Start-Up; Operation; Minimum Flow Rate; Selection Of Diaphragm Tank And Setting Of Precharge Pressure And Pressure Switch - Grundfos SQ Serie Montage- Und Betriebsanleitung

7. Start-up

Make sure that the well is capable of yielding a
minimum quantity of water corresponding to the
pump capacity.
Do not start the pump until it is completely
submerged in the liquid.
Start the pump and do not stop it until the pumped
liquid is completely clean, as otherwise the pump
parts and the non-return valve may choke up.

8. Operation

8.1 Minimum flow rate

To ensure the necessary cooling of the motor, the
pump flow rate should never be set to a value lower
than 50 l/h.
If the flow rate suddenly falls, the reason might be
that the pump is pumping more water than the
borehole can yield. The pump must be stopped and
the fault corrected.
The pump dry-running protection is
Caution
effective only within the recommended
duty range of the pump.
8.2 Selection of diaphragm tank and
setting of precharge pressure and
pressure switch
Warning
The installation must be designed for
the maximum pump pressure.
As the pump has a built-in soft starter giving a run-up
time of 2 seconds, the pressure at the pressure
switch and diaphragm tank during starting will be
lower than the pump cut-in pressure set on the
pressure switch (p ). This lower pressure is
cut-in
called minimum pressure (p
16
).
min
p is equal to the desired minimum pressure at the
min
highest tap + head and head loss in the pipe from the
pressure switch and diaphragm tank to the highest
tap (p = B + C). See fig. 12.
min
Pressure
switch
C
B
A
Q
max
Diaphragm tank
Fig. 12
A: Head + head loss from dynamic water level
to diaphragm tank.
B: Head + head loss from diaphragm tank to
highest tap.
C: Minimum pressure at highest tap.
Make sure that the selected pump can
Caution
deliver a pressure higher than p
+ A.
p : Precharge pressure of diaphragm tank.
pre
p : Desired minimum pressure.
min
p : Cut-in pressure set on pressure switch.
cut-in
p : Cut-out pressure set on pressure switch.
cut-out
Q : Maximum flow at p
max
p
cut-out
p
cut-in
p
min
p
pre
Q
cut-out
.
min