8
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.
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
b
– NPSHR – H
f
– H
v
– H
s
p
b
= Barometric pressure in feet absolute.
(Barometric pressure can be set to 33.9 feet at sea
level.)
In closed systems, p
b
indicates system pressure in
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
f
= Friction loss in suction pipe in feet.
(At the highest flow the pump will be delivering.)
H
v
= Vapor pressure in feet.
(To be read from the vapor pressure scale. "H
v
"
depends on the liquid temperature "T
m
".)
H
s
= Safety margin = minimum 2.0 feet.
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.
Fig. 4
Minimum inlet pressure – NPSHR
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 pr 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.
Note
The pumping of liquids above 248
°
F (120
°
C) may
result in periodical noise and reduced pump life.
TM0
4 368
9
4
80
8
Note
In order to avoid cavitation, never select a pump
whose duty point lies too far to the right on the
NPSHR curve.
66
49
39
33
26
20
16
13
10
6.6
3.3
2.6
2.0
1.3
0.9
0.7
0.3
4.9
250
230
194
212
176
158
140
122
104
86
68
50
32
Hv
(Ft)
tm
(°F)
300
270
280
82
115
148
131
98
320
340
360
370
203
259
328
413
H
f
p
b
NPSHR
H
v
H
Summary of Contents for CR-H
Page 1: ...CR H CRN H GRUNDFOS INSTRUCTIONS Installation and operating instructions ...
Page 2: ...2 ...
Page 62: ...62 ...
