Installer manual Fleck 2850 SXT - System sizing
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Ref. MKT-IM-030 / C - 12.05.2020
Caution - material
Risk of leakage due to unrespected service velocity !
Failure to respect the service velocity will lead to hardness leakage or even total softener
inefficiency.
Note that the water supply piping size may also be useful when estimating the nominal flow rate,
since the size of the piping allows a maximum flow rate to pass. Assuming the maximum velocity
of water in pipes is about 3 m/s, a good estimation for most common pressure [3 bar] and
temperature [16°C] is:
Piping size (internal diameter)
Max. flow rate
[in]
[mm]
[m
3
/h at 3 m/s]
0.5
12
1.22
0.75
20
3.39
1
25
5.73
1.25
32
8.69
1.5
40
13.57
2.0
50
21.20
2.5
63
34.2
3.0
75
49.2
4.2.2
Determining the required volume of resin
When sizing a softener, make sure that the volume of resin in the tank (bed volume) will be
sufficient so that even when the peak flow rate is reached, the velocity is still between the above
values depending on the hardness. When sizing a softener, always choose the resin volume and
tank size based on the peak flow rate but not on the nominal flow rate.
Caution - material
Risk of leakage due to wrong sizing !
Sizing on the nominal flow rate without taking the peak flow rate into account would
result in choosing smaller tank size and resin volume, and may lead in severe hardness
leakage during the service cycle when the peak flow is reached.
The maximum softened water flow rate that a softener can produce is given by the following
formula:
Q
service max
= Fs
service
× BV
with:
Q
service max
: service flow rate [m
3
/h]
Fs
service
: service velocity [BV/h]
BV: bed volume of resin [m
3
]
Knowing this required volume of resin, it is possible now to determine the needed tank. Note that
at least a third of the total volume of the tank must be kept as free space so that the bed
expansion during backwash is sufficient to ensure correct cleaning of the resin.
