GB2250596A

GB2250596A - Pressure difference indicator

Info

Publication number: GB2250596A
Application number: GB9124479A
Authority: GB
Inventors: Klaas Vonk
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1990-11-22
Filing date: 1991-11-18
Publication date: 1992-06-10
Also published as: SE9103408L; NL9002541A; GB9124479D0; JPH0744000U; DE9113858U1; FR2669733B3; SE9103408D0; FR2669733A3

Abstract

A pressure difference indicator (10) for use in an appliance, for example a vacuum cleaner, comprises a shaft (14) and a bellows (16) provided around the shaft, in which a first end (17) of the bellows is fixed to the shaft and the second end (19) is slidable relative to the shaft. An indicator arm (21, 22) is provided for indicating the pressure difference between the spaces inside and outside of the bellows (16), which indicator arm is movable under the influence of the bellows. The shaft (14) is fixedly connected to a frame (15) of the appliance and the indicator arm (21) is connected to the second end (19) of the bellows. In one embodiment a biassing helical spring (23) is provided inside the bellows. <IMAGE>

Description

DESCRIPTION PRESSURE DIFFERENCE INDICATOR The invention relates to a pressure difference indicator for use in an appliance, for example a vacuum cleaner.

Pressure difference indicators are known, for example, from DE-C-678608. The indicator is used in that case in a vacuum cleaner for indicating the degree of filling (or choking-up) of the dust bag. A bellows having a first and a second end is provided around a shaft and the first end of the bellows is fixed to the shaft. The second end of the bellows in this indicator is fixedly connected to a frame of the vacuum cleaner. During operation, the shaft slides through the said second end of the bellows as a result of the pressure difference between the spaces inside and outside of the bellows. The shaft presses against an indicator arm which is made to move thereby, which movement is rendered visible. A disadvantage of this known indicator is that it occupies too much assembly space. The space available for building an indicator into an appliance is often very limited.

An object of the invention is to provide a pressure difference indicator which is small and very reliable.

According to the present invention there is provided a pressure difference indicator for use in an appliance, comprising a shaft, a bellows provided around the shaft, a first of the bellows being fixed to the shaft and a second end of the bellows being slidable relative to the shaft, and a indicator arm for indicating the pressure difference between the spaces inside and outside of the bellows, which indicator arm is movable under the influence of the bellows, characterised in that the shaft is fixedly connected to a frame of the appliance and the indicator arm is connected to the second end of the bellows.

Since the shaft of a pressure difference indicator according to the invention is fixed, the overall length of the indicator is small, smaller than that described in the cited DE-C-678608.

This will be explained in more detail in the description with reference to the drawings below.

In one embodiment of the pressure difference indicator there is provided a bush with sliding possibility over the shaft, to which bush both the second end of the bellows and the indicator arm are fastened. The bush allows a smooth motion over the shaft without much friction, so that the pressure difference indication is reliable.

The shaft may be at least partly hollow and may be provided with an opening between the space inside the bellows and the hollow space in the shaft, which hollow space in the shaft is in connection with a pressure source.

A helical spring may be provided inside the bellows between the shaft and the second end of the bellows. The spring characteristic of a helical spring is better and more reproducible than that of a bellows. The operating range of the indicator can be well defined by means of a helical spring. The construction remains compact since the helical spring is provided inside the bellows.

An embodiment of the invention will now be explained by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagram of a pressure difference indicator according to the present state of the art, Figure 2 is a diagram of a pressure difference indicator according to the invention, and Figure 3 shows an embodiment of a pressure difference indicator according to the invention used in an appliance.

Figure 1 shows the principle of the pressure difference indicator according to DE-C-678608. The upper side 2 of a bellows 1 is fixedly connected to a frame 5 of an appliance (for -example, a vacuum cleaner). In the presence of a negative pressure difference between the inside and the outside of the bellows as shown in the right hand side of the figure, the lower side 3 of the bellows moves up and the shaft 4 also moves up.

The overall constructional length of the indicator is shown as al + a2.

Figure 2 shows the principle of a pressure difference indicator according to the invention. Equivalent parts are given the same reference numerals as those in Figure 1. The lower side 3 of a bellows 1 and the lower end of a shaft 4 are now fixedly connected to the appliance frame 5. In the presence of a negative pressure differential, as shown in the right hand side of the figure, the upper side 2 of the bellows moves down along the shaft 4. The shaft 4 is stationary relative to the appliance frame 5. The Figure shows that the constructional length of the indicator now is no more than a1 and thus is smaller than that shown in Figure 1.

Figure 3 shows a pressure difference indicator 10 used in a vacuum cleaner for displaying the degree of choking-up of a dust bag. Reference numeral 11 refers to a housing wall, for example the upper wall of the vacuum cleaner, and reference numeral 12 refers to the edge of a portion of this wall which is cut away in order to render the pressure indicator visible. An oval window 13 in the housing wall 11 is indicated by a thin line.

The pressure difference indicator 10 is built up from a shaft 14 which is shown partly in section and is fixedly connected to the vacuum cleaner through a frame plate 15. A bellows 16 is provided around the shaft 14, a first end 17 of the bellows being fixed to an end 18 of the shaft and the other, second end 19 of the bellows being fastened to a bush 20. The bush 20 can slide over the shaft 14. An indicator arm 21 provided with an indicator plate 22 is also fastened to the bush 20. Seen in the plane of the drawing, the frame plate 15 lies below the indicator plate 22.

Inside the bellows 16, a helical spring 23 is provided around the shaft 14. The spring 23 is a compression spring and is enclosed between the end 18 of the shaft and the bush 20. The shaft 14 is made partly hollow and provided with an opening 24 which connects a space 25 inside the bellows 16 with a hollow space 26 in the shaft. The hollow space in the shaft is in connection with a pressure source (not shown), for example a motor unit, through a tube 27.

When the motor unit is switched on, an underpressure is generated in the hollow space 26 of the shaft 14 and, through opening 24, also in the space 25 inside the bellows 16, i.e. a pressure which is lower than the pressure outside the bellows, where atmospheric pressure usually prevails. As a result, the bush 20 slides down over the shaft 14 against the spring pressure of the spring 23. The indicator arm 21 with the indicator plate 22 also moves down along the frame plate 15. The indicator plate 22 will assume a certain position depending on the prevailing underpressure and on the spring characteristic of the spring 23.

If the dust bag of the vacuum cleaner is empty or substantially empty, the upper edge 29 of the indicator plate 22 will be in the position indicated with a broken line 30. As the dust bag becomes more choked up, the pressure difference across the bellows becomes greater and the indicator plate 22 will move further down. This movement is visible through the window 13 in the housing wall 11. For example, if the indicator plate 22 is green while beneath it the surface 28 of the frame plate 15 is red, the surface visible through the window 13 will be green when a dust bag is empty, and as the dust bag becomes more and more choked up, the green indicator plate is increasingly moved away from this surface. The strength of the spring 23 may be selected so that when the green indicator plate has been entirely removed from above the red surface, the dust bag has become so choked up that replacement is necessary.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the design, manufacture and use of pressure difference indicators and component parts thereof and which may be used instead of or in addition to features already described herein.

Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

1. A pressure difference indicator for use in an appliance, comprising a shaft, a bellows provided around the shaft, a first end of the bellows being fixed to the shaft and a second end of the bellows being slidable relative to the shaft, and a indicator arm for indicating the pressure difference between the spaces inside and outside of the bellows, which indicator arm is movable under the influence of the bellows, characterised in that the shaft is fixedly connected to a frame of the appliance and the indicator arm is connected to the second end of the bellows.

2. A pressure difference indicator as claimed in Claim 1, characterised in that a bush is provided with sliding possibility over the shaft, to which bush both the said second end of the bellows and the indicator arm are attached.

3. A pressure difference indicator as claimed in Claim 1 or Claim 2, characterised in that the shaft is at least partially hollow and is provided with an opening between a space inside the bellows and a hollow space in the shaft, which hollow space in the shaft is in connection with a pressure source.

4. A pressure difference indicator as claimed in any one of the Claims 1, 2 or 3, characterised in that a helical spring is provided inside the bellows between the shaft and the second end of the bellows.

5. A pressure difference indicator substantially as hereinbefore described with reference to Figures 2 or 3 of the accompanying drawings.

6. A vacuum cleaner including a pressure difference indicator as claimed in any one of the Claims 1 to 5.