Determining The Required Volume Of Resin - Pentair FLECK 2910 NXT Installer Manual

Installer Manual Fleck 2910 - NXT - System sizing
Depending on the inlet water hardness, the service velocity for standard softening has to be between:
Service velocity
[bed volume per hour]
8 - 40
8 - 30
8 -20
A
Note
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 (external diameter)
[in]
0.5
0.75
1
1.25
1.5
2.0
2.5
3.0

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.
A
Note
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.
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Inlet water hardness
[mg/l as CaCO ]
3
< 350
350 to 450
> 450
[mm]
12
20
25
32
40
50
63
75
Ref. MKT-IM-002 / A - 18.11.2016
°F
°dH
°TH
<35 <19.6
35 - 45 19.6 - 25.2
>45 >25.2
Max. flow rate
3
[m /h at 3 m/s]
1.22
3.39
5.73
8.69
13.57
21.20
34.2
49.2