The present invention relates to a device for coupling together two vacuum lines, so that when coupled together, the lines can be rotated relative to one another, each of said vacuum lines including two mutually concentrical pipes (1, 2) which form therebetween a vacuum space (3) and the inner (2) of said pipes forming a fluid transport channel. The in¬ vention also relates to a first and a second coupling part of a first and a second vacuum lines respectively forming part of the coupling device.

Vacuum lines of the aforedescribed kind are used, among other things, to convey cryogenic liquids, the vacuum prevailing between the inner transport pipe and the surrounding outer pipe forming an effective insulation. Such vacuum line arrangements may, of course, also be used beneficially for the transportation of hot media.

Difficulties are experienced in the case of some ap¬ plications in which two sections of such a vacuum line are to be coupled together in a manner which will enable the sections to be rotated relative to one another, for instance when the vacuum line is to be used for the transportation of a coolant, e.g. liquid nitrogen, to movable equipment, these difficulties being particularly manifest when the application concerned requires frequent rotation between the line sec¬ tions. One problem in this respect resides in the fact that the requisite elastic sealing rings are unable to withstand the low or high temperatures concerned. Normally, a sealing ring made of some suitable material, for instance a rubber composition, cannot be subjected to temperatures beneath - 40°C and remain effective. This temperature shall be compared with the temperature of liquid nitrogen, i.e. -196°C, which one is often desirous of using for cooling (chilling) purposes among- others. The main object of the present invention is to provide a solution to the aforesaid problem, such that two vacuum lines can be mutually coupled in a manner which will enable the vacuum lines to be rotated relative to one another, with

the aid of elastic sealing rings, e.g. 0-rings, without the sealing rings being subjected to excessively low or excessively high temperatures, even when transporting very cold or very hot media respectively. This object is achieved in accordance with the present invention by configuring the parts that form said coupling device in a manner such that the sealing rings will not come into direct contact with the cold or the hot medium and by providing a wall which encloses said medium or with a wall which has become cold or hot respectively by thermal conduction from material in direct contact with the medium.

An inventive device intended for coupling together two vacuum lines so that, when coupled, the lines can be rotated relative to one another has the characteristic features set forth in Claim 1.

A first coupling part of a vacuum line which is intended to be coupled to a second coupling part of a second vacuum line has the characteristic features set forth in Claim 9, whereas a second coupling part of a vacuum line intended to be coupled to the first coupling part of the first vacuum line, in accordance with the invention, has the characteristic features set forth in Claim 17.

The invention will now be described in more detail with reference to the exemplifying embodiments illustrated in the accompanying drawings.

Figure 1 is a sectional view of an inventive first cou¬ pling part of a vacuum line.

Figure 2 is a sectional view of an inventive second coupling part of a vacuum line. Figure 3 illustrates an inventive coupling device which includes the coupling parts shown in Figures 1 and 2.

Figure 4 illustrates an inventive coupling device which includes a slightly modified version of the inventive coupling parts. In Figure 1, the reference numeral 1 identifies the outer pipe and the numeral 2 identifies the inner pipe of a vacuum line. The inner pipe 2 is intended for the transportation of fluid, e.g. a cryogenic liquid, such as

liquid nitrogen having a temperature of -196°C. The space 3 formed between the pipes 1 and 2 is sealed hermetically at the ends of respective line sections and is under an insulating vacuum in the order of 10 —6 mbars. This vacuum space results in the minimum of heat transfer between the pipe 1 and the pipe 2.

In the case of the coupling part illustrated in Figure 1, this coupling part hereinafter being referred to as the male part, the inner pipe 2 extends beyond the end of the outer pipe 1. Part of the outwardly projecting portion of the inner pipe 2 is surrounded by a first, sleeve-like thin-wall element, the front end of which is connected to the outer surface of the inner pipe 2 by means of a first end-wall 5 in a manner, to obtain a vacuum seal. The rear end of the sleeve 4 is connected to the outer pipe 1 by means of a second end- wall 6, also in a manner to obtain a vacuum seal. A first an¬ nular member 7 extends from the end-wall 6 in a direction towards the first end-wall 5, such as to form a narrow gap 8 between the inner surface of the annular member 7 and the outer surface of the sleeve 4, this gap extending from end-wall 6 and terminates at the front end of the member 7. This annular member 7 has a rear part 9 of smaller outer diameter than the front part 10 of said member. An engagement shoulder 24 is formed between the parts 9 and 10. Formed in the part 10 of constant outer diameter are two grooves which each accommodate a respective resilient sealing ring 11, e.g. O-rings.

The annular member 7, the sleeve 4 and the end-walls 5 and 6 are preferably made of a material of low heat conductivity, for instance stainless steel. It is par¬ ticularly important that the end-wall 5 and the sleeve 4 have a low heat-conduct * capacity. The sealing rings 11, i.e. the illustrated 0-: s, may consist of material sold under the designations B na-N or Viton, or some other suitable material that can be exposed to temperatures as low as -40°C. Figure 2 illustrates a second coupling part which is intended for connection with the male part illustrated in Figure 1, this second coupling part being hereinafter called

the female part. The components of the vacuum line in Figure 2 have been given the same reference numerals as those used in Figure 1.

In the case of the illustrated female part, the inner pipe 2 is shorter than the outer pipe 1 and a second sleeve¬ like member 12 having a larger inner diameter than the outer diameter of the pipe 2 extends concentrically with the pipe 2, from the end of said pipe to the end of the outer pipe 1. The rear end of the sleeve 12 is connected to the inner pipe 2 by means of a third end-wall 13, in a manner to obtain a vacuum seal. The front end of the sleeve 12 is connected to the outer pipe 1 by means of a fourth end-wall 14 in a manner to obtain a vacuum seal. A second member 15 of annular cross- section extends from the end-wall 14 in a direction away from the third end-wall 13, said second annular member 15 having a larger inner diameter than the sleeve 12 and merging at its front end with a connecting flange 16.

In the case of the illustrated embodiment, the front part 17 of the sleeve 12 has a larger diameter than the rear part 18, such that the wall 19 which connects the parts 17 and 18 forms an engagement shoulder, the function of which will be described hereinafter. The wall 19 may optionally extend somewhat into the sleeve 12. Alternatively, the sleeve 12 may have a constant outer diameter and an engagement shoulder formed at the junction between the fourth end-wall 14 and the sleeve 12. This shoulder may also extend somewhat into the sleeve 12, if desired.

The annular member 15 with associated flange 16 is pre¬ ferably made of stainless steel and has a relatively large mass and a large exposure surface to the atmosphere surrounding the coupling.

Figure 3 illustrates the male and female parts shown in Figures 1 and 2 respectively in a mutually coupled state, the same reference- numerals being used as those in the earlier Figures.

It will be seen from Figure 3 that the diameter of the front part of the first annular member 7 is so adapted that when coupling the male and female parts together, this part

is received with a small clearance in the hollow of the second annular member 15 of said female part. The sealing rings 11 will therewith form an effective seal between the mutually opposing surfaces of the annular members 7 and 15. Arranged between the sleeve 12 of the female part and the inner pipe 2 of the male part is a guide and bearing sleeve 20, which is made of a low-friction material capable of withstanding low and/or high temperatures, suitably polytetrafluoroethylene, referred to in the following and in the Claims as PTFE. The shoulder formed by the connecting wall 19 between the sleeve 12 and the parts 17 and 18 coacts with a corresponding shoulder formed on the outer surface of the bearing sleeve 20.

In order to ensure that the male and female parts of the coupling are held positively connected subsequent to being coupled together, the inventive coupling device also includes a loose flange 21. In the case of the Figure 3 embodiment, the inner diameter of the flange 21 is greater than the outer diameter of the front part 10, so as to enable the loose flange 21 to be fitted around the back part 9 of the first annular member 7. A two-piece or openable ring-shaped washer

25 made from, for instance, stainless steel and having an inner diameter which is smaller than the outer diameter of the front part 10 of the first annular member 7 is located in front of the flange 21. The flange 21 is drawn together with the end flange 16 of the female part with the aid of bolts 22 or like devices. In order to avoid metallic contact between particularly the first annular member 7 and the washer 25, a two-piece plate of low-friction material, suitably PTFE, is located between the flange 21 with the washer 25 and the member 7 and the flange 16 respectively.

Thus, when tightening the flange connection the male and female parts will be urged towards one another and held fixed in a compressed state by forces transmitted from the flange 21 to the male coupling part, via the washer 25, the plate 23 and the engagement shoulders 24, at the same time as one end of the guide-and-bearing sleeve 20 coacts with the first end- wall 6 and the sh* ilder formed by the wall 19 coacts with a

corresponding shoulder on the outer surface of the sleeve 20. Figure 4 illustrates an alternative embodiment of an inventive device, wherewith the same reference numerals have been used as those used in Figure 3. In the case of the Figure 4 embodiment, the sealing rings 11 have been located in the second annular member 15 of the female part, which therefore presents a part of constant inner diameter which is located opposite a corresponding part of the front part 10 of constant outer diameter of the first annular member 7. In other respects, these components may present conically con¬ figured parts, if desired. Such conical parts may also be included in the Figure 3 embodiment.

The washer 25 of the Figure 3 embodiment is omitted in the Figure 4 embodiment, in which the flange 21 is a two-part or openable flange and has an inner diameter which is smaller than the diameter of the front part 10 of the first annular member 7.

Those components of an inventive coupling which are liable to wear when the two connected vacuum lines are rotated relative to one another are the sealing rings 11, the bearing sleeve 20 and the plate 23, these components being readily replaced at low costs. In order to improve the seal and to reduce the friction on the sealing rings 11, the rings are preferably lubricated with a substance which will withstand lowor hightemperatures, for instance siliconegrease.

The most sensitive components of the coupling device, i.e. the sealing rings 11, are so located as not to be exposed to extreme temperatures, even when very cold or very hot media are transported in the inner pipe 2. The thermal transmission path through metal between the inner pipe 2 and the sealing rings 11 is long and continues over a long path of thin material, preferably material of poor thermal conductivity. This path thus includes the first end-wall 5, the thin-wall sleeve 4, the end-wall 6, the back part 9 of small diameter on the first annular member 7 and the front part 10 of said member. The labyrinth-like path exhibits high resistance to thermal transports, and hence the sealing rings 11 are exposed only to a moderately low temperature, even

when the pipe 2 transports liquid nitrogen.

Even though the b«- aring sleeve 20 forms a good seal with the sleeve 12, when the line comprising said mutually coupled line sections is used, for instance, to transport liquid nitrogen, a small quantity of nitrogen may possibly penetrate into the closed cavities or hollows formed between the sleeve 4 and the members 14 and 15, and 7 respectively. As described above, these cavities are closed, i.e. the sealing rings 11 cut-off the connection to ambient surroundings, and hence no medium is able to flow from the inner pipe 2 to the surroundings. Any liquid nitrogen which penetrates into said cavities will be vaporized and heated as a result, inter alia, of contact with the second annular member 15 of relatively large mass and relatively large heat-absorbing surface area, and will therewith be present in a gaseous state in said cavities. In order to minimize the quantity of coolant capable of penetrating into said cavities, the volumes of these cavities shall be as small as possible. Trials carried out with a coupling constructed in accordance with the invention have shown that when transporting liquid nitrogen (-196°C) along the inner pipe 2, the temperature of vaporized nitrogen resides in the vicinity of the sealing rings 11 is only about -6°C. Since the sealing rings shall be capable of withstanding temperatures down to -40°C, there is thus a comfortable safety margin.

A coupling of the aforedescribed kind can be used within many different fields, and is very compact and has a long useful life span. Furthermore, worn components can be readily replaced, as mentioned in the aforegoing. It will be understood that the inventive coupling device is not restricted to use for coupling together vacuum lines which, when coupled, shall be rotatable relative to one another. For instance, the inventive male or female coupling parts may be incorporated in a fluid receiving apparatus which is intended to rotate relative to a vacuum line. A corresponding male or female part respectively can be coupled to the receiving apparatus. The male or female coupling part present in the receiving apparatus must be configured so that

the sealing rings will not be exposed to extremely high or low temperatures when coupling to the vacuum pipe.