Cycle Time Calculation - Pentair FLECK 2750 NXT Installer Manual

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.
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 [
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.
Info
Several parameters need, potentially, to be adjusted.
For cycle time calculation the valve configuration must be known, which depends on:
• the tank size;
• the resin specifications for the velocity for backwashing the resin bed;
• the velocity of water for brine draw, slow rinse and fast rinse.
Further information needed for cycle time calculation are:
• the resin volume previously determined;
• the salt amount used per regeneration;
• the volume of water to use for backwash, brine draw, slow rinse and fast rinse.
Ref. MKT-IM-026 / C - 15.12.2020
Installer manual Fleck 2750 NXT/NXT2 - System sizing
with:
Q : total flow rate passing through the injector [L/h]
inj
BV: bed volume of resin [L]
→ Page 37] and Injector flow rates [ → Page 37].
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