GB2062822A - Coffee maker - Google Patents

Abstract

An automatic electric coffee maker has a tubular heating chamber (8) carrying an electrical resistance wire winding (9) for heating water flowing through the tube between a water reservoir (2) and discharge pipe (5). To promote an even boiling process within the tube, a flow control insert is provided which can be a series of internal rings (18) which are located along the tube length and supported on a spacer. Alternatively the insert may comprise a plurality of spaced grids. <IMAGE>

Description

SPECIFICATION Coffee maker The invention relates to a coffee maker having a water reservoir and a pumping device, which device comprises a quartz-glass tube around which a heating element is arranged, which tube at one end is connected to the water reservoir and at the other end is connected by a riser pipe to a discharge pipe, which terminates above a filtering device.

Such a coffee maker is known from Patent No.

1,559,261.

A pumping device whose tube is made of quartz glass has the advantage that quartz glass is an electrically insulating material, so that the heating element can be supported directly on the outer wall of the tube. In comparison with normai glass, quartz glass has the advantage that the coefficient of thermal expansion is very low.

Moreover, quartz glass has a smooth surface, which is favourable with respect to the formation of undesired scale deposit on the inner wall of the tube. However, a quartz glass tube also presents problems in respect of the pumping action, which will be explained hereinafter.

When water is being pumped bubbles are formed in the tube, which propagate from the inner wall of the tube. If the inner wall is clean, a bubble is formed on the quartz glass, the quartz glass underneath the bubble being dry.

Evaporation is effected only from the surface of the bubble. Overheating causes the bubble to be released from the wall. If the inner wall is soiled by scale deposit, which occurs already after coffee has been made a few times, the inner wall initially being perfectly clean, the bubble is formed on the soiled wall. However, this soiled wall is not dry.

The applied heat is used for the formation of vapour. Evaporation not only occurs from the surface of the bubble, but anywhere underneath the bubble from the soiled wall. The wall is also soiled at the inlet end of the tube. As a result of this the vapour bubbles which propagate along the hot upper wall in the direction of flow of the water grow very rapidly. A sort of explosive evaporation occurs, which impairs a satisfactory pumping action. Moreover, this may give rise to damage to the pump.

It is an object of the invention to reduce the occurrence of explosive evaporation.

To this end the coffee maker according to the invention is characterized in that in the tube there are provided means which prevent a uniform flow of water and steam along the surface in order to reduce the explosive evaporation of water within the tube. As a result of this a growing steam bubble can only wipe clean a limited portion of the surface and the build-up of pressure in the tube is limited. Moreover, a sufficient condensation area will be created in the colder water, so that the bubble growth is also limited. This step promotes a uniform boiling condition in the tube and has a favourable influence on the pumping action.

Explosive evaporation no longer occurs.

A preferred embodiment of the apparatus in accordance with the invention is characterized in that the means are constituted by a plurality ot annular discs, which are disposed substantially transversely to the direction of flow of the water.

By dividing the space near the tube wall surface into a plurality of portions which are sufficiently separated from each other no closed bubble can be formed on the surface.

In another embodiment the means may comprise a plurality of grids which are arranged substantially transversely to the direction of flow of the water.

Preferably, the said means are combined to one component, which is fitted in the tube as a separate insert.

In all these embodiments the flow resistance of the tube should remain sufficiently low.

The invention will now be described in more detail with reference to the accompanying drawing which shows an embodiment.

Figure 1 schematically shows the coffee maker to which the invention relates, Figure 2 is a side view of the coffee maker of Figure 1, Figure 3 is a plan view of the coffee maker of Figure 1, Figure 4 is the pumping device of the coffee maker of Figure 1, Figure 5 is a cross-sectional view taken on the line V - V of Figure 4, Figure 6 shows the insert for the tube of the pumping device of Figure 4, Figure 7 shows a part of the tube with insert.

Figure 8 shows an insert of different shape.

The housing of the coffee maker as shown in Figure 1 is constituted by a hollow base 1 on which a cold-water reservoir 2 is placed. In the hollow base underneath the water reservoir there is provided a pumping device 3 for heating water and pumping this water to a filtering device 6 through a riser pipe 4 and a discharge pipe 5. The filtering device 6 is situated above a receptacle 7.

The pumping device, which is shown on an enlarged scale in Figure 4, comprises a quartz glass tube 8 and a heating element 9, which is helically arranged on the outside of the tube. The heating element is provided with electrical connection tags 10 and 11. The pumping device furthermore comprises a non-return valve 12, included between the water reservoir 2 and the tube 8. Instead of a non-return valve it is possible to use a suitable restriction or a combination of the two. The quartz glass tube is connected to the non-return valve 1 2 and the riser pipe 4 by means of plastics coupling portions 1 3 and 14 respectively. Between the coupling portions 1 3 and 14 and the riser pipe 4 and the tube 8 respectively sealing rings 1 5, 1 6 and 1 7 are fitted.

Suitably, said sealing rings are made of a heatresistant rubber. The tube 8 slopes slightly upwards in the direction of flow of the water in order to promote the pumping action.

In accordance with the invention some annular discs 1 8 are arranged transversely to the direction of flow of the water through the tube. In order to keep the discs 18 spaced from each other, they are mounted on a pin 19, for example by a soldered or riveted connection. Alternatively, the discs and the pin may be manufactured as one plastics component. Together the discs constitute a separate insert 20, which can readily be fitted to the tube (see Figure 6).

By dividing the tube into a number of smaller portions the bubble growth is limited. The maximum length of the bubble is determined by the distance 21 between two discs 18. Towards the centre 22 of the tube the bubble growth is limited by condensation in the colder water (see Figure 7).

Figure 8 shows an insert of a different shape, namely a plurality of grids 23 arranged after each other which are secured to a pin.

Claims (5)

1. A coffee maker having a water reservoir and a pumping device, which device comprises a quartz-glass tube around which a heating element is arranged, which tube at one end is connected to the water reservoir and at the other end is connected by a riser pipe to a discharge pipe, which terminates above a filtering device, characterized in that in the tube there are provided means which prevent a uniform flow of water and steam along the surface in order to reduce the explosive evaporation of water within the tube.

2. A coffee making apparatus as claimed in Claim 1, characterized in that the means are constituted by a plurality of annular discs, which are disposed substantially transversely to the direction of flow of the water.

3. A coffee making apparatus as claimed in Claim 1, characterized in that the means are constituted by a plurality of grids which are arranged substantially transversely to the direction of flow of the water.

4. A coffee maker as claimed in any one of the preceding Claims, characterized in that the said means are combined to a single component, which can be fitted into the tube as a separate insert.

5. A coffee maker substantiallv as hereinbefore described with reference to Figure 1 of the accompanying drawing.