Grundfos CR series Montage- Und Betriebsanleitung Seite 13

9.1.1 Specification and calculation of inlet
pressure
Hf
H
Pb
Fig. 4 Schematic view of open system with a
CR pump
*Appendix:
The appendix referred to in this section is
found in the standard CR, CRI, CRN
installation and operating instructions:
http://net.grundfos.com/qr/i/96462123
Calculate the maximum suction lift "H" in m head as
follows:
H = Pb x 10.2 - NPSH - Hf - Hv - H
Pb = Barometric pressure in bar.
Barometric pressure can be set to 1 bar.
In closed systems, Pb indicates the
system pressure in bar.
(10 bar = 1 MPa)
NPSH = Net Positive Suction Head in m head, to
be read from the NPSH curve in the
appendix* (at the highest flow rate the
pump will be delivering).
Hf = Friction loss in the inlet pipe in m head
at the highest flow rate the pump will be
delivering.
Hv = Vapour pressure for water in m head.
See fig.5 in the appendix*. If the
pumped liquid is not water, then use the
vapour pressure for the liquid which is
being pumped.
tm = Liquid temperature.
Hs = Safety margin = minimum 0.5 m head.
NPSH
Hv
If the calculated "H" is positive, the pump can
operate at a suction lift of maximum "H" m head.
If the calculated "H" is negative, an inlet pressure of
minimum "H" m head is required. There must be a
pressure equal to the calculated "H" during
operation.
Example:
Pb = 1 bar.
Pump type: CR 15, 50 Hz.
3
Flow rate: 15 m /h.
NPSH (see the appendix*): 1.1 m head.
Hf = 3.0 m head.
Liquid temperature: 60 °C.
Hv (from fig.5 in the appendix*): 2.1 m head.
H = Pb x 10.2 - NPSH - Hf - Hv - Hs [m head].
H = 1 x 10.2 - 1.1 - 3.0 - 2.1 - 0.5 = 3.5 m head.
This means that the pump can operate at a suction
lift of maximum 3.5 m head.
Pressure calculated in bar: 3.5 x 0.0981 = 0.343 bar.
Pressure calculated in kPa: 3.5 x 9.81 = 34.3 kPa.
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