How to select a centrifugal pump
Table no. 3 Diagram of manometric suction head with water up to 100 °C
WATER TEMPERATURE IN DEGREES CELCIUS
0
10
20
30
40
50
60
70
80
90
100
110
5
4
3
2
1
0
1
2
3
4
5
6
7
8
9
10
11
0
10
20
30
40
50
60
70
80
90
100
110
WATER TEMPERATURE IN DEGREES CELCIUS
R
V
E
A
L
C
U
P
R
A
C
T
I
C
R
V
E
TH
E
O
R
E
T
IC
A
L
C
U
M
A
N
O
M
E
T
R
I
C
S
U
C
T
I
O
N
L
I
F
T
P
O
S
I
T
I
V
E
S
U
C
T
I
O
N
H
E
A
D
(
m
w
c
)
(
m
w
c
)
Diagram referred to pumps with manometric suction head of 7 mwc. at 20 °C
Problems at the pump
Faults
Possible causes
Jammed pump
This may happen after periods of inactivity due to inner oxidation.
To release smaller sized monobloc electropumps use a screwdriver at the notch on the back part of the shaft.
For the larger sizes, turn on the shaft or the flexible coupling
Pumps which do not prime
Pump and/or suction pipe with air entraped.
Uncomplete priming or totally unprimed.
Possible air entering from taps, drain or fill plugs, joints or stuffing box
Foot valve not fully immersed in the fluid or obstructed by deposits.
Suction lift too high compared with the capability of the pump.
Wrong direction of rotation
Wrong number of revolutions
Insufficient flow
Piping and accessories of too small a diameter which cause too high head loss.
Jammed impeller with presence of debris in the vanes.
Corroded or broken impeller
Impeller wear rings and/or pump casing worn by abrasion.
Gas presence in the water, or too high fluid viscosity in case of fluids different from water.
Noise and vibrations in the
pump
Unbalanced rotary part or worn ball bearings.
Pump and piping not properly secured.
Too low flow rate for the selected pump
Operation with cavitation
Overloaded motor
Pump characteristics higher than those of the plant
Fixed and rotary parts in contact tending to seize owing to a lack of lubrication
Too high rotation speed
Wrong mains supply
Poor unit allignement
Fluid with too higher density than the design
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