Multiple stage centrifugal pump

Details Multiple stage centrifugal pump Multiple stage centrifugal pump

1999-03-22

2001-01-30

Look, Edward K. (Department: 3745)

Rotary kinetic fluid motors or pumps

Plural runners supported for relative motion or on separate...

With means for selective runner operation or drive shaft...

C415S069000, C415S124100

Reexamination Certificate

active

06179553

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a multiple stage centrifugal pump for liquids with a plurality of rotors which are arranged on a shaft and which rotate in a pump housing.
Multiple stage centrifugal pumps are used when it is desired to produce a high pressure gradient and the required forwarding amounts or the nature of the forwarded medium is such that volumetric pumps do not come under consideration. A pump manufacturer will thus first attempt to manage with few pump stages and to make the peripheral speed or the speed of rotation of such a pump large. However, high entry accelerations arise in the rotor at the suction side of the pump at the first stage, which leads to cavitation when the net positive suction head available (NPSH
A
) in the installation, in which the pump is set up at the momentary forwarding amount, is not greater than the net positive suction head required (NPSH
R
), which is required according to the pump characteristic. The value of a pump thus essentially depends on its NPSH
R
value being as low as possible in order that too great a demand is not placed on the plant constructor due to the magnitude of the net positive suction head.
These relationships are described in detail in the Centrifugal Pump Handbook (1st edition, July 1985 by Gebr{umlaut over (u)}der Sulzer AG, 8401 Winterthur, Switzerland) in Chapter 1.5 “Kavitation und Saugverhalten”. The following are named as means for the improvement of the suction capacity or of the speed of rotation:
a) Use of special suction wheels in the most varied forms.
b) Use of a doubly fluted rotor as 1st stage.
c) Supplementary rotor.
d) Auxiliary or feeder pump.
Measures b) and d) signify considerable additional costs on pump manufacture, whereas measures a) and c) signify a restriction in the characteristic field since an optimization can actually take place only for one design point of a characteristic.
SUMMARY OF THE INVENTION
The object of the invention is thus to modify a multiple stage pump in such a manner that it can be driven at low NPSH
A
values of a plant permissible characteristic range.
This object is satisfied in that at least one rotor is journalled on the drive shaft as a hollow shaft and rotates with a speed of rotation n
2
which is different from the speed of rotation n
1
of the drive shaft, with the hollow shaft being driven by a mechanical converter which takes up mechanical power from the drive shaft in the housing and gives it off to the hollow shaft at this different speed of rotation n
2
in such a manner that the speed of rotation of the first rotor is lower in order to produce a lower NPSH
R
value for the multiple stage pump.
Thus, it is advantageous to execute the mechanical converter as a transmission with a fixed transmission ratio, with planetary transmissions being suitable. In order to reduce the relatively high losses which result in a mechanical toothing, a magnetic gearing or meshing is proposed. Instead of a wreath of teeth, cylindrical rings are provided which consist of permanent magnets which are arranged in layers over the periphery of a ring with alternating polarity. Since the division for the change of polarity is kept the same on the different cylinders, the oppositely disposed different polarities mesh like gears and can transmit torques. The drag losses and the noise production are substantially less than in fluted gear transmissions.
In multiple stage pumps with a large forwarding flow it is advantageous to design the first rotor as a hollow shaft journalled on the drive shaft and to drive the first rotor at a lower speed of rotation n
2
<n
1
with the mechanical converter.
In multiple stage pumps with a small forwarding flow and a large forwarding height it can be advantageous due to the investment costs of the pump and drive aggregate to attach the first rotor rigidly to the drive shaft and to journal further stages as a hollow shaft on the drive shaft. A planetary transmission must then drive the hollow shaft with a speed of rotation of n
2
>n
1
.
For the cases with a lower speed of rotation n
2
of the first rotor with respect to the speed of rotation n
1
of the drive shaft the mechanical converter can also be designed as a torque converter with slip, similarly to a liquid or hydraulic couping. Likewise it is conceivable to provide a turbine wheel additionally on the hollow shaft and to feed the latter with a partial flow from a later stage and to admix this partial flow to the flow on the suction side.
A further advantage consists in that the improved suction capacity is bought with a smaller enlargement of the constructional volume. In addition no feeder pump is required. A further advantage results for condensate pumps. When these are constructed vertically, they must usually run at a low speed of rotation, which requires more stages in order to arrive at the predetermined final pressure. Through the proposed improvement these pumps can be built with fewer stages and smaller installation depth, which considerably saves construction costs. In addition these measures are also effective for horizontally arranged pumps.


REFERENCES:
patent: 4190395 (1980-02-01), Ball
patent: 4780066 (1988-10-01), Bolleter et al.
patent: 442999 (1968-01-01), None
patent: 21611 (1912-01-01), None
Baibakov, O.V., et al., “Better power/ speed cavitation for centrifugal pumps” inRussian Engineering Journal, vol. 53, No. 11, 1973, pp. 31-35.
Dornaus, W.L. “New Ideas needed for the NPSH problem”, inPower, Jun. 1970, p. 74.

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