GB2029649A - Centrifugal fluid-circulation pumps - Google Patents

Abstract

A centrifugal fluid-circulation pump assembly comprises an impeller 10 driven by an electric motor M having a rotor (2) surrounded by the fluid, the impeller being driven by the motor via a drive shaft (4) carried by front and rear bearings (5 and 6). Lubrication of the bearings is provided by a quantity of the fluid to be circulated which is forced around a circuit including the chamber (7', 7'', 7''') occupied by the rotor (2) and a conduit (41) formed in drive shaft (4). An anti-vortex disc (8) is disposed on the front of the rear bearing (6). Fluid enters the lubrication circuit by means of the rotational clearance of the front bearing (5), then flows through the disc (8) and slots (63) to lubricate the rear bearing (6) before returning to the chamber (7') via the conduit (41). <IMAGE>

Description

SPECIFICATION Centrifugal fluid circulation pumps The present invention relates to centrifugal fluid circulation pumps, in particular such pumps driven by electric motors of fthe submerged rotor type.

Centrifugal fluid-circulation pumps are commonly, but not exclusively, used to accelerate circulation of heat-conveying fluid (e.g. water) in central heating instaliations. In such a pump having a submerged rotor the bearings and bearing bushes of the rotor of the motor are lubricated by water. This lubrication is not without difficulty. Lubrication water is generally introduced into the chamber occupied by the rotor of the motor by means of a passage linking the pump part to this rotor chamber; the passage is made through a plate disposed between and separating the pump part and rotor chamber. The lubrication water introduced into the rotor chamber is water from the installation served by the circulation pump.

In the case of a central heating installation, the water is that of the closed circuit which conveys heat around the installation. This water carries impurities of all kinds. Some are solid: iron, limestone, silica, various particulate impurities; other impurities are liquids, mainly oils from piping or parts of the installation put into service without previous cleaning.

To ensure non-damaging lubrication of the bearings of the rotor, dirty water is undesirable. It has been proposed that elimination of the solid particles from lubricating water be effected by means of a filter disposed upstream of the aforementioned passage, bored in the separation, or front, plate, connecting the pump part with the rotor chamber.

Elimination of liquid impurities is more difficult to achieve. It is recognised that to date elimination of liquid impurities has not been possible.

It has been proposed to restrict the quantity of water introduced into the rotor chamber by limiting the exchange of water between the pump part and the rotor chamber, for example by suppressing or preventing the passage of water through the front plate. This, however, gives rise to a disadvantage in that lubrication is not good and bearings and bearing bushes can be damaged prematurely.

According to the present invention there is provided a centrifugal fluid-circulation pump assembly comprising a forward pump part and a rear motor part having an electric motor with a submerged rotor, wherein the pump part and the motor have a common drive shaft carried by fron and rear bearings, and wherein lubrication of at least the rear bearing is provided by means of a circuit for fluid, including a chamber occupied by the rotor and a conduit formed in the common drive shaft, which circuit is in restricted communication with fluid passages in the pump part, whereby, in use, a quantity of the fluid to be circulated by the pump flows around the circuit in forced circulation and flow of fluid between the pump part and the lubrication circuit is small.

In embodiments of this invention correct lubrication of bearings and bearing bushes, promoting long working life, can be facilitated.

In an embodiment of this invention fluid exchange between pump and rotor chamber is limited to a strict minimum which, nevertheless, ensures sufficient lubrication by means of the forced circuit which obliges the fluid to flood permanently the bearings and bearing bushes.

In embodiments of this invention entry of the water into the rotor chamber is effected exclusively through the rotational clearance of the front bearing bush of the rotor, and the forced circulation circuit operates in a flow loop including the chamber occupied by the rotor and the conduit made in the central rotation shaft.

For example in a water circulating system employing a centrifugal circulation pump embodying the invention the forced circuit is a closed hydraulic circuit comprising a small quantity of water borrowed initially from the water circulating in the system, this small quantity of water, after penetrating, by way of the rotational clearance of the bearing bush of the front bearing of the rotor, into the front part of the rotor chamber, is conveyed, by the action of an anti-vortex disc disposed frontally in front of the rear bearing of the rotor, onto the said rear bearing which it floods then through a passage made for allowing water to pass from the rear bearing to a conduit hollowed into the common rotational shaft of the pump and the rotor, and through the conduit to debouche in the front part of the rotor chamber from whence it is conveyed again, by action of the anti-vortex disc disposed frontally in front of the rear bearing of the rotor, onto the said rear bearing which it floods and soon, to repeat the cycle.

More simply, in embodiments of this invention, lubrication of the front and rear bearings of the rotor is provided by a forced closed circuit between the front and rear bearings of the rotor, a circuit in which a very small quantity of fluid introduced once and for all is sufficient to maintain permanently a lubrication of the bearings.

Reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 is a schematic axial cross sectional view of an embodiment of the invention; Figure2 is a front view of an anti-vortex disc employed in an embodiment of the invention; and Figure 3 is a detailed cross-sectional view showing the disc of Figure 2 in co-operation with the rear bearing of the pump of Figure 1.

Figure 1 shows a pump embodying the present invention. The view of Figure 1 shows in detail those parts above axis of symmetry R'R of pump 1. The pump 1, of the centrifugal type, has, inside a general assembly, or pump body, a motor part M and, in front of the motor part, a so-called pump part P. The motor part M comprises an electric motor, having a rotor 2 visible in the Figure and surrounded by a stator 3. The rotor 2 occupies a chamber 7', 7D, 7ss/1, which is sealed by means of joints J and J' (e.g.

O-rings).

The motor part M and the pump part P have a common shaft 4. In the motor part the shaft is carried by a front bearing 5 and a rear bearing 6. An action wheel (impeller) ofthe pump part P can be seen at 10 in Figure 1. The impeller is preferably a wheel with blades, but the construction details are not shown in the Figure. The wheel 10 stirs up hydraulic fluid included in a pump chamber 11 of the pump part P.

A plate F separates the pump part P from the motor part M. One of the conditions to be satisfied if good functioning of the pump is to be obtained is the provision of adequate lubrication of the bearings of the motor in the motor part M. In the pump embodying this invention an anti-vortex disc 8 is placed in front of a front face of the rear bearing 6 in rear part 7"' of the chamber which is occupied by the rotor of the motor, further there is no passage for hydraulic fluid in the plate F as has been provided in the previously proposed centrifugal pumps. The plate F is therefore continuous and its inner axial edge 50 rests on front bearing bush 51. Clearance 51-5 is the normal rotational clearance of the bearing bush.

The common shaft 4 is bored through, in the rear part thereof, by an axial channel 41, the end openings of which are at 42 in front part 7' of the rotor chamber (the front opening), and towards the rear of the pump (the rear opening) at 43. This rear opening opens into a rear chamber 9, rearward of rear bearing 6, contiguous with (proximate to) a closing device 12 which seals the pump housing.

Figures 2 and 3 illustrate, by way of example, an anti-vortex disc and its location in an embodiment of the present invention.

It will be seen from Figure 2 that the anti-vortex disc 8 is a metallic disc, the disc is hollowed out in the centre and provided with a certain number of peripheral slots, such as slots 81 and 81"'. In the illustrated form of anti-vortex disc the peripheral slots are semi-circular in outline. Other shapes could be given to the slots. Finally as can be seen in the detailed view of Figure 3, the anti-vortex disc is provided with a flexible latticed tongue 82. This tongue, which is shown in Figure 3 bent at right angles against a horizontal wall 71 of the chamber of the submerged rotor 2, has the effect of simplifying the assembly of the anti-vortex disc 8 fixed in fixed bearing bush 61 of the bearing 6. Around the bearing 6 at least three longitudinal slots are arranged at 120 to each other, such as slot 63.

As can be seen in Figures 1 and 3, the hollow slots 63 in the bearing 6 are peripheral and longitudinal of the bearing and they have a length, parallel to the axis of rotation of shaft 4, greater than the length of the bearing bush that they overhang.

The arrangement of the parts and fittings in an embodiment of this invention allows the access of a small quantity of water into the rotor chamber from the pump. Indeed, the water from the chamber 11 of the pump percolates into the front chamber 7' solely by way of rotational clearance of the front bearing bush 51 of the front bearing 5. By virtue of the rotation of the rotor 2 in the rotor chamber, a slight radial pressure differential occurs (reduced pressure towards the axis) which is sufficient to cause water to flow into rotor chamber part 7" which provides a peripheral fluid passage around the rotor. On reaching the rear chamber 7"' this supply of liquid could not correctly lubricate the rear bearing 6 in the absence of the anti-vortex disc 8 as it would tend to bank up peripherally.However, the fixed anti-vortex disc 8, because of its peripheral apertures, obliges the supply of liquid to wash the bearing 6. The disc works as an anti-vortex disc in the sense that it breaks the cylinder of water which is effectively created by a vortex effect due to rotation of the rotor.

The disc is fixed in accordance with the radial plan of the shaft 4 in front of the rear bearing.

The existence of at least three slots 63 in the rear bearing further favours the drainage of the water along the rear bearing bush 61. The water which has thus lubricated the rear bearing 6 flows into the rear chamber 9 on leaving the slots 63. However, since there is a slight pressure reduction in the axial zone of the front chamber 7' of the rotor, water which appears in chamber 9 is drawn towards the front chamber 7' via the conduit 41.

The forced hydraulic circuit thus returns to the chamber 7' and forms a closed cycle.

Because of the arrangement adopted in embodiments of this invention, only a small quantity of water is introduced into the chamber of the rotor from the pump and this has the advantage of minimising the risks of pollution of the lubricating water. However, thanks to the structural arrangement provided, ample and permanent lubrication is set up, especially for the rear bearing of the motor, which can provide longer working life for the bearing bushes. The front bearing 5 is lubricated by contact of its front face with the water from the pump and by contact of its rear face with the water from the rotor chamber, a discrete percolation being maintained in the bearing bush clearance as compensation for any possible loss of pressure.

The risk of including solid particles in the lubricating water is also reduced due to the fact that the quantity of water introduced into the rotor chamber is small on the one hand and can be substantially permanently maintained on the other hand.

For the man skilled in the art it will be easy to draw from the above description of the invention the necessary information for application of the invention in connection with any particular shape of motor, bearing or pump.

As a further measure towards elimination of solid impurity particles it is suggested to dispose on the front face of the front bearing a lipped joint which prevents the passage of dust and solid particles into the rotor chamber to be protected.

Thus the present invention can provide satisfactory lubrication thereby optimising the working life of rotating parts in a pump.

Claims (8)

1. A centrifugal fluid-circulation pump assembly comprising a forward pump part and a rear motor part having an electric motor with a submerged rotor, wherein the pump part and the motor have a common drive shaft carried by front and rear bearings, and wherein lubrication of at least the rear bearing is provided by means of a circuit for fluid, including a chamber occupied by the rotor and a conduit formed in the common drive shaft, which circuit is in restricted communication with fluid passages in the pump part, whereby, in use, a quantity of the fluid to be circulated by the pump flows around the circuit in forced circulation and flow of fluid between the pump part and the lubrication circuit is small.

2. A pump assembly as claimed in claim 1, wherein the rotational clearance of the bearing bush of the front bearing affords the only passage by which the fluid to be circulated can enter the chamber occupied by the rotor.

3. A pump assembly as claimed in claim 1 or 2, wherein there is provided in the forced circuit an anti-vortex disc disposed in front of the rear bearing facing the rotor which is disposed between the front and rear bearings.

4. A pump assembly as claimed in claim 3, wherein at least one fluid passage is formed in the rear bearing for passing fluid in the forced circuit to the rear of the rear bearing to be taken into the conduit formed in the common drive shaft.

5. A pump assembly as claimed in claim 3 or 4, wherein the anti-vortex disc is a disc having peripheral slots formed therein.

6. A pump assembly as claimed in claim 3 read as appended to claim 2, wherein fluid for lubrication enters the circuit through the rotational clearance of the front bearing, passes to the rear bearing via the anti-vortex disc, from the rear bearing passes into the conduit formed in the common drive shaft and debouches from the conduit into a forward part of the chamber occupied by the rotor, thereby to resupply that chamber so that fluid for lubrication flows in a closed loop, percolation of fluid through the rotational clearance of the front bearing serving to compensate for any loss of pressure in the closed loop.

7. A pump assembly as claimed in any preceding claim, wherein the fluid to be circulated is water.

8. Acentrifugal fluid-circulation pump assembly substantially as hereinbefore described with referpence to Figure 1, or Figures 1 to 3 of the accompanying drawings.