DAB KVC Serie Installationsanweisung Und Wartung Seite 17

If the head at intake is negative, it is indispensable to fit a foot valve with suitable characteristics at intake.
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For suction depths of over four metres or with long horizontal stretches it is advisable to use an intake pipe with a diameter larger than
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that of the intake aperture of the pump.
Any passage from a pipe with a small diameter to one with a larger diameter must be gradual. The length of the passage cone must be
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5 to 7 times the difference in diameter.
Check accurately to ensure that the joins in the intake pipe do not allow air infiltrations.
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To prevent the formation of air pockets, the intake pipe must slope slightly upwards towards the pump. Fig. 3, page 1
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Interception valves must be fitted upstream and downstream from the pump so as to avoid having to drain the system when carrying
out pump maintenance. Do not run the pump with closed valve on the plant.
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If there is any possibility of the pump operating with the interception valves closed, provide a by-pass circuit or a drain leading to a liquid
recovery tank.
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To reduce noise to a minimum it is advisable to fit vibration-damping couplings on the intake and delivery pipes and between the motor
feet and the foundation.
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If more than one pump is installed, each pump must have its own intake pipe. The only exception is the reserve pump (if envisaged).
7.2 Minimum inlet pressure ( Z1 ) (negative suction head pump)
To have good performances of the pump avoiding cavitation phenomenon it is necessary to calculate the suction lift Z1. Fig. 4, page 1
To determine the suction level Z1, the following formula must be applied:
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. 90)
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. 90)
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.:
pb :
Hr:
t:
pV:
Z1
This means that the pump can operate at a suction lift of maximum 4,32 metres head.
7.3 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, page 2)
P1max + P2max + P3max ≤ PNHP (fig.5B, page 2)
7.4 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, page 2).
The pump must never operate with the delivery valve closed.
7.5 Electrical connections
Scrupulously follow the wiring diagrams inside the terminal board box and those on table C, page 89.
Ensure that the mains voltage is the same as that shown on the motor data plate.
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The pumps must always be connected to an external switch.
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Three-phase motors must be protected with an automatic switch (e.g. circuit breaker) calibrated at the values shown on the data
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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
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possible.(see table B,pag 88).
7.6 Starting
Before starting the pump and the suction pipe have to be properly primed pump and pipe have to be fully filled with
clean water.
To obtain priming, proceed as follows: KVC – KVCX (Fig.6, page 2)
After having removed the cap, fill the pump slowly through the filling hole so as to discharge any air pockets present inside.
ENGLISH
Z1= pb – rqd. N.P.S.H – Hr – correct pV– Hs
3,25 m
10,33 mcw (chart 1, pag. 90)
2,04 m
20°C
0.22 m (chart 2, pag. 90)
10,33 – 3,25 – 2,04 – 0,22 –0,5 = 4,32 approx.
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