Grundfos CR 95 - Page 16

Selection and sizing
CR, CRN 95-155
4
16
Thrust handling device
Fig. 12 Thrust handling device
A thrust handling device (THD) is factory-fitted on
pumps with 100 Hp (75 kW) motors or larger. The
system consists of two parts. A rotating part mounted
on the shaft end below the first impeller as well as a
non-rotating part mounted in or on the pump base.
The THD absorbs the main part of the thrust force
generated by the impellers and thereby reduces the
resulting axial force the motor bearings must absorb.
This enables the use of standard ball bearings in the
motor instead of special angular contact ball bearings.
Note: For applications involving CIP
(cleaning-in-place) and motors above 75 Hp (55 kW),
use a bearing flange and a base without THD.
Fig. 13 Position numbers for THD parts
* On request for CRN.
Operating pressure and inlet pressure
Do not exceed the limit values for these pressures:
• maximum operating pressure
• maximum inlet pressure.
Minimum inlet pressure, NPSH
We recommend that you calculate the inlet pressure
"H" in these situations:
• The liquid temperature is high.
• The flow rate is significantly higher than the rated
flow rate.
• Water is drawn from depths.
• Water is drawn through long pipes.
• Inlet conditions are poor.
To avoid cavitation, make sure that there is a minimum
pressure on the inlet side of the pump.
Calculate the maximum suction lift "H" in m head as
follows:
H = p
b
x 10.2 - NPSH - H
f
- H
v
If the calculated "H" is positive, the pump can operate
at a suction lift of maximum "H" ft (m) head.
If the calculated "H" is negative, an inlet pressure of
minimum "H" ft (m) head is required.
Fig. 14 Minimum inlet pressure, NPSH
Note: To avoid cavitation, do not select a pump with a
duty point too far to the right on the NPSH curve.
Always check the NPSH value of the pump at the
highest possible flow rate.
TM06 9669 2817TM06 9670 2817
Pos. Description Material
120a Thrust disc Stainless steel
120b Rotating ring Silicon carbide
120g Stationary ring
Silicon carbide*
Tungsten carbide
120h Lifting plate Stainless steel
- O-rings
EPDM
FKM
120a
120b
120g
120h
p
b
=
Barometric pressure in ft (bar).
Barometric pressure can be set to 39.9 ft (1 bar).
In closed systems, p
b
indicates the system pressure in
feet (bar).
NPSH =
Net Positive Suction Head in ft (m) head, to be read from
the NPSH curve at the highest flow the pump will be
delivering.
H
f
=
Friction loss in inlet pipe in ft (m) head at the highest
flow the pump will be delivering.
H
v
=
Vapor pressure in ft (m) head, to be read from the vapor
pressure scale. H
v
depends on the liquid temperature t
m
.
TM02 7439 3403 - TM02 7445 3503
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
20
15
12
10
8,0
6,0
5,0
4,0
3,0
2,0
1,0
0,8
0,6
0,4
0,3
0,2
0,1
1,5
120
110
90
100
80
70
60
50
40
30
20
10
0
Hv
(m)
tm
(°C)
150
130
140
25
35
45
40
30
160
170
180
190
62
79
100
126
NPSH
H
v
H
f
p
b
H