US2437125A - Floating roof for tanks - Google Patents

Description

March 2, 1948'.

F. 1.. PLUMMER FLOATING ROOF FOR TANKS Filed Sept. 9, 1944 s Sheets-Sheet 1 INVENTOR: FRED L. PLUMMER,

ATTORNEY "March2,1948 FLL, -M E 2,437,125

FLOATING ROOF FOR TANKS Filedssept. 9, 1944 5 Sheets-Sheet 2 I I INVENTOR: FRED L. PLUMMER,

ATTORNEY March 2, 1948.

F. L. PLUMMER FLOATING ROOF FOR TANKS Filed Sept. 9, 1944 3 Sheets-Sheet 3 ,INVENTOR:

FRED L PLUMMER,

ATTORNEY Patented Mar. 2, 1948 FLOATING ROOF FOR TANKS Fred L. Plummer, Warren,

mond Iron Works, Warren,

of Pennsylvania Pa., assignor to Ham- Pa., a corporation Application September 9, 1944, Serial No. 553,348

2 Claims.

This invention relates to storage tanks for liquids, for example oil storage tanks, requiring a roof, or top, or cover structure capable of moving piston-like up or down within the tank in accordance with changes of volume of the tank content and having sealing relationship with the tank wall.

More particularly, this invention relates to improvements in tanks having a pontoon-supported roof structure adapted normally to float upon the liquid in the tank by reason of the buoyancy of the pontoon bodies which are connected with or constitute part of the roof structure. The improvements according to this invention lie mainly in the provision of novel means for sealing the roof structure during its up and down movement against the inner side of the tank wall, although accessory features are also in' cluded in an example or the invention. Therefore, it is among the objects of this invention to provide sealing means which are non-binding and yet effective, which are adapted to compensate for structural inaccuracies of the roof structure relative to the tank, and which are of great durability.

These objects are attained by providing sealing means in the form of a ring-like structure which may be roughly likened to a piston ring in that it may expand in establishing sealing relationship between the tank wall and the roof structure. The ring-like structure is loosely eonfined in an annular space provided by and between the inner face of the tank wall and the roof structure. The ring-like structure is expansible by reason of being subdivided into sector-like blocks which will herein be termed the sealing blocks. The blocks are of buoyant material and normally sufficiently immersed in the 2 or members have sealing contact with an inverted conical portion unitary with the roof structure, whereby buoyancy is caused to urge the blocks outwardly into sealing contact with the tank wall.

According to another feature, the sealing blocks are of a high buoyancy material provided liquid in the tank and otherwise so disposed relative to associated structure that buoyancy urges them upwardly and outwardly into sealing engagement with both the tank wall and the roof structure. The deformation thus attainable of the ring structure as a whole helps to maintain an efiective seal without imposing undue friction or wear and tear upon the sliding members.

According to one feature the sealing blocks or component members of the sealing ring join or engage one another loosely butt-wise by way of an overlap allowing for a degree of individual and substantially horizontal compensatory motion of each block. I The overlap functions to prevent any appreciable escape or the gas-or vapor from the tank.

According to another feature the sealing blocks with wearing strips which present sealing faces for sliding contact with the inverted conical face of the roof structure and the inner face of the tank respectively.

According to another feature, the sealing blocks comprise a high buoyancy material having air bubbles occluded in it, such as foam glass. More specifically, a block of such buoyant material is provided with wearing strips. This material may be physically defined as a highly buoyant glass material deriving its buoyancy from innumerable shut-in minute air bubbles constituting a rigidified foam-like mass.

The best embodiment nowknown to me is illustrated in the accompanying drawings; but their showing and the description thereof should be taken as illustrative and not restrictive for, obviously, the invention lends itself to other embodiments and manifestations, as well as to modified details of construction.

In the drawings: Fig. 1 is a plan view upon the tank and the roof structure thereof. Fig. 2 is a part-sectional side view of Fig. 1 showing the roof construction including the arrangement of the sealing means and the resiliently yielding guide rollers. Fig. 3 is an enlarged detail view taken from Fig. 2 showing particularly and more clearly the sealing means and the guide roller arrangement. Figs. 4, 5 and 6 are further enlarged detail views showing structural details of the guide roller mounting. Fig. 7 is an enlarged plan view of a marginal portion of the tank shown in Fig. 1 with parts broken away to show the disposition of the sealing blocks, and Fig. 8 is a detail view in perspective of an individual sealing block.

There is herein shown an oil storage tank ID of round shape, having a bottom H and a cylindrical wall l2. The roof structure 13 is movable up and down within the tank and comprises a horizontal cover portion or plate 14 shown to be formed with a shallow central depression I5. Fixed to the underside of the cover plate M are pontoon bodies It by virtue of which th cover plate I4 may float upon the liquid in the tank. Extending fixedly along the margin of cover plate It is a depending annular plate or skirt portion l1 presenting outwardly an inverted frust-o-conical face 18. The skirt portion I1 is shown to be fixed or Welded to the cover plate It through an annular member l8 of angular profile. Further down from the frusto-conical skirt portion I! extend strips 19 of flat stock bent to form an inclined portion 20, a vertical portion 2| and the horizontal portion 22. lhe strips together with the skirt portion l1 and the tank wall define an annular space or cage "8 within which are loosely confined sealing means or a sectionalized sealing ring 23 presently to be described.

The sectionalized sealing ring 23 comprises or is composed of individual sector blocks '24 herein also called the sealing blocks. These blocks are shown to comprise mainly a body 25 of hi hly buoyant material, for example, a material in the nature of foam glass which derives its high buoyancy from the many air spaces or bubbles occluded in it. In the example shown the body 25 has a top face 26, an outer vertical face 27, a horizontal bottom face 28, a vertical inner face 29, and a frusto-conical face (it which corresponds to or is complementary to the frusto-con ical face l8 of the skirt portion ii. The faces 2?, 28, 29 and 33 are protected by wearing strips 21 28 29 and 39 nailed or otherwise suitably fastened to the body 25.

The blocks 24 join one another endwise in loose fashion by way of an overlapping engagement or overlap which is more clearly recognizable from Figs. 7 and 8; that is to say, each block 24 is shaped at one end with a lower overlap portion 3! and at the other end with an upperoverlap portion 32, the one being in fact complementary to the other.

The sealing blocks 24 must be sufiioiently immersed in the liquid in the tank so that buoyancy will produce adequate sealing pressure between the sealing faces of the blocks and the corresponding faces of the roof structure and of the tank wall respectively. The degree of immersion is indicated in Fig. 3 by the dot-and-dash line L designating the level of the liquid in the tank. Between the level L and the cover plate M is a space Q which maybe occupied by vapors forming due 'to the vaporizing of the liquid or of volatile constituents thereof such as the volatile constituents in oil that may be stored in the tank.

Liquid-sealed venting devices 33 are shown to be provided upon and fixed to the underside of the cover plate hi, which devices also function as syphon drains for rain water collecting on the roof, in the depression l thereof. Adevice 33 comprises a depending pipe 3 3 and a sealing tray or pan or open container 35 surrounding the lower end portion of the vent pipe 313 and having fixed relationship thereto. These devices as of which four are herein shown, are shown to be disposed at the lowest point of the shallow depression it of thecover plate Hi. The pipe 365- and pan are filled with water which may stand at an elevation of say five or six inches below the cover plate M since the liquid or oil stored in the tank has a lower specific gravity than the collected water. Thus when rain water falls on the roof 53 it flows to the low spots, that is to the devices 33 and then through the pipe to the pan and over the edges of the pan through the body of oil in the tank to the bottom of the tank whence it can be drained off or removed insoine suitable manner. The device 33 prevents the evaporation of the lighter than water liquid from the tank since the area vof the pan 35 presenting awater well for the pipe 34 is sufiiciently large so that water can evaporate from the pipe over a considerable period without any of the storage liquid such as oil from the tank entering the pipe; in other Words, the water in the pan thus acts as a seal against the oil rising into the pipe 34. The device 33 also has the advantage that the water in the pipe 36 stands several inches below the level of the roof plate l5, and, therefore, will not flow out onto the roof if for any reason such as additional weight on the roof, the roof with its pontoons should ride deeper in the stored liquid in the tank.

The roof structure is substantially centered relative to the surrounding tank wall by means of guide rolleri'units 36. As shown in Figs. 3, 4, 5 and 6, such a guide roller unit comprises a guide roller 3] engaging the tank wall l2 and mounted forrotation about a horizontal axis on a plunger member 33 which in turn is horizontally slidable in a cylindrical member or housing 39 extending horizontally and radially with respect to the tank wall. The plunger member 33 consists of a plunger head or plate 4! and a pair of parallel arms di and 42 extending from the plunger head to and carrying between them the guide roller 3?. The housing 353 comprises a cylindrical body portion 43, and a front end plate 44 having a square opening d5 bearing such relationship to the arms ii and 42 as to prevent undesired rotation of the plunger member 38.

The rear end of the cylindrical body portion 53 is closed by a screw cap member 46 into which is threaded a screw bolt ll secured in an adjusted position by a lock nut 48. Within the cylindrical housing 39 to screw bolt il engages a plate 49, the position of which can be adjusted by the adjustment of the screw bolt 4?. A compression coil spring 58 is provided within the housing 39 and confined between the adjustable plate :38 and the plate 46 of the plunger member 38. ihe housing 39 is fixed to the cover plate M as indicated by the front end plate 44 as well as a supporting brace portion 5! being welded to the cover plate M.

In order to protect the sealing means against the weather, that is from immediate contact with snow and rain, there are provided shielding members 52 winch are pivoted as at 53 upon the cover plate M. Openings 54 are provided in some of the shielding members to accommodate the guide roller units 36.

Vertically adjustable brace members 55 are shown to penetrate some of the pontoon bodies 16. allowing the roof structure tobe stopped at a lower limit of its downward movement, as the free lower end of the brace members 55 engage and come to rest upon corresponding abutments 55 rising from the bottom of the tank. When the tank top is thus resting upon supporting members 56 after the liquid has been drained from the tank the sealing members 25 will no longer be supported by a buoyant force due to the absence'of the liquid. They will however be positioned so as to enable them to resume their sealing relationship with the adjoining structural parts due to, the fact that they will'not drop to the bottom of the tank but will be intercepted 4 by and rest upon the lower free end portion 22 or on the strips it. These strips I 9 in efiect form a cage surrounding the inherent! bottom portions of the sealing elements constituting the sealin ring. Near the bottom the tank wall is shown to be provided with an opening 5'! for .7 access, comprising a short neck 53 having a flange 58 closed by a removable plate 59.

Iclaim:

1. A circular storage tank for holding a body of liquid, provided with a pontoon-supported roof structure adapted to float on the liquid in the tank at substantially the liquid-level in the tank and vertically-movable as that liquid-level fluctuates, an inverted conical skirt portion fixed to the roof and lying between the pontoons of the roof and the tank wall while extending from above the tanks liquid-level to below that level, spring pressed means for centering the roof in the tank, a freely floating sectionalized ring unconnected to either tank or roof and greater in width than the distance between the roof top and the tank wall so that the roof and ring are in overlapping relationship with the top of the ring being below the top of the roof whereby the ring has the sole function of sealing the space between tank wall and roof when there is liquid in the tank; said ring comprising buoyant sector blocks adapted to engage one another endwise to provide for substantially horizontal compensatory play therebetween, each block having an inner face complementary to the outer conical face of the skirt portion and having an outer face complementary to the wall of the tank, a representative specimen of said block being of a highly buoyant glass material deriving its buoyancy from innumerable shut-in minute air-bub bles constituting a rigidified ioamlike mass which is non-absorbent, non-corroding, non-puncturable, chemically inert, and non-sinkable, as well as impervious to liquid and gas, such block being urged upwardly by vertical buoyant force of such magnitude as to insure lateralforce components to exert a desired degree of self-sufficient sealing pressure with respect to said skirt portion and the tank wall respectively, and wearing strips on the blocks to engage slidably the respective complementary faces of the skirt and the tank wall.

2. A circular storage tank for holding a body of liquid, a pontoon-supported roof structure therefor adapted to float on the liquid in the tank at substantially the liquid-level thereof and vertically movable as that liquid-level fluctuates, an inverted conical skirt portion fixed to the roof and lying between the pontoons of the roof and the tank wall while extending from ring being below the above the tank's liquid-level to below that level, spring-pressed means for centering the roof in the tank, a freely floating sectionalized ring unconnected to either tank or root and greater in width than the distance between the roof top and the tank wall so that the tank and ring are inoverlapping relationship with the top of the top of the roof whereby the ring has the sole function of sealing the space between tank wall and roof when there is liquid in the tank, supports extending upwardly from the tank bottom for supporting the roof above the tank bottom when there is insufficient liquid in the tank to float the roof, and means depending from the skirt portion forming collectively a cage about the ring the lower tree extremity of which cage extending outwardly underneath the ring provides a limit defining a lower non-sealing position of the ring when the roof rests on said supports.

FRED L. PLUMMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Foamglass-Advertising leaflet published by Pittsburgh Corning Corp., May 1942. (Copy available in Div, 5).

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