Centrifugal pump having an inner casing and an outer casing

Abstract

 A centrifugal pump comprises an inner casing, an outer casing surrounding the inner casing in a fluid tight way, said outer casing having an inlet at an axial end and a tangentially oriented outlet at its circumference, an impeller which is rotatably mounted within the inner casing, and a shaft connected to the impeller and which at the other axial end extends out of the outer casing. The outer casing comprises a plastic material.

Description

[0001] The invention is related to a centrifugal pump, comprising an inner casing, an outer casing surrounding the inner casing in a fluid tight way, said outer casing having an inlet at one opposite axial end and a tangentially oriented outlet at its circumference, an impeller which is rotatably mounted within the inner casing, and a shaft connected to the impeller and which at the other axial end extends out of the outer casing.

[0002] Such a centrifugal pump is disclosed in United States patent 3.938.908, and comprises an inner casing which consists of a very hard material, for instance hardened steel or cast iron, with the aim of limiting wear. Wear may be caused by the materials which are be transported through such a centrifugal pump, for instance materials which have been obtained through dredging or mining operations and which may comprise highly abrasive components. Furthermore, such materials may comprise lumps of material which, when transported through the inner casing, may lead to impact forces. Additionally, pressure surges may occur within the inner housing when performing dredging or mining operations.

[0003] Very hard materials such as hardened steel or cast iron, however are not quite fit for accommodating impact forces or pressure surges, having regard to the brittle character of such materials. Such materials cannot yield very well and therefore cannot adapt to such loadings. This may lead to ruptures in the casing. The occurrence of rupturing is however very dangerous, having regard to the sizes of the centrifugal pump in question and the relatively high pressures which prevail therein. In the case of a rupture, the materials which are being pumped may be flung through the surroundings, which causes high risks to the personnel and environment.

[0004] With the aim of reducing this risk, the outer casing has been provided. Such outer casing has been devised with the aim of containing any materials which may be flung out of a ruptured inner casing. To that end, the outer casing comprises a material which is well fit for accommodating impacts and the like. Thus, the outer casing material preferably comprises a tough and yieldable material, which is also fit for maintaining the overpressure within the outer casing. As the outer casing however has relatively large dimensions, due to the fact that it should surround the inner casing fully, the costs and weight of such outer casing increase appreciably with increasing capacity of the centrifugal pump. The amount of steel material used, and the costs involved in manufacturing such outer casing, increase proportionately with increasing size of the centrifugal pump.

[0005] The object of the invention is therefore to provide a centrifugal pump of the type described before, that is a centrifugal pump which is fit for transporting highly abrasive materials in a safe manner, which is less heavy and costly. Said aim is achieved in that the outer casing comprises a plastic material.

[0006] A plastic material may very well attribute to the functions of the outer casing, depending on the materials selected. For instance, the plastic material may comprise fibre reinforcements, in particular layers of woven or non-woven materials. Furthermore, the fibre reinforcements may be oriented so as to improve the load-bearing capacity of the plastic material.

[0007] A plastic material outer casing of this type has the advantage of providing the required strength and stiffness with respect to the internal overpressure and possible ruptures of the inner casing, together with a lighter weight and the lower manufacturing costs. The application of such plastic material in the field of heavily loaded centrifugal pumps, exposed to extreme loadings generated by abrasive particles and lumps which occur in dredging or mining operations, is surprisingly well fit for providing the required safety standards in combination with reduced weight and cost.

[0008] The plastic material outer casing may be manufactured in many different ways. For instance, the outer casing may comprise at least two outer casing parts which are joined to each other in a fluid tight way, at least one of said outer casing parts comprising a plastic material. Preferably however, both outer casing parts comprise a plastic material. With the aim of increasing the stiffness of both casing parts with respect to the internal overpressure, both outer casing parts may be generally cup-shaped. In that case, they both comprise a free rim, said free rims being connected to each other in a fluid tight way. In this way, the outer casing may essentially fully consist of plastic material.

[0009] Alternatively, one of the casing parts is cup-shaped, and the other casing part is flat. The flat casing part may consist of plastic or steel, and may be provided with stiffening means.

[0010] Furthermore, in the centrifugal pump according to the invention, the outer casing may comprise a shaft cover through which the shaft extends in a fluid tight way, said shaft cover comprising a steel or plastic material. Furthermore, the outer casing may comprise an inlet cover through which an inlet tube part extends, said inlet cover comprising a steel or plastic material as well.

[0011] The invention will now be described further with reference to an embodiment shown in the drawings.

Figure 1 shows a top view of the centrifugal pump according to the invention.

Figure 2 shows a side view.

Figure 3 shows a front view.

[0012] The centrifugal pump shown in figures 1-3 comprises a housing 1, which consists of the inner casing 2 and the outer casing 3. The impeller 4 is rotatably mounted within the inner casing 2. To that end, the impeller 4 is mounted on a shaft 5, which by means of the bearing arrangement 6 is supported to rotatably with respect to the frame 20. At the side facing the bearing arrangement 6, the outer casing comprises a shaft cover 7 which by means of the sealing 8, which is known per se, is sealed with respect to the shaft 5. At the opposite end, an inlet cover 9 is provided, which by means of sealing 10, known per se as well, is sealed with respect to an inlet tube 11.

[0013] The inner casing 2 is mounted in a manner, known per se, within the outer casing 3. The inner casing 2 may consist of a hard, wear-resistant material so as to provide an acceptable service life for pumping abrasive particles which are present in dredged material or mining material. As the internal pressure within the inner casing 2 can for instance rise to about 40 atm or more, the inner casing 2 in a manner, known per se, is supported from the outside by pressurising the internal space 12 of the outer casing 3. To that end, the outer casing 3 comprises a pressure connection 13 by means of which an overpressure can be maintained which amounts to about 80% of the overpressure within the inner casing 2.

[0014] The outer casing 3 has been provided so as to support the inner casing 2 in the way described before, as well as to provide security against possible damages of the inner casing 2. In case the inner casing has a brittle, hard character, said inner casing 2 may disintegrate under the influence of the lumps or chunks of material which are transported as well when performing a dredging or mining operation. Such lumps or chunks may cause severe impact to loadings on the inner wall of the inner casing 2, which then may crack into several pieces which are flung away under the influence of the rotating impeller and the relatively high overpressure.

[0015] The outer casing 3 therefore exists of a yieldable, tough material which is able to withstand impact loadings. It is less exposed to wear, having regard to the fact that the dredged material usually is confined within the inner casing 2. According to the invention, the outer casing 3 may partly or fully consist of a plastic material. This plastic material may be reinforced by means of fibres, and may also comprise fibre-reinforced layers embedded in a plastic matrix.

[0016] The outer casing 3 consists of two outer casing halves 14, 15, which by means of flanges 16, 17 are bolted together in a fluid tight way. The two outer casing halves 14, 15 are both cup-shaped and have a rim 18, in such a way that they possess a certain inherent stiffness against the internal overpressure which may prevail therein.

[0017] The advantage of such outer casing is also that the inner casing can be used up to the phase in which the wall of the inner casing is almost completely worn down. At a certain point during the useful service life of the inner casing, a leak will occur, however the pump in that case is still able to function during a limited amount of time having regard to the fact that pumped material is confined within the outer casing.

Claims

1. Centrifugal pump, comprising an inner casing (2), an outer casing (3) surrounding the inner casing (2) in a fluid tight way, said outer casing (3) having an inlet at an axial end and a tangentially oriented outlet at its circumference, an impeller (4) which is rotatably mounted within the inner casing (2), and a shaft (6) connected to the impeller (4) and which at the other axial end extends out of the outer casing (3), characterised in that the outer casing (3) comprises a plastic material.

2. Centrifugal pump according to claim 1, wherein the outer casing (3) comprises at least two outer casing parts (14, 15) which are joined to each other in the fluid tight way, at least one of said outer casing parts (14, 15) comprising a plastic material.

3. Centrifugal pump according to claim 2, wherein both outer casing parts (14, 15) comprise a plastic material.

5. Centrifugal pump according to claim 3 or 4, wherein both outer casing parts (14, 15) are generally cup-shaped and have a rim (18), said rims (18) being connected to each other in a fluid tight way.

6. Centrifugal pump according to any of claims 1-3, wherein one of the casing parts is cup-shaped, and the other casing part is flat.

7. Centrifugal pump according to any of the preceding claims, wherein the outer casing (3) essentially fully consists of plastic material.

8. Centrifugal pump according to any of the preceding claims, wherein connections (13) are provided for maintaining an overpressure within the outer casing (3).

9. Centrifugal pump according to any of the preceding claims, wherein the inner casing (2) comprises a cast iron material.

10. Centrifugal pump according to any of the preceding claims, wherein the outer casing (3) comprises a shaft cover (7) through which the shaft (6) extends in a fluid tight way, said shaft cover (7) comprising a steel or plastic material.

11. Centrifugal pump according to any of the preceding claims, wherein the outer casing (3) comprises an inlet cover (9) through which an inlet tube part (11) extends, said inlet cover (9) comprising a steel or plastic material.

12. Centrifugal pump according to any of the preceding claims, wherein the plastic material comprises fibre reinforcements.

13. Centrifugal pump according to any of the preceding claims, wherein the plastic material comprises a series of layers of woven or non-woven fibre reinforcements.

Drawing