Housing structure WTH pivotally movable walls

A structure which includes a container (16) which forms a housing (20) and, mounted to the housing, a plurality of walls (52,54,56,58) which are pivotally interconnected and which are movable between a compact stored configuration and an extended operative configuration.

BACKGROUND OF THE INVENTION

This invention relates to a structure which can be stored and transported in a compact mode and which, at an installation site, can be erected to provide an enclosure, a shelter, a reservoir or the like.

SUMMARY OF THE INVENTION

In a broad sense the invention provides a structure which includes a container which forms a housing and, mounted to the housing, a plurality of walls which are pivotally interconnected and which are movable between a compact stored configuration and an extended operative configuration.

More particularly the invention provides a structure which includes a container which forms a housing of parallelepiped form with a longitudinal axis and with a base, a roof, first and second sides, first and second ends, and first, second, third and fourth corners located respectively at junctions of the first side and first end, first end and second side, second side and second end, and second end and first side, first, second, third and fourth support arrangements located respectively at the first, second, third and fourth corners, each support arrangement respectively including an elongate member with an upper end which is fixed to the roof and a lower end which is fixed to the base, a cylinder, a hinge mechanism which secures the cylinder to the elongate member and which permits the cylinder to be moved between an operative position at which the cylinder is displaced from the corner and a storage position at which the cylinder is retracted to the corner, and a piston, telescopically connected to the cylinder, which is actuable with the cylinder in the operative position to extend downwardly from the cylinder whereby a lower end of the piston is brought into ground-engaging contact and the piston thereby exerts a force which elevates the housing relative to the ground, at least a first wall which is substantially rectangular in outline and which has a lower horizontal edge, an upper horizontal edge, an inner vertical edge and an outer vertical edge, and a first pivotal connection which connects the inner vertical edge to the elongate member at the first corner whereby the first wall is pivotally movable about the elongate member between a storage position at which the first wall is located at the first side and is generally parallel to the longitudinal axis and a deployed position at which the first wall extends transversely to the longitudinal axis.

The structure may include a second wall which is generally rectangular in outline and which has a lower horizontal edge, an upper horizontal edge, a first vertical edge and a second vertical edge, and a second pivotal connection which connects the first vertical edge to the outer vertical edge of the first wall whereby the second wall is pivotally movable about the second pivotal connection relative to the first wall between a first position at which the second wall is generally adjacent the first wall and a second position at which the second wall extends transversely to the first wall.

The structure of the invention may be employed, as indicated, in various ways, for example to provide an enclosure, a shelter, a reservoir or the like. Two or more of the structures may be employed in combination and the respective walls of the structures may be interconnected in any appropriate way to enclose a defined area.

The structure of the invention may include third and fourth walls which are secured via a respective support arrangement and a pivotal connection, similar to what has been described, to the fourth corner i.e. on the same side of the container as the first and second walls. Also, if required, additional similar walls can be provided on the second side.

If the structure is to be used to provide a shelter then, preferably, the first wall and the second wall are used to form at least part of an enclosure which bounds a ground area and the structure may then include a roof component which is formed from sheet material which is fixed, at least, to the upper horizontal edges of the first and second walls and which overlies, and which is spaced from, the ground area. Use may additionally be made of a mast or similar support structure to keep the sheet material at an elevated position.

One or more floor elements or panels, e.g. in the nature of rigid sheet material, may be fixed to the walls and may be deployed e.g. by pivotal action into ground-engaging contact in order to overlie and be supported by the ground area.

When the walls are moved between storage and deployed positions use may be made of level sensors to ensure that each wall is correctly orientated relative to the ground.

An important benefit of the invention is that the respective elongate member, provided at each corner of the housing, is fixed between the roof and base in a load-transferring manner. These members are sized so that they can transfer significant loads—a feature which enables containers of a number of similar structures to be stacked one on the other for transport or storage purposes.

The long sides of a conventional shipping container add substantial rigidity to the container particularly between a floor and a roof of the container. In one form of the present invention the material normally used on a side of a shipping container is replaced by the walls referred to. Consequently when that material is removed, the roof, in particular, is not well-supported. The roof can therefore be flimsy and if the container is moved the container can deform. According to one aspect of the invention when the first wall is moved to the storage position referred to it is designed to re-engage, directly or indirectly, with the base and the roof and to provide support for these components so that the container is both firm and rigid enough to be moved, lifted and transported, without fear of deformation.

When the structure is to be used as a reservoir, substantial pressure may be generated by a liquid at a base of each wall. This pressure can distort the wall. To rigidify the wall different bracing mechanisms are employed. One technique makes use of a flap on an inner side, and a flap on an outer side, of the wall, at the base thereof. Each flap is pivoted down to rest on the ground when the wall is erected. Thereafter a fluid-impervious liner is placed over the inner flap, abutting an adjacent wall surface, to form a liquid enclosure. The wall can nonetheless distort due to the force of the liquid. If a solid hinge connection is used between each flap and the wall then the hinge connection could be bent by the force. To address this aspect a steel cable is employed as a hinge pin. The cable bends under load but, when the liquid is emptied from the enclosure, the cable can take up its original shape. Also, to a substantial extent, through appropriate design, the wall and the flaps are not adversely affected and do not bend materially.

Cables or other retention members can be anchored directly or indirectly to lower edges of the walls e.g. via the inner flaps referred to, spanning an area enclosed by the walls in order to brace the walls against liquid forces.

Flexible sheet material can be connected to the walls to make a roof. Preferably this material has a bead along its periphery which is positioned in a shaped, undercut channel retention device. The retention device is effectively permanently attached to the sheet material via the bead. When the roof is erected each retention device is hooked or otherwise easily attached to an upper edge of a wall—in this way a roof can be erected rapidly.

It is possible that the structure will be erected on terrain which is not level and that lower ends of the walls will then not always directly contact the ground. To address this aspect adjustable supports are used. Also, closure members can be used to obscure gaps between the lower horizontal edge of a wall and an opposing ground surface. Each closure member may be attached in a hinged manner to a lower region of a wall. Apart therefrom the closures can be used to brace the walls, particularly if a reservoir is to be made.

In making a shelter, boundary walls may be interconnected by means of partitioning to provide smaller rooms or enclosures inside the boundary walls. Reticulation for communications and electrical and other services may be provided within or on the walls.

Each wall may be made from inner and outer skins with bracing components between. This type of construction is rigid yet light in weight.

The use of the structure of the invention is not limited for it may be adapted to be used as a centre to house electrical equipment, for housing of personnel, to act as a hospital theatre, for food storage or kitchen purposes, or the like. Another application is to attach to the walls a roof of a transparent material so that an underlying volume can be used as a greenhouse. The walls may then also be wholly or partly transparent.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1of the accompanying drawings illustrates a mechanical horse10with a low-bed trailer12which carries a structure14according to the invention. The structure is based on the use of a container16which is substantially the same as a conventional shipping container.

The container16comprises a housing20of parallelepiped form. The container has a longitudinal axis22, a base24, a roof26, first and second sides28and30respectively, first and second ends32and34respectively, and first, second, third and fourth corners36to42respectively—seeFIGS. 2, 3 and 4as well. The corners are respectively located at junctions of the first side and first end, first end and second side, second side and second end, and second end and first side.

At each corner a respective support arrangement44to50is positioned.

Referring to the simplified view shown in plan inFIG. 3the structure includes, adjacent the first side28, first and second walls52and54respectively and third and fourth walls56and58respectively. Each wall is rectangular in outline with opposed lower and upper horizontal edges, and opposed vertical edges.

FIG. 9is an enlarged perspective view illustrating the support arrangement44. In general terms these support arrangements are identical to one another although minor differences are made to facilitate implementation of the principles of the invention.

Each support arrangement includes a respective elongate support member60of substantial dimensions. The support member has an upper end62which is fixed to the roof26and a lower end64which is fixed to the base or floor24of the container. A conventional shipping container has securing lugs or lock blocks66at each of its corners. These are important structural components for they allow the container to be fixed in position on a truck—an aspect which is essential for safe transport of the container. Additionally these lock blocks act as load-bearing and load-transferring elements which allow a number of containers to be stacked one on the other. Again this is an important aspect given the fact that a container, when fully loaded, can have a mass of many tons.

If a conventional shipping container is to be modified to make up the container of the invention (in one embodiment) the resulting container would not include at least one conventional side structure i.e. where the walls52to58are positioned and the container, along this side, would be significantly weakened. It is important therefore that provision should be made to impart rigidity and load-bearing characteristics to the container. The support arrangements are designed to achieve, at least, this purpose. The elongate member60has a substantial load-bearing capability and is positioned, as noted, with opposed ends abutting the upper and lower load-bearing lock blocks66at the respective corner of the container. Secondly, the elongate member is made in the form of a circular shaft so that it can act as a hinge pin for a cylinder and piston arrangement68, and as a hinge pin to the particular wall which is directly connected to it.

The cylinder and piston arrangement68is mounted in a tube70. A number of steel leaves72extend from the tube to the elongate member. These leaves are pivotally connected to the elongate member by respective bushes72A and are rotatable to a limited extent around the elongate member60which acts as a hinge pin. The cylinder and piston arrangement68, mounted inside the tube70, is in the nature of a ram comprising a piston74which extends from a cylinder74A and which is actuable hydraulically so that a lower end74B of the piston can extend downwardly into ground-engaging contact, as is shown inFIG. 2. Each wall has a number of bushes80which are connected in a rotatable manner to the elongate member.

FIG. 3shows the container in plan. The elongate members at the corners of the container are designated, respectively,60A,60B,60C and60D. Each elongate member is within the confines of a boundary line82formed by outer sides and ends of the container, viewed in plan. Thus, the structure of the invention (in a storage mode) does not extend outside the normal dimensional boundaries of a conventional shipping container.

The wall56is connected to the elongate member60A by means of hinge bushes80, as shown inFIG. 9. The wall52is connected to the elongate member60D—this is along what is referred to as an inner vertical edge84of the wall. At an opposed, or outer, vertical edge86, the wall52is connected to a pivotal arrangement87. The second wall54has a first vertical edge88which is connected to the pivotal arrangement87and an opposed second vertical edge90which is anchored in position so that, in the storage mode shown in plan inFIG. 3, the wall54is adjacent and substantially parallel to the wall52and to the longitudinal axis22of the container.

The leaves72which connect the tube70to the respective elongate member have a radial dimension which enables the tube to be moved from the storage position shown inFIG. 3to an operative position shown inFIG. 4. In the storage position the tube is within the dimensional boundaries (82) of the container, viewed in plan. This means that each tube does not interfere with movement, transport and storage of the container. However, when necessary, the tube can be swung to the operative position shown inFIG. 4at which the tube is displaced to be outside the dimensional boundary (82) of the container. At this position the respective ram inside the tube can be actuated so that the lower end74B of the piston inside the tube70can be extended downwardly into ground-engaging contact as shown inFIG. 2.

The wall52is on an “outer” side of the corresponding elongate member60D. This allows the walls52and54to be positioned close to the side28. The wall56is however on what may be referred to as an “inner” side of the corresponding elongate member60A, i.e. it is displaced laterally to one side. This construction allows the walls56and58, which are interconnected by a pivot arrangement94, to be positioned close to, yet adjacent and not interfering in any way with, the walls52and54.

At the elongate member60A, the corresponding tube70A is shown inFIG. 3in a storage position i.e. more or less aligned with the walls52and54. When the tube is moved to an operative position as shown inFIG. 4the tube is moved through about 90° so that it extends radially from the elongate member—note that the opposing tube70D moves through approximately 180° when it is moved between operative and storage positions.

An important aspect of the invention thus lies in the provision of an elongate member (60), at each respective corner of the container, which serves a number of functions. The elongate member acts as a hinge pin for the support arrangement at the corner and as a hinge pin for the respective wall which is attached directly to it. Also the elongate member has sufficient strength so that it can act as a load-transferring member between the roof and base of the container. This last-mentioned feature means that a number of structures, each of which embodies a container of the kind described, can be stacked one above the other for storage or transport purposes.

When the structure is to be deployed the support arrangements44to50are moved so that they are spaced sufficiently far apart, as shown inFIG. 4, so that each respective piston can be extended, hydraulically, into ground-engaging contact. The housing of the container can then be elevated and the low bed trailer, shown inFIG. 1, can be driven away. Thereafter the container can be lowered to rest on the ground. Conversely, when the container is to be removed from a particular site the support arrangements44to50are extended and the low bed trailer is then manoeuvred so that it underlies the container. As the support arrangements are retracted the container housing settles onto the low bed trailer. This arrangement obviates the need for a crane at an installation site, to lift the container off a low bed trailer and subsequently to place the container onto a low bed trailer.

FIG. 5illustrates in perspective the housing20once it has been placed on the ground and the support arrangements44to50have been retracted. The walls52and54are respectively pivoted about the elongate member60D and the pivot connection87into positions at which they extend outwardly from the housing and at which the walls are no longer parallel to one another. Similarly the walls56and58are deployed to radially extending positions. In this arrangement there are four walls on one side of the container. This is illustrative only and non-limiting. For example, an opposing side of the container, viewed in plan, could have, in a similar way, four walls which are radially deployed in opposing directions to what are shown inFIG. 5.

Another possibility is that at one corner of the container two walls could be provided and at an opposing corner a third wall. These walls could then be arranged in a triangular closed configuration.

With the arrangement inFIG. 5the four walls could be brought together to form a five-sided enclosure i.e. with four sides formed by the walls and a fifth side formed by the housing20itself. If multiple containers are used each container could be deployed generally in the manner shown inFIG. 5to achieve different polygonal structures. The invention is thus not limited by the number of sides in a structure which can be erected.

FIG. 6illustrates a situation in which two housings designated20A and20B respectively are positioned opposing each other. Four walls are extended from each housing. Extremities98and98A of the extending sets of walls are connected to each other to form a ten-sided enclosure100.

FIG. 7shows a typical wall102from one side and in cross-section. The wall carries a first strut104in a hinged arrangement which can be pivoted downwardly from the position shown inFIG. 7, to a ground-engaging and bracing position shown inFIG. 8. The strut is located on an outer side102A of the wall102. On an inner side102B close to a lower end of the wall a small flap106is positioned. When the wall is deployed the flap is pivoted downwardly and away from the lower end of the wall into the ground-engaging position shown inFIG. 8. The strut braces the wall against forces which are directed outwardly i.e. from an inner side towards the outer side.

The flap106is one of a number of similar flaps some of which are optionally made from rubber or smooth sheet metal, for example. The flaps extend along the length of the wall so that the flaps can generally follow the contours of the ground on which the wall is located. The wall may not be generally level or flat and the flaps can thus to a substantial extent close gaps which might otherwise exist between a lower end of the wall and the opposing ground surface.

As noted, a conventional shipping container has substantial rigidity. If that type of container is adapted to be used as a container for making a structure according to the present invention, then the wall structure on one side of the container is removed.FIG. 10illustrates from one side a container16according to the invention which includes support arrangements44to50as described. The wall52extends from the end34to the end32over practically the full length of the container. This wall obscures the inner walls54,56and58. The wall52is supported, in this instance, at the left end. If the wall is moved away from between the roof26and the base24then, due to the mass of the structure, the roof and the base can sag down, as shown by arrows106and106A. This aspect can be addressed, in use, by providing a custom-designed brace or braces between the base and the roof. These braces can be positioned at a number of locations as appropriate. Another possibility, in addition to or in place of the aforegoing, is to brace the roof and the base by using guidance brace structure108, notionally indicated only inFIG. 10, at a number of locations along the lower and upper horizontal edges of the wall52or on the roof and floor, or on all three components. When the wall is pivoted to the storage position shown inFIG. 3the structures108are between the wall and the base on the one hand, and between the wall and the roof on the other hand. This positive interaction or engagement of the wall with the base and roof helps to rigidify and stabilise the container, an aspect which is important, particularly if the container is to be transported.

Another feature of the invention is disclosed inFIG. 9.FIG. 9shows that the bushes80which connect the wall56to the elongate member60A are positioned on the elongate member60A above the bushes72A which connect the support arrangement68to the elongate member60A. In fact there is a substantial amount of play110, as high as 150 mm, between these components. Thrust washers112are provided between opposing surfaces of adjacent bushes80and72A. In practice when the support arrangement is actuated the bushes72A move along the elongate member60A and then firmly contact the respective thrust washers112which are driven into tight engagement with undersides of the respective bushes80. The force which is transmitted lifts the walls56and58along the elongate member60A until upper sides of the walls nearly contact an underside of the roof. The full weight of the wall is thereby transferred to the support arrangement and is not carried by the remainder of the container. This allows the walls56and58to be disengaged from the base24and the roof26. The walls can be disengaged from the braces108shown inFIG. 10and can be swung out, as necessary, to deployed positions e.g. as shown inFIG. 5.

The container should be made from a lightweight material such as aluminium. Those portions of the container which are required to exhibit significant load-bearing characteristics i.e. the support arrangements and the elongate members are however made from appropriate steel. In order for the walls, which have substantial longitudinal dimensions, to be rigid yet lightweight, use is preferably made of a double skin structure of the kind shown inFIG. 11. This Figure illustrates part of the wall52in cross-section. The wall has an outer skin52A, an inner skin52B and a number of bracing components52D which are strategically positioned between the inner and outer skins and which are designed to space the skins apart so that a beam-type arrangement results.

When a wall is moved it may be difficult, particularly due to the size of the wall and the terrain on which the container is used, to ascertain whether the wall is correctly orientated. To overcome this aspect level sensors are attached to the wall to provide an indication of whether each wall is horizontally true and vertically positioned, during and after deployment.

FIG. 12shows two walls52,54at a corner of the container16. At an installation site the two walls are initially pivoted jointly outwardly about a vertical axis114which coincides with the longitudinal axis of the respective elongate support member60, at that corner. The walls have substantial dimensions and a reasonable weight and, to assist in this regard, hydraulic cylinders116are actuated to bring wheels118into ground-engaging contact. The wheels provide a means which supports the walls as they are moved to their desired positions.

The cylinders116are controlled, as necessary, using level sensors to provide input signals and, in this way, the walls are correctly orientated, i.e. extending horizontally and vertically, once they are at an installation position.

FIG. 13illustrates a different type of support120which can be used when the wall52is to be pivoted relative to the container. A small trolley124which has spaced sets of wheels126has a locating formation128on an upper surface. When a piston rod130is extended a lower end of the rod is engaged with the locating formation128. Subsequently two stabilisers132,134which may be either rods or cables are connected between respective ends of the trolley and the wall52. This arrangement is capable of taking the load of the wall and additionally helps to restrict flexing of the wall52as it is being moved.

FIGS. 14 and 15show a floor structure136which can be used to cover an area of ground which is enclosed by a number of walls. The floor structure includes a floor panel138which is attached at a longitudinal edge to a respective wall52by means of an appropriate hinge140. At an installation site the floor panel is folded into ground-engaging contact—seeFIG. 15. A number of these structures are used for complete ground coverage.

FIGS. 16 to 19show aspects of a shelter148made from the structure of the invention. A plurality of walls150are erected to form an enclosure on the ground. A mast152, which is tubular, is held in a vertical orientation by means of a number of stay wires154. The mast is centrally positioned within the enclosure formed by the walls. The mast has an upper end156and terminates at a lower end in a hemispherical formation158which is positioned inside a large, upwardly facing, dish-shaped formation160which is at an upper end of a peg162which is embedded in the ground.

A catch164is fixed to the mast near an upper end. The catch is spring-loaded so that it is biased outwardly, away from the mast in the direction of an arrow166. The catch has a downwardly facing inclined surface168and a transverse, flat upper surface170. A flexible lead (not shown), extends inside the mast from the catch to a lever which is near ground level.

A locating member172, seeFIG. 18, is slidably engaged with the mast. The locating member has a sleeve174which bears closely yet slidably against an outer surface of the mast and which thus acts to some extent as a seal. A disc176is attached to the sleeve. The disc includes a number of holes or equivalent anchor formations.

Flexible sheet material180is fixed to the disc and surrounds the mast152. The sheet material has a periphery184which is attached more or less in a leak-proof manner to upper edges of the walls. The sheet material comprises at least two layers of material namely, a relatively large area, upper layer180A, and a smaller area, lower layer180B. The upper layer is fixed to the disc. The lower layer180B is fixed to a ring186which is below the locating member and which is connected to the locating member by means of cables (not shown).

An air blower or fan190optionally forms part of the system. The blower may be fixed to one of the walls150, if required.

When the blower is actuated it introduces air under pressure into a volume192below the sheet material. The air in this volume is contained to a substantial extent and thereby is pressurised, forcing the sheet material to move upwardly. Air can pass through the lower layer180B but not through the upper layer180A which thus rises with its movement being guided by the locating mast152. When the member172strikes the catch164it rides over the inclined surface168. The catch is moved inwardly against the biasing action of the spring which is attached to it. The locating member172, at an uppermost position, comes to rest on the relatively flat surface170of the catch. The layer180A is then suspended from the locating member substantially in the form of a tent and forms a roof over the area enclosed by the walls. The lower layer180B is also elevated by means of the cables to a position at which the lower layer180B acts as a ceiling over the enclosed area.

To the extent which may be necessary air can flow into an interior of the tubular mast or out of the mast through various apertures which are formed through a wall of the mast.

FIG. 18also illustrates a cover200which fits over an upper end of the mast for aesthetic and weather proofing purposes.

When the flexible sheet material is to be lowered the catch164is operated by a cable. The catch is then drawn inwardly and disengages from the locating member172. The sheet material180then settles downwardly under gravity action and air is expelled, as required, through the various apertures upwardly through an interior of the mast to atmosphere.

In a different technique the double layer of sheet material (180A,180B) and the air blower190are not used. A single sheet of material is, instead, raised on the mast to an elevated position using a crank or pulley system.

FIG. 19illustrates an effective way in which the flexible sheet material180can be attached to the walls150. The sheet material180has a cord or rope202enclosed in a seamed peripheral section so that along a periphery204of the sheet material a continuous bead206is formed. Attached to this bead are a number of extrusions208. Each extrusion208has an undercut channel formation210and the bead referred to can be slid into engagement with the channel in a longitudinal direction. The extrusion may be relatively short and a plurality of extrusions may be employed along the periphery of the sheet material. Each extrusion has one or more hook formations212and these are engageable, when required, with corresponding formations at the upper edge of the wall150in order to attach the sheet material to the wall. Once this has been done the sheet material can be elevated either by using air as described or by hoisting a central section of the sheet material upwardly on the mast using a crank, crane or the like. Both techniques can of course be employed.

One application of the structure described, is in the erection of a reservoir. In this instance the walls150are deployed in the manner which has been described and an enclosure is formed. Subsequently the enclosure is lined with a liner220of a stout plastics material, see for exampleFIG. 21. This shows the wall150with the liner220on an area of the ground222which is bounded by a plurality of the walls150. The liner closely abuts an inner surface150A, and extends over an upper end150B, of each wall150.

At a lower end150C of each wall two flaps226,228respectively are used. These flaps serve two functions. Firstly an inner flap226which is pivotally attached to the wall150is movable to seal a gap230between the lower end150C of the wall and the ground222and, in this way, the flap provides support for the liner as it moves from the ground to the wall.

Secondly the flap228which is positioned on an opposing side of the wall is moved downwardly so that a lower end232digs into the ground222and provides support for the wall. It is to be borne in mind in this respect that when a liquid e.g. water242is placed into the reservoir there is a substantial radial outward pressure exerted by the water and the pressure is at its highest at the lower end of each wall. Thus the flap228helps to brace the wall to take this load. Additionally, encircling cables244can be located at spaced locations on an outer surface of the walls. These cables extend circumferentially around the walls and help to brace the walls when the reservoir is filled with water.

The flaps226,228are preferably attached with a hinge connection to a lower end150C of each wall by means of a hinge pin260which is not solid but, instead, is in the form of a steel cable. When the flaps226,228are deployed they lie flat on the ground222, on inner and outer sides of the walls150A. Part of the liner overlies the inner flap. The walls, despite being braced in this way, may still be inclined to bow under liquid pressure. By using a flexible hinge pin i.e. the cable260, the walls are allowed to bow to some extent. The cable nonetheless acts to keep the components together and allows the flaps to brace the walls. If the liquid is removed from the reservoir the cable260, which has not been distorted in any way, simply takes up its original elongate shape. Generally the flaps226,228are not materially affected and the walls have sufficient resilience to take up their substantially planar configurations.

FIG. 22shows a container270from which four articulated walls272,274,276and278are deployed to form a bounded enclosure which is generally in the form of a pentagon. The four walls form four sides of the pentagon and the container forms a fifth side of the pentagon.

Cables280stretch between opposing pairs of walls and are tied, directly, to respective edges of inner flaps226(of the kind described).

Optionally, a cover in the form of a roof, is placed over the reservoir. The cover may be supported by cables or alternatively may have air-filled “bubbles” which allow the cover to float on a liquid which is introduced into the reservoir.