% Recovery= Product Rate x100%
Water Production Rate = Rated Flow
Feed Rate
x Pressure Correction
xTemperatureCorrection
EXAMPLE: EXAMPLE:
The product water rate is 14 gpd
What should the expected performance of a
The drain water rate is 56 gpd
15 gpd T.F.C~ Membrane be g~ven the foilow
ing conditions: feed water at 40 psi, 500 ppm
NOTE: The total flow or feed water rate into
T.D.S., 60•F and discharging into an open
the system is the sum of the product flow and
reservoir (no holding tank pressure)?
the drain flow.
Feed Rate = 14 gpd + 56 gpd = 70 gpd
Net Pressure Differential = Feed Water Pressure
-Holding Tank Pressure
% Recovery = 14 gpd x 100%
-Osmotic Pressure
70 gpd
Net Pressure Differential =
% Recovery = .20 x 100% or 20%
40 psi - 0 psi - 5 psi
Net Pressure Differential = 35 psi
C. Water Pressure and Temperature
Referring to Table C. page 14, percent
rejection is 93% or:
Most R.O. Membranes are rated at a standard-
Percent Rejection =
ized condition of 77F (25C) and 60 psi (414
Feed T.D.S. - Product T.D.S. x 100%
kPa) discharging to atmospheric pressure.
Feed T.D.S.
1.
Product water quality and quantity greatly
Solving the equation for Product T.D.S.
depend upon the Net Pressure Differential
across the R.O. Membrane. This pres-
Product T.D.S. = Feed T.D.S. -
sure differential is a summation of the feed
( Percent Rejection x Feed T.D.S.)
water pressure at the Membrane, which tries
100%
to push the water through, the pressure in the
Product T.D.S. = 500 ppm -
Holding Tank, which tries to push the water
93%
backwards and the osmotic pressure, which
( 100% x 500 ppm)
also tries to push the water backwards.
Product T.D.S. = 500 ppm - (.93 x 500 ppm)
The Osmotic Pressure is in proportion to
the dissolved minerals in the water and can
Product T.D.S. = 500 ppm - (465 ppm)
be approximated by 1 psi for each 100 ppm
of T.D.S.
Product T.D.S. = 35 ppm
EXAMPLE:
A feed water with 1500 ppm of T.D.S. would
Referring to Table C and D. page 14, the
exert a backward pressure of about 15 psi on
correction factor for a Ap of 35 psi is .58 and
the membrane.
that for a temperature is 60F is .70.
Net Pressure
Water Production Rate = Rated Flow
Differential
= Feed Water Pressure
x Pressure Correction
-Holding Tank Pressure
x Temperature Correction
-Osmotic Pressure
The higher the net pressure differential, the
Water Production Rate = 15 gpd x .58 x .70
higher the quantity and quality of water
Water Production Rate = 6.1 gpd
produced (refer to Table C. page 14).
Some loss of production when using a
pressurized Holding Tank is normal.
EXAMPLE:
How does a pressurized Holding Tank affect
performance?
Typical Automatic Shut Off Valves stop water
production when the tank pressure is 2/3
feed pressure. If the feed pressure is 60 psi,
the shut off would be at a tank pressure of 40
psi, or a Ap of 20 psi. In worst case, just
before shut off at the highest tank pressure,
output would be at .33 of rated flow and 90%
rejection (from Table C. page 14).
2.
Feed Water Temperature also has an af
fect on water production. The lower the
temperature, the lower the quantity of water
produced (see Table D. page 14).
Summary of Contents for RO-25T
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