US3033413A - Magnetic seal for floating roof - Google Patents

Description

May 8, 1962 A. F. FINO ET AL 3,033,413

MAGNETIC SEAL FOR FLOATING RooF Filed April 21, 1961 s sheets-sheet. 1

INV EN TOR /amzzaffw ATTORNEYS May 8, 1962 A. F. FlNo ET AL MAGNETIC SEAL FOR FLOATING ROOF 3 Sheets-Sheet- 2 Filed April 2l, 1961 IN VEN TOR` hm/m2105752@ fr* ATTORNEYS May 8, 1962 A. F. FINO ET AL MAGNETIC SEAL FOR FLOATING ROOF 3 Sheets-Sheet 3 Filed April 2l 1961 INVENTOR izda/1f' 15220# ruim ATTORNEYS States 3,033,413 Patented May 8, 1962 fre v 3,033,413 MAGNETIC SEAL FOR FLOATIYG RUF Alexander F. Fino and .lohn M. Swich, Warren, Pa., assigners to Pittshurghnes Moines Steel Company, Pittsburgh, Pa., a corpcration of Pennsylvania Filed Apr. 21, 1961, Ser. No. 104,749 9 Claims. (Cl. 2ML-26) This invention relates in general to floating covers or roofs for tanks and pertains, more particularly, to novel sealing means therefor.

It has been a problem in the art for many years to assure an effective and adequate seal between floating roofs and the tanks within which they are con-lined and which they protectively cover. This is due to many factors, including such Variables as uniformity of the tank Wall structure and weather conditions such as, for example, the presence or absence of ice and snow. lt is, in general, conventional to employ a roof structure which is of smaller diameter than the inside diameter of the tank and to provide extending radially therefrom some generally flexible means which engages the inside of the tank wall to form the proper seal. However, such ilexible sealing means are usually of a fairly complex nature and are generally formed entirely separately from a secondary sealing means normally referred to as a weather shield which tends to deflect water and other precipitation or foreign material centrally towards the physical confines of the roof itself and away from the space between the roof and the tank. Although weather shields may be of a relatively simple construction and design such as will permit their easy removal and inspection, the primary seals which are usually located adjacent the lower edge of the roof are normally of such complexity, size and character as to preclude a ready inspection and removal thereof while the tank is in service.

It is, therefore, of primary concern in conjunctionwith the present invention to provide an improved form of seal for the floating roofs of tanks which will be entirely adequate and effective in service and which, at the same time, is capable of inspection and removal while the tank is in service, these results being achieved by virtue of the use of an improved magnetic means for achieving the sealing effect.

Another object of this invention is to provide an improved seal for the floating roofs of tanks in which the seal assembly is an integrated assembly, including not only a weather shield, but also a primary seal capable of accommodating for variations in the diameter of the tank at various elevations therein and in which there is a peculiar and specific cooperation, hereto-fore unknown, between the primary seal and the weather shield rendering both seals as a unit more effective and adequate.

A further object of this invention is to provide a novel arrangement of component parts for effecting a seal between a floating roof and its associated tank and in which certain flexible elements are so physically associated with each other and with magnetic means as well as a relatively stiff weather shield as to admirably perform a sealing action under any and all conditions and in conjunction therewith, tnere being magnetic anchoring means of a novel form tending to prevent damage to the seal during downward movement of the roof should frozen moisture accumulate between the seal and the tank tending to adhere the two together.

Further, it is an object of this invention to provide a novel seal assembly in lwhich the same may be easily inspected and replaced during the time when the tank is in service.

Further in connection with the instant invention, it is to be understood that existing seal structures normally employ connecting apparatus, clips, springs and so forth which are located in the rim space area and which, as a result, take up a certain amount of physical space therein. This type of connecting means includes some sort of resilient or spring means for urging the conventional seals into engagement with the tank wall, therefore, considerably restricting the amount of physical movement of which the seal is capable. Consequently, under aggravated conditions such as unusual discrepancies in the contour of the tank wall, seals which employ such types of connecting Vapparatus cannot properly and effectively achieve their desired end result since their movement and conforming adjustment do not have a sufficient degree of freedom to enable them to eect the proper seal under aggravated conditions. According to the present invention, however, all connecting apparatus, clips, springs and the like which are usually located vin thev rim space area are eliminated, and the magnetic means of the present invention provides for the automatic adjustment of the seal whereby it may achieve at all times a proper and highly efficient sealing action.

Additionally, the seal in accordance with the present invention is not restricted in physical limits to expansion or contraction and accommodates for variations in distances between the roof and the wall of the tank within those limits which would normally be encountered in service regardless of the degree of variation within such practical limits. The present improved magnetic means will follow the tank wall for all required variations, Whereas with other conventional seals, the conformity thereof with the surface of the tank wall is limited lby the action of the mechanical device exerting an outward or spring force on the seal or by the internal supporting structure of the sealing mechanism.

A further object of the present invention is to provide an improved seal for the floating roofs of tanks in which the seal assembly interposed between the roof and its associated tank embodies in association with inner and outer llexible curtain members, annular bands of magnetic character associated with the inner surfaces of said curtain elements for attraction toward the adjacent tank wall and roof structure to impose compression of the curtain elements against the associated tank wall and roof and wherein additional auxiliary magnetic means are provided for concentrating such pressure of the outer curtain element against the adjacent tank wall along a prescribed annular line.

More particularly the present invention has for its object to provide a new and novel means for supporting magnetic elements along an annular line and against the inner surface of the magnetic band which is disposed l against the inner side of that curtain which lies against the inner surface of the tank outer wall.

The invention arrangement is also highly advantageous due to the novel construction thereof which permits the roof itself to rise above the upper edge of the tank while maintaining an effective seal therewith thereby enabling the utilization of the full storage volume of the'tank. This is accomplished by providing a novel means of suspending the sealing means from the root` whereby the portion of the seal which engages the tank wall when the roof is above the top edge of the tank is effectively supported by a portion of the weather shield of the sealing means.

ln the drawings:

FIG. l is an elevation partly broken away of a storage tank with a floating roof therein showing the improved novel magnetic sealing means operatively associated with the roof of the tank.

IG. 2 is an enlarged perspective broken away view of a portion of the roof and tank illustrating the manner in whichthe sealing means is operatively mounted between 3 the roof and tank wall with the roof structure in a lowered position.

FIG. 3 is another enlarged perspective view partially broken away and corresponding to FIG. 2 but illustrating the roof extending above the upper edge of the tank.

FIG. 4 is a sectional view illustrating a portion of the tank and roof structure with the magnetic sealing means in operative lowered position within the tank.

FIG. 5 is a sectional view corresponding to FIG. 4 but illustrating the roof in position extending above the upper edge of the tank.

FIG. 6 is an enlarged view of a portion of the structure shown in FIG. 4 illustrating the manner of supporting the inner portion of the weather shield.

FIG. 7 is a sectional view showing the position of the sealing means during downward movement of the roof wherein the portion of the sealing means contacting the tank may be frozen or adhered thereto and illustrating the effect of the auxiliary magnetic means coacting with the magnetic band.

FIG. 8 is an enlarged view 0f the lower portion of the sealing means illustrating a modification of the structure.

FIG. 9 is a sectional detail on an enlarged scale showing the attachment of a magnet supporting strap to the bottom portion of the sealing structure.

FIG. 10 is an enlarged sectional detail illustrating the individual magnet supporting pockets carried by the outer curtain.

FIG. 11 is an enlarged perspective corresponding to FIG. 2 and illustrating another means of mounting auxiliary magnetic elements along the inner side of the outer magnetic band.

The present application is based upon our allowed prior application Serial No. 6,764, filed February 4, 1960, and now Patent No. 2,981,436, and FIG. 1 of the drawings illustrates a conventional tank indicated generally by the reference numeral 10, which is adapted to store gasoline, oil and the like, the tank being of conventional construction and including an outwardly extending flange 10' at the upper end thereof defining the upper edge portion of the tank. A floating cover or roof is indicated generally by reference numeral 11, the roof being of substantially circular configuration and having a diameter less than that of the tank, the sealing means of the present invention being adapted to seal the annular space between the :roof and the tank. The roof or cover floats on the upper surface of the tank in a well-known manner, and accordingly rises and falls with the level of the liquid within the tank.

The roof 11 is of relatively simple construction and includes a cylindrical outer wall 12, a lower circular wall 13 being sealingly secured to the lower edge of wall 12, and an upper circular wall 14 being secured to the inner surface of wall 12 at a point spaced below the upper edge thereof. It will be noted that the upper edge of cylindrical wall 12 includes an inturned annular flange 16.

As mentioned previously, the sealing means of the present invention includes a weather shield which slopes upwardly and outwardly of the roof in such a manner as to cause rain water and such to drain toward the center of the roof whereat it is removed from the roof by conventional means (not shown). The sloping weather shield of the present invention is of annular configuration and includes an inner marginal edge 17 and an angularly related intermediate portion 18 which is of relatively stiff construction such that it will remain in the proper operative position as shown in the drawings during operation. An outer marginal edge portion 19 extends integrally from the outer edge of intermediate portion 18, the outer edge portion being considerably more flexible than the intermediate portion 18, and being so constructed and arranged that it inherently tends to flex outwardly due to its natural resilience.

The weather shield is preferably constructed of rubber or similar material and the outer marginal edge portion 19 is preferably provided with more rubber than the intermediate portion 18 to provide the characteristics mentioned above. This natural resilience of portion 19 normally tends to carry the outer edge of the weather shield toward the inner surface of the tank so as to produce a seal with the tank. An annularly extending curtain means provides the primary seal between the roof and the tank, the curtain means including an inner portion 20 having the top edge thereof seated upon the upper edge of flange 16. The curtain means also includes an outer portion 22 disposed adjacent the inner wall of the tank and an intermediate portion 24 extending between the lower parts of portions 2) and 22. As shown, portions 20, 22 and 24 are separate members which are suitably secured to one another, it being evident that the various portions may be formed integral as one sheet, if desired.

As seen most clearly in FIGS. 2, 3 and 6, for example, an annular support strap or restraining flange 28 is provided, member 28 including an inner flange portion 29 and an angularly disposed outer flange portion 31. The inner flange portion 29 of the restraining flange is disposed in overlying relationship to the upper edge 21 of the inner portion of the curtain, and the innermost flange portion 17 of the weather shield is disposed in overlying relationship to inner flange portion 29. The entire assembly including the portions 17, 29, 21 and 16 are maintained in operative position by means of threaded studs 36 which are secured to inturned flange 16, the studs extending up through suitable openings in the various members and through openings in an annular clamping plate 17' disposed in overlying relationship to the inner portion 17 of the weather shield. Suitable nuts 37 are mounted on the upper ends of threaded studs 36 for maintaining the entire assembly in tight sealed relationship.

An upper annular edge portion 22' of the outer portion 22 of the curtain is secured to the flexible outer portion 19 of the weather shield by cementing or the like to support the outer edge of the curtain from the upper edge portion of the weather shield. Preferably, the curtain means including portions 241i, 22 and 24 are formed of synthetic sheet or flexible plastic or like material.

The means of the present application for retaining the inner and outer portions 20 and 22 of the curtain means in sealing contact with the tank and roof comprises magnetic means embodying outer and inner units 23 and 30 respectively.

The cylindrical wall 12 of the roof as well as the wall of the tank are formed of steel or similar metallic material whereby the magnetic units 23 and 30 are continually attracted thereto.

Each of the magnetic means embodying the units 23 and 3) defines an annular band or strip of magnetic material which has a substantial width and is of relatively small thickness as will be seen particularly upon reference to the drawings, each such means extending in the form of the annular strip within the curtain means. Each of the annular strip forming means may comprise a plurality of short sections or short strips placed in end-toend relationship with one another, the inherent magnetic characteristics of the sections maintaining them in such relationship one with the other and in proper operating position. The annular magnetic units may be formed each in a continuous piece or in the short sections referred to of a suitable magnetic roof-like material which, for example, may comprise a product named Denmag made by the Deriman Rubber Company, PD. Box 951, Warren, Ohio.

The magnetic means comprised in the units 23 and 30 may also be formed of annular bands of flexible magnetic material as disclosed in Patent No. 2,627,097 to R. Ellis, issued February 3, 1953, wherein the flexible strips are formed of rubber or similar material having magnctizable particles inherently mixed therein.

The structure thus far described for maintaining the curtain sections 21 and 22 in operative relationship with the roof wall 12 and the tank wall surrounding the roof functions satisfactorily under normal conditions. However, under` certain unusualV operating conditions a higher magnetic attraction is required for penetration through heavy crude residues which may accumulate on the tank wall. Accordingly, a means is provided for augmenting the action of the magnetic material comprised inthe magnetic means described, particularly in the unit 23 thereof.

One such means for augmenting the magnetic action of the band or annular strip embodied in the unit 23 comprises the application to the inner side of the strip or band of a number of permanent magnet supporting pockets in each of which a permanent magnet is placed.

In the structure here illustrated the annular band disposed against the inner side of the outer apron portion 22 has applied thereto two circular rows of pockets 123 which may be formed of suitable rubberized fabric or rubber material vulcanized to the band section and having an open top for the reception of a concentrated magnet body 124 such, for example, as the magnet known as Alnico. As stated, these auxiliary magnet bodies may be arranged in l, 2 or more circular rows on the inner side of the annular strip or band forming a part of the unit 23.

In place of the individual magnet units24 disposed in pockets 123'use may be made of tubular members 125 as shown in FIG. ll disposed against and around the inner surface of the annular band forming a part of the unit 23 and which tubular bodies are iilled with magnetic powder 126 and are secured in place upon the supporting annular band by suitable straps 127 looped over the tubes and attached as by welding or any other suitable manner to vthe supporting band body. y

While the magnet bodies 124 illustrated as disposed in individual pockets, each of which is attached directly to the inner `face of the supporting annular strip, such pockets may be joined to a separate band or ribbon which in turn may be attached to the annular strip of magnetic material.

In assembling the apparatus the inner edge of the inner curtain portion 20 is iirst vclamped in operative position by means of the plate 17 whereupon the magnetic units 23 and 30 are inserted in their operative position whilev holding the upper edge of the portion 22. The two annular magnetic units 23 and 30 will be maintained in their proper operating position by the magnetic attraction between these units and the adjacent walls of the roof and the tank. The upper e-dge portion 22' of the curtain 22 is then cemented in operative position as previously described. The apparatus is then fully assembled for operation and as will be apparent from the foregoing description with the inclusion of the additional magnetic elements 124 or 126 on the inner surface of the outer annular band the outer curtain 22 will be pressed with greater force against the inner surface of the tank wall along two annular paths or lines which the rows of magnets 124 or the magnetized powder carrying tubes 125 dene.

The bottom portion 24 of the curtain structure is preferably provided with a width which, when in the operative position shown, is substantially greater than the normal spacing between the outer portion of the roof and the inner portion of the tank wall. This permits the dimension of the annular space to vary within wide limits thereby compensating for eccentricity of the roof with respect to the tank without pulling the magnetic units 23 or 30 from a point 'adjacent to the associated walls of the roof and the tank secured to the curtain structure entirely around the bottom portionthereof adjacent to the bottom edge of the inner portion 2t) by a plurality of circumferentially spaced straps 25 vulcanized or other- ,wise suitably secured to the bottom portion 24. Each of these strips has a free end to one side of which is attached a pocket 225 in which is placed a permanent magnet such as the Alnico magnet hereinbefore referred to. The pockets containing the magnetsare disposed on the proper side of the strap 25 whereby the magnet can be placed against the bottom wall 13 of the roof structure by drawing the strap down and across the iiange portion 13 of the roof wall 12. These straps and the means for Vattaching. the sa'me to the bottom of the roof serve the purpose hereinafter described. Y

Referring now to FIG. 8 of the drawing, a modification is illustrated wherein like portions yhave been indicated by the same reference numerals primed. The sealing means between the roof wall 12 and the tank wall 10 includes a curtain formed of an inner portion Ztl', an intermediate portion 24 and an outer portion 22a which are supported in the same manner discussed in connection with the aforede'scribecl modification.

Inner and outer sealing means 30" and 23 embodying annular bands are similar to sealing means 30 and 23 respectively as described hereinbefore, the primary distinction of this modification over the previously described modification being the provision of an annular strip of material 4t) which may havea substantially rectangular cross-section as shown and including opposite faces 41 and 42 which are disposed in abutting relationship with the adjacent surfaces of magnetic means 30 and 23 respectively. Body means 40 may be formed of a suitable material such as polyethylene foam and is adapted to serve as a spacer for maintaining the annular bands of the sealing means in the spaced position as shown so that the sealing means wiil be maintained in the operative position shown in FIG. 8 during normal operation of the apparatus.

Y eferring again to FIG. l, the roof is disclosed in its normal operative position wherein the roof is disposed below the upper edge 10' of the tank. In this position, the resiliency of portion 19 of the weather shield urges this outer edge of the weather shield as well as the rcemented portion of the upper part 22' of the curtain against the inner surface of the tank to effect a good seal therewith.v It is evident 'that the resilient outward force of portion 19 tends to take up variations in the space between the roof and the inner wall of the tank. As mentioned previously, it is a particular object of the invention to provide an arrangement which permits maximum utilization of the storage space within the tank itself. This isV accomplished in the present invention due to the fact that magnet unit means 23 comprising the annular band and auxiliary magnet elements will retain the outer portion 22 of the curtainin sealing engagement with the wall of the 'tank even when the roof has moved a substantial distance above the upper edge of the tank as illustrated for example in FIGS. 3 and 5. This mode of operation is possible due to the novel manner of suspending the outer portion of the curtain from the outer edge of the weather shield. The weather shield although being of relatively flexible construction is enabled to support the curtain seal in operative position due to the fact that the intermediate portion 18 thereof is of relatively stiff construction, vthe stiffness of the intermediate portion 18 being enhanced by the provision of reinforcing ribs R as seen most clearly in FIGS. 2 and 3, which extend outwardly of the roof along the major' part of intermediate portion 18 of the washer shield, the ribs R being located at spaced circumferential points along the weather shield. Ribs R may comprise a suitable rigid means such as metallic strips or bars which are suitably secured to the material vof intermediate portion 18 of the weather shield. Injaddition, the outer flange portion 31 of restraining flange 2.8k further supports the inner 'part of intermediate portion 18 togensure Vthat it remains in the upright position lillustrated in FIGS. 3 and 5 when the roof rises above the upper edge of the tank. It will be observed that when the tank is in such elevated position, the outermost portionV 19 of the weather shield bows outwardly due to its natural resilience.

As seen most clearly in FIGS. 2 and 4, whenthe sealing means is in normal operation, the lower part of the outer curtain. portion 22 will be urged into sealing engagement with thejwall of the tank by the magnetic unit means 23 embodying the annular outer` band and the additional magnetic elements 124 or 125 and the upper 47 part of the outer portion 22 will normally hang in the position shown such that it is spaced a small distance from the inner wall of the tank, this space being indicated by letter S.

During downward movement of the roof as, for example, as shown in FIG. 7, there will be a tendency for the roof to move first without imparting a corresponding movement of the outer curtain portion 22 and this can occur to varying degrees depending upon conditions until such a situation as is specifically shown in FIG. 7 occurs. In FIG. 7, the roof has moved downwardly a suflicient extent to impart substantially a taut condition to the bottom portion 24 of the curtain which tends to pick the lower extremity of the outer curtain portion 22 away from the surface of the tank as indicated by the reference character 35. At the same time, as soon as the bottom portion 24 is fully tensioned, a further and further peeling action of the curtain 22 will occur until the entire curtain may become tensioned. This is particularly advantageous should the outer curtain become frozen to the tank as can sometimes occur in cold weather. In this case, the sealing action shown in its initial stages in FIG. 7, will very advantageously separate the outer curtain from the tank without imparting undue strain thereto such as might otherwise occur were not the peeling action present.

On the other hand, during downward movement of the deck or roof, it will be appreciated that the relatively stiff weather shield 18 will move downwardly relatively quickly and substantially instantaneously as the deck or roof moves down. Should, however, the weather shield be frozen to the tank, the weight of the roof will positively peel the weather shield away from the tank wall and a continued peeling action will also occur as the roof drops further.

This continued peeling action by the weather shield will pull that part of the curtain portion 22 which is above magnet unit means 23 away from the wall of the tank. The magnetic unit means 23 has sufllcient weight so that it always tends to slide down along the tank shell and accordingly, the adjacent area of the outer curtain portion 22 will tend to pull away from the tank wall. It will be evident that when it is desired to inspect the seal structure, a person can reach down through the space between the roof and the tank to detach the magnets 226 carried by the straps 25 from the bottom of the tank. The entire curtain structure may then be pulled up out of the annular space between the roof and the tank for inspection and for removal or replacement, if necessary.

It is apparent that there is provided according to the present invention a new and novel magnetic sealing means for floating roofs wherein the sealing means includes a flexible weather shield and a highly flexible curtain means which is maintained in sealing relationship with the walls of the roof and tank by novel magnetic means. The sealing means is free to flex or be tensioned under different conditions depending on the direction of movement of the roof, and regardless of the relative positions of the members, an effective seal is maintained between the roof and tank at all times. The construction permits the roof to rise a substantial distance above the upper edge of the tank thereby providing a maximum utilization of the storage space within the tank and at the same time an effective seal is maintained with the tank.

It will also be seen from the foregoing description that the mounting upon the inner surface of the band unit 23, of additional magnetic means either in the form of the individual strong magnets 124 arranged in the circular order described or the tubular bodies 125 filled with magnetic material, will augment the magnetic action of the annular band so that along the circular path where this additional magnetic means is placed the outer curtain 22 will be pressed with increased force against the tank wall. This additional pressure or force applied to the curtain against the outer wall of the tank, augmenting the pressure of the annular band will result in the maintenance of the desired contact between the curtain and the tank wall under those conditions where heavy crude residues may accumulate on the tank wall or tank sill.

The apparatus of the present invention is relatively simple and economical in construction, and yet is effective and reliable in operation.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, and since the scope of the invention is defined by the appended claims, all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents are therefore intended to be embraced by those claims.

We claim:

l. A seal for a floating roof tank in which a generally cylindrical tank is provided with a cylindrical floating roof therewithin of a diameter less than the inside diameter of the tank, the seal comprising an annular relatively stiff weather shield flexibly connected at its inner marginal edge to the roof structure and having a flexible marginal outer edge for sealing engagement against the inner surface of the tank, an outer curtain of flexible material in the form of an annular band secured along its upper marginal edge adjacent the outer marginal edge of said weather shield and hanging therefrom in close proximity to the inner surface of the tank, magnetic means carried by said outer curtain along the lower marginal edge thereof attracting the curtain toward the inner surface of said tank, an inner curtain in the form of an annular band of flexible material secured along its upper marginal edge to the roof structure and hanging therefrom from a point adjacent the point of attachment between the inner marginal edge of the weather shield and the roof, magnetic means carried by the lower marginal edge portion of said inner curtain attracting the same toward said roof structure, a flexible bottom sheet in the form of a generally horizontal annulus having its inner and outer edges secured respectively to the inner and outer curtains, strap means secured to and hanging from the lower marginal edge of said inner curtain, there being a permanent magnet carried by each strap means adapted to secure the strap means to the underside of the roof.

2. In a liquid storage tank having a cylindrical outer wall and a cylindrical floating roof therewithin with there being an annular space between the roof and the inner surface of said wall, a seal assembly carried by said roof and engageable with the inner surface of said outer wall, said seal including a weather shield extending upwardl and outwardly from the periphery of said roof for contact along its outer edge with the inner surface of said outer wall, inner and outer flexible curtain members attached adjacent the inner and outer edges respectively of said weather shield and hanging therefrom respectively along the outer surface of said roof and the inner surface of said outer wall, a flexible bottom sheet interconnecting said curtains along the lower edges thereof, magnetic band means disposed against and carried by said curtains adjacent to the lower edges thereof for holding the latter in engagement respectively with said roof and said inn'er surface of the outer wall, and auxiliary magnetic units carried by that magnetic band means which is attached to the outer flexible curtain member, said auxiliary magnetic units being positioned upon the side of the said carrying means remote from the outer wall.

3. In a liquid storage tank having a cylindrical outer wall and a cylindrical floating roof therewithin with 'there being an annular space between the roof and the inner surface of said wall, a seal assembly carried by said roof and engageable with the inner surface of said outer wall, said seal including a weather shield extending upwardly and outwardly from the periphery of said roof for contact along its outer edge with the inner surface of said outer wall, inner and outer flexible curtain members attached adjacent the inner and outer edges respectively of said weather shield and hanging therefrom respectively along the outer surface of said roof and the inner surface of said outer wall, a flexible bottom sheet interconnecting said curtains along thel lower edges thereof, magnetic means attached to the lower edges of said curtains for holding the same in contact respectivelyl with said roof and the inner surface of said outer wall, said magnetic means being in the form of annular bands of rubber having magnetic particles embedded therein, and auxiliary magnetic units secured to that band which is attached to the curtain having contact with said outer wall, said auxiliary magnetic units being on the side of the latter band remote from the outer wall and functioning to augment the magnetic action of the band to increase the pressure along a relatively narrow line with which the curtain is held in contact with the outer wall.

4. In a liquid storage tank having a cylindrical outer Wall and a cylindrical floatingiroof therewithin with there being an annular space between the roof and the inner surface of said wall, a seal assembly carried by said roof and engageable with the inner surface of said outer wall, said seal including a weather shield extending upwardly and outwardly from the periphery of said roof for contact along its outer edge with the inner surface of said outer wall, inner and outer iexible curtain members attached adjacent the inner and outer edges respectively of said weather shield and hanging therefrom respectively along the outer surface of said roof and the inner surface of said outer wall, a flexible bottom sheet interconnecting said curtains along the lower edges thereof, magnetic means attached to the lower edges of said curtains for holding the same in contact respectively with said roof and the inner surface f said outer wall, a plurality of straps lixed to the lower edge of said inner curtain and depending therefrom, and a permanent magnet unit carried by and at the end of each strap for connection by magnetic attraction with and to secure the strap to the roof.

5. In a liquid storage tank having a cylindrical outer wall and a cylindrical floating roof therewithin with there being an annular space between the roof and the inner surface of said wall, a seal assembly carried lby said roof and engageable with the inner surface of said outer wall, said seal including a weather shield extending upwardly and outwardly from the periphery of said roof for contact along its outer edge with the inner surface of said outer wall, inner and outer flexible curtain members attached adjacent the inner and outer edges respectively of said weather shield and hanging therefrom respectively along the outer surface of said roof and the inner surface of said outer wall, a flexible bottom sheet interconnecting said curtains along the lower edges thereof, magnetic means attached to the lower edges of said curtains for holding the same in contact respectively with said roof and the inner surface of said outer wall, said weather shield having a ilexible inner marginal edge portion fixed to said roof, a stiff intermediate portion and terminating at its outer marginal edge in a iiexible portion for deformed engagement with the inner surface of said outer wall, a supporting strap having a rigid annular inner por- 10 tion fixed to said roof underlying said inner marginal edge portion of the weather shield and having a rigid upwardly and outwardly directed outer edge portion underlying a portion of said intermediate portion of thev weather shield to support the same when its outer marginal edge portion is out of contact with said outer Wall, a plurality of straps fixed to the lower edge of said inner curtain and depending therefrom, means forming a pocket at the terminus of each strap, and a permanent magnet in each pocket for magnetically connecting the strap to said roof.

6. In combination, a substantially cylindrical tank, a substantially cylindrical floating roof disposed in said tank and having an outer diameter less than the inner diameter of said tank, and sealing means disposed between said roof and said tank, said sealing means comprising an annular weather shield means secured to the upper portion o-f said roof and extending upwardly and outwardly with respect to said roof for engagement with the inner surface of said tank and being of a relatively stiff material, curtain means supported by said roof and including a first inner portion, the inner portion being supported at the upper outer edge portion of the roof and depending adjacent to the outer surface of the roof, said curtain means including `an outer portion supported on the upper outer edge portion of said weather shield and depending adjacent the inner surface of said tank, said inner and outer portions being joined by an intermediate portion, and magnetic means associated with said inner portion and said outer portion for retaining said inner and outer portions in contact with the outer surface of said roof and the inner surface of said tank respectively, said magnetic means including a first substantially annularly extending body of magnetic material having a substantial width and a relatively small thickness, said first body of magnetic material engaging the inner surface of said outer portion, said magnetic means also including a second substantially annularly extending body of magnetic material disposed in engagement with the surface of said inner portion which is opposite to the sur-face thereof in engagement with the outer surface of said roof, and auxiliary magnetic means supported upon the inner side of said first body along a relatively narrow line between the edges thereof for augmenting the pressure along such line with which the curtain means inner portion is held against the inner surface of the tank.

7. The invention according to claim 6, wherein the said auxiliary magnetic means comprises a plurality of strong permanent magnets.

8. The invention according to claim 6, wherein said auxiliary magnetic means comprises a tubular body lled with magnetic material.

9. The invention according to claim 6, wherein saidauxiliary magnetic means comprises a plurality of strong magnetic members and the support for said magnetic members comprises upwardly opening pockets secured to the said lirst body whereby said magnetic members may be readily placed in operative position upon and removed -from said rst body.

No references cited-

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