Rayne RayneClear Installation, Operation & Service Manual - page 14
C. Net Pressure Differential
Most R.O. Membranes are rated at a
standardized condition of 77°F (25°C) and 65
psig (450kPa) discharging to atmospheric
pressure.
Product water quality and quantity greatly
depend upon the Net Pressure Differential
(
∆
p) across the R.O. Membrane. This pressure
differential is a summation of the feed water
pressure at the Membrane, which tries to push
the water through, the pressure in the Holding
Tank, which tries to push the water backwards
and the osmotic pressure, which also tries to
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push the water backwards.
The Osmotic Pressure is in proportion to the
dissolved minerals in the water and can be
approximated by 1 psi for each 100 ppm of TDS.
EXAMPLE: A feed water with 1500 ppm of TDS
would exert a backward pressure of about 15 psig
on the membrane.
Net Pressure Differential =
Feed Water Pressure – Holding Tank Pressure –
Osmotic Pressure
The higher the net pressure differential, the
higher the quantity and quality of water produced.
Some loss of production is normal when using a
pressurized Holding Tank.
NOTES: