GB2177016A - Breather desiccator for closed container - Google Patents

Abstract

A breather desiccator for a container comprises a relatively narrow tube 60, adapted to be extended through an aperture in a wall of the container, a wider screw-threaded portion 20 adapted to be screwed into said aperture, and a still wider portion 12 which remains outside the container. The tube 60 contains desiccant material and a passageway 40, 42 is provided, through portions 12 and 20 for the passage of air between the exterior and the interior of the container. The opening to said passageway in the portion 12 is provided by an annular passage between a skirt 28 and a core part and this opening is closed by valve means in the form of an annular rain skirt 52 of silicone rubber which can flex to allow the passage of air in either direction under a small pressure difference, but serves to prevent liquid water, such as rain or condensation, from running into the container through the passageway 40, 42. <IMAGE>

Description

SPECIFICATION Improved breather desiccator for closed container This invention relates to a combined desiccator and breather, herein referred to as a breather desiccator, which may be used to control relative humidity and relieve pressure in closed containers such as those used to house electrical, electronic or mechanical equipment orto protect engineering products during transit and storage.

In such containers, a breather desiccator performs several functions: 1. It isfrequently not practical to makean equip ment container which is completely moisture-proof, e.g. because holes are required for plugs, sockets, switches and the like and thesewill be imperfectly sealed. There may also be small leaks th roug h joi nts.

Under conditions of varying temperature or barometric pressure, for example, pressure differences will be produced between the interior and exterior of a container which is sealed but for small leaks, and in such conditions, when the container is in an exposed situation and a lower pressure exists within the containerthan outside it, liquid water from the external surfaces ofthe container may be sucked into the containerthrough such small leaks. A breather desiccator provides a controlled leak of much lower impedance which prevents the development of significant pressure differences between the interior and exterior of the container, whilst affording a means of humidity control.

2. In the case of airborne equipment, the provision of a breather eliminates the need to provide a strong, and therefore, heavy container able to withstand the pressure differences developed under flight conditions, whilstthe combination of such a breather with a desiccatorstill allows control of hum iditywithinthecontainer.

3. In any container provided with a breather desiccator, pressure differences between the interior and exterior of the container are relieved by breathing through the breather desiccator, whilst the desiccator removes moisture introduced into the container during the breathing and thus the desiccator maintains the low internal relative humidity which is essential to prevent corrosion and mould growth.

In conventional designs of breather desiccator, incoming air passes through the desiccant to allow some of its moisture to be removed before it reaches the inside of the equipment. Tests have shown that very little moisture is removed during such passage and that internal relative humidity can be controlled just as effectively by allowing the moist air to pass directly into the container to be subsequently removed by a desiccator. This arrangement permits a marked simplification in design.

According to one aspect of the invention, there is provided a breather desiccator for use with a container comprising a first relatively narrow portion, adapted to be extended through an aperture in a wall of the container, a second, wider portion adapted to engage firmly in said aperture, and a third, yet wider portion adapted to remain outside the container when the breather is fitted in such a wall, said first relatively narrow portion being hollow to provide a chamberto contain desiccant material and wherein at least one passageway is provided, through said third and second portions at least, for the passage of air between the exterior and the interior of the container, said passageway being closed by valve means allowing the passage of air in either direction under a small pressure difference, but serving to prevent liquid water, such as rain or condensation, from running into the containerthroug h said passageway.

Said first relatively narrow portion is preferably in the form of a hollow tube, containing desiccant material, and closed at one end by an end wall provided by said third portion, said end wall being in the form of a transparent window, and a piece of colorimetric humidity indicating paper being mounted within the third portion and extended over the innerface of said window, said third portion, at least, being formed as a unitary body of plastics material providing said window, thus eliminating entry of moisture and other contaminants.

An embodiment of the invention is described below byway of example with reference to the accompanying drawings in which :- Figure 1 is a view, partly in side elevation and partly in axial section of a breather desiccator emb- odying the invention, taken along the line I - I in Figure 3, Figure2 is a view partly in side elevation and partly in axial section, of the breather desiccator of Figure 1, taken along the line II - II in Figure 3, and thus at right angles to the view of Figure 1, and Figure 3 is a view in cross-section along the line lil Ill of Figure 1 and Figure 2.

The breather/desiccator shown in the drawings comprises a first portion intheformofagenerally cylindrical hollow cartridge 10 and a body 12,14 within which the cartridge 10 is inserted, the body comprising an outer part 12 and an inner part 14, each having the general form of a respective solid of rotation coaxial with the cartridge 10. The inner part 14 ofthe body is generally tubular, having a central bore 16 into which a narrower end part 18 of the cartridge 10 is inserted, the body inner part 14 having externally, adjacent one end thereof, a screwthread indicated at 20 adapted for engagement in a complementary internal screwthread formed around an aperturethroughthewall 22 of a container to which the desiccator is fitted.It will be noted that the assembled desiccator may be regarded as having a first, relatively narrow portion, afforded by said cartridge 10 and which can be passed freelythrough said aperture in the container wall, a second part, of somewhat greater diameter, which is adapted to engage firmly (by the screw th read 20) in the aperture, and a third part, of yet greater diameter, provided by the outer part 12 of the body, and which remains outside the container. The body outer part 1 takes the general form of a frusto-conical cap providing an end wall 24which closes offthefree end of the narrow end portion of the cartridge 10, a hub formation 26 disposed radially outwardly of the end wall 24 and a flaring, frusto-conical skirt 28 which extends from the hub formation 26 radially outwardly and rearwardly to terminate in a free edge 30. The end of the body inner part 14 remote from the thread 20 is provided with diametrally opposed castellations 32, (only one of which is shown in Figure 2) which are received in complementary pockets 34 formed in the portion of the central area of the body outer part 12 which faces towards the container wall 22, the pockets 34 being disposed on diametrally opposite sides ofthe end wall 24.The sectioned portion of Figure 1 is a section in a plane which lies intermediate the two castellations 32. As shown in Figure 1, a longitudinal groove 40 extends over the entire axial extent of the body inner part along the surface ofthe bore 16 and communicates with a slot 42 cut across the front end ofthe body inner part 14 at between the two cas tellations 32, whereby the groove 40 is placed in communication with the annular space 44 defined between the skirt 28 and the inner body part 14. Asimilar groove 40 is formed overthe body inner part dia metrally opposite the groove 40 shown in Figure 1.

The inner body part 14 is, for example, adhesively bonded to the outer body part 12. It will be appreciated that the body is formed in two parts 12, 14 as des- cribed simplyforease offabrication.

The groove 40 defines, with the adjacent outer surface ofthe cartridge 10, an elongate, narrow air pas sagewaywhich connects the space on the exterior of the associated container with the interior of the container. In an alternative arrangement (not shown), a longitudinal groove is formed on the exterior surface of the cartridge 10 instead of in the part 14, to define, with the adjacent surface of part 14, a similarly elongate narrow air passageway which connectsthe exterior and interior of the container. In a third altern ativetheairpassagewayisformedbytwo mating grooves, one in the exterior surface of the cartridge 10 and the other on the adjacent surface of part 14.

It will be appreciated that in a closed container provided with a breather, (orwith other intentional or unintentional openings into the container) and having a desiccant within the container, even when internal and external pressures are equal, moisture may still enter the container by diffusion due to the difference in the partial pressure ofwatervapour contained in the interior and exterior of the container. It has been found, however, that a breather affording an elongate passageway for air and having a length to internal diameter ratio greaterthan 10:1 provides a substantial barrier to ingress of moisture to the container by diffusion. The passage defined between the groove 40 and the cartridge 10 in the preferred embodiment meets this criterion.The provision of the breather passage between two separately formed and subsequently assembled com ponents, i.e. by a groove formed along one of these components, allows the components in question to beformed by injection moulding,withouta subsequent machining step to provide the passage. twill be appreciated that it is not practicable to form an elongate passage ofthe appropriate dimensions in a unitary body by injection moulding.

On its radially outer side, the inner body part 14is formed, intermediate its ends, with a radial enlargement or collar 50 in which is formed a circumferential groovewhich receives the base of an annular rain skirt 52 of elastomeric material such as silicone rubber and which tapers radially outwardly to a fine edge which lightly engages the radially inner side of the skirt 12 adjacent the free edge 30. An O-ring 54 disposed between the collar 50 and the wall 22 of the container serves to seal the exteriorofthe inner body part 14 with respect to the container.

The cartridge 10 has a first part in the general form of an open-ended cylindrical tube 60 and a second part in the form of an end cap 62 fitted over and closing the rear end ofthe tube 60. Internally, the tube 60 has a first cylindrical bore 63 extending from approximatelythe middle of thetube 60 to the front end thereof and a second, slightly enlarged bore 64 extending from the rear end of the bore 63 to the rear end ofthetube 60. In the assembled desiccator, the bore 64 is lined with a rolled porous paper sheet 65, retained axially between the cap 62 and the slight shoulderformed internally between the bores 63 and 64.Externally, the cartridge 10, rearwardly ofthe body 12, 14, comprises a major, rearward portion of uniform external diametersomewhatgreaterthan that of narrower part 18 and merging, via a shallow taper, with the narrower part 18 which is received within the inner body part 14. At its rear end, this major portion is joined by an end portion of reduced external diameter over which is fitted the peripheral wall, of substantially the same outer diameter as said major portion, of the cap 62.

Equally spaced around the periphery of said major rearward portion of cartridge 10,arefourrectangular longitudinally elongate slots70 each extending en tirelythrough the wall ofthe cartridge and providing, through the porous paper sheet 65, communication between the interior and exterior of the tubular body of the cartridge, whereby watervapourwithin the container in which the breather desiccator is fitted can come into contact with the desiccant (not shown) within the cartridge 10 and surrounded by the porous paper sheet 65.

The cartridge 10 may be detachably connected with the body, being, for example, a push fit within the bodyinnerpart 14 and being retained therein bya catch arrangement. In the embodimentshown,the cartridge 10 is held in place in the body inner part by a catch arrangement comprising a resilient beam 76 defined in the wall of the cartridge by slots formed therethrough, the beam 76 being free at its forward end and carrying, at its forward end, a sawtoothfor- mation 78 which, in the assembled condition ofthe desiccator, engages in a rectangular slot 80 formed inthewall ofthe body part 14immediatelyrearwa- rdlyofthe screw thread 20. The arrangement is such that the cartridge may simply be pushed axially into the body inner part 14, the sloping ramp face on the sawtooth formation 78 being displaced radially inwardly by engagement with the inner edge ofthe rearwardmost part of the inner body part 14to spring radially outwardly into the slot 80 when the cartridge has been fully inserted. Towithdrawthe cartridge 10 from the inner body part 14, the beam 76 must be displaced radially inwardly slightly, for example by exerting pressure with a finger nail. To facilitate this action, the outer surface of the beam 76 may be provided with a raised pip. As an alternative the cartridge may be retained in the body part 14 by selectively applied adhesive.

The outer part 12, at least, of the body, and preferably also the inner body part 14, is formed oftransparent plastic. The end wall 24 is formed atthe bottom of a circular recess formed centrally atthe forward end of the body outer part 12, the opposite faces of the end wall 24 being optically smooth so that the end wall forms a transparent window.The front portion of the outer body part 12 which lies immediately radially outwardly of the window 24 forms an annularwall surrounding the window 24, and at diametrally opposing positions this wall is formed with slots 90 in orderthatan appropriate tool maybe laid across the front end of the desiccator and engaged in the slots 90, the tool being turned to rotate the body 12, 14 and thus the desiccator as a whole about its axis and allow the body part 14thereby to be screwed into or out ofthe complementary aperture in the wall 22 of the container until the O-ring 54 is com- pressed between the collar 54 and the waIl 22 of the container to seal the body part 14 with respect to the container. The slots 90 are shallowerthan the recess so that damage to the smooth surface of the window 24 is avoided.

A colorimetric disc, i.e. a disc 92 of paper impregnated with a substance which undergoes a marked colour change in passing from a relatively dry state to a relatively moist state extends across the inner face of the window 24 and is held at its periphery between the window 24 and the forward end of the tubular body of the cartridge 10. The disc 92 can be easily inspected from outside the container through the window 24, so thatthe exhaustion of the desiccant, resulting in a rise in humidity within the cartridge 10, can readily be detected before conse quent deterioration of the contents of the container.

The provision of the outer body 12 as a one-piece component offerstwo advantages over known designs. Thus, there is no possibility of a false reading being given by the humidity indicator paper due to the ingress of water, oil orothercontaminants through leaks between different parts of the outer body.

The window in the breather desiccator shown in the drawings is much larger in relation to the device as a whole, than in current designs. This facilitates judgement of indicator paper colour. This is important since the indicator paper shows when relative humidity inside the equipment has reached an unsafe level and the desiccator needs a fresh charge.

In use, the cartridge 10 is filled with an appropriate desiccant material and is fitted into the body 12,14 and the body 12, 14 is screwed into place in the con- tainer in conjunction with which the device is to be used. The skirt 52, when there is no pressure difference between the interior and exterior of the container, makes contact with the body 12 and seals off the interior of the container, preventing, for example, the entry of liquid water such as rain water into the container (e.g. if the latter is exposed to the weather).

However, the skirt is readily deflected resiliently outwardly or inwardly away from the outer rim to allow the passage of airthrough the breather, in response to pressure differences arising between the interior and exterior of the container, even where such pressure differences are of a low order. Air thus passing into the container flows pastthe skirt 52, through the annular space 44 and the slots 42 and thence, along the passages defined between the grooves 40 and the opposing wall ofthe cartridge 1 O, to the interior of the container. Airthus flowing from the container to the outside follows the same path in the opposite direction.When inspection of the disc 92 reveals that the desiccant is becoming exhausted, the breather desiccator is simply unscrewed from the container, the cartridge 10 is removed from the body 12, 14and the exhausted desiccant is replaced with a fresh charge. In the alternative arrangement where the car- tridge is retained by adhesive the end cap 62 is removed to permit the change of desiccant. After re charging, the breather desiccator is replaced in the container.

However a breather desiccator of the design shown in the drawings can be made so cheaply that, in many cases it can be made as a 'throw-away' item which is simply discarded in its entirety when the desiccant is exhausted and replaced by a new desiccator breather with a fresh charge of desiccant.

Asignificantdifference between the breather desiccator described with reference to the drawings and current known breatherdesiccators is that air entering and leaving the container in which the breather desiccator is installed does not pass directly through the desiccant. Moisture is removed from the air after it enters the container and tests have shown that, with this arrangement, control of internal relative humidity is just as effective as with current designs.

It has been found that, in practice, it is unnecessary for the air passing into the container to pass through the desiccant within the cartridge in order to secure adequate protection for the contents of the container, since the desiccant material is exposed to the interior of the containerthrough the slots 70 in the body of the cartridge and the air within the container is thereby kept dry. This discovery has allowed the simple design described with reference to the drawings to be adopted. Such a design, in certain specific cases, may utilise a very small number of discrete parts, which can be formed by moulding from appropriate plastics material and which can be readily and quickly assembled to form the complete breather desiccator, and as readily fitted to a container.

Whilstthe parts 10, 12, 14 and the cap 62 may be made as unitary plastics mouldings, each oranyof these parts could be fabricated from a number of components ofsimplerform or from plastics stock and this is an approach which it may be economical to adopt, for example, where the breather desiccator is to be of large physical size and the required production volume is insufficient to justify the capital outlay which wou Id be involved in making the tools which would be necessary for manufacture of these parts as unitary mouldings and in the set-up of associated machinery.

As indicated above, breathers of the kind described with reference to the drawings may be utilised in permanent housings provided for electronic equipment in use. It is frequently necessary for such equipment to be adequately screened against radio frequency electro-magnetic radiation and in such cases the breathing desiccator must also be screened against radio frequency radiation. That is, the breather desiccator must prevent the passage of radiation at radio frequencies, either in or out1 through the hole in which the desiccator is fitted.This will require that the inner body 14 is made of metal or a conductive plastics for example plastics filled with aluminium flakes or aluminium powderto render it electrically conductive, and that a disc of conductive gauze or otherforminous conductive material providing a screen against electromagnetic radiation, said disc making contact with the inner body 14 is fitted behind the indicator paper, thus providing electrical continuity with the equipment container. Such a disc may, for example, be of metal gauze or perforated sheet metal.

The breathing desiccator described with reference to the drawings is capable of meeting various requirements and is able: a) to minimise the build-up of a pressure differ- ence between the interior and exterior of an equip mentcontainerunderflightconditions orwhen exposed to temperature or barometric pressure changes, b) to restrict the diffusion of water vapour through the breathing path when breathing is not taking place, c) to preventthe ingress of liquid water into an equipment container during heavy rain, d) to contain a charge of desiccant sufficiently exposed to the internal atmosphere of the equipment container so thatthe relative humidity ofthe internal air is effectively controlled, e) to indicate when the relative humidityofthe internal air of an equipment container has reached the level at which the desiccant charge should be changed, f) to permit changing ofthe desiccant charge without opening up the equipment containerto which the breathing desiccator is fitted, g) to be made sufficiently robust to survive the environmentto which the equipment container may be subjected, and the handling necessary in fitting, replacing or re-charging, h) to be manufactured from materials compatible with electronic and optical assemblies.

Claims (12)

1. A breather desiccator for use with a container, comprising a first relatively narrow portion, adapted to be extended through an aperture in a wall ofthe container, a second, wider portion adapted to engage firmly in said aperture, and a third,yetwider portion adapted to remain outsidethecontainer when the breather is fitted in such a wall, saidfirst relatively narrow portion being hollow to provide a chamberto contain desiccant material and wherein at least one passageway is provided,through said third and second portions at least,forthe passage of air between the exterior and the interior ofthe container, said passageway being closed by valve means allowing the passage of air in either direction under a small pressure difference, but serving to prevent liquid water, such as rain or condensation, from running into the containerthrough said passageway.

2. A breather desiccator according to claim 1, wherein said passageway includes an annularcrosssection passage defined between an inner part of said third portion and an outerannularwall provided by an outer part of said third portion, and said valve means comprises an annular skirt of elastomeric material fitted sealingly around said inner part of said third portion and tapering radially outwardlyto terminate in a fine edge sealingly engaging the inner surface of said annularwall.

3. A breather desiccator according to claim 2 wherein said annular cross-section passage is defined between an inner part of said third portion and an outer annularwall provided by an outer part of said third portion, wherein said outer annular wall flaresfrusto-conicallyoutwardlyfromthe axis of the desiccator from a region relatively remote from said first relatively narrow portion towards said first portion to terminate in a free annular edge of said wall which, when the desiccator is fitted, lies close to the outer surface of the container wall in which the breather is fitted, whereby water droplets striking said wall ofthe containerfrom outside the container will tend to be deflected by said frusto-conical wall, so as not to enter said passage.

4. A breather desiccator according to any of claims 1 to 3 wherein said passageway does not include said chamber within said first, relatively narrow portion, and opens, on the inside of a said containerto which the breather desiccator is fitted, on the outside of said first part whereby, in use, air can pass into and out of the container through said passageway without passing through the desiccant in said chamber.

5. A breather desiccator according to any of claims 1 to 4 wherein said passageway includes a portion having a length to diameter ratio of at least 10:1, said passageway portion being defined between mating surfacesofseparatelyformed moulded integers, by a groove formed in at least one of said integers and the opposing surface of the other said integer.

6. A breather desiccator according to claim 5 wherein one of said integers is in the form of a hollow cartridge adapted to receive a desiccant, and the other of said integers includes a part which provides a socket to receive an end of said cartridge and which partformsthe exterior of said second wider portion of the breather desiccator.

7. A desiccator according to claim 6 wherein releasable catch means is provided between said cartridge and said member providing said second and third portions.

8. A desiccator according to claim 6 or claim 7 wherein said cartridge is intheform ofatube having openings in the wall thereofto allow air within such a container to contact the desiccant, the tube being linedinternallywitha porous sheet adapted to contain the desiccant and prevent loss of the desiccant through said openings.

9. A desiccator breather according to claim 1 wherein said first relatively narrow portion is in the form of a hollowtube, containing desiccant material, and closed at one end by an end wall provided by said third portion, said end wall being intheform of a transparent window, and a piece of colorimetric humidity indicating paper being mounted within the third portion and extended over the inner face of said window, and wherein said third portion, at least, is formed as a unitary body of plastics material providing said window.

10. A desiccator according to claim 9 wherein said second portion has an external screw thread whereby the desiccator may be screwed into a correspondinglythreaded hole in such a containerwall, wherein a slot is provided across the outer end of said third portion for engagement by a complementarytool to be used as a screw-driverto assist in screwing the desiccator into or out of such a threaded hole, said window being provided by the bottom of a recess extended axially into said third portion from said outer end thereof to a greater extentthan said slot, whereby said window is protected from damage by said tool or by other objects.

11. A desiccator according to claim 9 or claim 10 wherein said second wider portion is made of elec tricallyconducting material, and said transparent window incorporates or is covered by conductive gauze or other conductive foraminous material providing a screen against electromagnetic radiation and electrically continuous with said second portion whereby, in use, said screen is connected electrically with an electrically conductive container in which the desiccator is fitted.

12. A desiccator substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.