COMBINED HEATER PUMP APPARATUS

Background to the Invention

The invention relates to combined heater pump apparatus for providing a flow of heated pressurised fluid, particularly but not exclusively, for providing such a flow in a dishwashing machine.

In known dishwashing machines, mains pressure water is supplied to a reservoir or sump within the machine from where it passes to a pump, which pumps it into a pipe fitted with a heating device. The heating device comprises a tubular electric heating element and the water is flash heated as it passes through the heating element. The heated water is then supplied to the compartment in the machine in which washing takes place. Heating devices of this type can be obtained from Bleckmann GmbH & Co Kg. A problem with having a separate pump and heating device connected in series like this is that the two parts must be connected by fitting operations and it is necessary to find space within the dishwashing machine to house two parts and the piping connecting them.

EP-A-I 139 852 discloses a combined heater and pump. The pump has an electric heating device fitted to the exterior of the pump housing. This can provide problems in matching the heating element(s) to the shape of the pump housing and ensuring that the heat produced by the heating element is efficiently transferred to the fluid passing through the pump.

Summary of the Invention

The invention provides a combined heater pump apparatus comprising a pump housing and an electric heater, wherein said pump housing defines an opening and said electric heater is disposed such that it at least partially closes said opening and, in use, is in direct contact with fluid that is pumped through the pump housing.

The invention also includes a combined heater pump apparatus comprising: a pump housing defining a chamber having an inlet and an outlet and defining an opening; a pumping device housed in said chamber for pumping fluid between said inlet and outlet; and an electric flat plate thick film heater disposed in said opening such that said heater at least partially closes said opening and, in use, contacts the fluid that is in said chamber.

Brief Description of the Drawings

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

Figure 1 is a cutaway perspective view of a combined heater pump apparatus according to the invention with the pump impeller removed;

Figure 2 is a view of the combined heater pump apparatus of Figure 1 rotated through approximately 90° and showing the pump impeller; and -

Figure 3 is a schematic representation of a dishwashing machine fitted with the combined heater pump apparatus of Figures 1 and 2.

Detailed Description of the Embodiment

Referring to Figures 1 and 2, a combined heater pump apparatus 10 includes a pump housing comprising a cylindrical wall 12, a planar wall 14 at one end of the cylindrical wall that closes a cylindrical chamber 16 defined by the pump housing and a lip 18 at the other end of the cylindrical wall. An aperture 20 is provided in the planar wall 14 to provide access to the chamber 16. A relatively short pipe 22 projects from the planar wall 14 and in combination with the aperture 20 defines a pump inlet. The pump outlet is defined by an aperture 24 defined in the cylindrical wall 12 and a

relatively short pipe 26 projecting from the cylindrical wall. In this embodiment, the respective axes of the pump inlet and pump outlet are in substantially mutually perpendicular planes.

The lip 18 defines an opening in the pump housing, which is closed by an electric heater 28 that is fitted in the opening. The electric heater 28 is a flat plate thick film heater and, as can be seen from the drawings, it effectively forms a wall of the pump housing. Thick film heater elements per se axe known and are, for example, used incorporated in electric kettles. Typically, a flat plate thick film heater element will comprise a resistance heating track laid on an insulating substrate provided on a thin metal plate made of, for example, stainless steel.

An annular seal element 30 is seated in an annular recess 32 defined by the lip 18. The seal element 30 is provided with a circumferential groove in which the periphery of the electric heater 28 is sealingly engaged. The seal element 30 may be bonded in the annular recess 32 or fixed by a suitable mechanical fitting(s) so as to provide a seal between the annular recess and the seal element. As examples of alternatives to bonding, the annular cover plate might be fitted to the outer face 36 of the lip 18 and secured to the pump housing by fasteners, such as screws, a suitable snap- fastening arrangement comprising cooperable formations provided on the pump-housing and the cover plate, or a separate clip arrangement. Those skilled in the art will be aware of suitable sealing devices and materials, which include, for example, "O" rings made of neoprene or silicone rubber.

An impeller 40 is disposed in the chamber 16. The impeller 40 has a drive shaft 42 that extends through an aperture provided in the electric heater 28. Suitable seals 44 are provided about the aperture and the drive shaft 42. In use, the impeller is driven by an electric motor (not shown), which is connected with the drive shaft 42. The seals and bearing supports for the impeller may be the same as those of conventional pumps used in such machines, or of any other suitable type, and have been omitted from the drawings, so that the invention is more clearly illustrated.

The impeller 40 comprises an annular planar member 46 and a planar member 48 disposed parallel to the annular planar member 46. The planar member 48 is in the form of a disc and is fitted to the drive shaft 42. A plurality of impeller blades 50 is disposed between and interconnects the planar members 46, 48. The face of the planar member 48 that faces the electric heater 28 is provided with a plurality of agitators 52. In this embodiment, the agitators comprise a plurality of radially extending projections formed integrally with the planar member 48 and evenly spaced around the periphery thereof.

An annular wall 54 extends from the inner face of the planar wall 14 such that its free end is located adjacent the outer face of the annular planar member 46. The wall 54 separates the chamber 16 into an, inner, low pressure region in which fluid passes from the pump inlet into the interior of the impeller 40 and an, outer, high pressure region, which surrounds the low pressure region and receives relatively higher pressure fluid from the impeller 40.

Use of the combined heater pump apparatus in a dishwashing machine 100 will now be described with reference to Figure 3. The inlet pipe 22 is connected to a reservoir, or sump, 102. The sump 102 is connected with a source 105 of mains pressure water by suitableηpipήϊg 106 and valving 107. Typically, a solenoid valve ^~ lO7 is used to control the flow of water from the mains pressure source 105 to the sump 102. Similarly, suitable piping 108 is used to connect the outlet pipe 26 with spray heads 110, or the like, disposed in the washing compartment 112 of the dishwashing machine.

When the solenoid valve 107 is opened, mains pressure water passes into sump 102. The water level in the sump 102 is controlled by level switches connected with a controller, which provides control signals for the solenoid 106. The level switches and controller are not shown in the drawing for the sake of clarity and may be of any conventionally-used type. The level switches may, for example, be float switches.

From the sump 102, the water passes to an inner, low pressure, region of the chamber 16 via the inlet pipe 22 and aperture 20. The impeller 40 raises the pressure of

the water which is expelled into an, outer, high pressure region of the chamber 16. Here, the pressurised water is flash heated by the electric heater 28 before passing out of the chamber 16 via the aperture 24 and outlet pipe 26. It will be appreciated that as the impeller 40 rotates, the agitators 52 are rotated and prevent the formation of a pool of stagnant water on the electric heater 28 so that the water is more evenly heated.

It will be understood that the arrangement shown in Figure 3 is intended to be merely illustrative. Other suitable arrangements will be known to the skilled person and, so, will not be described in further detail herein.

It will be appreciated that the combined heater pump apparatus 10 has many advantageous features. Since the electric heater 28 forms a wall of the pump housing and is in direct contact with the fluid to be heated, a good coefficient of heat transfer is obtained. Heat is not lost to heating the pump housing, as in the prior art. The pump . housing can be manufactured from materials that do not have good heat transfer properties and it is not necessary to use heat transfer pastes and the like to ensure heat is conducted from the heater element into the wall of the pump housing. Thus, for example, a pump housing in an embodiment of the invention may be a plastics moulding. This, in itself, provides advantages in terms of weight, ease of manufacture in that scale will not generally form on a plastics material. Where the pump housing is a plastics moulding, the annular seal 32 may be incorporated in the moulding during the moulding process.

A further advantage of the combined heater pump apparatus 10 is that the electric heater does not have to be foπned to take account of the shape of the pump housing. A simple planar element can be used to fill the opening in the pump housing.

A further advantage is that the combined heater pump apparatus 10 is relatively compact as compared with apparatus of similar capacity comprising a separate pump and electric heater.

Advantageously, the electric heater is sized to fit an opening sufficiently large to permit easy withdrawal of the impeller and is removably fitted into the opening. This facilitates servicing of the combined heater pump apparatus. Where it is desired to use a proprietary electric heater and it is desirable to have an opening in the pump housing that is larger than the heater, for example to facilitate filling of the impeller, the size of the seal element may be suitably adjusted and/or a collar, or other suitably sized part, could be fitted to the electric heater to make the fit.

It will be understood that where the electric heater is a flat plate thick film heater, the surface of the heater that contacts the liquid can be coated with a suitable material, such as fluoropolymers (for example materials based on PTFE), so as to prevent scaling.

It will be understood that the combined heater pump apparatus may use electrical heaters other than a thick film heater. For example, the opening in the pump housing may be closed by a relatively thin plate member having an electric heater element secured to the outer side thereof by soldering or clenching. The heater element may, for example, be a metal sheathed, mineral insulated, resistance wire heater clenched or soldered to a stainless steel plate.

The combined heater pump apparatus 10 comprises a vaned impeller 40. However, other forms of pump device may be used. For example a "Rootes" type of iobed compression pump, or a "Wankel" cylinder arrangement. In both of these cases, a heater could be provided in one or both flat side walls of the pump cylinder.

The combined heater pump apparatus has been described in use in a dishwashing machine. It is to be understood that the invention is not limited to such use and, in principle, can be used in any apparatus in which a pumped fluid is to be heated. For example, the apparatus might be incorporated into a power shower, clothes washing machine or high pressure hot washing machine.

A further advantage of fitting an electric heater into an opening in a pump housing is that the electric heater can be configured such that a simple proprietary overheat protection device can be fitted to it to reduce or interrupt the electric current supply to the heater in the event is temperature exceeds a predetermined level. Ch'erheating might be due to a failure in the water supply or blockages forming upstream or downstream of the apparatus 10. One suitable overheat protection device would be the X2 element protector produced by Otter Controls Ltd and described in GB 2 308 921, the content of which is incorporated herein by reference.

In use, it is preferable that the apparatus 10 is mounted such that the electric heater 28 forms the lower end of the chamber 16, as is shown in Figure 2. In this way, it can be ensured that the heater will always be covered by a pool of fluid. This reduces the likelihood of overheat damage of the electric heater.