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3.2 Minimum suction pressure
(negative suction head pump)
Check the characteristic curves of the electric pump
to evaluate the NPSH factor and thus avoid cavitation
problems (case in fig. 1.B pg. 4).
The maximum height between the pump and the level of
liquid "H" can be calculated using the following formula:
H = pb x 10.2 – NPSH - Hf - Hv – Hs
pb = bar pressure [bar]
(value 1 can be used) )
NPSH = Net positive suction head [m] (see technical
catalogue)
Hf = friction and entrance head losses in the suction
piping [m]
Hv = steam pressure [m] in relation to the temperature of
the liquid (tm) (see fig.3.A pg. 5)
Hs = Safety margin [m] (minimum 0,5)
(see fig.3.B pg. 5).
The height between the pump and the level of the liquid
to be sucked must not exceed the "H" value calculated.
Example
pb = 1 bar
Type of pump: EV9
Capacity: 9 m3/h
NPSH: 1,5 m
Hf = 2,5 m
Liquid temperature: +50°C +50°C
Hv: 1,3 m
H = pb x 10,2 - NPSH - Hf - Hv - Hs [m].
H = 1 x 10,2 - 1,5 - 2,5 - 1,3 - 0,5 = 4,4 [m]
This means that the maximum height between the pump
and the level of the liquid to be sucked is 4.4 metres.
3.3 Minimum suction pressure
(positive suction head pump)
It is important to maintain the sum of the inflow pressure
and that developed by the pump, the latter with feeder
closed, always lower than the maximum pressure rating
(PN) permitted by the pump (case in fig. 1.A pg. 4).
P1max + P2max <= PN
P1max + P2max + P3max <= PNHP
(see fig.4.A and 4.B pg. 6).
3 .4 Minimum nominal capacity
The function of the pump at a lower level than the
minimum permitted nominal capacity may cause
excessive and detrimental overheating of the pump.
For liquid temperatures higher than 40°C, the minimum
capacity should be increased in relation to the
temperature of the liquid (see fig.5.A pg. 6)
m
The pump must never operate with the delivery
valve closed.
4 INSTALLATION OF THE PUMP
c
Before starting work on the electric pump,
make sure the electrical connection has been
disconnected from the power supply network
and that it cannot be reconnected accidentally.
The installation of the electric pump is an operation that
may prove complex.
It should therefore be carried out by skilled and authorised
installers.
Legend figure 1 pg. 4
1. Strainer
2. Base valve
3. Gate valve
4. Manometer
5. Check valve
6. Floater
7. Clamping for pipes
Two main application situations may occur:
• Case outlined in fig. 1.A pg. 4:
System with positive suction head pump, be it a tank
as seen in the figure or from a civil water supply
system, the system must include protection for lack of
water.
• Case outlined in fig. 1.B pg. 4:
System with suction pump.
4.1 Assembly
Install the electric pump in an accessible area, protected
from frost and as close as possible to the water drawing
point.
The electric pump must be firmly fixed to the base with
bolts, for hole measurements and their spacing, see
tab. pg. 8.
To reduce the noise generated during operation to
a minimum, it is recommended that anti-vibration
couplings be mounted on the tie bolts fixing the base
to the floor.
Make sure the pump is vertical before permanently
fixing it to the base, otherwise correct its position with
suitable shims.
On the base of the pump, the direction of the inflow and
outflow of the pumped fluid is marked by arrows.
Arrows on the bracket show the rotation direction of the
motor.
The pump can be mounted vertically or horizontally; in
any case it must not be positioned vertically with the
motor positioned in the lower part. (see fig.6.A and 6.B
pg. 7).
Leave enough space around the electric pump to allow
for use, maintenance operations and possible collection
of harmful liquids or liquids that need to be drained at a
temperature higher than 60°C.
In any case ensure there is a free space of at least
100mm from the cooling fan.
To avoid unnecessary stress to the pump casing, use
frames (fig.1, note 7 pg. 4) to support the inflow and
outflow pipe.
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