Valve Configuration; Cycle Time Calculation - Pentair FLECK 3150 NXT Installer Manual

4.2.4

Valve configuration

Knowing the volume of resin, tank size and specifications of the resin, it is possible to
determine the required valve configuration. The resin specification will give the
backwash velocity, as well as the brine draw and slow rinse velocity that must be
respected in order to ensure a proper regeneration of the unit. From this data,
determine the required backwash flow rate as well as the brine draw and slow rinse
flow rate. In most cases, the fast rinse flow rate will be the same as the backwash flow
rate, however for certain valve types the fast rinse flow rate will be the same as the
service flow rate.
To determine the backwash flow rate:
Q = Fs
backwash
The DLFC installed on the valve has to limit the backwash flow rate to the above
calculated flow rate.
To determine the injector size:
The velocities to be respected for brine draw and slow rinse are given on the resin
manufacturer specifications. Generally speaking, the injector has to allow a flow rate of
about 4BV / h (corresponding to the flow rate of brine being drawn added to the flow
rate of raw water passing through the injector nozzle to create the suction effect).
Q = 4 x BV / h
Inj
Info
This value does not correspond to the brine draw flow rate but to the total flow rate
passing through the injector. Then refer to the injector diagrams at the inlet pressure
in order to check if the injector will give a correct flow rate. See chapters Salt amount
definition [}Page 34] and 1800 Injector flow rates [}Page 34].
4.2.5

Cycle time calculation

From this point, the volume of resin, the tank size, the capacity of the softener and the
valve configuration are determined. Next step is to calculate the regeneration cycle
duration, which depends on the valve configuration and once again on the resin
specifications.
Ref. MKT-IM-010 / C - 18.10.2019
Installer manual Fleck 3150 NXT/NXT2 - System sizing
x S
backwash
with:
Q : backwash flow rate [m
backwash
Fs : backwash velocity [m/h]
backwash
S: Tank cross section area [m
with:
Q : total flow rate passing through the injector
inj
[L/h]
BV: bed volume of resin [L]
3
/h]
2
]
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