Pentair FLECK 3900 NXT Installer Manual page 38

Installer manual Fleck 3900 NXT/NXT2 - System sizing
To calculate the backwash duration:
T = (N × BV) / Q
backwash BVbw
Info
The typical value of the volume of water to be used for backwash is between 1.5 and
4 times the bed volume, depending on the inlet water quality.
To calculate the brine draw duration:
Knowing the injector draw flow rate at the working pressure:
T = V / Q
brine draw brine draw
Tip
Multiply the amount of salt in kg by 3 to get a approximation of the brine volume to
draw !
To calculate slow rinse duration:
The volume of water to be used for slow rinse is given in the resin manufacturers specifications.
Generally speaking, it is advised that between 2 and 4 BV of water is used to perform the slow
rinse after brine draw. The slow rinse cycle allows brine to be pushed slowly through the resin
bed, allowing the resin to be in contact with brine for sufficient time and therefore to be
regenerated.
Refer to the injector curve at the common working pressure to determine the slow rinse duration.
T = (N x BV) / Q
slow rinse BVsr
To calculate fast rinse duration:
The fast rinse is aimed at eliminating an excess of salt in the resin bed and also recompacting the
resin in the tank.
38 / 184
with:
DLFC
T
N
BV: bed volume [L]
Q
with:
T
V
calculation [
Q
with:
SR
T
N
BV: bed volume [L]
Q
: backwash duration [min]
backwash
: number of bed volume for backwash
BVbw
: drain line flow controller size [L/min]
DLFC
: brine draw duration [min]
brine draw
: brine volume to be drawn [L], see Refill
brine
→ Page 39].
: injection draw flow rate [L/min]
draw
: slow rinse duration [min]
slow rinse
: number of bed volume for slow rinse
BVsr
: injector slow rinse flow rate [L/min]
SR
Ref. MKT-IM-015 / D - 28.08.2020