GB2122259A

GB2122259A - Casings for centrifugal pumps

Info

Publication number: GB2122259A
Application number: GB08307646A
Authority: GB
Inventors: Niels Due Jensen; Kurt Frank Nielsen
Original assignee: Grundfos AS
Current assignee: Grundfos AS
Priority date: 1982-03-23
Filing date: 1983-03-18
Publication date: 1984-01-11
Also published as: GB2122259B; JPS58172497A; DE3210526C1; FR2524081B1; GB8307646D0; FR2524081A1

Abstract

An in-line centrifugal pump, comprises a pressure-tight hollow casing of metal plate pressed to shape, having a suction stub 8 and a delivery stub 9 which lie on a common centre line 10, which intersects the axis of rotation of the impeller 11 insertible into the pressure space 7 via a lateral assembling opening at right angles, the suction space 6 connected to the suction stub 8, and the pressure space 7 connected to the delivery stub 9 substantially being separated from each other by a partition 5 installed as a separate component and are in communication moreover only via an opening provided in the partition. This enables a pump casing to be manufactured simply and from few parts by virtue of the fact that it comprises two pressings joined together along a parting plane extending longitudinally through the casing, and that the said centre line and the said axis of rotation lie in the parting plane. <IMAGE>

Description

SPECIFICATION Casings for centrifugal pumps The present invention relates to a casing for single-stage in-line centrifugal pumps, comprising a pressure-tight hollow element of plate pressed to shape, having a suction stub and a delivery stub which lie on a common centre line, which intersects the axis of rotation of the impeller insertible into the pressure space via a lateral assembling port at right angles, the suction space connected to the suction stub and the pressure space connected to the delivery stub being substantially separated from each other by a partition arranged as a separate component, and are in mutual communication moreover via an opening formed in the partition. Hereinafter such casings will be referred to as "of the kind described".

Centrifugal pumps of the kind described for example for heating and tap water installations, are machines of the single-stage monoflow type, in which the impeller is the energy-transfer element, whereas the casing comprising a guiding means constructed as a volute has the task, amongst other things, of ducting the fluid which is to be conveyed to the impeller at the intake side and of ducting the same away from the impeller at the delivery side. Furthermore, the pump casing may also form the pressure-tight delimitation between the internal pump volume and the environment.

Most of the centrifugal pumps available on the market today for heating and tap water plants have a cast casing which is heavy and has to be machined at considerable cost. Apart from these shortcomings, cast casings also have the disadvantage of a rough surface, causing pressure losses and adverseiy affecting the efficiency of the pump.

Metal plate casings are better in this respect.

Casings formed in pot-iike manner are known, comprising a separate insert which as a partition separates the internal volume of the casing into a suction space and a pressure space. The intake and delivery stubs consist of shaped pipe sections which in the case of in-line pumps lie on a common centre line and also have an identical nominal bore. The casing-side extremities of these stubs are interwelded with the pot-like hollow element, that is to say in a plane extending transversely to the centre line of the stubs.

It was observed in practice that although the outer pot-like casing section may be produced comparatively easily in the case of such substantially cylindrical casings, the shape and production of the partition which is to be installed are quite complex however, since the same is not only intended to subdivide the casing volume into the suction and delivery spaces but should moreover form the volute in the pressure or delivery space required for reasons of flow technique.

Other problems may also arise if the piping system of the plant in question has not been laid in load-free manner from the beginning, or if load changes can occur in the pipes connected to the pump, since such loads and the resultant forces are transferred to the pump casing via the stubs and may result in warping the casing or causing the welding seams between the metal plate casing element and the stubs to fracture and begin to leak, because the welding seams extend transversely to the compressive and tractive stresses incurred and consequently have to bear the full brunt of such stresses.Furthermore, if the two stubs first have to be produced from pip sections by pressing to shape, then provided with screw-threads and aligned with the casing by using an instrument, and then finally welded on via a circular seam, this represents a sizeable degree of complexity as regards production technology. Apart from this, at least four components which have to be prefebricated, are required moreover for production of a casing of this nature.

It is an object of the invention to provide a metal plate casing for centrifugal pumps wherein the aforesaid disadvantages are minimised or substantially avoided by advantageously shaping the casing elements. The casing should thus be produced from few and uncomplicated parts and primarily in simple manner, and should also be able to withstand high tractive and compressive stresses.

The invention solves this problem by providing a casing of the kind wherein the hollow element comprises two pressings which are joined together along a parting plane extending longitudinally through the casing, and the centre line and the said axis of rotation lie in said parting plane.

By virtue of the particular positioning of the parting plane, the hollow element forming the pressure-tight delimitation between the inside of the casing and the environment and inclusive of the two stubs or connectors, may be produced by means of only two metal plate pressings. Even complex shapes, in particular also the volute form of the casing and other geometrically difficult shapes of the passages and spaces ducting the fluid may easily be produced without structural components having to be installed complementarily, so that the partition may finally also be a component comparatively easy to product.

The two pressings forming the hollow casing element are angled over or flanged over appropriately to form flanges at their points of connection, the flanges bearing flush against each other along the parting plane being able to be joined together by welding or bonding and form fins for reinforcement of the casing. In the area of the stubs, which are commonly of cylindrical or tapering form, these fins extend parallel or at least approximately parallel to the centre lines of the stubs, so that possibly incurred compressive or tractive forces applied by the piping system connected to the stubs on the pump casing act in the direction of extension of the fins and may thus easily be borne by the fins and the casing without exposing the casing and the joints to excessive strains.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which show one embodiment thereof diagrammatically and in simplified form by way of example, and in which: Figure 1 shows a side view of a pump casing, Figure 2 shows the longitudinal cross-section A-A through the casing, and Figure 3 shows the cross-section B-B, turned through 900, through the casing according to Figure 1.

Referring now to the drawings, the hollow element forming the outer delimitation of the pump casing comprises two pressings 1 and 2 made by pressing to shape from precut metal plate flats, which are assembled and joined together along a parting plane extending longitudinally through the casing. Referring to Figure 1 , the parting plane extends at right angles to the plane of illustration, that is to say it lies in the cross-sectioning plane A-A, so that referring to Figure 2, the parting plane should be envisaged as lying in the plane of the drawing.

A partition 5 which is to be installed as a separate component in the direction of the arrow 3 via the assembling opening 4, divides the internal casing volume into a suction space 6 and a pressure space 7. The space 6 is in communication with the suction stub 8, whereas the space 7 is in communication with the delivery stub 9. Both stubs lie on a common centre line 10. The impeller 11 shown dotted is situated in manner known per se on the extremity of the driving shaft which is not shown, and revolves around the axis 12. Concentrically to this axis is also arranged a collar 5a formed in the partition, with an aperture through which the suction space and the pressure space are in communication and on which is aligned the suction opening of the impeller 11.

According to the illustration, the centre line 10 of both stubs as well as the axis of rotation 12 or centre line of the circular collar 5a, lie in the parting plane extending longitudinally through the casing. This yields an optimum division of the casing as regards production of the two pressings 1, 2, so that the volute form apparent from Figure 1, as well as the other passages ducting the fluid, may be produced in one operation whilst pressing the two parts 1, 2.

In the area of their joints, the two pressings 1, 2 are angled over or flanged over to form flanges 13, 14, in such manner that they bear flush against each other after joining the two pressings along the parting plane (Figure 1) and may be joined together by welding or bonding. This forms fins which reinforce the casing and extend in the area of the two stubs 8, 9 substantially in the direction of the forces which may be exerted on the casing by the ducting pipes which are to be connected to the stubs.

The partition 5 may be formed from plastics material or, like the remainder of the casing, from metal plate. It is inserted into the pressure space 7 via the opening 4 and, in the position shown in Figures 2 and 3, is connected to the previously assembled pressings 1, 2. In this case too, the connection may be established at the corresponding joints 1 5 by bonding or welding.

A pump casing ready for installation is produced in this manner, which by virtue of advantageous adoption of the parting plane is produced from three parts only, namely the two pressings 1 and 2 and the partition 5. The pipes which are to be connected to the pump casing may simply be inserted into the openings of the subs 8 and 9 and then joined to these, for example by interwelding, so that a simplification is also obtained in this respect as compared to connections by means of screw-threads, or fittings or the like.

Should it be discovered that the casing lacks adequate strength in the area of the assembling opening 4 or at the extremities of the stubs 8, 9, these casing sections may also be reinforced complementarily, for example by means of rings or ring segments which are inserted or pressed into the assembling opening or into the stubs and which may if appropriate also be complementarily joined to the casing by welding, brazing or bonding.

Claims

1. A casing of the kind described, wherein the hollow element comprises two pressings which are joined together along a parting plane extending longitudinally through the casing, and the ecntre line and the axis of rotation lie in said parting plane.

2. A casing as claimed in claim 1, wherein the two pressings are angled over at their points of connection to form flanges, and said flanges bear flush against each other in the parting plane and are joined by welding or bonding.

3. A casing of the kind described, substantially as hereinbefore described with reference to the accompanying drawings.

4. A single-stage in-line centrifugal pump incorporating a casing as claimed in any of the preceding claims.