US2490767A

US2490767A - Seal for floating roof tanks

Info

Publication number: US2490767A
Application number: US625993A
Authority: US
Inventors: John W Allen
Original assignee: Chicago Bridge and Iron Co
Current assignee: Chicago Bridge and Iron Co
Priority date: 1945-11-01
Filing date: 1945-11-01
Publication date: 1949-12-13
Anticipated expiration: 1966-12-13

Description

Dec. 13, 1949 4. w. ALLEN 2,490,767

SEAL FOR FLOATING ROOF TANKS Filed Nov. 1, 1945 2 Sheets-Sheet 1 WWJ Dec. 13, 1949 w, ALLEA 2,490,767

SEAL FOR FLOATING ROOF TANKS Filed NOV. 1, 1945 2 Sheets-Sheet 2 H= jiz've 7515/" Patented Dec. 13, 1949 FFICE SEAL FOR FLOATING ROOF TANKS John W. Allen, Chicago,

Bridge & Iro

Ill., assignor to Chicago n Company Application November 1, 1945, Serial No. 625,993 Claims. (Cl. 220-85) This invention relates to a storage tank for liquids of the type using a floating roof to cover the liquid, and relates particularly to a seal for sealing the edge of the roof to the shell of the tank.

In order to prevent evaporation losses during the storage of volatile liquids, these liquids are often stored in floating roof tanks wherein the roof floats on top of the liquid and rises and falls as the quantity of stored liquid within the tank is increased and decreased. In these tanks there are provided seals between the edge of the roof and the shell of the tank in order to prevent evaporation losses and contamination in this area. These seals must be of the type that will not prevent the roof from rising and falling.

I have invented a new type seal for a floating roof tank wherein the seal does not lift when the roof rises and falls, and yet provides a tight seal between the roof and the tank shell. This new seal comprises a flexible substantially liquidimpervious member extending around the tank from the floating roof to the inside surface of the tank shell and forms a trough therebetween at all positions of the roof. The flexible member is preferably a fabric impregnated with a flexible liquid-impervious material such as a synthetic rubber. One of the best synthetic rubbers for this use is neoprene. The trough formed by the fabric seal is substantially filled with a-liquid having a specific gravity greater than that of the liquid within the tank. This liquid will substantially fill the trough at all positions of the roof, as when the roof is in its highest position the trough is long and narrow, and as the roof falls the trough becomes shorter and wider. In a preferred embodiment the fabric seal is provided with expandable stiiiening members that serve to prevent the heavier sealing liquid from forcing the seal inward due to its greater specific gravity.

One embodiment of the invention is set out in the accompanying drawings. Of the drawings, Fig. 1 is a partial vertical section through the floating roof tank with the roof at its topmost position; Fig. 2 is a section similar to Fig.1 with the roof in its lowest position; Fig. 3 is an enlarged fragmentary vertical section of the edge of the roof; Fig. 4 is an enlarged fragmentary vertical section showing the bottom of the trough; Fig. 5 is a fragmentary elevation showing a portion of the edge of the roof with the seal fabric attached thereto; Fig. 6 is a fragmentary elevation showing a portion of the seal fabric with an expandable stifl'ening member attached thereto; Fig. 7 is a plan view of a tank I to hang down between them embodying this invention; and Fig. 8 is an elevation of said tank with portions broken away for clarity of illustration. 7

The floating roof tank shown in the accompanying drawings comprises an outer cylindrical shell I it having a liquid 1 I stored therein. On top of the stored liquid is located a roof I! which floats thereon. The floating roof includes a, flat base i3 around which is positioned a vertical channel beam I 4. On top of the flat base i3 of the floating roof are located air chambers IS.

A fabric seal curtain I8 is fastened to the floating roof i2 and the shell in of the tank so as and form a trough IT. The fabric curtain is fastened to the floating roof by bolting it on the channel beam I 4 by bolts l8 passing through the beam 14, the fabric seal I 6, and a circular metal bar IS. The other edge of the fabric is fastened to the inner surface of the shell Ill by bolting this edge to the shell, and the curtain is held in place by means of a second circular metal bar 20 fastened to the tank by means of bolts 2|.

The liquid-impervious curtain l 6 hangs between the floating roof I2 and the shell ill to form a" I trough in all positions of the roof.

In a tank 43 feet high the outer edge of the curtain is fastened approximately 25 feet beneath the top of the tank, and when the tank is full, as shown in Fig. 1, the trough extends substantially 2 feet beneath the line where it is fastened to the shell. Thus, as there is a trough provided when the tank is full this trough will exist at all lower positions of the roof.

A liquid seal is provided by filling the space between the curtain l6 and the shell ill with a sealing liquid 22 having a specific gravity greater than that of the liquid ll within the tank. The volume of the sealing liquid 22 remains constant throughout the travel of the floating roof, and the abric changes shape as shown in Figs. 1 and The fabric curtain used to hold the sealing liquid must be liquid-impervious so that there can be noleakage through the curtain. A suitable curtain is made from a fabric impregnated with a liquid-impervious, flexible solid material, such as synthetic rubber. One of the best materials for this purpose is neoprene.

Because the sealing liquid has a specific gravity greater than that of the liquid within the tank, stiffening members must be provided for the fabric to prevent the sealing liquid from sinking to the bottom of the trough, thereby permitting the top of the fabric to contact the shell and produce a rubbing action as the roof rises and falls. These sealing members comprise spaced, horizontal circular pipes 23 attached to the fabric curtain on the side away from the: trough. These circular pipes 23 are vertically spaced from each other and are attached to the curtain by means of a plurality of fabric strips 24. The circular pipe nearest the floating roof is spaced therefrom an appreciable distance. The fabric strips it that hold the circular pipes in place may be attached to the curtain in any desired manner, such as by means of rivets 25 extending through the strips and the curtain.

As the roof travels from its highest to its lowest position the circular pipes 23 are placed in contact with the shell II. In order to accomplish this the pipes must be expandable. On one end of each circular pipe there is provided a collar 25 concentric with the end of the pipe and extending therefrom. This collar slidably holds the other end of the pipe with the two ends bein in abutting relationship when the roof is in its highest position. Thus as the roof falls the force of the sealing liquid 22 causes each pipe to expand.

At the top of the fabric curtain near the floating roof there are provided tension strips 21 attached to the fabric. These tension strips are horizontal strips of fabric that are attached to the curtain by means of adhesives, rivets, or the like. The strips are preferably of the same impregnated fabric as used for the curtain. As

these tension strips are made of flexible fabric they permit the top of the curtain to bow inward at intermediate positions of the roof.

The top of the fabric curtain is attached to the floating roof in a series of overlapping puckers 28 positioned about 4 inches apart.

The sealing liquid 22 within the trough ll will ordinarily be suflicient to hold the fabric curtain down at all times. In order to provide a more positive holding down of the curtain there is provided a weight at the bottom of the trough. This weight may be a circular rod 29 within a coil spring 30 having a diameter larger than the diameter of the rod. the spring 30 will roll and prevent substantial frictional contact between the rod 29 and the curtain.

In order that the curtain IE will not be folded upon itself and pressed down by the roof when the tank is substantially empty of liquid, there is provided a framework 3| upon which the floating roof rests when in its lowest position (Fig 2).

Having described my invention as related to one embodiment of the same, it is my intention that the invention be not limited by any of the details of the description unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

I claim:

1. A seal for a floating roof tank or the like comprising a flexible substantially liquid-impervious cylindrical curtain extending around the tank, said curtain having one peripheral edge secured to the floating roof and having the other edge secured to the side of the tank to form a trough therebetween at all positions of the roof, the length of the curtain between its edges being substantially equal to twice the minimum depth of the desired trough plus one half of the vertical travel of the roof within the tank plus the distance between the point of attachment of the curtain to the tank and the midpoint of the roof travel within the tank whereby said curtain forms a trough having a substantially. constant As the roof rises and falls volume at all positions of the roof. the trough being substantially fllled with liquid at all positions of the roof within the tank and said liquid having a specific gravity greater than that of the liquid within the tank.

2. A seal for a floating roof tank or the like comprising a flexible substantially liquid-impervious cylindrical curtain extending around the tank, said curtain having one peripheral edge. secured to the floating roof and having the otheredge secured to the side of the tank to form a trough therebetween at all positions of the roof. the length of the curtain between its edges being substantially equal to twice the minimum depth of the desired trough plus one half of the vertical travel of the roof within the tank plus the distance between the point of attachment of the curtain to the tank and the midpoint of the roof travel within the tank whereby said curtain forms a trough having a substantially constant volume at all positions of the roof and a weight located at the bottom of the trough, said trough being substantially filled with a liquid at all positions of the roof within the tank, said liquid having a specific gravity greater than that of the liquid within the tank.

3. The seal of claim 2 wherein the weight is freely movable relative to the said member as the roof rises and falls.

4. A seal for a floating roof tank or the like comprising a flexible substantially liquid-impervious cylindrical curtain extending around the tank, said curtain having one peripheral edge secured to the floating roof and having the other edge secured to the side of the tank to form a trough therebetween at all positions of the roof, the length of the curtain between its edges being substantially equal to twice the minimum depth of the desired trough plus one half of the vertical travel of the roof within the tank plus the distance between the point of attachment of the curtain to the tank and the midpoint of the roof travel within the tank whereby said curtain forms a trough therebetween at all positions of said roof, a plurality of substantially horizontal spaced stiffening members attached to the flexible curtain on the side away from the trough and extending around said curtain, said stiffening members comprising circular pipes with each pipe having a collar attached to one end extending therefrom with the other end of the circular pipe slidably held within said collar and with the two ends of the pipe abutting each other when the roof is in its highest position, and a substantially constant volume of a liquid having a specific gravity greater than that of the'liquid within the tank substantially filling the trough at all positions of the roof within the tank.

5. A seal for a floating roof tank or the like comprising a flexible substantially liquid-impervious cylindrical curtain extending around the tank, said curtain having one peripheral edge secured to the floating roof and having the other edge secured to the side of the tank to form a trough therebetween at all positions of the roof, the length of the curtain between its edges being substantially equal to twice the minimum depth of the desired trough plus one half of the vertical travel of the roof within the tank plus the distance between the point of attachment of the curtain to the tank and the midpoint of the roof travel within the tank whereby said curtain forms a trough having substantially constant volume at all positions of said roof. a plurality of spaced substantially horizontal circular pipes attached to the flexible curtain on the side away from the trough and extending around said flexible member with the circular pipe nearest the floating roof being spaced therefrom a substantial distance, each of said circular pipes having a collar attached to one end and extending therefrom with the other end of the circular pipe slidably held within said collar with the two ends of the pipe abutting each other when the roof is in its highest position, a plurality of spaced horizontal flexible strips attached to the flexible curtain on the trough side near the floating roof and a substantially constant volume of liquid having a specific gravity greater than that of the liquid within the tank substantially fllling the trough at all positions of the roof within the tank.

6. The seal of claim 5 wherein the flexible member and the flexible strips are fabric impregnated with a flexible liquid-impervious material and the member is attached to the floating roof in a series of overlapping puckers.

7. A seal for a floating roof tank or the like comprising a flexible substantially liquid-impervious cylindrical curtain extending around the tank, said curtain having one peripheral edge secured to the floating room and having the other edge secured to the side of the tank to form a trough therebetween at all positions of the roof, the length of the curtain between its edges being substantially equal to twice the minimum depth of the desired trough plus one half of the vertical travel of the roof within the tank plus the distance between the point of attachment of the curtain to the tank and the midpoint of the roof travel within the tank whereby said curtain forms a trough having substantially constant volume at all positions of said roof, a plurality of spaced substantially horizontal circular pipes attached tothe flexible curtain on the side away from the trough and extending around said flexible member with the circular pipe nearest the floating roof being spaced therefrom a substantial distance, each of said circular pipes having a collar attached to one end and extending therefrom with the other end of the circular pipe slidably held within said collar with thetwo ends of the pipe abutting each other when the roof is in its highest position, a plurality of spaced'horizontal strips of the same material as the curtain attached to the curtain on the trough side near the floating roof, a weight positioned in the bottom of the trough and freely movable as the floating roof rises and falls, and a liquid having a '6 specific gravity greater than that of the liquid within the tank substantially fllling the trough in all positions of the roof within the tank. I

8. A seal for a floating roof tank or the like comprising a flexible substantially liquid-impervious cylindrical curtain extending around the tank, said curtain having one peripheral edge secured to the floating roof and having the other edge secured to the side of the tank to form a trough therebetween at all positions of the roof, the length of the curtain between its edges being substantially equal totwice the minimum depth of the desired trough plus one half of the vertical travel of the roof within the tank plus the distance between the point of attachment of the curtain to the tank and the midpoint of the roof travel within the tank whereby said curtain forms a trough having a substantially constant volume at all positions of said roof, a plurality of spaced substantially horizontal stiffening members extending around the flexible curtain and attached thereto on the side away from the trough, and a substantially constant volume of liquid substantially fllling the trough at all positions of the roof within the 9. The seal of claim 8 wherein the stiffening members are expandable when the roof moves from its highest position to its lowest position within the tank.

10. The seal of claim 8 wherein the stifiening members are circular pipes with each pipe having a collar attached to one end and extending therefrom with the other end of the pipe slidably held within the collar, said two ends of each pipe being in abutting relationship when the roof is in its highest position.

JOHN W. ALLEN.

REFERENCES crrnn The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 135,172 Tiflany Jan'. 21, 1873 2,050,686 Wiggins Aug. 11. 1936 2,102,299 Wiggins Dec. 14, 1937 2,330,366 Jayne Sept. 28, 1943 2,408,538 Wiggins Oct. 1, 1946 FOREIGN PATENTS Number Country Date 106,097 Australia Dec. 22, 1938 Certificate of Correction Petent No. 2,490,767 N December 13, 1949 JOHN W. ALLEN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: I

Column 5, line 26, for the W0 room read roof;

and that the said Letters Patent should be read with this correction therein that the some may conform to the record of the case in the Patent Oflice.

Signed and sealed this 25th day of April, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oomnpiuiomr of PM.