DK2582983T3 - Dobbeltstrømningscentrifugalpumpe - Google Patents

Description

The invention relates to a preferably single-stage, double-flow centrifugal pump, in particular a cooling water pump for a marine diesel engine or a ballast water delivery pump on a ship, according to the preamble of claim 1. The invention also relates to a use according to claim 9.

In known double-flow centrifugal pumps the sealing gaps, formed as annular gaps, run in axial direction and are formed between the impeller and the pump housing. During the operation of the known centrifugal pumps a resulting radial force component acting on the shaft supported on one side occurs, in particular if the centrifugal pumps are not operated at their optimum working point, so that the shaft with the impeller rotationally fixed on it is deflected in radial direction. In order to prevent the impeller from contacting the pump housing during this deflection movement the sealing gaps formed as axial gaps must be dimensioned to be appropriately wide. However, this results in a drop in performance of the pump as continually delivered medium from the radial positive pressure region flows in axial direction through the sealing gaps into the negative pressure region (suction area). As a consequence, the efficiency of the known centrifugal pumps is significantly reduced. Previously cited centrifugal pumps are only suitable for applications, if the shaft is supported on one side, in which comparatively low volume flows are to be conveyed. In the case of double-flow centrifugal pumps for large-volume flow applications, for example, for example in the case of cooling water pumps for a marine diesel engine or ballast water delivery pumps on a ship, the shaft carrying the impeller is generally supported on both axial sides of the impeller in order to minimise the radial deflection movement during operation. In the case of an only one-sided support of the shaft for these applications a shaft would have to be used with an appropriately large diameter and/or a complex bearing.

From FR-A-723344 a double-flow centrifugal pump is known for conveying small volume flows. The centrifugal pump comprises sealing gaps between the impeller and a position-variable, i.e. non-stationary pump component. The known centrifugal pump is not suitable for use on ships. GB 242230 A also shown a centrifugal pump, wherein the sealing gap measurement between the impeller and a non-stationary installation part can be adjusted.

On the basis of the aforementioned prior art the invention addresses the problem of providing a double-flow centrifugal pump, for large-volume flows of at least 500 m3/h, in particular for use on ships, with which a high degree of efficiency is possible without complex constructive measures. The centrifugal pump shaft supporting the impeller should preferably be supported exclusively on one side and have the smallest possible diameter. The striking of the impeller on the pump housing should be reliably avoided.

Said problem is solved by a double-flow centrifugal pump with the features of claim 1.

Advantageous further developments of the invention are indicated in the subclaims. The scope of the invention includes at least two features disclosed in the description, the claims and/or in the figures. In order to avoid repetition, features disclosed for device are considered as disclosed and claimed for the method. Likewise, features disclosed for the method are considered as disclosed for the device and can be claimed as such.

The invention is based on the concept that the sealing gaps between the impeller and at least one pump part with which the suction side of the centrifugal pump is sealed relative to the pressure side are to be designed running in radial direction relative to its longitudinal extent, i.e., as an axial gap. In other words, the impeller according to the invention is distanced in the axial direction by the sealing gaps from the at least one, preferably exclusively one pump component. The width of the sealing gap, which width extends at least approximately in the axial direction, is lower at least at one position, preferably over its longitudinal extent, than the distance between the impeller and all other pump components arranged with a radial distance to the impeller. In other words, the gap width of the sealing gap is less than the radial distance of the impeller to all pump components located radially outside of the impeller. The sealing gaps are characterised in that their axial extension is (considerably) less than their radial extension. The gap width of the axial gap, (sealing gap) measured in the axial direction, is greater than the gap width, measured in the radial direction, of a radial gap arranged between the impeller and the pump component limiting the axial gap.

The centrifugal pump according to the invention is designed for large-volume flow applications, in particular marine applications. The centrifugal pump is preferably designed for delivering a volume flow from a value range between approximately 500 m3/h and approximately 4000 m3/h, preferably between approximately 800 m3/h and approximately 1500 m3/h (for example in the case of smaller cooling water pumps) or between approximately 1500 m3/h and approximately 2300 m3/h (for example in the case of average-size cooling water pumps) or between 2300 m3/h and 3500 m3/h (for example in the case of larger cooling water pumps), preferably at a maximum delivery level from a value range between approximately 20 m and approximately 50 m, preferably approximately 30 m. It is especially preferable for reasons of space, especially for marine applications, if the doubleflow centrifugal pump has a vertical construction, that is so that the shaft runs vertically to a standing surface of the centrifugal pump.

As already indicated, according to the invention with respect to having an embodiment variant of the centrifugal pump that is as inexpensive as possible, the shaft supporting the impeller is mounted solely on one side, preferably on an upper side.

The gap width of the sealing gap is preferably at least 20%, preferably at least 12% and even more preferably 6% of the radial distance of the impeller 7 to the pump component limiting the axial gap, i.e. the pump housing and/or the insertion part preferably forming a housing section.

It is, of course, possible to provide several sealing gaps formed as an axial gap on both axial sides of the radial discharge area of the impeller. However, it is preferable to provide only one sealing gap formed as an axial gap, whereby the gaps with the smallest gap width are understood to be sealing gaps. A variant of an embodiment is especially preferred in which preferably exclusively two sealing gaps are arranged in an area radially inside circumferentially closed radial gaps via which the impeller is spaced apart from the at least one, preferably exclusively one pump component. It is especially preferable if the axial gaps starting from the radial gaps in radial direction extend inwardly. Therefore, a variant of an embodiment is especially preferred in which the axial gaps have, at least in a radially inner area, a smaller distance from the shaft than the radial gaps. The sealing gaps are advantageously located inside an imaginary circular cylinder whose generated surface receives the radial gaps. As a result of such a variant of an embodiment the sealing action is improved.

It is especially purposeful if the impeller has a circular, cylindrical casing contour, whereby it is even more preferred if the sealing gaps (axial gaps) are formed between a front side of the impeller comprising a cylindrical casing contour and between the at least one, preferably exclusively one pump component.

Alternatively, a casing contour can also be provided in which the impeller extends with its discharge area further to the outside in radial direction. However, as explained below, it is also preferred in the case of such a geometry if the axial sealing gap is arranged in an area that has a smaller radius than a possible radial gap arranged between the pump jet and the impeller.

Based on the formation of the sealing gaps as axial gaps according to the invention, it is possible to dimension the gap width of the sealing gaps considerably smaller than in the prior art without there being the danger that the impeller strikes the pump component limiting the sealing gaps upon a radial deflection. It is therefore possible by means of the design of the sealing gaps in accordance with the invention to achieve a high efficiency of the centrifugal pump since the amount of liquid that flows from the pressure region into the suction area (negative pressure region) is minimised by the small gap width of the sealing gaps. The distance between the impeller and the pump component and/or other components of the pump can be dimensioned in the radial direction in such a manner that even in case of the greatest possible deflection of the impeller occurring during operation there is no danger of collision.

It is therefore possible, even for applications with a large-volume flow, in particular for marine applications, to realise only a onesided support of the impeller shaft since greater radial deflections of the impeller can be accepted than previously. Furthermore, the dimensioning of the shaft as such can be minimised.

One embodiment has an especially simple construction and is therefore preferred in which the sealing gaps run — within tolerances — exactly in the radial direction relative to their longitudinal extension. However, a slightly curved or slightly oblique design of the sealing gaps by an appropriate shaping of at least one structural component (impeller and/or pump component, especially pump housing) limiting the sealing gaps is possible, in particular in such a manner that the gap geometry of the curved deflection movement of the impeller takes place especially with a one-sided shaft support so that the gap width remains at least independently constant independently of the degree of the deflection of the impeller during operation. The radius of curvature corresponds in an especially preferred manner at least approximately to the distance of the impeller to the support of the shaft carrying the impeller.

It is advantageously provided in a further development of the invention that the gap width of the sealing gaps formed as axial gaps is selected from a value range between 200 pm and 2000 pm, particularly preferably between 200 pm and 400 pm.

It is especially advantageous if the minimal, i.e. the least radial distance of the impeller to the pump component of the centrifugal pump, which pump component limits the sealing gaps formed as axial gaps, (with the impeller standing still) is selected from a value range between 2 mm to 10 mm. In other words, the distance between the impeller and the previously cited pump component is preferably greater than the distances of the indicated value range. The previously cited minimal radial distance is especially preferably not only the minimal radial distance of the impeller to the at least one, preferably exclusively one pump component limiting the sealing gaps, but rather the minimal radial distance of the impeller to all structural components of the pump, in order to reliably prevent a collision upon a radial deflection.

An embodiment of the double-flow centrifugal pump has an especially preferred construction in which the sealing gaps are arranged between the front sides of the impeller, which front sides face in the axial direction, and between the at least one pump component. In other words, it is preferred if the sealing gaps have the greatest possible axial distance from each other. This can be achieved for example in that the impeller has a casing contour that is at least approximately circularly cylindrical. An imaginary generated surface of a centrifugal cylinder which surface receives the radial gaps especially preferably surrounds the axial gaps radially on the outside.

As already explained above the phrase axial gap (sealing gap) extending in radial direction denotes not only an embodiment in which the sealing gaps run exactly in the radial direction relative to the longitudinal extent, within tolerances, that is they are constructed, for example, in the shape of annular discs. An embodiment is also possible in which the sealing gaps have a slight angle of rise or are slightly curved, i.e. have a large radius of curvature that preferably corresponds at least approximately, in particular in the case of a shaft supported on one side, to the distance of the particular sealing gap from the shaft support. The particular sealing gap is thus designed in such a manner that the gap width during the operation of the centrifugal pump does not change or changes only as little as possible, that is upon a possible radial deflection of the impeller since the gap geometry follows the deflection movement. The curvature or bevelling of the sealing gap can be achieved by an appropriate geometric shaping of the impeller and/or of the at least one, preferably exclusively one pump component limiting the sealing gap on the axial side opposite the impeller. The angle (angle of inclination) of the particular sealing gap to an imaginary radial plane arranged orthogonally to the longitudinal extension of the shaft is quite especially preferably selected from a value range between 0.01° and 2.0°. A possible radius of curvature is preferably selected from a value range between 200 mm and 1000 mm, preferably 300 mm and 700 mm.

The radius of curvature of the particular sealing gap, more precisely at least of a surface (of the impeller and/or of the pump component) limiting the sealing gap preferably corresponds at least approximately to the distance of the particular sealing gap (in particular on a radially innermost area of the sealing gap) to the shaft support, in particular in the case of a pump shaft supported on one side. In a corresponding manner the angle of inclination of the gap explained in the specification refers to the angle of at least one surface (of the impeller and/or of the pump component) limiting the sealing gap relative to the previously cited radial plane.

It is especially preferable if the centrifugal pump is a single-stage centrifugal pump, that is a pump comprising exclusively one impeller .

It is especially advantageous if the pump housing is a so-called spiral housing that sets the flow path on the suction side to the two axial sides of the impeller and combines preferably two outlet channels in a helical manner on the pressure side.

The invention also comprises the use of a double-flow centrifugal pump designed in accordance with the concept of the invention as a cooling water pump for a marine diesel engine or as a ballast water delivery pump on a ship.

Further advantages, features and details of the invention are given in the following description of preferred example embodiments and with reference to the figures.

In the latter:

Fig. 1 shows a cross-sectional view of an example embodiment of a double-flow centrifugal pump constructed according to the concept of the invention,

Fig. 2 shows a schematic illustration of the gap proportions,

Figs. 3-7 show a plurality of embodiments of the sealing gaps.

In the figures the same elements and elements with the same function are denoted by the same reference numerals.

Fig. 1 shows a cross-sectional view of a double-flow centrifugal pump 1 in a vertical orientation. The example embodiment shown is a cooling water pump for a marine diesel engine designed for delivering a volume flow of 2300 m<3>/h at a maximum delivery level of 30 m.

The centrifugal pump 1 comprises a pump housing 2 designed as a spiral housing with a suction-side inlet 3 as well as a pressure-side outlet 4. A shaft 5 supported on one side extends into the pump housing 2 from above downward in a vertical direction and is supported by a bearing 6 constructed as a ball bearing. The shaft 5 supports on its end side a double-flow impeller 7 with a substantially circularly cylindrical casing contour. The impeller 7 sits in a rotationally fixed manner on the shaft 5. A shaft seal 8 is located in an area axially between the bearing 6 and the impeller 7. As is apparent from Fig. 1 the shaft 5 extends in an area above the shaft seal 8 through a cover 9 fixed by screwing on the pump housing 2 .

The impeller 7 separates a negative pressure region 10 (suction side) from a positive pressure region 11 (pressure side).

The shaft 5 can be rotated in a known manner by an engine (not shown), in particular by an electric motor, whereby the impeller 7 rotating with the shaft 5 sucks fluid, here cooling water, from both axial sides out of the negative pressure region 10 and delivers it in a radial direction out into the positive pressure region 11, whereby the positive pressure region 11 is subdivided into two helically arranged flow channels 12, 13 separated from one another by a dividing wall 14. The two flow channels 12, 13 and the fluid currents are brought together again in the area of the outlet 4.

During the operation of the centrifugal pump 1, especially when the centrifugal pump 1 is not working at an optimal working point, a loading of the shaft 5 with a radial force occurs in the area of the impeller 7 which load has the tendency to deflect the shaft 5 with impeller 7 in radial direction. In order to prevent the impeller 7 from colliding with the pump housing 2 (pump component) in radial direction two axially spaced radial gaps 15, 16 extending in axial direction are dimensioned to be so wide that even a maximum possible deflection of the shaft 5 during operation cannot result in a collision of the impeller 7 with the pump housing 2. The radial gaps 15, 16 are not designed as sealing gaps and fulfil no sufficient sealing function on account of their comparatively large gap width (measured at the narrowest position) from the one in the example embodiment shown of approximately 5 mm. The radial gaps have the form of circular, cylindrical surfaces. If the radial gaps 15, 16 were the only sealing gaps, the centrifugal pump 1 would be extremely inefficient on account of the comparatively large gap width, since liquid, here cooling water, would constantly flow in large amounts through the radial gaps 15, 16 from the positive pressure region 11 into the negative pressure region 10 and would thus be conveyed directly in a circuit.

In order to achieve the desired sealing effect while avoiding the risk of collision between the impeller 7 and pump housing 2 (pump component) the pump housing 2 (pump component) extends over the impeller 7 on both axial sides, i.e., above and below in inward radial direction in such a manner that a sealing gap, 19, 20 that is constructed as an axial gap and extends as regards its longitudinal extension in radial direction is formed between each front side 17, 18 of the impeller 7 and the pump housing 2 (pump component) . It is essential that these sealing gaps, 19, 20, measured at their narrowest position, have a smaller gap width than the radial gaps 15, 16.

The sealing gaps, 19, 20 are located radially inside the radial gaps 15, 16, whereby the radial gaps 15, 16 merge into the sealing gaps, 19, 20 and the sealing gaps, 19, 20 border directly on the radial gaps 15, 15. In the example embodiment shown the width of the sealing gaps 19, 20 is about 400 pm.

The sealing gaps, 19, 20 are, as explained, limited on the one hand in the axial direction by the impeller 7, in the example embodiment shown by a front side 17, 18 of the impeller 7 and on the opposing side by a wall surface 21, 22 of the pump housing 2, which wall surface is aligned here parallel to the respective front side 17, 18.

If a deflection of the impeller 7 occurs in a radial direction during operation the front sides 17, 18 are shifted substantially parallel to the wall surfaces 21, 22 of the pump housing 2, so that no collision can occur there. The radial gaps 15, 16 are, as explained, dimensioned to be so wide that even here a collision with the impeller 7 is impossible, even at a maximally admissible deflection.

Fig. 2 shows the gap proportions schematically.

The schematically shown impeller 2 is shown which is arranged in a rotationally fixed manner on a rotatably mounted shaft 5.

The impeller 7 is surrounded by a pump component 23, here the pump housing 2, more precisely an inserted part 24 that forms a component of the pump housing 2. Alternatively, the inserted part may not be designed and arranged to form a component of the housing, therefore inside the pump housing and at a distance to an outer housing side. Upon a rotation of the impeller 7 the liquid flows in the direction of the arrows from the suction side (negative pressure region) 10 to the pressure side (positive pressure region) 11.

Two sealing gaps 19, 2 0 are formed between the pump component 23, that can be designed to be in one piece or multiple parts, and the impeller 7, more precisely between the front sides 17, 18 of the impeller 7 comprising a circular, cylindrical casing contour. Said sealing gaps 19, 20 are axial gaps that are formed axially between the pump component 23 and the impeller 7. The gap width s of the sealing gaps 19, 20 is 400 pm in the example embodiment shown. The two sealing gaps 19, 20, in the form of flat annular discs are distanced from one another in axial direction and also separated from one another by the radial outlet area or areas of the impeller 7.

In the example embodiment shown, in addition to the sealing gaps 19, 20 between the impeller 7 and the pump component 23 two radial gaps 15, 16 are provided whose gap width a is greater than the gap width s of the sealing gaps. In the example embodiment shown the gap width "a" is approximately 5 mm when the impeller 7 is at a standstill. The sealing gaps 19, 20 are located radially inside the radial gaps 15, 16 and therefore are closer to the shaft 5 than the radial gaps 15, 16. The radial gaps have the form of circular, cylindrical casing. The sealing gaps 19, 20 have approximately the form of a circular ring disc. The provision of (narrow) radial gaps 15, 16 can also be avoided in a modified structural design of the pump component 23. It is also possible to provide several sealing gaps 19, 20 provided in parallel planes that are axial gaps on at least one of the two axial sides, preferably on both axial sides of the impeller 7. In such cases, two axially adjacent sealing gaps are preferably connected to one another via a radial gap with a larger gap width than the gap width of the sealing gaps on at least one axial side of the impeller 7. Thus, a stepped gap would be formed, whereby the axial gap section would represent the sealing gaps. Thus a stepped gap design is achieved.

Possible alternative sealing gap geometries are shown in the Figs. 3 to 7, whereby the angles or radii of curvature are shown in an exaggerated manner for reasons of clarity. In reality there are minimal rises and large radii of curvature.

All example embodiments have in common that the sealing gaps are axial gaps that run as regards their longitudinal extension substantially in radial direction and their axial extension is (substantially) less than their radial extension.

In the example embodiment according to Fig. 3 a sealing gap 19 is formed between the impeller 7 and a pump component 23. The section of the impeller 7 limiting the sealing gap 19 runs relative to the longitudinal extension of the shaft exactly in radial direction, whereas on the contrary the surface section of the pump component 23, that limits the sealing gap 19, is slightly inclined relative to a radial plane, here at an angle a of <1°. This results in a sealing gap inclination about this angle a relative to an imaginary radial plane in which in the shown example embodiment the represented surface section of the impeller 7 lies.

In the example embodiment according to Fig. 4 the surface section of the impeller 7 limiting the sealing gap 19 as well as the surface section of the pump component 23 that is opposite to and limits the sealing gap 19 are inclined relative to a radial plane, in the example embodiment shown both at the same angle a of here <10°. The use of different but similar angles of inclination is also possible .

In the example embodiment according to Fig. 5, the surface area of the impeller 7 limiting the sealing gap 19 is located in a radial plane relative to the longitudinal extension of the shaft, in contrast to which the surface area of the pump component 23 limiting the sealing gap 19 is curved, which curvature preferably has a radius that has the sealing gap 19 from the support of the shaft 5 (not shown).

In the example embodiment according to Fig. 6 both surfaces limiting the sealing gap 19 as well as the surfaces of the impeller 7 and the surfaces of the pump component 23 are designed to be slightly curved.

In the example embodiment according to Fig. 7 the surface of the impeller 7 limiting the sealing gap 19 is designed to be level but inclined at an angle a of <10° to the radial plane, in contrast to which the surface of the pump component 23 limiting the sealing gap 19 is slightly curved and preferably has a radius of curvature of 500 mm.

List of reference numerals 1 double-flow centrifugal pump 2 pump housing 3 inlet (inlet nozzle) 4 outlet (outlet nozzle) 5 shaft 6 bearing 7 impeller 8 shaft seal 9 cover 10 negative pressure region 11 positive pressure region 12 flow channel 13 flow channel 14 dividing wall 15 radial gap 16 radial gap 17 front side 18 front side 19 sealing gap 20 sealing gap 21 wall surface 22 wall surface 23 pump component 24 inserted part s gap width, sealing gap a gap width, radial gap

Claims (9)

A double-flow centrifugal pump, in particular a cold water pump for a marine diesel engine or ballast water supply pump, with a pump housing (2) and with a double-flow impeller (7) arranged in a rotationally fixed manner on a rotary drive shaft (5), where by using the impeller a fluid can be sucked from two axial sides from a negative pressure area (10) and can be delivered in the radial direction to an overpressure area (11), where the negative pressure area (10) is closed tightly relative to the overpressure area (11) by means of at least two sealing slits (19, 20 ) spaced axially apart, the sealing slits (19, 20) being formed as axial slits extending in the peripheral direction and in the radial direction, where the gap width (s) is less than the radial distance (a) from the impeller (7). ) to all the components mounted with a radial distance to the impeller (7), characterized in that the centrifugal pump is designed to deliver a volume flow in a range between 500m3 / h and 4000m3 / h and is manufactured as a vertical construction type, and in that the shaft (5) is mounted only on one side, and in that the sealing gaps (19,20) are formed axially between the impeller (7) and the stationary pump housing (2) and / or a stationary insert part (24). Centrifugal pump according to Claim 1, characterized in that the gap width (s) of the sealing gap (19, 20) has a value in the range between 200 μm and 2000 μm. Centrifugal pump according to one of Claims 1 or 2, characterized in that the minimum radial distance (a) of the impeller (7) to the pump component (23) of the centrifugal pump when the impeller (7) is stationary is selected from the range between 2 mm and 10 mm. . Centrifugal pump according to one of Claims 1 or 3, characterized in that the sealing slots (19, 20) are located between the front side (17, 18) of the impeller (7) and the pump housing (2) or the mounting part (24). Centrifugal pump according to any one of the preceding claims, characterized in that the sealing slits (19, 20) are formed continuously precisely in the radial direction, or constitute an angle in the range between about 0 ° and 1 ° with a radial plane, preferably between 0.5 ° and 5 °, and / or that the sealing gap (19, 20) has a radius of curvature in the range between 200 mm and 1000 mm, preferably between 300 mm and 700 mm. Centrifugal pump according to any one of the preceding claims, characterized in that the centrifugal pump is designed to deliver a volume flow in the range between about 800 m3 / h and about 1500 m3 / h, or between about 1500 m3 / h and about 2300 m3. / h, or between 2300 m3 / h and 3500 m3 / h, preferably with a maximum pressure height in the range between 20m and 50m, preferably about 30m. Method according to one of the preceding claims, characterized in that the, preferably only, two sealing slots (19, 20) have a lower radial distance to the shaft (5) than between the impeller (7) and the radial slot (15, 16). formed as a pump component. Method according to one of the preceding claims, characterized in that the impeller (7) has a circular cylindrical shell outline. Use of a centrifugal pump according to any one of the preceding claims as a cold water pump for a marine diesel engine or as a ballast delivery pump.