Minimum Inlet Pressure - Npshr; Maximum Inlet Pressure - Grundfos CR-H Serie Instrucciones De Instalación Y Funcionamiento

CRN-H pumps using a type H shaft seal with EPDM rubber parts,
HxxE, can be cleaned in place (CIP) with liquids up to 302 °F
(150 °C) for maximum 15 minutes.
CR-H and CRN-H pumps are not suitable for the pumping of
liquids above 248 °F (120 °C) for long periods.
The pumping of liquids above 248 °F (120 °C) may
Note
result in periodical noise and reduced pump life.
6.4 Minimum inlet pressure – NPSHR
Calculation of the inlet pressure "H" is recommended in the
following cases:
• When the liquid temperature is high.
• When the flow is significantly higher than the rated flow.
• When the water is drawn from depths.
• When the water is drawn through long pipes.
• When the inlet conditions are poor.
To avoid cavitation, make sure that there is a minimum pressure
on the suction side of the pump.
The maximum suction lift "H" in feet can be calculated as follows:
H = p – NPSHR – H – H – H
b f v s
p = Barometric pressure in feet absolute.
b
(Barometric pressure can be set to 33.9 feet at sea
level.)
In closed systems, p
feet.
NPSHR = Net Positive Suction Head Required in feet.
(To be read from the NPSHR curve at the highest
flow the pump will be delivering.)
H = Friction loss in suction pipe in feet.
f
(At the highest flow the pump will be delivering.)
H = Vapor pressure in feet.
v
(To be read from the vapor pressure scale. "H
depends on the liquid temperature "T
H = Safety margin = minimum 2.0 feet.
s
If the "H" calculated is positive, the pump can operate at a suction
lift of maximum "H" feet.
If the "H" calculated is negative, an inlet pressure of minimum "H"
feet is required.
8
indicates system pressure in
b
"
v
".)
m
H
f
H
p
b
NPSHR
H
v
Fig. 4 Minimum inlet pressure – NPSHR
In order to avoid cavitation, never select a pump
Note whose duty point lies too far to the right on the
NPSHR curve.
Always check the NPSHR value of the pump at the highest
possible flow. The NPSH curves can be found on pages 17
and 18.

6.5 Maximum inlet pressure

The table on page 21 states the maximum permissible inlet
pressure. However, the actual inlet pressure + maximum pump
pressure (at no flow) must always be lower than the maximum
operating pressures stated on pages 19 and 20.
The pumps are pressure-tested at a pressure of 1.5 times the
values stated on pages 19 and 20.
tm Hv
(°F) (Ft)
370 413
360 328
340 259
320 203
300
148
131
280
115
98
270
82
250
66
49
230
39
212
33
26
194
20
16
176
13
158
10
140
6.6
4.9
122
3.3
2.6
104
2.0
86
1.3
0.9
68
0.7
50
0.3
32