Motor-Driven - EBARA EVM Series Operating And Maintenance Manual

12.5. RATING PLATE
1) "TYPE" Pump model
2) "Q" Indicates upper and lower fl ow rate limits
Indicates head limits corresponding to mini-
3) "H"
mum and maximum fl ow rate
4) "Hmax" Maximum head
5) "Hmin" Minimum head
6) "P2" Rated power of the motor (output at shaft)
Rated power of the motor expressed in HP
7) "HP"
(Horse Power)
8) "Hz" Frequency
9) "min-1" Speed of rotation
10) "P/N°" Pump item number
11) "N" Material code
12.6. WARNINGS FOR CORRECT OPERATION OF EVM
MOTOR-DRIVEN PUMPS (FIG. 1 - FIG. 2)
12.7. AVOIDING CAVITATION
Cavitation, as you may know, is a destructive problem for pumps,
a phenomenon that is encountered when the water drawn in is
transformed into steam inside the pump. EVM pumps, fi tted
with internal hydraulic parts made from stainless steel, suffer
less than other pumps built with materials of poorer quality,
though they are not entirely immune to the damage that cavita-
tion brings.
Hence pumps must be installed in compliance with the laws of
physics and with rules relating to fl uids as well as to the actual
pumps.
Below we give you just the practical results of the above-men-
tioned rules and laws of physics.
Under standard environmental conditions (15°C, at sea level),
water turns into steam when subjected to a negative pressure
greater than 10.33 m. Hence 10.33 m is the water's maximum
theoretical suction height. EVM pumps, like all centrifugal
pumps, cannot exploit theoretical suction height to the full ow-
ing to their internal loss, known as NPSHr, which has to be de-
ducted. Hence the theoretical suction lift of each EVM pump is
10.33 m less its NPSHr at the work point in question.
The EVM pumps' NPSHr can be determined by consulting the
standard curves featured in the brochures and must be taken
into consideration when fi rst selecting the pump.
When the pump is part of a fl ooded installation or has to draw
cold water from 1 or 2 m with a short pipe with one or more wide
bends, NPSHr can be disregarded. Consequently, the more dif-
fi cult the installation, the more the NPSHr value has to be taken
into consideration. Installation becomes diffi cult when:
a) Suction height is high;
b) Suction line is long and/or has lots of bends and/or has
several valves (high pressure losses along suction line);
c) Foot valve has high fl ow resistance (high pressure losses
along suction line);
d) Pump is used with a fl ow rate close to the maximum rated
fl ow rate (NPSHr increases as fl ow rate increases over the
rate where effi ciency is highest);
e) Water temperature is high. (It is likely you will have to install
the pump with a fl ooded arrangement where values ap-
proach 80-85°C);
f) Altitude is high (in the mountains).
FIG. 1
a) Good immersion;
b) Positive slope;
c) Wide-radius bend
d) Pipework with independent supports;
e) Suction pipe diameter ≥ pump port diameter;
f) Reducing coupling for eccentric pipes.
FIG. 2
a) Insuffi cient immersion;
b) Negative slope, air pockets created:
c) Tight bend, pressure loss;
d) Pipe diameter < pump port diameter, pressure loss.
GB
13