6
Water quality from an RO system is normally
determined with a TDS Meter, which measures
total
dissolved solids
in water, measuring conductivity.
The results are normally measured in parts per
million or milligrams per liter.
Fewer dissolved
solids results in higher quality water.
RO membranes are rated by the amount of
dissolved solids they reject, expressed as “rejection
percentage”.
For example if feed water contains
100 ppm of dissolved solids and the product water
after the membrane has 10 ppm of dissolved solids,
the rejection rate is 90%. The formula is as follows:
Percent rejection =
Feed water TDS – Product water TDS X 100%
Feed water TDS
Water production
Product water rate
Usable water production from an RO system is
designated
product water rate,
produced on a daily
basis. The rate is normally described in gallons per
day (gpd) or milliliters per minute (ml/min.).
Reject water rate
The flow of water to drain is designated as
reject
water rate,
as measured in gallons per day (gpd) or
milliliters per minute (ml/min.).
Using a graduated cylinder the formulas are:
Milliliters per minute X 0.38 = gallons per day
Ounces per minute X 11.2 = gallons per day
Reject ratio
The
reject ratio
is the amount of water produced
compared to the amount of water flowing to drain.
The formula is as follows:
Reject rate
Reject ratio =
Product rate
Percent recovery
The
percent recovery
is another way to measure
the amount of water produced compared to the
amount of water which is actually used.
The formula to determine
percent recovery
is as
follows:
Product water rate X 100%
Percent recovery =
Feed water rate
Note:
Product water rate is the sum of the feed
water flow rate and reject water flow rate.
Example:
Product water rate = 10 gpd
Reject water rate = 40 gpd
Feed water = 10 gpd + 40 gpd or 50 gpd
Percent recovery = 20%
Water pressure and temperature
Product
water
quality and
production
of
RO
systems
is
dependent
on
pressure
and
temperature. Typically, RO membranes are rated
at standard conditions of 77
F (25
C) and 60 psi
(4 bar) discharging to atmosphere. In general, the
higher the pressure differential and temperature,
increased quality and quantity of water is produced.
These factors should be considered when sizing
RO systems for a particular application.
John Guest® brand fittings
Many RO systems utilize John Guest brand fittings.
These
user-friendly
fittings
provide
superior
performance and may be provided with this system.
Proper use of these
push-in
fittings is shown below.
Along with these fittings, all tubing selected must be
of high quality and must be cut with a plastic tube
cutter or sharp razor with a clean, square cut.
Should a leak occur at a fitting, the cause is
generally defective tubing.
To fix a leak, relieve
pressure, release tubing, cut off at least 1/4" from
the end (square cut), reattach the tubing and
confirm the connection is leak free.
Each time a
new connection is made, it is advisable to cut off
1/4" from the end of the tubing using these fittings.
Conventional fittings
If John Guest fittings are not used, it is essential to
install
inserts
at the ends of all tube connections
when conventional fittings are used.
