CA1069269A - Method of tensioning a floating cover for a liquid reservoir - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

This invention relates to a method on tensioning a flexible floating cover for a liquid storage reservoir wherein the surface level of the stored liquid varies. A peripheral envelope formed at least adjacent a portion of the peripheral edges of the floatable cover is adapted to be inflated with a compressible fluid, such as air, for proper tensioning of the cover as the level of the stored liquid varies in the reservoir and for preventing wrinkling of the cover.

Description

~69269 1 This application is a divisional of application 284,637 filed August 9, 1977.
Back~round of the Invention The present invention relates generally to floating covers, particularly of the type to be used over large reservoirs, and more particulary to a method of tensioning the floating covers.
Floating covers for contained fluids, generally speaking, are well known in the prior art. Some of this art is directed towards fluids contained within a tank or vessel rather than a fluid to be contained in a reservoir. Numerous patents such as United States Patent Nos. 3,228,702; 1,775,758; 1,712,321;
3,343,708; 3,016,814 are directed towards providing seals for floating coverings that engage the sides of a suitable tank.
Similarly, United States Patent Nos. 3,159,301 and 3,557,994 are directed towards floating diaphragms adapted to be used in various pressure tanks. Other non-floating types of diaphragm covers for tanks are disclosed in United States Patent Nos. 1,917,623 and 3,028,040. However, all of such prior art is directed towards floating structures that are contained within a substantially en-closed housing such as a tank or vessel. Such floating covers arenot exposed to the adverse environmental conditions such as wind, ice and water accumulations on the surface thereof as well as the problems incumbent in providing floating structures for large expansive reservoirs rather than comparatively small storage tanks. ~
Floating covers, such as disclosed in United States ~ ;
Patent Nos. 3,462,040; 3,592,009; and, 3,740,902, have long been in use. However, a recurring problem that has plagued reservoir covers of the prior art is how to control the tension of the floating cover on the fluid while accommodating fluid elevational changes in a reservoir having sloping or tapered surfaces adjacent reservoir perip]heries. In United States Patent Nos. 2,986,302 and 3,079,030, movable segmented sections are used to support the .~.
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, ~L~G9;~69 1 floatin~ cover as the fluid level experiences elevational variations. United States Patent 3,330,11~ discloses the use of a plurality of circular floaters for suppor~ing the cover of a sun~en tank as the fluid varies in elevation while U.S. Patent No. 2,970,716 uses multiple sections in combination with pontoons to support the floating roof for an oil storage reservoir.
United States Patent No. 3,815,367 discloses the use of a complex tensioning line-arrangement for providing for the proper tension of a floating cover assembly for a reservoir to insure tO biasing thereof. Further, the present inventor disclosed in United States Patent Nos. 3,313,443 and 3,667,641 floating cover arrangements which provide for a variety of drain configurations to prevent unwanted accumulation of liquid on the upper surface of such a li~uid storage reservoir cover in an effort to prevent damage due to the weight of unwanted liquid on the upper surface of the cover and/or the detrimental environmental effects due to freezing and the like. Further, ~nited States Patent No.
3,736,754 discloses a combination two-cover assembly wherein one cover is used to float on the surface of the stored liquid while another roof is inflated thereover for protection of the floating roof. This dual roof assembly not only is expensive but requires maintenance on both the floating cover as well as the inflatable roof.
Not only is it important that a floating cover have the proper tension thereon to prevent damage thereto as a result of high wind and/or water accumulations thereon, but also it is important to provide for ease in reservoir maintenance thereof without necessitating removal of the cover. Typically, prior art repairs and other reservoir maintenance was accomplished by divers submerged in the reservoir fluid below the reservoir cover.
However, no provisions are made in the prior art for providing an ~
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1 effective system for maintenance and repair of both the floating cover as well as the storage reservoir in combination with means for compensating for elevational cha.nges of the fluid within the reservoir while providing the necessary tension on the reservoir cover.
Also, in the prior art, fle:xible and/or inflatable structures have been used for a wide variety of applications which include use in a variety of shelter or building configurations such as those disclosed in United States Patent Nos. 3,924,363; 3,626,836; .
and, 3,885,360 as well as an inflatable covering for swimming pools as disclosed in United States Patent No. 3,918,221 and collapsible dams and damming methods as disclosed in United States - Patent ~o. 3,834,167.
Although these relate generally to inflatable structures, these are of little consequence in considering the requirements that must be met by a reservoir cover that must not only float on .
; the surface of the reservoir fluid having a required tensioning - :
. thereof ~ut also have appropriate provisions for ease in reservoir or cover maintenance. ~ :
. Summary of the Invention .
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In one of its aspects the present lnvention provides a method for tensioning a flexible floating cover for a liquid storage reservoir where the surface level of the stored liquid . .
varies relative to the berm of the reservoir to substantially eliminate wrinkling of the flexible cover, comprising the steps . :.
of disposing a sheet of flexible, floatable material on the liquid stored in the reservoir with the sheet having a marginal edge having envelope means attached to said marginal edge, means .:^

for securing said envelope means to the berm of said reservoir, inflating the envelope means with a regulated amount of compressible fluid to tension the sheet to prevent the formation of wrinkles 1 ~ .. .
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1 in the floating sheet as the level of the stored liquid in the reservoir varies relative to the berm oE the reservoir.

Brief Description of the Drawings Fig. 1 is an isometric view of the floating cover assembly;
Fig. 2 is an isometric, sectional view of the sheet adapted to float on the surface of the stored liquid of the liquid storage reservoir, o~ the floating cover assembly;

Fig. 3 is a schematic elevational view of the liquid storage reservoir having the floating cover assembly for maintenance of the sheet and/or reservoir; -Fig. 4 is an elevational view of the floating cover assembly showing ballasting of the sheet during maintenance operations;

Fig. 5 is an elevational view of the floating cover assembly, showing tensioning of the sheet to eliminate formation of wrinkles in the sheet when floating on the surface of the level-varying liquid stored in the reservoir;
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Fig. 6 is a sectional side view of the floating cover assembly having a center ballasted pneumatic support column;

Fig. 7 is a view similar to Fig. 6 and illustrating a plurality of ballasted pneumatic support columns;

Fig. 8 is a sectional side view of the ballasted pneumatic support column;

Fig. ~ is an isometric view of the floating cover in the inflated cc,ndition;

; Fig. 10 is a sectional side view of a drain sump of the floating cover; and ' .

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: -9;~69 1 Fig. 11 is a sectional side view of another form of drain sump.
Description o~ the Praferred Embodiment Referring to the drawings, the letter C designates thefloating cover assembly. The floating cover assembly C includes a sheet S adapted to be secured to a reservoir R by securing means M with the sheet S having envelope means E formed therewith for covering the liquid storage reservoir R.
The floating cover assembly C is adapted to be used in conjunction with a liquid storage reservoir R. Such liquid storage reservoirs R are well known in the art and may be of a variety of sizes and shapes as well as types of construction.
As shown shchematically in Fig. 3, the reservoir R may be formed of an excavated portion of a tract of land such that the reservoir R includes a reservoir floor 10, side walls 12 and berm 14.
Although the side walls 12 are illustrated as being inclined,they .:
may be arranged vertically or otherwise formed as desired. The reservoir floor 10, side walls 12 and berm 14 may be formed of :. . .
earth as shown in Fig. 3 or may have concrete wrappers lOa, 12a, 20 14a, respectively (Figs. 4, 5). Alternatively, the wrappers `~

` lOa, 12a, 14a may be of metal or any other suitable material.
The reservoir floor 10 will ordinarily be flat as shown in Fig. 3 and additionally, the inner surface of the reservoir may be lined ;
with suitable fluid-impervious material such as a liner (not shown) formed of a flexible sheet material such as a rubber-coated fabric, multi-ply butyl rubber, nylon, polyvinyl chloride, or the like.
The liqu:id L to be stored in the liquid storage reservoir R may bls supplied to and withdrawn from the reservoir R by any suitable or conventional means (not shown) and will normally be maintained at a predetermined level no greater than ,~

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~6~6~2~9 1 the maximum level 16 (Fig. 3~. The predetermined level may vary as described more fully hereinbelow. Such normal level variations will,of course, be determined by the anticipated supply and re-moval of the stored liquid L for whi.ch the reservoir R is pro-vided and may differ in every installation.
The cover assembly C of the present invention includes a sheet S. The sheet S is preferably formed of a flexible material which is impervious to the stored liquid L and will not be attacked by nor deteriorate in the presence of the stored liquid L in the reservoir R. Further, it is desired that the sheet S be adapted to ~ -float on the surface of the stored liquid L. Preferably, the sheet S may be formed of a laminated rubber or plastic cover material 18 as shown in Fig. 2. The laminated cover material 18 is pre~erably formed of an upper layer 18a and a lower layer 18b mounted there-with and which may be formed of different rubber or plastic materials. Preferably, the upper layer 18a is adapted to be ex-posed to the adverse environmental conditions surrounding the reservoir R, such as rain, wind, ice, heat and the like without deterioration thereof. Preferably, the upper layer 18a is formed of a material such as that sold under the trademark "Hypalon", by the Dupont Company, further having a reinforcement filament 18c formed of polyester to add strength to the upper layer 18a.
; Preferably, the lower layer 18b is formed of a closed cell polyethylene foam with the lower layer 18b being laminated to `~ upper layer 18a at interface 18d. As such, the lower layer 18b acts to floatably support itself as well as the upper layer 18a on the stored liquid L within the reservoir R.
Typically, the stored liquid L is water, however, the reservoir R may contain oil, hydrocarbons or other liquids and : .:
consequently, the! sheet S must be appropriately formed ' ' -" , ;

1 of a material that is not only impervious to the stored liquid L but also will float on such liquid.
The floating roof material 18 is selected and designed to be inflated as well as to float. The material must also be lightweight to balloon when in~lated with a relatively low air pressure in the range of 1-3 lbs. per square foot. The con-tinuous form layer will prevent a section of the roof to sink if the material 18 is inadvertently punc~ured and will also serve to insulate the water in the reservoir from undesired extremes ;
of cold and heat.
The sheet S includes a peripheral edge 20 adapted to be secured to the berm 14 of the reservoir R by securing means M.
The securing means M may include an appropriate cleat or fastener 22 which may be embedded in the concrete wrapper l~a of the berm 14 for securing the sheet S thereto adjacent the peripheral edge 20 thereof. The sheet S for the reservoir R should have an area which is greater than the area of the reservoir R where the securing means M for the sheet S are located.
The floatable cover assembly C of the present invention further includes envelope means E formed with the sheet S at least adjacent a portion of the peripheral edge 20 and preferably of the cover material 18. The envelope means E includes envelope 24 formed of an upper portion 24a and a lower portion ~ ;~
24b which preferably is formed of the same material as the laminated cover material 18. The envelope means E is preferably located adjacent the berm 14 o the reservoir R therebetween the peripheral edge 20 of the sheet S and the interior cover portion 26 at the marginal edge 26a thereof. It should be recognized that if there should be a portion of the sheet S
not having an envelope means E therewith, then the marginal edge ~ 7 ~ ~ ;~

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,. :- , - ,, : . - - . , - ~ ~6~9~69 1 26a of the sheet S will act as the peripheral edge 20 to be secured to the berm 14 and fasteners 22 therewith. Alternatively, if the envelope means E is in fact therebetween the marginal edge 26a of the interior cover portion 26 and the peripheral edge 20, then the envelope means E will preferably be formed as shown in Figs. 4 and 5 of portions 24a, 24b. The upper portion 2~a and lower portion 24b are appropriately affixed or bonded to the marginal edge 26a in fluid-tight engagement adjacent the bonding edge schematically represented at 28 (Figs. 4, 5). Similarly, upper portion 24a and lower portion 24b of envelope 24 are bonded or suitably affixed theretogether in fluid-tight engagement adjacent the peripheral edge 20 - at schematic location 30.
The envelope means E is further formed having at least one inlet port 32 and at least one outlet port 34. The ports 32, 34 are adapted to be opened and closed and in the closed position, provide a fluid-tight seal with the interior portion 36 of the envelope means E.
Valve means V is mounted with envelope means E pre-ferably adjacent inlet port 32 in communication with the interior portion 36 of the envelope means E. The valve means V acts ;
to regulate the amount of compressible fluid within the envelope ~` -means E as discussed more fully hereinbelow.
In the use or operation of one form of the cover assembly C of the present invention, the cover assembly C is to provide ;~
for proper tensioning of the floating sheet S wherein the .
surface level of the stored liquid in the liquid storage reservoir R varies. ~he sheet S is disposed on the stored liquid L in the reservoir R with the peripheral edge 20 being secured to 30 the berm 14 of the reservoir R by securing means M and having ~ -, . .,,, ::

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1 envelope means E therewith at least adjacent a portion o~ the peripheral edge 20 of the sheet S. The envelope means E is adapted to be filled with a compressible fluid such as air, , or any suitable gas, for expancling the envelope means E as shown in Fig. 5. The expansion or ballooning action of the envelope .'.
means E contracts the sheet S resulting in tensioning of the interior cover portion 26 to eliminate the formation of wrinkles .
in the sheet S when floating on the surface of the level-varying liquid stored in the reservoir R. Thus, the envelope means E
is expanded in balloon-like fashion to result in a lateral tensioning force on the sheet S tending to stretch the sheet S
outwardly whereby wrinkles and cavities in the surface of the sheet S will be reduced facilitating flow of rain and water from melting snow off of the sheet S towards an appropriate drain.
during adverse environmental conditions while also preventing pooling of fluid on the exterior surface thereof. The pre-vention of wrinkles results in facilitating the removal of any accumulation and retained liquid on the surface of the sheet S
which helps facilitate the reduction of stresses and strains on the laminated cover material 18.
` The envelope,means E is inflated to a desired amount : , to ensure such proper, lateral tensioning of the sheet S to .~ ,~
eliminate the formation of wrinkles in the sheet S when floating : : ;
~: on the surface of the stored liquid L in the reservoir R. As .~ :
the liquid level varies, it may be necessar~ to add or remove ''.. '.~
compressible fluid from within the envelope means E. As shown ':':
in Fig. 5, the envelope means E is at a high level of stored ~.
liquid L as inclicated at position 38~ Should the stored liquid ~' L level drop to that such as indicated at position 40, additional laterial tension is effectuated upon the sheet S. This increased :' : ` ' ' ' '.;':
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~;9Z69 1 lateral tension tends to flatten the envelope means E therefore increasing the pressure of the compressible fluid within the interior portion 36 of the envelope means E.- Should this pressure increase overcome a predetermined pressure release settin~ within the valve means V, the valve means V acts to re-lease the excess pressure in a "pop-of" valve ~ashion to effectuate release o~ such excess pressure build-ups within the envelope means E, but only reducing the pressure within the interior portion 36 to that of the predetermined amount.
Thus, with the envelope means E in a position such as that designated at 42 on stored liquid level indicated at 40, the internal pressure within the interior portion 36 is sub-stantially the same as that of the envelope means E as positioned at the high level stored liquid position 3~, while retaining substantially the same tensioning on the sheet S. This results in the sheet S being of substantially a uniform tension while the liquid level of the stored liquid in the reservoir R is of a changing nature. :
Similarly, should the stored liquid L ~all to a 20 position indicated at level 44, the tension on the sheet S .
increases, further compressing the interior portion 36 of the .
envelope means E to such a position as noted at 46 wherein the valve m~ans V again vents the excess pressure within the interior `:
portion 36 such that the appropriate non-compressible fluid . . pressure within the envelope means E remains substantially the same to insure a proper tensioning of the sheet S as the liquid continues to va;ry. Should the liquid level rise from that . ~.
of level 44 to that of level 40, it would be necessary to add ... `
or increase the amount of compressible fluid within the envelope .
means E by supp.lying such through inlet port 32 in an appropriate ' .
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~(369;Z~9 1 fashion to thereagain assure proper tensioning of the sheet S.
Further, it should be noted that the sheet S may have plural envelopes E about the peripheral edge thereof, shown schematically in E`ig. 6 for sheets S having extremel~ large surface areas and where one envelope means E is nok sufficient to provide the proper tensioning of such a sheet S.
The cover assembly C of the present invention may be ef~ectively incorporate~ for properly maintaining the liquid storage reservoir R and sheet S for maintenance thereof should the reservoir R and/or sheet S require maintenance thereof.
During such a maintenance operation, it is preferred that the reservoir R be drained of stored liquid L by any appropriate conventional means (not shown). Thereafter, the envelope means -E, as shown in Fig. 4, is appropriately filled through inlet ~; port 32 with any suitable non-compressible fluid 48 such as water, or any other desired fluid resulting in the envelope means E restin~ upon the concrete wrapping 12a of side walls 12 dueto the weight of the fluid 48 within the envelope means E.
Thereafter, blower means B, which may be of any suitable high- ~-capacity blower 49 or the like, is connected with the sheet S
; by port 50 and flexible hose 52 therebetween such port 50 and the blower means B. The blower means B is appropriately en-; ergized resulting in the movement of compressible fluid, such as air, from the blower means B under pressure through the flexible hose 52 into port 50 and thereinto a cavity 54 formed therebetween the reservoir R and the lower surface of the sheet S, resulting in inflation of the sheet S which is heretofore ~
unsupported due to the stored liquid having been drained. The ~ ;
blower means B results in the sheet S being inflated to permit inspection and repair of the sheet S and cleanout of the storage - 11 - . :: -'., ' .:
,~ -.
_ ~6~Z69 1 reservoir R. The envelope means E being filled with the non-compressible fluid 48 acts as a ballast about the peripheral edge 20 of the sheet S to prevent the sheet S from flapping in an unwielding fashion which could damage, tear, rupture and/or destroy the sheet S while being in such an inflatably supported position. It is desired that the sheet S be at substantially the same elevation as the berm 14 of the reservoir R to prevent any undue wind damage to the sheet S during such maintenance operations. The reservoir R and the lower surface of the sheet S may be accessed by an appropriate access hatch mounted with the sheet S. Thus, the sheet S and reservoir R may be duly inspected, repaired or otherwise maintained without the need of divers or other aquatic gear which has heretofore been the maintenance procedure of the prior art.
Should the sheet S be of a significantly expansive size, it may be necessary to provide one or more intermediate ballasts 58 to prevent the sheet S from extending significantly thereabove the berm 14 of the reservoir R which could cause wind damage to the sheet S. The intermediate ballast 58 may include one or more ballast arrangements of any suitable size, shape and/or weight in order that the sheet S may be kept substantially the same as that of the elevation of the berm 14 ~ :
of the reservoir R. The intermediate ballast 58 is preferably of a plastic tube adapted to be filled with fluid such as water so that the ballast may be positioned, then filled with water during maintenance operations, and thereafter be drained to eliminate the need in moving heavy intermediate ballasts 58 about the sheet S prior to positioning same for proper maintenance ` operations.
The envelopes E as filled with fluid 48 help to ', ', ' ' 9Z6~

1 keep a proper tensioning of the sheet S while being supported by the fluid pressure generated by the blower means B and help to prevent damage to the sheet S in its expanded, inflatably supported configuration. For examp:Le, the sheet S as shown in Fig. 4, upon draining of the reservoir R, results in the sheet overlying the concrete wrapping 12a of the sloping sides 12 of the reservoir R whereinafter being inflated, the sheet S
moves to a position such as that indicated by dotted lines at position 60 or in such a configuration as schematically shown in Fig. 3. Thus, the cover assembly C of the present invention provides for a method and apparatus for properly maintaining the reservoir R and sheet S during the maintenance operations thereof. After maintenance operations have been completed, preferably, the blower means B is removed and the non-compressible fluid 48 is drained from the envelope means E by means of out-let port 34 being released and/or the fluid 48 being pumped outwardly from the interior portion 36 of the envelope means E
through the inlet port 32 and outwardly therefrom. Thereafter, the reservoir R is preferably again filled with liquid to be stored therein and the sheet S is thereafter tensioned by in-flating the envelope means E of the sheet S with a compressible `~
fluid to thereafter tension the sheet S as it floatably overlies the stored liquid L in accordance with the hereinabove described procedures to prevent the formation of wrinkles on the sheet S
for protecting the same.
Thus, the cover assembly C of the present inventionprovides not only the means and method for approprlately tensioning a sheet S on the stored liquid L of a storage reservoir R but also provides for ease of access, maintanance and repair of the sheat S and reservoir R during maintenance operations thereof.

' ' ' i9269 1 Modified foam cover assembly of the present invention is illustrated as C-l in Fig. 6 and 9 having a single center ballast pneumatic support column, generally designated X
for both supporting and ballasting the sheet S when the cover assembly C-l is in the inflated condition as illus~rated. Another modified cover assembly C-2 is il:Lustrated in Fig. 7 having a plurality of the ballasted pneumatic support columns X.
As best illustrated in F:ig. 8, the ballasted pneumatic support column X is secured to the underside of the sheek at 18 60. The support column X may be secured by sewing, glueing or the like and as illustrated in Fig. 9 extends substantially - across the reservoir R.
The pneumatic support column X includes a lower enclosed ballast chamber 62 and an upper pneumatic chamber 64.
The lower or ballast chamber 62 is formed of a material im-pervious to water and preferably extends beyond the ends of the upper chamber 64 a short distance for a purpose to be described -~
hereinafter. The upper chamber 64 is also formed of a flexible material and in addition to being secured with the roof S at 10 is secured on opposite sides of the lower tubular reservoir 62 at 66a and 66b. The flexible material 64 is preferably formed with a foam floa~tion characteristic in order that the sheet 64 will float adjacent the sheet S when the pneumatic support column is in the inoperative condition and the reservoir R is full of water. Suitable connections 67 are provided for communicating with a supply of air to an auxiliary blower AB
`; as illustrated in Fig. 9. With the ends of the chamber closed ;
pneumatic pressure in the support column X will be greater than that under the roof S and will tend to provide a support column at that point on the sheet S. The water ballast in the ' ~ . ' ":

~69~69 1 lower chamber will of course prevent the lifting of the sheet S and the pneumatic support column X from the floor 10 of the reservoir R.
It will be apparent to those skilled in the art that other means than those illustrated herein ma~ be used to ballast the cover. ~or instance, the ballast chamber 62 may be attached to the cover by flexible lines or a single sheet of material which will enable the cover to inflate sufficiently to provide adequate worker access to the reservoir.
As mentioned previously the enclosed ends of the lower ballast chamber protrude slightly beyond the pneumatic support column chamber 6~. This is done to provide access to the ballast chamber 62 for controlling the filling of the ballast.
When the roof is in the normal operating condition floating .
on the liquid reservoir the foam cover 64 will pull the opening :
in the top of the ballast chamber 62 extending beyond the chamber .
64 adjacent the sheet S. A zippered opening or access port in the sheet S is provided adjacent this fill pc~int and when it is desired to maintain the reservoir using the pneumatic column X these access ports to be closed to contain the water normally present therein when the reservoir R is drained of the liquid L. When the sheet S is in the floating condition these ports are left open and the water is left free to flow in and ~ :
out of the ballast chamber 62. . ~ .
To prevent an undesired accumulation of rain water and the like on the upper side of the cover apparatus A one or more drain sumps DS may be provided as illustrated in S1. The drain sumps DS provide a gathering spot for the rainwater as well as pro~ding for the elimination of the rainwater from the top of the cover where it could possibly contaminate the lic~uid L in the reservoir R.

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~69~69 1 The drain sump DS as best illustrated in Fig. 10 is provided with sides 72 and 74 made of impervious flexible material.
The bottom or floor 76 of the drain sump DS is also made of impervious material and is preferably ballasted to hold the bottom 76 in a position below the sheet S in order that the water will drain into the pocket 78 formed by the drain sump DS.
To remove the rainwater from the pocket 78 of the drain sump DS a pump 80 may be positioned in the pocke-t 78 to remove the water preferabl~ a submersible type electrically driven pump is used with electrical connection 82 being connected to a source of electrical power. Also, jet pumps or aductors may be employed as illustrated in Fig. 1.
~ In Fig. 1 a source of fluid under pressure is provided such as by pump 84 is separated into two flowlines 86a and 86b. `~
As illustrated in Fig. 11 the conduit 86a extends out-wardly on the cover S until it reaches drain sump DS. An aductor or jet pump is connected into conduit 86a in the drain ` sump DS. The aductor 88 discharge may then be run to the edge of the reservoir to a discharge location or it may be run to another drain sump as illustrated in Fig. 1. The aductor 88 is provided with a suitable backflow valve 90 in the conduit :.
86a and a foot valve 92 on the inlet of the aductor 88 ~or the ~luid to be evacuated from the drain sump DS. Such arrangement of using a jet pump is old and well known to those skilled in the art.
The fo:regoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the 'size, shape and materials as well as in the details of the illustrated construction may be made without departing from the spirit o~ the invention.
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Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for tensioning a flexible floating cover for a liquid storage reservoir where the surface level of the stored liquid varies relative to the berm of the reservoir to substantially eliminate wrinkling of the flexible cover, comprising the steps of:
disposing a sheet of flexible, floatable material on the liquid stored in the reservoir with the sheet having a marginal edge having envelope means attached to said marginal edge;
means for securing said envelope means to the berm of said reservoir; and inflating the envelope means with a regulated amount of compressible fluid to tension the sheet to prevent the formation of wrinkles in the floating sheet as the level of the stored liquid in the reservoir varies relative to the berm of the reservoir.

2. The method of claim 1, further including the step of:
regulating the tension of the sheet as the level of the stored liquid varies by valve means in communication with the envelope means.