GB2218241A

GB2218241A - Liquid presence detector

Info

Publication number: GB2218241A
Application number: GB8908659A
Authority: GB
Inventors: Arthur Leonard Lewis
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-04-19
Filing date: 1989-04-17
Publication date: 1989-11-08
Anticipated expiration: 2009-04-17
Also published as: GB8908659D0; GB2218241B

Abstract

The detector includes apparatus in the form of a pad 10 for use over a liquid detector 12 comprises an upper absorbent portion 14, 16 and spacer means 18 which space the upper portion 14, 16 from the detector 12. The upper portion 14, 16, in use, retains liquid until saturated, and thereafter allows liquid to pass down through the layer 18 towards the detector 12. The spacing provided by the spacer means 18 is sufficient to prevent the detector being activated by liquid retained in the upper portion 14, 16 before saturation thereof. <IMAGE>

Description

Apparatus for use in Detecting the Presence of Liquid The present invention relates to apparatus for use in detecting the presence of liquid.

It has previously been proposed to detect liquid by applying a voltage across electrodes, and detecting a rise in current when an electrically conducting liquid forms a connection between the electrodes. In this way, leaks from pipes or tanks or from other sources can be detected.

In many circumstances, it is necessary to have accurate detection of the presence of liquid in bulk, as a result of a leak, overflow or the like. However, some sensors previously proposed would also give rise to many false alarms resulting from the presence of small amounts of liquid such as drops of condensation, rodent urine, or normal atmospheric humidity.

It is an object of the present invention to seek some means for discriminating between small amounts of liquid which are not of concern, and the presence of liquid in bulk.

According to the invention, there is provided apparatus for use over a liquid detector, the apparatus comprising an upper absorbent portion and spacer means which space the upper portion from the detector, the upper portion, in use, retaining liquid until saturated, and thereafter allowing liquid to pass down towards the detector, and the spacing provided by the spacer means being sufficient to prevent the detector being activated by liquid retained in the upper portion before saturation thereof.

Preferably the upper absorbent portion comprises a first layer sufficiently absorbent to absorb condensation without becoming saturated. The absorbency of the first layer is preferably such that the first layer becomes saturated by bulk liquid, whereby bulk liquid will pass through the first layer.

The first layer may be impregnated with a material, such as salt, which lowers the freezing point of water.

The first layer may be impregnated with a fungicide. The first layer may be impregnated with a material, such as potassium permanganate, which causes staining in the presence of water.

Preferably the first layer has perforations of a size which is sufficient to allow liquid to evaporate out of the pad through the first layer, and which is insufficient to allow liquid for detection to flow through the perforations into the pad.

The first layer is preferably impregnated with a material which reduces the surface tension of liquid to be detected, to enhance the absorption thereof by the first layer. Preferably the first layer is impregnated with surface tension reducing material at spaced locations, separated by areas in which no material for reducing surface tension is impregnated. The spaced locations may form boundaries of areas without impregnation. The said impregnation locations may form a grid of square areas without impregnation. The surface tension reducing material may be soap or detergent.

The first layer may consist of paper, such as tissue paper.

The upper absorbent portion may further comprise a second layer having a higher capacity for retaining liquid than the capacity of the first layer, whereby liquid in sufficient quantity to saturate and pass through the first layer is initially absorbed by the second layer. The second layer may be impregnated with a material which reduces surface tension to enhance the penetration of liquid into the second layer from the first layer. The second layer may be impregnated with detergent. The second layer is preferably impregnated with a material which is soluble in an electrically non-conducting liquid to render that liquid electrically conducting.

The second layer preferably consists of a sponge or a sponge like structure, such as a reticulated synthetic sponge having a ppi value between 70 and 100. The second layer can preferably absorb between 5 ml and 15 ml of liquid at a single point before saturating.

The pad preferably further comprising means operable by capillary action to draw liquid from the second layer to the first. The capillary means may comprise elongate members of capillary material extending from the second layer to the first.

The first layer may be discontinuous to expose the second layer at a plurality of locations, at which liquid may directly penetrate the second layer without passing through the first layer.

The spacing means preferably provides electrical insulation between the upper portion and the detector. The spacing means may comprise a water permeable structure which passes water substantially without absorption thereof. The water permeable structure may consist of a non-absorbent material. The structure may be a sponge or sponge-like structure, such as a reticulated 10 ppi synthetic sponge.

Preferably the apparatus forms a tile which may be placed alongside a plurality of similar tiles to form a larger apparatus of the same type.

The edges of the upper portion may be raised to prevent liquid flowing off the pad along the upper surface thereof.

The apparatus preferably further comprises a shield member which shields part of the upper portion at the edge thereof, to prevent liquid entering the upper portion through the shielded part. The shield member may include a sloping surface which guides liquid away from the shielded part, toward the centre of the upper portion. The shield member is preferably perforated to allow liquid to evaporate from the shielded part.

The apparatus may further comprise means for sealing the exposed edges of the upper portion to prevent liquid leaving the upper portion. The sealing means and the shield member may be provided by respective walls of a channel member in which the edge of the upper portion is located. The channel member may be attached to the spacing means.

The apparatus may further comprise envelope means for enveloping the upper absorbent portion and the spacing means and a sensor with which the apparatus is used, the envelope means being adapted to retain the relative positions of the apparatus and the sensor without restricting the passage of liquid into or out of the apparatus. The envelope means may comprise or consist of netting.

One embodiment of the present invention, and some alternatives, will now be described in more detail, by way of example only and with reference to the accompanying figures in which: Fig. 1 is a perspective view of apparatus according to the invention in position over an electric liquid sensor; and Fig. 2 is a partial vertical section through a modification of the apparatus of Fig. 1.

The apparatus is in the form of a pad 10 which is used over a liquid detector 12. The pad comprises an upper absorbent portion 14, 16 and spacer means 18 which space the upper portion 14, 16 from the detector 12. The upper portion 14, 16, in use, retains liquid until saturated, and thereafter allows liquid to pass down towards the detector 12. The spacing provided by the spacer means 18 is sufficient to prevent the detector being activated by liquid retained in the upper portion 14, 16 before saturation thereof.

In more detail, the upper portion 14, 16 consists of a first layer 14 at the top of the pad, and a second layer 16 immediately beneath the first layer 14. The first layer 14 consists of paper, such as tissue paper. This is of sufficient thickness to absorb condensation drips or other similar small amounts of liquid without becoming saturated. The first layer 14 is impregnated with a material such as salt (sodium chloride) to lower the freezing point of water, and may also be impregnated with a fungicide in order to allow extended use in damp conditions without degradation caused by fungal growth on top of the pad. The first layer 14 also has potassium permanganate or another staining agent impregnated into it, so that the layer 14 becomes stained after wetting.

This allows for swift identification of the position at which the sensor 12 has been activated.

Perforations 20 are spaced across the first layer 14. The size of the perforations is sufficient to allow liquid to evaporate out of the pad from the second layer 16 through the perforations 20, but is sufficiently small that surface tension prevents liquid flowing from the top of the first layer 14 down into the pad through the perforations 20.

The first layer 14 may also be impregnated with material which reduces the surface tension of the liquid to be detected. This may be soap or a detergent.

Preferably, strips 22 of the first layer 14 are impregnated in this way, leaving areas 24 without impregnation.

In the embodiment shown, square areas 24 arranged in a square grid are defined by strips 22 of impregnated detergent. The purpose of the strips 22 is to absorb any droplets of liquid which run across the surface of the first layer 14 without being absorbed. Such droplets would eventually reach a strip 22 where the surface tension would be reduced to enhance the absorption of the liquid into the first layer. The extreme edges of the pad 10 may be raised to trap any droplets which reach the edge. These will then build up until being absorbed, rather than running off the pad 10.

The strips 22 could be replaced by gaps in the paper, so that the second layer 16 is periodically exposed. Liquid can then directly penetrate the second layer 16 at these positions, without passing through the first layer 14.

The second layer 16 consists of a sponge or spongelike structure, such as a reticulated synthetic sponge in the range 70 ppi to 100 ppi. The thickness and material of the second layer 16 are chosen to give the second layer a higher capacity for retaining liquid than the capacity of the paper layer 14. Thus, for example, a tissue paper layer 14 would be expected to be saturated by a few millilitres of liquid at a single point. A 70 ppi or 100 ppi reticulated sponge layer having a thickness between 5 mm and 10 mm could be expected to absorb approximately 5 to 15 ml of water at a single point before becoming saturated.

The sponge layer 16 is again preferably impregnated with a material, such as soap or a detergent, which reduces the surface tension of the liquid to be detected.

This makes it easier for liquid from the first layer 14, when saturated, to pass down into the sponge layer 16.

The versatility of the arrangement shown can be increased to include detection of electrically nonconducting liquids by impregnating one or both of the layers 14, 16 with a material which is soluble in the liquid to be detected, and which renders that liquid electrically conducting.

At the boundary between the first and second layers 14, 16, there are a series of short wicks 26 of capillary material which extend generally vertically into both layers 14, 16. These wicks 26 draw liquid from the second layer 16 to the first layer 14, in the event that the second layer 16 is saturated, but the first layer 14 has dried off.

The third layer of the pad is the spacing means 18, which in this example is another sponge layer. The sponge 18 is highly water permeable, so that any water entering the layer 18 from the second layer 16 will pass straight through to the sensor 12, with virtually no liquid being absorbed in the layer 18. The main purpose of the sponge layer 18 is therefore to space the second layer 16 above the sensor 12, not to absorb or retain liquid. Reticulated synthetic sponge of 10 ppi can be used for the layer 18.

Many other means for spacing the second layer 16 above the sensor 12 could be used.

The sponge layer 18 is preferably made of an electrically insulating material.

In use, the pad 10 is placed on a sensor 12 with the first layer 14 uppermost. The structure of the sensor 12 does not form part of this invention, and has not been described in any detail. However, it is envisaged that the pad 10 is most likely to be used over a sensor which comprises electrodes which become shorted by the presence of liquid in order to give rise to a current which is detected and used to sound an alarm.

If a small amount of liquid lands on the first layer 14, such as a drip of condensation, this will normally be absorbed into the first layer 14. The paper 14 will cause the drop to spread widely, and will retain the drop without releasing liquid down into the second layer 16.

If the drop is not immediately absorbed into the paper, but runs across the surface, it will eventually meet a strip 22 and will then be absorbed as its surface tension is reduced by the material impregnated into the paper.

In the case of a drip of condensation, no further liquid may be expected to land on the paper 14 for some time. This provides an opportunity for the first droplet to evaporate, leaving a dry layer 14. Thus, the sensor has been prevented from giving rise to a false alarm in response to a condensation drip.

If liquid is present in bulk, for instance as a result of a leak, burst pipe, spillage etc., liquid will initially be absorbed into the first layer 14, causing staining by dissolving the potassium permanganate impregnated into the layer. The layer 14 will quickly become saturated in a serious case, so that water passes into the second layer 16. Initially, the liquid will be retained in the second layer 16 until the layer 16 becomes saturated. Thus, if bulk liquid arises, for instance from a spillage rather than a continuous leak, this may be absorbed down into the second layer 16 but without saturating the second layer 16. After the spilt liquid has been fully absorbed by the pad 10, it may then evaporate off, to leave both layers 14, 16 dry. Evaporation is made easier by the perforations 20 which allow liquid to evaporate directly from the layer 16 to the atmosphere above the pad 10.In addition, the wicks 26 encourage liquid to move from the second layer 16 up to the first layer 14 in order to evaporate off.

In the event of a continuing leak or serious spillage, the second layer 16 will become saturated and will no longer be able to contain the liquid entering from the first layer 14. Liquid will then begin to pass through the layer 16. Liquid leaving the layer 16 will pass straight through the layer 18 onto the detector 12, which will be activated. The location of the problem can quickly be detected by looking for a stained patch on the pad.

When the leak or other fault has been corrected, the stained section of the pad 10 can be removed, the detector 12 dried, and a fresh section of pad replaced. It is therefore convenient if the pad 10 is constructed in the form of identical tiles, such as square tiles, which can be fitted together to form a larger pad, and which can be individually replaced.

Fig. 2 is a vertical section through the edge of the pad 10 in a modified embodiment. In this embodiment, the edge of the layers 14, 16 of the pad 10 are located in the channel of a channel member 30. The channel of the channel member 30 is defined by a lower wall 32, an upper wall 34 and a web 36. The web 36 covers the vertical face of the edge of the layers 14, 16 to prevent liquid leaving the layers. The lower wall 32 is attached to the spacing means 18 to mount the channel member 30 permanently in position.

The upper portion 14, 16 of the pad 10 is not attached to the channel member 30, so that the upper portion can be removed and replaced at will, whereupon the channel member 30 will help locate the layers 14, 16.

The web 36 extends above the layer 14 and the upper wall 34 slopes back down towards the layer 14, thereby shielding a portion 38 of the edge of the pad 10. Close to the junction between the wall 34 and the web 36 there is formed a row of perforations 40 through the channel member 30.

The purpose and function of the channel member 30 is as follows. In the absence of a channel member as described, a droplet of water landing on the upper layer 14 close to its edge (in the region 38) could leave the pad 10 through the vertical face thereof without being correctly dealt with and triggering the sensor 12, if appropriate. The channel member 30 obviates this difficulty in two ways. Firstly, the upper wall 34 forms a guide surface which causes droplets landing on the wall 34 to run down and be guided away from the edge of the pad 10, towards the centre of the pad. The edge portion 38 is therefore shielded by the upper wall 34 and does not absorb liquid directly through its upper surface.The dimensions of the wall 34 can be set so that it shields a sufficient part of the edge to ensure that droplets of the expected size can be absorbed where they run off the wall 34, without the absorbed liquid spreading out to the edge of the pad 10. It is expected that this "edge effect" can be overcome by shielding a strip about 20 mm wide at the edge of the pad 10.

The second effect of the channel member 30 is to prevent liquid leaving the edge of the layers 14, 16.

Thus, if bulk liquid was absorbed near the edge of the pad 10 (having been deflected by the upper wall 24) it could not leave the layers 14, 16 except by re-evaporation, or movement down to the layer 18. Small amounts of condensation can, however, leave the edges of the spacing means 18, if they penetrate that far through the layers 14, 16.

It may assist in securing the various structures in their correct relative positions if the pad, channel member and sensor are- enveloped in a net or similar structure which has no effect on liquid entering or leaving the pad.

It will be apparent from the above description that many variations and modifications to the pad described above can be made without departing from the spirit or scope of the present invention. The thicknesses and materials chosen for the various layers of the pad will be selected according to the operating characteristics required for any particular application. Thus, in some circumstances, a great deal of condensation might be expected, and a relatively thick paper layer 14 would be used. In other circumstances where little condensation is expected, a thin paper layer could be used.

The thickness and material chosen for the second layer 16 determines the amount of bulk liquid which is absorbed before passing through to the detector 12. This sets an upper limit on the size of spillage which can go undetected, and on the delay which will occur before a persistent leak is sensed by the detector 12. The thickness and material of the layer 16 will therefore be selected according to the proposed application. In some circumstances, the layer 16 may be omitted altogether, with the paper layer 14 being laid directly on the spacing means 18.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. Apparatus for use over a liquid detector, the apparatus comprising an upper absorbent portion and spacer means which space the upper portion from the detector, the upper portion, in use, retaining liquid until saturated, and thereafter allowing liquid to pass down towards the detector, and the spacing provided by the spacer means being sufficient to prevent the detector being activated by liquid retained in the upper portion before saturation thereof.

2. Apparatus according to claim 1, wherein the upper absorbent portion comprises a first layer sufficiently absorbent to absorb condensation without becoming saturated.

3. Apparatus according to claim 2, wherein the absorbency of the first layer is such that the first layer becomes saturated by bulk liquid, whereby bulk liquid will pass through the first layer.

4. Apparatus according to any preceding claim, wherein the first layer is impregnated with a material which lowers the freezing point of water.

5. Apparatus according to claim, 4 wherein the said material is salt.

6. Apparatus according to any preceding claim, wherein the first layer is impregnated with a fungicide.

7. Apparatus according to any preceding claim, wherein the first layer is impregnated with a material which causes staining in the presence of water.

8. Apparatus according to claim 7, wherein the staining material is potassium permanganate.

9. Apparatus according to any preceding claim, wherein the first layer has perforations of a size which is sufficient to allow liquid to evaporate out of the pad through the first layer, and which is insufficient to allow liquid for detection to flow through the perforations into the pad.

10. Apparatus according to any preceding claim, wherein the first layer is impregnated with a material which reduces the surface tension of liquid to be detected, to enhance the absorption thereof by the first layer.

11. Apparatus according to any preceding claim, wherein the first layer is impregnated with surface tension reducing material at spaced locations, separated by areas in which no material for reducing surface tension is impregnated.

12. Apparatus according to claim 11, wherein the spaced locations form boundaries of areas without impregnation.

13. Apparatus according to claim 12, wherein the impregnation locations form a grid of square areas without impregnation.

14. Apparatus according to any of claims 10 to 13, wherein the surface tension reducing material is soap or detergent.

15. Apparatus according to any preceding claim, wherein the first layer consists of paper.

16. Apparatus according to any preceding claim, wherein the upper absorbent portion further comprises a second layer having a higher capacity for retaining liquid than the capacity of the first layer, whereby liquid in sufficient quantity to saturate and pass through the first layer is initially absorbed by the second layer.

17. Apparatus according to claim 16, wherein the second layer is impregnated with a material which reduces surface tension to enhance the penetration of liquid into the second layer from the first layer.

18. Apparatus according to claim 16 or 17 wherein the second layer is impregnated with a material which is soluble in an electrically non-conducting liquid to render that liquid electrically conducting.

19. Apparatus according to any of claims 16 to 18, wherein the second layer consists of sponge or a spongelike structure.

20. Apparatus according to claim 19, wherein the second layer is a reticulated synthetic sponge having a ppi value between 70 and 100.

21. Apparatus according to claim 19 or 20, wherein the second layer can absorb between 5 ml and 15 ml of liquid at a single point before saturating.

22. Apparatus according to any of claims 16 to 21, further comprising means operable by capillary action to draw liquid from the second layer to the first.

23. Apparatus according to claim 22, wherein the capillary material extending from the second layer to the first.

24. Apparatus according to any of claims 16 to 23,- wherein the first layer is discontinuous to expose the second layer at a plurality of locations at which liquid may directly penetrate the second layer without passing through the first layer.

25. Apparatus according to any preceding claim, wherein the spacing means preferably provides electrical insulation between the upper portion and the detector.

26. Apparatus according to any preceding claim, wherein the spacing means comprises a water permeable structure which passes water substantially without absorption thereof.

27. Apparatus according to claim 26, wherein the water permeable structure is constituted by non-absorbent material.

28. Apparatus according to claim 26 or 27, wherein the water permeable structure is a sponge or a sponge-like struture.

29. Apparatus according to claim 28, wherein the water permeable structure is a reticulated 10 ppi synthetic sponge.

30. Apparatus according to any preceding claim, wherein the apparatus forms a tile which may be placed alongside a plurality of similar tiles to form a larger apparatus as aforesaid.

31. Apparatus according to any preceding claim, wherein the edges of the upper portion are raised to prevent liquid flowing off the pad along the upper surface thereof.

32. Apparatus according to any preceding claim, and further comprising a shield member which shields part of the upper portion at the edge thereof, to prevent liquid entering the upper portion through the shielded part.

33. Apparatus according to claim 32, wherein the shield member includes a sloping surface which guides liquid away from the shielded part, toward the centre of the upper portion.

34. Apparatus according to claim 32 or 33, wherein the shield member is perforated to allow liquid to evaporate from the shielded part.

35. Apparatus according to any preceding claim, further comprising means for sealing exposed edges of the upper portion to prevent liquid leaving the upper portion.

36. Apparatus according to claim 35 and any of claims 31 to 33, wherein the sealing means and the shield member are provided by respective walls of a channel member in which the edge of the upper portion is located.

37. Apparatus according to claim 36, wherein the channel member is attached to the spacing means.

38. Apparatus according to any preceding claim, further comprising envelope means for enveloping the upper absorbent portion and the spacing means and a sensor with which the apparatus is used, the envelope means being adapted to retain the relative positions of the apparatus and the sensor without restricting the passage of liquid into or out of the apparatus.

39. Apparatus according to claim 38, wherein the envelope means comprises or consists of netting.

40. Apparatus substantially as described above with reference to the accompanying drawings.

41. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.