US3466886A

US3466886A - Fluid-conveying arrangement

Info

Publication number: US3466886A
Application number: US667056A
Authority: US
Inventors: Conrad Doose; Hans Hemmerich; Wolfgang Sassin
Original assignee: Kernforschungsanlage Juelich GmbH
Current assignee: Forschungszentrum Juelich GmbH
Priority date: 1966-09-08
Filing date: 1967-09-08
Publication date: 1969-09-16
Anticipated expiration: 1986-09-16
Also published as: DE1300380B; SE313471B; GB1202557A

Description

Sept. 16, 1969 c. noose ETAL 3,466,886

FLUID-CONVEYING ARRANGEMENT Filed Sept. 8, 1967 5 Sheets-Sheet 1 /NVE roar 1%! Van/"mi 67 1 fm' z. f Q'Mad W 'W-w 4H Sept. 16, 1969 c. DOOSE ET AL 3,466,886

FLUID-CONVEYING ARRANGEMENT Filed Sept. 8, 1967 5 Sheets-Sheet 2 W n/rap: W M M JQMM'K mmtzwm Sept. 16, 1969 c. DOOSE ETAL 3,466,886

FLUID-CONVEYING ARRANGEMENT Filed Sept. 8, 1967 5 Sheets-Sheet 3 Wrzwropg Sept. 16, 1969 c. noose ETAL FLUIDCONVEYING ARRANGEMENT 5 Sheets-Sheet 4 Filed Sept. 8. 1967 nu... Ir fir-Prim /NVEN 7095 W -0- Sept. 16, 1969 Filed Sept. 8, 1967 C. DOOSE E AL FLUID-CONVEYING ARRANGEMENT 5 Sheets-Sheet 5 AWE/Wop! United States Patent O 3,466,886 FLUID-CONVEYING ARRANGEMENT Conrad Doose, Hans Hemmerieh, and Wolfgang Sassm, Julich, Germany, assignors to Kernforschungsanlage Julich des Landes Nordrhein-Westfalen-e.V., Julich, Germany Filed Sept. 8, 1967, Ser. No. 667,056 Claims priority, application Germany, Sept. 8, 1966, K 60 206 U.S. C]. 6255 19 Claims ABSTRACT OF THE DISCLOSURE A fluid-conveying arrangement includes a jacket which is surrounded by ambient atmosphere at a first temperature. A supply conduit is received with clearance in the jacket and is arranged to convey a fluid at a second temperature which greatly differs from the first temperature. A thermal shield surrounds the supply conduit with spacing therefrom. A return conduit extends along the supply conduit in heat-exchanging connection with the thermal shield and is adapted to contain the aforementioned fluid at a third temperature which is close or identical to the second temperature.

BACKGROUND OF THE INVENTION The present invention relates to a fluid-conveying arrangement in general, and in particular to a fluid-conveying arrangement for conveying cold gases between a refrigeration unit and a user unit.

In the transportation of certain fluids, particularly cold gases or liquid gases, certain difficulties have heretofore been encountered. This is particularly true of the transportation of gases such as liquid helium, which must be maintained at extremely cold temperatures to remain in their desired state. Such gases must be transported from a refrigeration unit to a user unit, and must be recirculated from the user unit to the refrigeration unit because at the user unit the temperature rises above the required op timum temperature and the gases must therefore be re turned to the refrigeration unit so as to be again subjected to cooling. Unfortunately, the gas being circulated from the refrigeration unit to the user unit is subject to undesirable thermal influences during its transportation to the user unit. In particular, proximity of the return flow conduit connecting the user unit with the refrigeration unit to the supply conduit has tended to unduly warm the gas in the latter because the gas in the former is of course at a relatively higher temperature, perhaps, to mention an example, at minus 260 C. while the gas in the supply conduit is at minus 270 C. Much more importantly, the heat radiated by the ambient atmosphere, which is of course greatly warmer than the temperature of the gases in question which may, as first pointed out, reach values in the vicinity of minus 270 C. has presented such a problem. Warming of the gas in the colder supply conduit by proximity to the warmer return flow conduit has been overcome by separating the two conduits from one another. Influx of heat into the system from the ambient atmosphere, however, has never been satisfactorily prevented and compared to this problem the heating of the supply conduit by the return flow conduit is of minor nature, again speaking in relative terms. Attempts have been made to overcome this latter problem by using suitable insulating materials for shielding the conduits from the heat of the ambient atmosphere. However, in many applications, it is necessary to construct the conduit systems of individual sections which are connected by axially movable couplings so as to make possible Patented Sept. 16, 1969 connection to different user units which may be positioned at a variety of different locations. At such couplings the influx of heat from the ambient atmosphere heretofore has been relatively great with the result that the gas, for instance liquid helium, was heated in the supply conduit to such an extent that it arrived at the user device in form of a liquid and steam mixture. This is, of course, totally unacceptable and had to be overcome, in the absence of any means for preventing the undesired influx of exterior heat, by providing excess cooling capacity beyond that actually needed to supply the required extent of cooling to the user device.

The reason for the undesirable performance of the known couplings used in conduits of the type here under discussion resides in the fact that the jackets which surround the actual supply and return conduits, and which are maintained at a vacuum, were so constructed that each section in itself was fluid-tight and could be evacuated. Successive sections were telescoped to the necessary extent but were individually maintained in evacuated condition. Successive sections of the actual conduits were provided with a so-called warm connection at the end of the labyrinth formed by the telescoped ends of the jacket sections. Air cushions at ambient temperature became entrapped in the labyrinth in the vicinity of the connections of the conduits, and heat exchange between these air cushions and the conduits through the medium of the jacket material defining the labyrinth was un avoidable.

This, however, was by no means the only disadvantage of known couplings of this type. Many solder connections and welded joints along the conduits, and at the points of connection between adjacent conduit sections, are completely enclosed within the jacket thus making it impossible to gain access to these joints or seamsas is necessary because of repair and maintenance requirementswithout destroying the jacket itself.

All of this is of course highly undesirable and it has therefore long been attempted to overcome these problems. No satisfactory solution has, however, heretofore become known.

SUMMARY OF THE INVENTION The present invention overcomes the disadvantages outlined above.

More particularly, the present invention provides a fluid-conveying arrangement, particularly for supplying cold or liquid gases in which the influence of the temperature of the ambient atmosphere on the contents of the conduits is extremely insignificant.

Furthermore, the arrangement according to the present invention makes possible the connection of conduit sections and jacket sections to one another, and with freedom of certain movements with reference to one another, without thereby increasing the susceptibility of the system to the influx of undesired heat from the ambient atmosphere.

The arrangement according to the present invention is relatively uncomplicated and requires no excessive expenditures of either a technical or an economic nature. It thus lends itself to a wide variety of uses, of which chemical and nuclear applications are exemplary.

In accordance with one feature of our invention we provide a fluid-conveying arrangement which is particularly suited for supplying a fluid at a first temperature from a supply station to a user station and returning such fluid at -a second temperature from the user station to the supply station. This arrangement includes jacket means whose circumferential wall is surrounded by ambient atmosphere at a first temperature. Supply conduit means is received with clearance in this jacket means and is adapted to convey a fluid, such as a cold gas or a gas in liquid state, at a second temperature greatly different from the first temperature. Thus, if the gas being conveyed is liquid helium, its temperature, namely the aforementioned second temperature, may be on the order of 270 C. whereas the ambient temperature surrounding the jacket means may be on the order of +30 C. The existing temperature differential between the jacket means and the supply conduit means in which the liquid helium is being conveyed, therefore would be on the order of 300 C. and it can readily be seen why extraordinary precautions are necessary to prevent heat exchange under these circumstances.

Further, in accordance with our invention, our fluidconveying arrangement comprises thermal shielding means which extends along the supply conduit means within the jacket means and which is operative for preventing heat exchange between the jacket means and the supply conduit means. The shielding means includes return conduit means through which the fluid is recirculated from the user device to the refrigeration device from where it has originally been supplied through the supply conduit means. Of course, during use at the user device, the fluid has undergone a rise in temperature. It will, however, still be significantly below the temperature of the jacket means. In fact, the temperature at which the fluid is conveyed in the return conduit means, while being intermediate the temperature of the fluid in the supply conduit means and the temperature of the jacket means, is likely to be significantly closer to the temperature of the fluid in the supply conduit means than to the temperature at which the jacket means is maintained by contact with the ambient atmosphere. Thus, by making use of the temperature of the fluid in the return conduit means as a factor in our thermal shielding means, we are able to shield the supply conduit means against direct heat exchange with the jacket means.

We also provide coupling means for coupling successive conduit sections and successive sections of the jacket means to one another for relative rotational displacement, as will be discussed in more detail subsequently.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary axial section through a fluidconveying arrangement embodying our invention;

FIG. 2 is a section taken on the line IIII og FIG. 1;

FIG. 3 is a section taken on the line IIIIII of FIG. 1;

PG. 4 is a fragmentary axial section through a fluidconveying arrangement embodying our invention and showing a novel coupling according to the invention;

FIG. 5 is a fragmentary enlargement of portions of the embodiment illustrated in FIG. 4;

FIG. 6 is a view along the lines of FIG. 4, but illustrating another embodiment of a coupling according to our invention;

FIG. 7 is a schematic side view of a system utilizing our novel fluid-conveying arrangement; and

FIG. 8 is a view of FIG. 7 as seen in the direction of the arrow A associated with the latter figure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing in detail, and firstly FIGS. 7 and 8 thereof, it will be seen that there is illustrated a refrigeration device W of any desire-d or suitable type. The particular type of refrigeration device is of no consequence as far as the present invention is concerned. From the refrigeration device W a refrigerated fluid is to be supplied to a user device V which again may be any one of many devices utilizing such refrigerated fluids, and whose particular constructions is of no importance for the present invention. Of course, the fluid must be recirculated from the user device to the refrigeration device, but only the supply conduit is illustrated in FIGS. 7 and 8 because this will suflice to explain the aspect of the invention which is to be clarified by these figures. The refrigeration device W and the user device V are connected by means of 1a fluid-conveying arrangement R constructed in accordance with the present invention, as will be more fully developed hereafter. To make possible the connection of the refrigeration device W to the user device V regardless of where the same may be located, or Where it may be moved, our fluid-conveying arrangement R is provided with elbow-bends T. It is evident from FIG. 7 that the arrangement R consists of a plurality of individual sections each of which comprses at least one of the bends T. These sections are connected to one another by means of the couplings U and in such a manner that successive sections can be rotationally displaced with reference to one another. Thus, and as illustrated in FIG. 8, the user device V can be moved from the fullline position to the dashed line position illustrated in FIG. 8, and it is simply necessary to adjust the novel arrangement by rotating successive sections about their respective couplings U. This is illustrated in dashed lines in FIG. 8. Evidently, this procedure also applies if the user device V is not to be moved, but if the refrigeration device W is simply to be connected to a second user device which may be positioned as indicated by the dashed lines in FIG. 8.

Thus, FIGS. 7 and 8 indicate by way of example a simple system utilizing our novel invention.

Discussing now the invention in more detail, and firstly FIGS. 1-3 thereof, it will be seen that we have provided two conduits 1 and 2. The conduit 1 is assumed in this illustrated embodiment to be the supply conduit which connects a non-illustrated refrigeration devicecorrespond ing to the device W in FIGS. 7 and 8to a similarly nonillustrated user device which corresponds to the device V in FIGS. 7 and 8. The flow of fluid is indicated by the arrow associated with conduit 1. Conduit 2 is the return conduit through which the fluid, having been used at the user device and having undergone a temperature increase, is recirculated in the direction of the arrow associated with conduit 2 to the refrigeration device. Both of these conduits are arranged within a jacket 3 which is exposed to the ambient atmosphere and Whose interior is evacuated to reduce heat exchange with the circumferential wall of the jacket.

In accordance with the invention, the return conduit 2 is connected in heat-exchanging relationship with a tubular radiation shield 4 which surrounds the conduit 1 with clearance, as best seen in FIGS. 2 and 3. Conduit 1 is maintained spaced from the inner wall of the radiation shield 4 by provision of a plurality of spacing members 6 of which one is shown in FIGS. 1 and 3. The particular configuration of these spacing members 6 is of no consequence. The radiation shield 4 and the return conduit 2, which conduit is secured to the radiation shield 4 in heat-exchanging relationship therewith, are maintained in spaced relationship from the wall of jacket 3 by means of spacing members 5 which again may be of any conventional configuration. However, in accordance with the invention, it is advantageous that the spacing members 5 and 6 be ofiset from one another in axial direction of the conduits to prevent establishment of a thermal bridge between the wall of the jacket 3 and the supply conduit 1. For the same reason it is advisable that the connection in heat-exchanging relationship between the return conduit 2 land the radiation shield 4 be interrupted in the region where a thermal bridge exists between the wall of jacket 3 and the radiation shield 4. The entire assembly consisting of the conduits 1 and 2 as well as the radiation shield 4 is surrounded within the jacket 3 by a sleeve of thermal insulating material 7, which material need not be more specifically identified because many such materials are well known to those skilled in the art.

By providing heat-exchanging connection between the return conduit 2 and the radiation shield 4, the latter is maintained substantially at the temperature of the fluid which returns from the user device to the refrigeration device. This fluid, while at a temperature higher than the temperature of the fluid passing through the supply conduit 1, is nevertheless at a temperature which is significantly below that of the wall of jacket 3, and thus the temperature differential between the supply conduit 1 and the radiation shield 4 is only a fraction of what it would be if the radiation shield 4 were to be allowed to rise to a temperature on the order of that at which the wall of jacket 3 is maintained by contact with the ambient atmosphere.

In accordance with an embodiment of the invention the conduits 1 and 2, as well as the jacket 3, consist of individual sections which are to be connected by a coupling for the reasons already explained earlier. FIG. 4 shows such an arrangement and it will be seen that in accordance with the invention the free ends of the conduits 1 and 2, which latter otherwise extend in axial parallelism with one another as evident both from FIGS. 1 and 4, are arranged so that they extend coaxially with one another. FIG. 1 shows that the free end of the conduit 1 is arranged within the free end of conduit 2. Where the change from axially parallel to coaxial relationship takes place it is advantageous to provide a collector 8 or a similar arrangement of known construction. It is this change-over from axial parallelism to a coaxial relationship which permits coupling of sucessive conduit sections in such a manner that they can be rotationally displaced with reference to one another.

FIG. 4 shows that compensation for longitudinal extension and contraction of the conduits 1 and 2 is made by means of bellows-shaped connectors 9. Only the connectors for the conduit 1 are illustrated in FIG. 4 but similar connectors can also be used for the conduit 2.

Coupling of the coaxial free ends of the conduits 1 and 2 of adjacent sections is effected in accordance with the invention by means of a pair of bellows members 10, 11 which are respectively aifixed to the free ends of the conduit sections which are to be connected. FIG. 4 illustrates that the bellows member 10 is aflixed to the free end of the conduit 2 of one section, whereas the bellows member 11 is aflixed to the free end of the conduit 2 of the next section. The facing ends of the bellows members 10 and 11 in turn are provided with flange-shaped

portions

12 and 13, respectively, and to effect proper sealing engagement between the abutment faces which are provided on the

portions

12 and 13, these abutment faces are advantageously complementarily stepped, provided with an annular projection and a complementary annular groove, or made to interlock in a similar manner. The free ends of the conduit sections 1 which are to be joined are advantageously telescoped at 14, 15 in fluid-tight manner although a connection can be eflected in any other suitable well-known way.

It is of course necessary to assure that the telescoped free ends will not separate, and for this purpose the bellows members 10, 11 are prestressed, that is they exert a pressure in axial direction toward the respective other bellows member. The members 10, 11 and the return conduit 2 are guided by means of a tubular section 16 which surrounds the adjacent free ends of the connected conduit sections 2 within the bellows members 10, 11. A ring member 17 surrounds the flange-shaped member 13 and is secured by means of the illustrated bolts to the member 12. By providing a suitable arrangement of apertures in the members 17 and 12, the flange-shaped

members

12 and 13 can be connected in a variety of position in which they are rotationally displaced with reference to one another. This type of adjustable connection is of course well known in the art and need not be specifically discussed for this reason.

FIG. 5 illustrates a preferred embodiment of the engagement between the

members

12 and 13, which provides a particularly good sealing action between the abutment faces. Member 12 is provided with a conically tapering annular abutment face 18 which is jointed at its opposite axial ends by radially extending annular abutment faces 21 and 23. Member 13, in turn, is provided with a recess comprising an abutment face 19, complementary to the face 18, and joined at its opposite axial ends by radially extending abutment faces 20 and 22. In accordance with the invention, a sealing member 24, which may consist of various different materials but advantageously is an annulus of ductile metal, is disposed between these abutment faces of the

members

12 and 13 so that, when the bolts securing the ring member 17 to the member 12 are tightened, the member 24 will be deformed between the abutment faces and will thus provide a reliable fluidtight connection therebetween. It is to be noted with respect to FIG. 5 that the arrangement illustrated there has, in section, two mirror-symmetrical sides and it is therefore evident that it suflices to illustrate only one of these sides, as has been done in FIG. 5.

While this has not been specifically illustrated in either FIG. 4 or FIG. 5, it should be understood that upon completion of assembly the coupling thus far described is surrounded with a well-insulating material, that is a thermally insulating material which is connected to the insulation surrounding the conduits 1 and 2 where the same are arranged in axially parallel relationship. This latter insulation is the insulating sleeve identified with reference numeral 7 in FIGS. l3.

We have found it advantageous to have the sections of the jacket 3 terminate approximately at the point where the conduit 2 emerges from its axially parallel relationship to coaxial relationship with the conduit 1. To establish a through-going connection between the successive jacket sections 3, that is a connection which is fluidtight so that vacuum can be maintained throughout the composite jacket consisting of the two sections 3, we connect each of the jacket sections 3 by means of any well known releasable vacuum-tight connection 25 with sleeves 26 which each carry at their respective free ends a flange. The flanges are respectively provided with cooperating abutment faces 28 and 29 and coupling means 27 is provided for drawing the flanges together so that the abutment faces 28 and 29 engage in fluid-tight relationship. The sealing action can be enhanced by disposing a sealing elementwhich is illustrated in FIG. 4, but not identified with a reference numeral-between the abutment faces 28 and 29, and such a sealing element may be an annulus of elastomeric material or the like. We have found it advantageous if the abutment faces 28 and 29 are of arcuate- 1y curved configuration to assure that variations in manufacturing tolerances do not adversely affect tightness of the connection.

Corning, finally, to the embodiment illustrated in FIG. 6, it will be seen that this is an illustration of a coupling for effecting connection between two adjoining sections of the conduit 1 as well as between two adjoining sections of conduit 2. The fluid flow in the respective conduits is indicated by the arrows. The purpose of the embodiment in FIG. 6 is to provide a thermal decoupling between the conduit 1 and the conduit 2 at the point where the former passes through the latter in coaxial relationship therewith. For this purpose, we provide an insert 30 consisting of an outer tube 31 and a coextensive inner tube 32 which is coaxially arranged Within the outer tube 31. The insert 30 has a length corresponding to the distance for which the conduit 1 is coaxial with the conduit 2 and the outer and

inner tubes

31 and 32 are fluid-tightly connected to one another at their respective ends, thus defining between themselves an inner annular space 33. To effect thermal decoupling, that is to thermally insulate the fluid passing 7 through the inner tube 32 from the conduit 1, this annular space 33 may be either evacuated and maintained at a vacuum, or it may be filled with a high-boiling gas which freezes when the arrangement is subjected to the operating temperatures of the fluid passing through the conduits.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of arrangements differing from the types described above.

While the invention has been illustrated and described as embodied in a fluid-conveying arrangement, it is not intended to be limited to the details shown, since various modifications and structural changes may be made with out departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present inventiton that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended Within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

We claim:

1. A fluid-conveying arrangement, particularly for supplying a fluid at one temperature from a supply station to a user station and for returning such fluid at another temperature from the user station to the supply station, comprising in combination, jacket means comprising a circumferential wall surrounded by ambient atmosphere at a first temperature; supply conduit means received with clearance in said jacket means and adapted to convey a fluid at a second temperature greatly different from said first temperature; and thermal shielding means operative for preventing direct heat exchange between said jacket means and said supply conduit means, said shielding means including a radiation shield surrounding said supply conduit means with spacing from the same as well as from said circumferential wall of said jacket means and said return conduit means extending at least in part within the confines of said radiation shield along said supply conduit means spaced therefrom and from said radiation shield, said return conduit means being adapted to contain said fluid at a third temperature close or identical to the said second temperature.

2. An arrangement as defined in claim 1, wherein said return conduit means extends along one side of said supply conduit means.

3. An arrangement as defined in claim 1, wherein said thermal shielding means further comprises connecting means connecting said return conduit means in thermally conductive relationship with said radiation shield.

4. An arrangement as defined in claim 1, wherein said return conduit means comprises conduit portions extending along one side of said supply conduit means in thermally conductive relationship with said radiation shield.

5. An arrangement as defined in claim 4, wherein said conduit portions of said return conduit means extend along said one side of said supply conduit means exteriorly of said radiation shield.

6. An arrangement as defined in claim 5, wherein said conduit portions of said return conduit means extend in axial parallelism with said supply conduit means.

7. An arrangement as defined in claim 6, wherein said supply conduit means and said return conduit means each comprise an end portion, and wherein one of said end portions surrounds the other in coaxial relationship therewith.

8. An arrangement as defined in claim 1, and further comprising a thermal insulating sleeve surrounding said shielding means Within said jacket means.

9. An arrangement as defined in claim 1, wherein said jacket means is fluid-tight and adapted to be evacuated.

10. A fluid-conveying arrangement, particularly for supplying a fluid at a first temperature from a supply station to a user station and for returning such fluid at a second temperature from the user station to the supply station, comprising in combination, at least two sections each including jacket means having an open end and surrounded by ambient atmosphere at a third temperature; supply conduit means having a first end portion and being received with clearance in said jacket means and adapted to convey a fluid at said first temperature greatly different from said third temperature; thermal shielding means extending along the respective supply conduit means and including a radiation shield surrounding said supply conduit means spaced from the same and from said jacket means, and return conduit means extending along said supply conduit means within the confines of and spaced from said radiation shield and having a second end portion coaxial with said first end portion, said return conduit means being adapted to contain said fluid at said second temperature close or identical to said first temperature and said shielding means being operative for preventing direct heat exchange between said jacket means and said supply conduit means; and coupling means fluidtightly connecting the respective open ends of said jacket means, the respective first end portions and the respective second end portions.

11. An arrangement as defined in claim 10, said coupling means connecting said jacket means and said supply conduit means of the respective sections in axial alignment with one another and being constructed and arranged for enabling relative rotational displacement of said sections with reference to one another.

12. An arrangement as defined in claim 11, wherein said coupling means includes two bellows-shaped memhers each having a first end connected to the end portion of one of said conduit means in one of said sections, and a free second end provided with a flange having an annular abutment face adapted to sealingly engage the corresponding abutment face on the other of said bellowsshaped members.

13. An arrangement as defined in claim 12, wherein said abutment faces are provided with complementary conically configurated annular shoulders.

14. An arrangement as defined in claim 12, wherein said abutment faces are respectively provided with an annular shoulder and a complementary annular recess, each of arcuate cross-sectional configuration.

15. An arrangement as defined in claim 12, wherein said coupling means further comprises securing means for sealingly securing said members to one another in a plurality of positions of relative rotational displacement.

16. An arrangement as defined in claim 13, wherein said annular shoulders each comprise a conically configurated first surface, and a pair of annular second surfaces extending radially of said first surface at opposite axial ends thereof; said coupling means further comprising an annular element of deformable material interposed between said abutment faces and deformed into sealing engagement with said first and second surfaces.

17. An arrangement as defined in claim 11, wherein said coupling means includes an insert comprising an outer tube having opposite open ends, an open-ended coaxial inner tube received in and coextensive with said outer tube and sealingly connected to the same at said opposite ends thereof so as to define an internal annular space with said outer tube, said opposite ends of said outer tube being fluid-tightly received in said end portions of one of said conduit means of the respective sections so that said one conduit means in the respective sections communicates through the intermediary of said inner tube.

18. An arrangement as defined in claim 17, wherein said annular space is evacuated.

19. An arrangement as defined in claim 17, wherein 3,302,419 2/1967 Walter 62-55 said coupling means comprises a quantity of high-boiling 3,315,478 4/1967 Walsh et a1. 6255 gaseous matter received in said annular space and adapted to freeze in response to the presence of said fluid FOREIGN PATENTS in said conduit means, 5 1,685,695 10/ 1954 Germany.

Ref r n Cit d LLOYD L. KING, Primary Examiner UNITED STATES PATENTS CL 3,068,026 12/1962 McKamey 28547 62-514 3,201,947 8/1965 Post et a1. 62-55 10