ENGLISH
18
To determine the suction level Z1, the following
formula must be applied:
Z1= pb – rqd. N.P.S.H – Hr – correct pV– Hs
where:
Z1 =
difference in level in metres between the
intake mouth of the pump and the free
surface of the liquid to be pumped.
pb =
barometric pressure in mcw of the place of
installation.( chart 1, pag. 115 )
NPSH =
net load at intake of the place of work.
Hr =
load loss in metres on the whole intake
duct.
pV =
vapour tension in metres of the liquid in
relation to the temperature expressed in
°C. ( chart 2, pag. 116 )
Hs =
safety margin = minimum 0.5 metres head.
If the calculated “Z1” is positive, the pump can
operate at a suction lift of maximum “Z1” metres head.
If the calculated “Z1” is negative, than the pump has
to be fitted with a positive lift of at least “Z1” mt.
Ex. : installation at sea level
and fluid at 20°C
required N.P.S.H:
3,25 m
pb :
10,33 mcw ( chart 1, pag. 115 )
Hr :
2,04 m.
t :
20°C
pV :
0,22 m. ( chart 2, pag. 116 )
Z1 : 10,33 – 3,25 – 2,04 – 0,22 – 0,5 = 4,32 approx.
This means that the pump can operate at a suction lift
of maximum 4,32 metres head.
8.3 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.
P1max + P2max
≤ PN (fig.5A)
P1max + P2max + P3max
≤ PNHP (fig.5B)
8.4 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. 5A)
The pump must never operate with the
delivery valve closed.
8.5 Electrical connections
ATTENTION!!
ALWAYS
OBSERVE THE SAFETY
REGULATIONS!!
Electrical installation must be carried out by an
authorised, skilled electrician who assumes all
responsability.
THE SYSTEM MUST BE
CORRECTLY AND SAFELY
EARTHED!!
Scrupulously follow the wiring diagrams inside the
terminal board box and those on table C, pag. 114.
−
Ensure that the mains voltage is the same as that
shown on the motor data plate.
−
The pumps must always be connected to an
external switch.
−
Three-phase motors must be protected with an
automatic switch (e.g. circuit breaker) calibrated at
the values shown on the data plate of the
electropump.
−
In the case of three-phase motors with star-delta
start, ensure that the switch-over time from star to
delta is as short as possible.(see table B,pag.113 ).
P1max + P2max
≤ PN
P1max + P2max + P3max
≤ PN
P1max
P2max
P3max
P1max
P2max
A
B
Std. Pump
HP Pump
Std. Pump
Fig. 5
