GB2219347A

GB2219347A - Pump unit for heating systems

Info

Publication number: GB2219347A
Application number: GB8902653A
Authority: GB
Inventors: Neils Due Jensen; Gerhard Munk Jakobsen
Original assignee: Grundfos International AS
Current assignee: Grundfos AS
Priority date: 1988-02-09
Filing date: 1989-02-07
Publication date: 1989-12-06
Anticipated expiration: 2009-02-07
Also published as: GB8902653D0; DE3803774C2; FR2626940A1; GB2219347B; DE3803774A1; FR2626940B1

Description

2219347 PUMP-UNIT_FOR_HEATING-SYSTEMS

DESCRIPTION

The invention relates to a pump unit forheating systems comprising a circulating pump, and a canned motor between whose rotor compartment and the pump compartment is arranged a dividing wall in which are provided a plurality of passages connecting the pump compartment to the rotor compartment.

is Pump units of this kind having output ratings of up to approximately 2kW are normally fitted with canned motors. For reasons of safety in operation, the pump manufacturers require that units of this kind (DE-Al 2460748 and 2639541) should always be installed with the shaft positioned horizontally. This creates problems when the pumps first go into operation.

Before the unit is started up for the first time, the rotor compartment must be filled with water from the system by removing the bleed plug which is located on the axis of rotation. However, only partial filling is possible because, while the rotor is stationary, the water which enters the rotor compartment can only drive out the air up to the level of the gap in the plain bearing at the end adjacent the pump. If the bleed opening is closed again and the pump switched on, the water circulating in the rotor compartment forces the remaining bubble of air towards the centre of rotation and the bearings run dry or run under conditions of mixed friction.

Nor, in pump units with a low output rating and a high pressure in the heating system, is it easy to remove the air bubble by taking out the bleed plug while the pump is running because the pressure pattern pushes the rotor towards the bleed opening. Because the majority of pumps only have a thrust ring and not an axial bearing at this end, the rotor is braked, which means that the air bubble then migrates upwards and cannot escape to atmosphere through the bearing gap.

Practical experience shows that many heating pumps are started up with an only partly water-filled rotor compartment and are run for quite a long time with is inadequately lubricated and cooled bearings. To shorten this phase of operation, which is hazardous for the pump, various manufacturers pierce the dividing wall between the pump and rotor compartments in order to connect the said two compartments.

This connection between the heating system and the rotor compartment, which is always present in the dividing wall in the form of a bearing gap, increases the flow of water through the rotor compartment and thus shortens the time taken for the air bleed-off.

However, though an advantage is thereby gained, it is at the expense of the disadvantage that more dirt can now make its way into the rotor compartment, thus increasing the risk of the unit, or rather the motor, seizing. An attempt is made to alleviate this disadvantage by fitting in the dividing wall sintered rings or slugs which act as filters. Provisions of this kind are however complicated and expensive to make.

Furthermore, although it is possible, by using sintered material, to allow the passage in it to become blocked by particles of dirt in the heating water as time passes and thus to prevent any direct exchange of water between the pump and rotor compartments through the passages once the rotor compartment has been bled of air, it is still not possible, despite great care in the manufacture and selection of the sintered material, to have any direct control over its absolute permeability. Hence there is no way of determining beforehand with at least some degree of certainty approxmiately when the passages, whose size and path are irregular, will become blocked. Thus, it may happen that the passages are is already plugged before the rotor compartment has been completely bled of air, or that contaminated water continues to make its way through the passages and into the rotor compartment for quite a long time after the air has been bled off.

The main object of the present invention is to overcome or at least substantially reduce the aforementioned disadvantages. More particularly, the intention is to propose a possible way of achieving a connection between the pump compartment and the rotor compartment which can be quickly and inexpensively put into practice, the purpose of this connection being on the one hand to ensure that the rotor compartment is effectively bled of air but on the other, reliably to prevent heating water and any particles of dirt it may contain from penetrating into the rotor compartment after the bleeding process.

To this end, and from one aspect the present invention consists in a pump unit for a heating system, comprising a circulating pump, and a canned motor 4 - between whose rotor compartment and the pump compartment is arranged a dividing wall in which are provided a plurality of passages connecting the pump compartment to the rotor compartment, said passages being formed in the dividing wall each with a straight centre line with the equivalent mean diameter d of the passages in relation to the thickness a of the dividing wall being in the range of 0.01 s. dls 0.5.

By means of the invention, thepassage and their cross-sections can be positively adjusted in such a way that they will be blocked within a specific period by dirt particles present in the heating water and any is futher direct exchange of water between the pump compartment and the rotor compartment will be prevented.

Thus, the connection between the pump and rotor compartments via the passages situated in the dividing wall will remain in being for only a short period and will have ceased by, at latest, a relatively short time after the air-bleeding phase. Since the bubble of air which is present in the rotor compartment before the unit is first run is generally of only a small volume, the cross-sectional area of the connecting passages does not need to be very large.

Preferably, the sum Al of the cross-sectional areas of all the passages is substantially smaller than the surface area A2 of the dividing wall, the relationship which applies being Al/A240.00005.

The passages will be swiftly and reliably blocked if their cross-section decreases in the direction of flow. Thus, what this implies is that the cross-sectional area of the passages is larger at the end adjacent the pump than at the end adjacent the rotor.

Accordingly, from another aspect, the present invention consists in a pump unit for a heating system, comprising a circulating pump having a canned motor between whose rotor compartment and the pump compartment is provided a dividing wall having a plurality of passages, wherein the cross-sectional area of each passage is greater at the end adjacent the pump than at the end adjacent the rotor.

The blocking process will be further accelerated if a ridge is present at the entrances to the passages which projects from the surface of the dividing wall in the direction of the pump compartment and by which the dirt particles are caught and channeled into the relevant passage.

Advantageously, to prevent the rotor compartment from being polluted by chemical changes to the surface of the dividing wall, the dividing wall is die-pressed from corrosion-resistant metal or injection moulded from non-metallic material.

Depending on the material, the passages, whose diameter is preferably from 30 to 30OA4m, are conveniently formed in the dividing wall by laser techniques or by means of jets of liquid, in which case the centre lines of the passages may extend parallel to the axis of the pump unit and the passages may be arranged on at least one circular path which extends concentrically to the axis of rotation of the unit.

In order that the invention may be readily understood an embodiment thereof will now be described, by way of example with reference to the accompanying drawings in which:

Figure 1 is a longitudinal section through a pump unit constructed in accordance with the invention and Figure 2 is a section to a larger scale through part of a dividing wall showing one cross-sectional configuration for passages therethrough.

Referring to the drawing, the pump unit has a cast -pump casing 1 connected to the heating system (not shown) by a suction nozzle 2 and a delivery nozzle 3.

The casing 1 encloses an impeller 4 which is mounted on a shaft 5 carrying a rotor lamination assembly 6.

The shaft 5 is carried and located by two radial bearings 7 and a thrust bearing 9.

A can 10 forms one of the boundaries between the heating system and the exterior. The stator 11 has a dry winding. A dividing wall 12, in which the radial bearing 7 is mounted, divides the pump compartment 13 from the rotor compartment 14. The latter can be partly bled of air by removing a plug 15 located on the axis of rotation.

In the dividing wall 12 are passages 16 connecting the pump compartment 13 to the rotor compartment 14, through which passages water can pass into the rotor compartment 14 during the start-up phase of the pump, As a result of their cross-sectional shape and as dictated by the nature, size and quantity of the dirt particles present in the heating water, the passages 16 will be blocked by the dirt particles towards the end of, or after, the air bleeding process, in particular by dirt particles whose diameter substantially corresponds to that of the passages.

This will then allow any exchange of water between the pump compartment 13 and the rotor compartment 14 to be reduced to a minimum during operation since in this state water can only be exchanged through the bearing gaps.

Figure 2 shows a particularly advantageous cross-sectional configuration for the passages 16. The end of a passage 16 situated in the pump compartment 13 has a ridge 17 and has the larger cross-sectional area. This passage 16 tapers in the direction of flow and is of smallest cross-section at the outlet into the rotor compartment 14. This cross-sectional configuration means that particles of dirt entering the passages will be more reliably caught and held than if the cross-section of the passage were uniform, although it is of course essential that the maximum diameter of the dirt particles should be smaller than the inlet opening and larger than the outlet opening of the particular passage.

Furthermore, the mean equivalent diameter d of the passages 16 relative to the thickness s of the dividing wall 12 should be of the order of 0.0l-cd/s-.,z 0.5mm, which means that in practice the diameter will be between 0.01 and 0.5mm when the dividing wall is lmm thick. Also, an appropriate number of passages will be provided as dictated by the size of the rotor compartment and the volume of air to be channeled off, the number of passages involved being generally 10 to 100.

The cross-sectional configuration for the passage 16 which is shown in Figure 2 can be obtained in a particularly simple fashion, almost automatically, without using mechanical tools and by a non-cutting process, by using laser beams, if the beams impinge on the wall from its face situated on the pump side.

By using this technique it is also possible to form the passages particularly quickly. Practical tests have shown that in a period of 3 s, at least 40 passages can be formed in a dividing wall which is rotated on its axis in the process.

As mentioned above the centre line 18 of the passages 16 may extend parallel to one another, the passage being disposed on at least one circle whose centre coincides with the centre of the rotary shaft of the unit. This will also be the case if the passages are positioned on a plurality of concentric circles.

-0._

Claims

1. A pump unit for a heating system comprising a circulating pump, and a canned motor between whose rotor compartment and the pump compartment is arranged a dividing wall in which are provided a plurality of passages connecting the pump compartment to the rotor compartment, said passages being formed in the dividing wall each with a straight centre line and the equivalent mean diameter d of the passage in relation to the thickness s of the dividing wall being in the range 0.01<d/s<0.5.

2. A pump unit as claimed in claim 1, wherein the diameter of the passages is in the range 30 to 300 1.4M.

3. A pump unit as claimed in claim 1 or claim 2, wherein the centre lines of the passages extend parallel to the axis of the pump unit and the passages are arranged on at least one circular path extending concentrically around the axis of rotation of the unit.

4. A pump unit as claimed in any one of claims 1 to 3, wherein the sum A1 of the cross-sectional areas of all the passages is substantially smaller than the area A2 of the dividing wall and wherein the relationship A1/A2s0.00005 applies.

5. A pump unit for a heating system, comprising a circulating pump having a canned motor between whose rotor compartment and the pump compartment is provided a dividing wall having a plurality of passages, in particular in accordance with any one of claim51 to 4, wherein the crosssectional area of each passage is greater at the end adjacent the pump than at the end adjacent the rotor.

6. A pump unit as claimed in any one of claims 1 to 5, wherein a ridge projecting from the dividing wall is provided at the end adjacent the pump of each of the passages.

7. A pump unit as claimed in any one of claims I to 6, wherein the dividing wall is die-pressed from non-corroding metallic material.

8. A pump unit as claimed in any one of claims 1 to 6, wherein the dividing wall is injection moulded from non-metallic material.

9. A pump unit as claimed in any one of claims 1 to 8, wherein the passages are produced by a laser technique.

10. A pump unit as claimed in any one of claims 1 to 81 wherein the passages are produced by a liquid-jet technique.

11. A pump unit for a heating system, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

12. A pump unit for a heating system, substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

Published 1989 atThe Patent Office, State House, 66 71 3bgh Holborn. London WClR 47P. Further copies maybe obtainedfrom The Patent Office. Sales Branch, St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray. Kent, Con. 1187