Maintenance
STULZ UltraWater 3-stage reverse osmosis system SUW
© STULZ GmbH, Hamburg
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12.5. Checking the pure water quality and throughput
Determine the actual permeation rate
Check the pure water quality and throughput of the reverse osmosis membrane. For this purpose, the
system should be in operation and the pure water must drain away freely (pressure tank disconnected from
the system).
Fill the water produced by the system into a container with a scale (in liters), and time how long it takes to
produce a defined quantity. Calculate the amount of water produced in one hour. It should be within the
range of the nominal water quantity (see technical data), and at least 60% of the nominal rate if the water
is very cold.
Determine the retention rate
To determine the retention rate, the system should be in operation for at least 15 min before you start the
measurement. Measure the pure water quality using a conductivity measuring kit or a hardness test. You
should also know the values for the untreated water.
Calculate the retention rate using this formula:
The retention rate should be at least 90%.
Note:
Regular inspection of the water treatment system is important. This is the only way to ensure that malfunc
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tions and damage to the pure water consumer are detected early and suitable action is taken promptly.
Untreated water conductivity
in µS/cm
Pure water conductivity
in µS/cm
with functioning membrane
100
10 - 3
200
20 - 6
500
50 - 15
750
75 - 23
1000
100 - 30
1250
125 - 38
1500
150 - 45
Untreated water hardness
in °dH
Pure water hardness
in °dH
with functioning membrane
2
0.2 - 0.1
5
0.5 - 0.2
7
0.7 - 0.2
10
1.0 - 0.3
15
1.5 - 0.5
20
2.0 - 0.6
25
2.5 - 0.8
The pressure tank pressure must be checked regularly during maintenance work.
Note:
Retention rate
Pure water conductivity
Untreated water conductivity
in %
= −
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(
)
1
100