 77°F (25°C) operating temperature and with no more
than 500 ppm total dissolved solids.
Membrane output gallons per day (GPD) depends on operating pressure,
water temperature and the TDS in the feed water.
Expected GPD = Rated GPD × PCF × TCF
PCF
is the pressure correction factor
TCF
is the temperature correction factor
Calculation of Pressure Correction Factor (PCF):
The output (GPD) from
the membrane is directly proportional to the applied pressure.
NOTE: The membrane is rated to produce the rated GPD at 60 psi. For any
pressure other than 60 psi the output GPD is multiplied by the PCF.
PCF = Line Pressure (in psi) ÷ 60
Calculation of Temperature Correction Factor (TCF):
The output (GPD)
decreases with a decrease in temperature. This is due to water viscosity
increasing with a decrease in water temperature.
