GB2359339A - Centrifugal pump with means for assisting the flow of air entrained in a liquid - Google Patents

Abstract

A centrifugal pump for a bathroom shower unit comprises an inlet 9, an outlet 10, a casing and an impeller. The inlet 9 may include axial vanes 11 which are intended to prevent swirling of incoming water. Blades 14 of the impeller may have extensions 16 (see also figure 2) which extend across an impeller inlet 15 and which are intended to break up entrained air bubbles in the incoming water and prevent the formation of air pockets. A gap between an outer peripheral edge of the impeller and a side wall 22 of the casing may increase in size around the circumference of the impeller until it reaches a maximum at the outlet 10. An annular partition wall 21 may extend from around the inlet 9 towards the impeller to prevent the back-flow of water from a pump chamber 5 towards the inlet 9.

Description

2359339 1 PUMP The present invention relates to pumps and in particular,

but not exclusively, water pumps.

Centrifugal pumps typically comprise an impeller rotatable in a pump chamber having an inlet coaxial with the rotational axis of the impeller and an outlet tangential to the outer edge of the impeller. The impeller is provided with radial blades forming channels arranged so that water entrained by the impeller is thrown out at the outer peripheral edge of the impeller thereby increasing the pressure.

Heretofore, it has been usual to provide an annular gap between the radial blades and the central hub or eye of the impeller into which water can flow from the inlet to be entrained by the impeller.

With this design, if there is air in the water, the water is thrown out in preference to the air because it is heavier. The air tends to form an air bubble or pocket trapped in the eye of the impeller, restricting the flow of water from the inlet which can be undesirable for certain applications of the pump. For example, in the application to an instantaneous shower.

Thus, in instantaneous showers of the type in which cold water is heated as it flows through a heat exchanger prior to delivery to a spray head, the user controls the water temperature for a given power input to the heat exchanger by adjusting the flow rate.

Where the mains supply pressure is low or more usually where a feed from a storage cistern is employed, a pump is required to boost the 30 pressure of the water supply to the heat exchanger to enable the required 2 adjustments to be made to the flow rate for controlling the water temperature over the operating range of the heat exchanger with a sufficient flow to produce an acceptable spray.

if a centrifugal pump is used to boost the water pressure, the formation of an air bubble at the eye of the impeller restricting water flow has an adverse affect on operation of the heat exchanger. In particular, control of flow and therefore the water temperature by the user will be unreliable. Also, the shower will become excessively noisy.

This is a particular problem in situations where air can be induced into the water supply in addition to any air normally present in the water supply. For example, in some countries, such as Ireland, the mains water supply can be turned off at night which can induce air into the system. This is a particular problem with a feed from a storage cistern which may run dry when the mains supply is turned off allowing air to enter the system.

For this reason, other types of pump less susceptible to the pressure of air 20 in the system are generally employed. Such pumps are often more complex and add to the cost of installation.

Another problem with installations requiring a pump to boost the pressure of the water supply is that the pump can be difficult to prime, especially if the pump is supplied from a storage cistern and in particular if the available head is low.

The present invention has been made with the foregoing problems and disadvantages in mind.

3 More particularly, it is an object of the present invention to provide a centrifugal pump of improved construction which is less susceptible to the formation of an air bubble or pocket at the eye of the impeller.

It is a preferred object of the present invention to provide such a centrifugal pump as a booster pump in a shower installation and in particular in an instantaneous electric shower installation.

According to a first aspect of the invention there is provided a centrifugal pump having an inlet and an outlet communicating with a pump chamber containing an impeller, and means for assisting flow through the pump of air entrained in a liquid supply to the pump impeller.

By this invention, the formation of an air pocket within the pump is 15 prevented or reduced by directing entrained air towards and through the impeller for discharge from the pump.

The means for assisting the air flow may include a flow guide in the pump inlet. The flow guide preferably comprises one or more axial vanes which confine the flow of liquid and any air entrained therein to a straight path towards the impeller. In this way, swirling movement of the liquid which slows down travel of entrained air towards the impeller and may create dead spots where air can be trapped is eliminated and the entrained air is directed and moves steadily towards the impeller.

The means for assisting the air flow may include a flow divider in the impeller inlet. The flow divider preferably comprises one or more radial vanes which break up any air bubbles entrained in the liquid to assist flow through the impeller. In this way, the air flow through the pump is 4 facilitated to prevent the entrained air collecting to form an air pocket at the eye of the impeller.

The radial vanes may be extensions of the radial blades that define the flow channels of the impeller. Thus, the radial vanes may extend across the annular gap between the radial blades and the central hub of the impeller.

According to a second aspect of the present invention there is provided an impeller for a centrifugal pump, the impeller comprising radial flow channels extending to the outer edge of the impeller for discharging liquid, and an inlet communicating with the flow channels provided with radial vanes to break up air bubbles entrained in the liquid to assist air flow through the impeller.

Preferably the radial vanes are formed as integral extensions of some or all of the radial blades defining the flow channels, According to a third aspect of the invention there is provided an ablutionary shower installation provided with a centrifugal pump according to a first aspect of the invention.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings wherein:- Figure 1 is a perspective view of a centrifugal pump and motor assembly embodying the invention; Figure 2 is an exploded perspective view of one half of the casing and impeller of the centrifugal pump shown in Figure 1; Figure 3 is a side view, partly in section, of the casing and impeller shown in Figure 2; Figure 4 is a cross-section of the casing and impeller shown in Figure 2; Figure 5 is an end view, partly in section, in the direction of arrow X in Figure 4 of the casing and impeller; Figure 6 is a perspective view of an instantaneous electric shower incorporating the centrifugal pump and motor assembly shown in Figure 1; and Figure 7 is a view of the shower control unit shown in Figure 6 with the front cover removed.

Referring first to Figures 1 to 5 of the drawings, there is depicted an assembly of a centrifugal pump 1 and an electric motor 2 for driving the pump 1. The motor 2 is adapted for connection to a power supply and may be of any type suitable for driving the pump 1. The motor 2 forms no part of this invention and is not described in detail other than to explain the operation of the pump 1 as referred to later herein.

The pump 1 comprises a casing 3 in which an impeller 4 is mounted on a drive shaft (not shown) of the motor 2 for rotation about an axis A in a pump chamber 5.

The casing 3 is in two parts, a pump housing 6 and a pump body 7 30 releasably secured together by a plurality of screws 8. The pump body 7 6 is mounted on the motor 2 by any suitable means (not shown) and has an opening (not shown) with a suitable seal (not shown) through which the drive shaft extends for rotation of the impeller 4 without leakage of water from the pump chamber 5.

The pump housing 6 has an inlet 9 coaxial with the rotational axis A of the impeller 4 and an outlet 10 tangential with the outer peripheral edge of the impeller 4.

The inlet 9 is arranged on the side of the impeller 4 remote from the drive shaft and is provided with an axial flow guide consisting of four vanes 11 extending normal to each other. The vanes 11 may be a separate insert located and arranged in the inlet 9 or may be formed integrally with the inlet 9.

The impeller 4 is of annular shape with front and rear plates 12, 13 separated by a plurality of radial blades 14. The front plate 12 has a central annular inlet 15 facing the inlet 9 and provided with a flow divider consisting of a plurality of the radial vanes 16. The vanes 16 are formed as integral extensions of the blades 14 and extend across the inlet 15 to a central hub 17 integral with the rear plate 13.

The hub 17 has a stepped bore 18 for reception of the drive shaft which may be secured by a circlip or any other suitable means. As best shown in Figure 2, the inner end 18a of the bore 18 is of non-circular crosssection to receive a complementary end portion of the drive shaft to lock the impeller 4 for rotation with the drive shaft.

The radial blades 14 are curved in the radial direction and define therebetween channels 19 of increasing width towards the outer peripheral 7 edge of the impeller 4, and the front plate 12 is inclined towards the rear plate 13 so that the height of the channels 19 reduces towards the outer peripheral edge of the impeller 4.

The pump chamber 5 is defined by a recessed portion 6a of the pump housing 6 that is closed by the pump body 7 on the side remote from the inlet 9.

An end wall 20 of the recessed portion 6a is inclined to match the inclination of the front plate 12 of the impeller 4 and is provided with an annular partition wall 21 extending around the inlet 9 towards the impeller 4 to restrict backflow of water from the pump chamber 5 to the inlet 9.

The end wall 20 terminates in a side wall 22 of the recessed portion 6a which extends around and is spaced from the outer peripheral edge of the impeller 4. As best shown in Figure 5, the gap between the side wall 22 and the outer peripheral edge of the impeller 4 increases in the direction of rotation Y of the impeller 4 to a maximum at the outlet 10.

The outlet 10 is provided in the side wall 22 opposite the outer peripheral edge of the impeller 4 and, downstream of the outlet 10 the gap between the outer peripheral edge of the impeller 4 and the side wall 22 is a minimum. The reduction in the size of the gap creates a barrier to the flow of water in the circumferential direction and causes the water to flow 25 into the outlet 10 for discharge from the pump 1.

The side wall 22 terminates in a step 23 leading to an annular flange 24 providing a seating for locating the pump body 7 to close the pump chamber 5. A seal (not shown) such as an 0ring is provided between the 8 pump housing 6 and pump body 7 to prevent water leaking from the pump chamber 5.

2 D' In use, incoming water entering the inlet 9 is confined to flow in an axial direction by the guide vanes 11. By keeping the flow straight the water is prevented from swirling and any air bubbles entrained in the water flow move towards the inlet 15 in the impeller 4. The bubbles are broken up by the radial vanes 16 extending across the inlet 15. By breaking up the bubbles, the air is prevented from collecting at the eye of the impeller 4 and moves with the water through the channels 19 for discharge from the outlet 10.

As will now be appreciated, the axial guide vanes 11 direct entrained air towards the impeller 4 where the radial vanes 16 extending across the inlet 15 break up any air bubbles to prevent formation of an air pocket restricting flow of water through the pump 1. This assists priming of the pump which may be termed "self -priming ".

in a comparison of the performance of the pump 1 with a conventional centrifugal pump having no guide vanes 11 in the pump inlet 9 and no radial vanes 16 in the impeller inlet 15, the invented pump removes air introduced in the water flow in less than 5 seconds without being manually assisted. With the known pump. however, an air lock was formed which could only be removed by manually increasing the pressure of the water supply to the pump.

Referring now to Figures 6 and 7, an instantaneous electric shower 30 is shown incorporating the pump 1 and motor 2 assembly in a control unit 31 for the shower.

9 The control unit 31 has a manually rotatable control knob 32 for adjustable selection of one of three different power settings identified by the markings "low", "medium" and "high" on the front of the unit 31.

The control unit 31 also has a manually rotatable control knob 33 for adjustable selection of the desired water temperature between minimum and maximum temperatures identified by scale markings on the front of the unit 31.

In this embodiment, the control unit 31 has a start/stop push button 34 which the user can actuate independently of the control knobs 32, 33 to start and stop water flow through the unit 31. In this way, the user can pre-set the power input and desired water temperature so that the water is heated to the required temperature each time the control unit 31 is started.

This is not essential, however, and the start/stop function could be combined with either of the control knobs 32, 33.

As best shown in Figure 7, the control unit 31 has an inlet 34 which can be adapted as appropriate for connection to a rising, falling or rear water supply. The inlet 34 leads to the inlet 9 to the pump 1, and the outlet 10 from the pump 1 leads to a flow control valve 35 operable by the temperature control knob 33 to vary the flow rate and thus the water temperature for a given power input.

The flow control valve 35 is connected to the inlet to a heat exchanger tank 36 containing one or more electric heating elements (not shown) having terminals 37 externally of the tank 36 for connection to a power supply (not shown). An outlet 38 from the heat exchanger tank 36 is connected via a flexible hose 39 to a handset 40 having a spray head 41 for discharging water heated to the pre-selected temperature.

The spray head 41 is supported by a bracket 42 adjustable on a slide rail 43 to vary the height of the spray head 41. The bracket 42 may also allow the inclination of the spray head 41 to be adjusted and the handset 40 can be detached from the bracket 42 to allow the user to position the spray head 41 as desired. The hose 39 extends through an opening 44 in a plate 45 on the slide rail 43 to limit the height to which the spray head 41 can be lowered when detached from the bracket 42. Also mounted on the slide rail 43 is a soap dish 46.

The push button 34 controls an on/off valve for water flow which, in this embodiment, is integral with the flow control valve 35, and a switch assembly 47 controls the power supply to the heating elements to provide the power input to the heat exchanger tank 36 selected by the control knob 32. The switch assembly 47 is arranged to respond to the water pressure so that the heating element(s) are energised only when there is sufficient water flow through the tank 36 and are switched off prior to the water flow to allow flushing of the tank 36 with cold water to remove any residual heat in the heating elements. In this way, the risk of an initial shot of hot water being produced on start up is reduced, especially if the flow is turned on again shortly after having been turned off.

The motor 2 is controlled by the push button 34 or by the switch assembly 47 to operate the pump 1 which boosts the pressure of the water supplied to the control unit 31 so that the flow rate can be adjusted to allow the user to select any desired temperature for any of the power inputs with sufficient flow to produce an acceptable spray from the spray head. Thus, it will be appreciated that the flow rate is reduced to increase water temperature for a given power setting and is increased to reduce the water temperature. Accordingly, if the water pressure of the supply is too low it 11 may not be possible to select all combinations of water temperature and power input.

The construction of the pump 1 with guide vanes 11 in the pump inlet 9 and radial vanes 16 in the impeller inlet 15 ensures that air entrained in the water flow is discharged and does not collect to form an air pocket at the eye of the impeller 4 restricting flow of water and thereby reducing the efficiency of the pump 1 with consequential adverse effect on the performance of the control unit 31.

It will be understood that the invention is not limited to the embodiments above-described. For example, the number and arrangement of the guide vanes 11 in the inlet 9 may be varied to provide more or less than four guide vanes 11. Generally, the number and spacing of the guide vanes 11 should be chosen so as not to reduce significantly water flow through the pump. The radial vanes 16 extending across the inlet 15 in the impeller 4 may be formed as integral extensions of the blades 14 defining the flow channels 19 for discharging the water or they may be formed separately. Where the radial vanes 16 are integral extensions of the blades 14, they may be provided on all of the blades 14 as described. Alternatively, only some of the blades 14 may be extended with integral radial vanes 16. For example, alternate blades 14 may be extended across the opening 15 to the hub.

Although the pump 1 has particular application for boosting water pressure in an instantaneous electric shower, it will be understood that the pump 1 may be used in other installations where it is desirable to prevent formation of an air pocket obstructing flow within the pump. For example, the pump may be employed to boost the pressure of hot and/or 30 cold water supplies to a mixing valve for supplying temperature controlled 12 water to a washbasin, bath, shower or similar ablutionary appliance. Other possible applications include boosting cistern fed domestic hot water.

13

Claims (20)

1. A centrifugal pump having an inlet and an outlet communicating with a pump chamber containing an impeller, and means for assisting flow 5 through the pump of air entrained in a liquid supply to the pump impeller.

2. A pump according to claim 1 wherein the air flow assist means directs entrained air towards and through the impeller for discharge from the pump.

3. A pump according to claim 1 or claim 2 wherein the air flow assist means includes a flow guide in the pump inlet.

4. A pump according to claim 3 wherein the flow guide comprises one or more axial vanes which confine the flow of liquid and any air entrained therein to a straight path towards the impeller.

5. A pump according to claim 3 or claim 4 wherein the flow guide comprises a separate insert received in the pump inlet.

c 0

6. A pump according to claim 3 or claim 4 wherein the flow guide comprises an integral part of the pump inlet.

7. A pump according to any one of the preceding claims wherein the flow assist means includes a flow divider in the impeller inlet.

8. A pump according to claim 7 wherein the flow divider comprises one or more radial vanes which break up any air bubbles entrained in the liquid to assist flow through the impeller.

14

9. A pump according to claim 8 wherein the radial vanes are extensions of radial blades that define flow channels of the impeller.

10. A pump according to claim 9 wherein the radial vanes extend across an annular gap between the radial blades and a central hub of the impeller.

A pump according to any one of the preceding claims further comprising a pump casing and the pump chamber is defined between the outer peripheral edge of the impeller and an opposed side wall of the pump casing.

12. A pump according to claim 11 wherein a gap between the outer peripheral edge of the impeller and the side wall of the pump casing increases in the direction of rotation of the impeller to a maximum at the outlet.

13. A pump according to claim 12 wherein the gap is a minimum downstream of the outlet to create a barrier to the flow of water in the circumferential direction.

14. A pump according to any one of the preceding claims wherein an annular partition wall extends around the inlet towards the impeller to prevent backflow of water from the pump chamber to the inlet.

15. A centrifugal pump substantially as hereinbefore described with reference to Figures 1 to 5 the accompanying drawings.

16. An ablutionary shower installation provided with a centrifugal pump according to any one of the preceding claims.

4 c'

17. An ablutionary shower installation substantially as hereinbefore described with reference to Figures 6 and 7 of the accompanying drawings.

18. An impeller for a centrifugal pump, the impeller comprising radial flow channels extending to the outer edge of the impeller for discharging liquid, and an inlet communicating with the flow channels provided with radial vanes to break up air bubbles entrained in the liquid to assist air 10 flow through the impeller.

19. An impeller according to claim 18 wherein the radial vanes are formed as integral extensions of some or all of the radial blades defining the flow channels.

. 4 -40 c

20. An impeller for a centrifugal pump substantially as hereinbefore described with reference to the accompanying drawings.