Device for sealing an enclosure containing an expandable fluid, especially within an electrical connection assembly

A sealing device for an enclosure containing an expandable fluid, particularly for high-voltage connectors, ensures fluid-tightness over a broad temperature range and provides a safety function by accommodating variations in volume of the fluid by the use of an O-ring seal displaceably clamped within an annular recess. A sectional length L1 of the recess in which the seal can take up n positions is constituted by an initial-clamping space and by a clearance space into which the seal can penetrate under the pressure of fluid.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a device for sealing an enclosure which contains 
an expandable fluid, this device being particularly suitable for sealing 
within a high-voltage electrical connection assembly which makes use of an 
electrical insulating fluid. 
2. Description of the Prior Art 
Electrical connection assemblies are in common use, especially in the field 
of radiology in which they are used for supplying high voltage to x-ray 
tubes. 
To take as an example the supply of an x-ray tube, at least one of the 
positive or negative polarities of the high voltage applied to the x-ray 
tube exhibits a considerable difference in voltage with respect to ground. 
The x-ray tube is usually contained within a protective housing which is 
brought to ground potential and in which the x-ray tube is connected to 
electrical connection means which are rigidly fixed to the housing and 
terminate outside this latter. These connection means associated with the 
housing usually constitute receptacles formed by a female component in the 
bottom of which is placed at least one electric contact element connected 
to the x-ray tube. The high voltage produced by a high-voltage generator 
is supplied to the receptacle by means of a high-insulation-resistance 
cable provided with an end-piece on the cable end to be connected to the 
receptacle. The end-piece constitutes a male component having a diameter 
which is smaller than the internal diameter of the receptacle and provided 
at its extremity with at least a second contact element which is brought 
to the high-voltage potential. The end-piece is engaged in the receptacle 
in such a manner as to establish an electric contact between the contact 
elements. 
The male and female components or so-called end-pieces and receptacles, are 
fabricated from electrically insulating materials and are each endowed 
with the requisite electrical insulation properties. Along the walls 
opposite to the end-piece and the receptacle, however, the interface space 
between these walls is liable to cause breakdown or sparking if this 
interface space does not have sufficient dielectric rigidity. 
Consequently, in order to achieve higher electrical insulation, it is a 
known practice to fill the interface space with an insulating fluid such 
as oil or grease while taking steps to ensure that no air is incorporated 
in the fluid. The interface space is closed by a seal which usually has a 
toric shape so as to be placed around the male component and so as to be 
clamped between this latter and the female component. 
In accordance with a customary practice, the housing which contains the 
x-ray tube is caused to assume different positions and angles of slope in 
which the seal prevents the insulating fluid from flowing out to the 
exterior of the enclosure. It is none the less found that leakages of 
insulating fluid occur when the x-ray tube has been subjected to intensive 
operation and when it produces a temperature rise of the housing and 
consequently a temperature rise of the entire electrical connection 
assembly. 
The inventor has considered that these leakages were due to expansion of 
the insulating fluid which is not compressible and accordingly exerts on 
the seal a thrust which is greater as the temperature attained is of 
higher value, this phenomenon being evidenced by leakages of the 
insulating fluid which appear only when the x-ray tube is subjected to 
intensive use and when the entire volume of the enclosure is filled with 
the expanded fluid. A point worthy of note is that, in the prior art, this 
phenomenon could eventually produce breakdown of the entire electrical 
connection assembly in the event that perfect fluidtightness is provided 
by the seal. Stated in different terms, the seal assumes a safety function 
by imperfect performance of its sealing function. 
SUMMARY OF THE INVENTION 
The present invention relates to a sealing device designed in accordance 
with a novel arrangement which is applicable to all assemblies containing 
an expandable fluid, especially in an electrical connection assembly for 
high voltage, which makes it possible to ensure leak-tightness with 
respect to the expandable fluid over a broad temperature range and which 
also makes it possible to ensure a safety function as mentioned earlier 
when the fluid undergoes excessive expansion. 
In accordance with the invention, a device for sealing an enclosure fitted 
with at least one O-ring seal, the enclosure being constituted by the 
assembly of at least two components between which an internal space 
contains an expandable fluid, the seal being contained within an annular 
recess located between the two components about an axis of symmetry, said 
recess being adapted to communicate with the internal space, said seal 
being clamped between two opposite walls of the recess, is distinguished 
by the fact that provision is made along the section of the annular recess 
for a length in which the seal is capable of moving and of occupying n 
positions, the length of the annular recess being constituted by an 
initial clamping space and by a clearance space, the initial clamping 
space being such as to correspond to an initial position of the seal and 
the clearance space being located on one side of the seal which is remote 
from the internal space, with the result that the seal penetrates into the 
clearance space under the pressure of the expanded fluid.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows by way of non-limitative example a sealing device according to 
the invention as employed in a high-voltage electrical connection assembly 
1 of the type which is intended to be mounted on a housing 2 containing an 
x-ray tube (not shown in the drawings) in the conventional manner. 
The connection assembly 1 includes an end-piece 3 or male component engaged 
within a receptacle 4 or female component having the general shape of a 
cylindrical vessel 12. The housing 2 has an orifice 5 of circular 
cross-section formed by a tube 6 having an axis of symmetry 7. The closed 
end 8 of the receptacle 4 is engaged within the orifice 5 along the axis 
of symmetry 7. 
The receptacle 4 is provided at its second extremity 9 with an annular 
attachment flange 10, the external diameter D1 of which is larger than the 
second external diameter D2 of the cylindrical vessel 12 of the receptacle 
4. The receptacle 4 is inserted in the tube 6 so as to ensure that the 
annular attachment flange 10 is applied against an abutment flange 11 
located within the interior of the tube 6. In the non-limitative example 
described and illustrated in FIG. 1, the annular attachment flange 10 has 
a top face 14 remote from the abutment flange 11. A hollowed-out portion 
located above said top face is intended to form an annular recess 16 which 
is substantially centered about the axis of symmetry 7 and is formed 
within the thickness E of the annular attachment flange 10. Along the 
plane of section S1 in which it is represented in the figure, the annular 
recess 16 has a first extremity 18 in proximity to the interior of the 
cylindrical vessel 12 and extends over a distance L1 towards a peripheral 
portion 24 of the annular attachment flange 10 up to the second extremity 
23 of the annular recess 16 at which this latter is closed by said 
peripheral portion 24. The annular recess 16 has a third external diameter 
D3 which is smaller than the external diameter D1 of the annular 
attachment flange 10, with the result that the full thickness E of this 
latter is located in its peripheral portion 24 whereas a reduced thickness 
(not indicated in the figure) is located in the portion corresponding to 
the annular recess 16 or in other words between the bottom wall 19 of the 
recess 16 and the abutment flange 11. 
The top face 14 of the annular attachment flange 10 thus constitutes on the 
peripheral portion 24 a bearing face 15 which is employed for attachment 
of the receptacle 4. 
The receptacle 4 is fixed within the orifice 5 by means of a ring 13 which 
is screwed into an internally-threaded portion 31 of the tube 6 until it 
is clamped against the bearing face 15 of the annular attachment flange 
10. The receptacle 4 and the end-piece 3 are provided respectively with a 
first and a second electric contact element 20, 21 which are brought into 
contact with each other when the end-piece 3 is fully engaged within the 
receptacle 4. The first contact element 20 is connected in a conventional 
manner (not shown in the drawings) to the device to be supplied and the 
second contact element 21 is also connected in a conventional manner by 
means of an electric cable 22 to a high-voltage generator (not 
illustrated). 
One extremity 26 of the end-piece 3 which is not engaged within the 
receptacle 4 is provided with a second annular attachment flange 27 having 
a fourth external diameter D4 which is substantially equal to or greater 
than the third external diameter D3 of the annular recess 16. The body 28 
of the end-piece 3 is engaged within the receptacle 4 so that an underface 
29 of the second annular attachment flange 27 is applied above the recess 
16 and compresses an O-ring seal 30 within said recess 16. If necessary, 
the aforesaid underface 29 may also be applied against the bearing face 
15. 
The end-piece 3 is joined to the receptacle 4 by means of a second ring 35 
which is screwed into the internally-threaded portion 31 of the tube 6 in 
order to clamp the second annular flange 27 against the seal 30 and to 
compress this latter. 
The internal surface 17 of the cylindrical vessel 12 of the receptacle 4 
and the external surface 41 of the body 28 of the end-piece 3 are in 
oppositely-facing relation but are not juxtaposed and these surfaces 17, 
41 define between each other an internal space 42 which contains an 
insulating fluid 48. The internal space 42 communicates with the annular 
recess 16 which is formed between a first wall constituted by the bottom 
wall 19 of this latter and a second wall constituted by the underface 29 
of the second annular flange 27. The seal 30 is thus clamped between the 
two opposite walls 19, 29 or in other words between the receptacle 4 and 
the end-piece 3 so as to ensure leak-tightness of the internal space 42. 
The O-ring seal 30 and the annular recess 16 constitute a sealing device in 
accordance with the invention. 
In accordance with a distinctive feature of the invention, the length L1 of 
the annular recess 16 is formed by an initial space 44 to which is added a 
clearance space 45. The initial space 44 corresponds to the space occupied 
by the seal 30 in an initial position P1 of this latter, for example a 
position in which the seal 30 is clamped between the walls 19, 29 at the 
moment of fastening of the end-piece 3 to the receptacle 4 and when the 
fluid 48 is not in the expanded state. This first position P1 is 
materialized in the figure by a dashed line which passes through the 
center 46 of the section S2 of the O-ring seal 30. The clearance space 45 
constitutes an additional space on one side 47 of the seal 30 remote from 
the internal space 42 within which the seal 30 can be displaced under the 
pressure of the fluid 48. 
Assuming that, at the outset or in other words in the cold state, the fluid 
48 contained in the internal space 42 is flush with the first extremity 18 
of the annular recess 16, expansion of the fluid 48 will cause this latter 
to thrust the seal 30 towards the second extremity 23 of the recess 16 as 
shown by the arrows 48. The seal 30 being clamped between the walls 19, 29 
in the first position P1, for example under a load which is sufficient to 
prevent leakages of fluid caused by tilting of the connection assembly 1, 
the seal 30 can occupy n additional positions P2, . . . - Pn with a view 
to increasing the useful internal space 42 as a function of the expansion 
of the fluid 48. 
The advantage of this configuration lies in the fact that the internal 
space 42 can be defined by the position P1, P2, . . . - Pn of the seal 30 
at the precise value which is necessary in order to compensate for 
variations in volume of the fluid 48. 
In the non-limitative example herein described, the seal 30 has a toric 
shape in accordance with a conventional design and a circular 
cross-sectional shape as shown in the figure. It must nevertheless be 
understood that there would be no departure from the spirit of the 
invention if the section S2 of the seal 30 were given a different shape. 
Said seal 30 is placed within the annular recess 16 around the body 28 of 
the end-piece 3 in a plane substantially normal to the axis of symmetry 7 
which also constitutes an axis of symmetry of the seal 30. 
The seal 30 being in the first position P1, the O-ring formed by said seal 
has a first mean radius R1 and the section of said seal 30 has a first 
radius r1 designated in the remainder of this specification as the short 
radius r1 in order to differentiate this latter more effectively from the 
mean radius R1 of the O-ring. Moreover, the annular recess 16 itself 
constitutes an annulus having the same axis of symmetry 7 as the O-ring 
formed by the seal 30. The difference between an internal radius ri and an 
external radius rE of the annulus formed by the recess 16 constitutes the 
length L1 of this latter in which the seal 30 is displaceable. In 
consequence, by moving over the distance L1 of the recess 16 from the 
first position P1 to the second position P2, for example, the seal 30 
undergoes a deformation and changes from the first mean radius R1 to a 
second mean radius R2, this second mean radius R2 being of greater length 
than the first. Consequently, when the O-ring formed by the seal 30 
changes from the first mean radius R1 to the second mean radius R2 of 
greater length, the section S2 of the seal 30 (represented in dashed lines 
in the second position P2) changes from the first short radius r1 to a 
second short radius r2 which is smaller than the first. In order to take 
into account the reduction in cross-section of the seal 30 with a view to 
ensuring that clamping of this latter remains substantially constant 
irrespective of the position P1, P2, . . . - Pn which it occupies within 
the annular recess 16, the distance d1, d2 between the walls 19, 29 is 
made progressively variable along the length L1 so that a first distance 
d1 between the walls 19, 29 near the first extremity 18 of the annular 
recess 16, that is to say in the first position P1, is greater than a 
second distance d2 between the walls 19, 29 in the second position P2. 
The seal 30 is of flexible elastic material such as, for example, rubber of 
the acrylonitrile-butadiene type. The O-ring formed by this seal therefore 
retains a substantially constant volume V when it changes from the first 
initial mean radius R1 to a second mean radius R2 of greater length and 
conversely. This conservation of volume of the O-ring formed by the seal 
30 can be employed for defining the slope P along which the distance d1, 
d2 between the two walls 19, 29 must vary. Since the slope P is the ratio 
of variation in distance .DELTA.d=d1-d2 to a second length L2 which 
separates the positions P1, P2 and which has produced this variation in 
distance .DELTA.d, the slope P is equal to: 
##EQU1## 
In the non-limitative example described, the length L1 of the annular 
recess 16 in which the O-ring seal 30 is capable of displacement is 
substantially perpendicular to the axis of symmetry 7 and the difference 
between the second and the first mean radius, that is to say R1-R2, 
directly corresponds to the second length L2 which constitutes the length 
of displacement of the seal 30 within the recess 16 between the positions 
P1, P2. However, the section S1 of the annulus formed by the recess 16 can 
have the same shape while being disposed in a different manner, for 
example with a view to giving the annular recess 16 a length L'1 
(represented by a dashed line in FIG. 1) such as to make with the axis of 
symmetry 7 an angle .alpha. having a value different from 90.degree., in 
which case the second length or length of displacement L2 is equal to: 
##EQU2## 
The first mean radius R1 as well as the first short radius r1 are known at 
the outset since the seal 30 is not deformed in the first position P1 and 
the volume V of the seal 30 is known and corresponds to: 
EQU V=2.pi..sup.2 .multidot.R1.multidot.r1.sup.2 (3) 
Since the volume V is constant in the deformations of the seal 30, the 
second short radius r2 exhibited by the section of the seal 30 in the 
second position P2 is given by the following relation: 
##EQU3## 
where R2 is the second mean radius exhibited by the annulus formed by the 
seal 30 in the second position P2. In consequence, the mean angle of slope 
P at which the distance d1, d2 between the walls 19, 29 varies is given by 
the following relation: 
##EQU4## 
In this first embodiment of the invention in which the O-ring seal 30 is 
displaced within the annular recess 16 under the pressure of the expanded 
fluid 48 along a length L1 which is not parallel to the axis of symmetry 
7, the seal 30 is deformed during these displacements, for example when it 
moves from the first initial position P1 to the second position P2. 
Deformation of the O-ring seal constitutes an advantage which assists this 
latter in returning to the initial first position P1 when the fluid 48 has 
been restored to its initial volume. In fact, when the fluid undergoes 
expansion, the seal 30 is thrust back within the recess 16 with a force of 
greater magnitude than the force exerted within said recess on the first 
side of the seal 30 which is remote from the internal space 42 by the air 
which may or may not be trapped within said recess 16. When no provision 
is made for special sealing means, the pressure which prevails within the 
recess 16 is that of the external pressure or in other words atmospheric 
pressure which tends to act in opposition to a movement of penetration of 
the seal 30 into the recess 16. For example, when the seal 30 has been 
moved to the second position P2 under the pressure of the expanded fluid 
48, said seal remains in this position as long as the volume of expansion 
of the fluid is maintained. When the fluid 48 subsequently decreases in 
volume and no longer exerts a thrust on the seal 30, this latter is 
returned under the action of atmospheric pressure towards the enclosure 42 
in the directions shown by the second arrows 60. 
To this action of air or atmospheric pressure which tends to thrust the 
seal 30 towards the initial first position P1 is added the effect produced 
by elasticity of the seal 30 which has been deformed so as to take up the 
second position P2 and tends under the action of its own elasticity to be 
restored to its first mean radius R1 which corresponds to the first 
position P1 or initial position of the seal 30. 
This first embodiment of the invention is particularly advantageous by 
virtue of the fact that, as a result of a small increase in the mean 
radius R1 of the O-ring which forms the seal 30, it is possible to obtain 
an increase in the internal space 42 which is considerably greater than 
the increase in volume which the fluid 48 is capable of acquiring by 
expansion. In fact, assuming that the electrical connection assembly 1 is 
of a conventional type and that the diameter (not shown) of the body 28 of 
the end-piece 3 is of the order of 20 mm: 
the insulating fluid 48 contained within the internal space 42 in the cold 
state or in other words at room temperature has a volume of substantially 
5 cm.sup.3 ; with a conventional insulating fluid such as oil or grease, 
this volume increases by approximately 0.5 cm.sup.3 in respect of an 
increase in temperature of the order of 100.degree. C.; 
and assuming that, in the first position P1, the first distance d1 between 
the walls 19, 29 is of the order of 5 mm or slightly less than the section 
of the seal 30 and that the first mean radius R1 is of the order of 22 mm, 
a displacement of the seal 30 over a second length L2 of the order of 2.5 
mm frees a space having a volume greater than 2.5 cm.sup.3 or in other 
words several times greater than the increase in volume of the insulating 
fluid 48 over a temperature range of 100.degree. C. 
In the non-limitative example herein described, the annular recess 16 is 
formed between the wall 29 or underface of the end-piece 3 and the wall 19 
of the receptacle 4. More specifically, the annular recess 16 is formed by 
a channel formed in the top face 14 of the first annular flange 10 which 
forms part of the receptacle 4. However, it must be understood that, in 
the -spirit of the invention, the recess 16 can be formed differently, for 
example by hollowing-out the underface 29 of the second annular flange 27. 
It is also possible to form the recess 16 in an intermediate member (not 
shown in FIG. 1) so as to avoid any need for complementary machining of 
the receptacle 4 and the end-piece 3 which, in the case of standardized 
electrical connection assemblies 1, constitute standard elements having 
fixed and standardized dimensions. 
FIG. 2 shows the electrical connection device 1 in which the sealing device 
in accordance with the invention includes an intermediate member for the 
purpose of forming the annular recess 16, the seal 30 being deformed in 
the same manner as in the preceding example when displaced within said 
recess 16. 
The receptacle 4 is applied against the abutment flange 11 of the tube 6 by 
means of the first annular attachment flange 10 and is clamped in position 
by means of the first ring 13. In the non-limitative example herein 
described, a clamping face 61 of the first ring 13 which is oriented 
towards the top face 14 of the first annular flange 10 has been cut in a 
second thickness E2 of the ring 13 so as to constitute the annular recess 
16. In this embodiment, the first ring 13 constitutes the aforementioned 
intermediate member. The recess 16 thus extends along its length L1 from 
the internal space 42 to a second peripheral portion 62 of the ring 13 
which closes the second end 23 of the recess 16. In this peripheral 
portion 62, the ring 13 has its full thickness E2. The second face 63 of 
the ring 13 which is oriented towards the second annular flange 27 of the 
end-piece 3 has a groove 64 in which is fitted a second seal 65 or 
so-called static seal. The end-piece 3 is engaged within the receptacle 4 
in the same manner as in the previous example and is clamped in position 
by the second clamping ring 35 so as to compress the static seal 65. 
Under these conditions, leak-tightness of the internal space 42 is achieved 
in the first place by the static seal 65 which retains a fixed position in 
the conventional manner. In the second place, leak-tightness of the 
enclosure 42 is achieved by means of the movable seal 30 which, as in the 
previous example, is capable of displacement in a movement of penetration 
into the annular recess 16 as a function of the expansion of the 
insulating fluid 48. In this embodiment of the invention, the walls of the 
annular recess 16 are formed in the case of the first wall by the top face 
14 of the annular flange 10 and in the case of the second wall by the 
surface 70 which is cut in the first clamping ring 13. These two walls 14, 
70 are relatively spaced at a distance d1, d2 which progressively 
decreases along the length L1 as considered in a direction of motion away 
from the internal space 42, and as in the previous example. The advantage 
of this embodiment of the invention lies in the fact that it permits the 
formation of a recess 16 having the same properties as in the previous 
example but without modifying either the receptacle 4 or the end-piece 3, 
this result being achieved by simple machining of the first clamping ring 
13. 
FIG. 3 shows the electrical connection assembly 1 and illustrates an 
embodiment of the sealing device according to the invention in which the 
length L1 of the annular recess 16 is substantially parallel to the plane 
of symmetry 7. 
The receptacle 4 is fixed within the tube 6 by means of the first clamping 
ring 13 which is brought into a position in which it is applied against 
the first annular flange 10. The end-piece 3 is engaged within the 
receptacle 4, with the result that its second annular flange 27 is applied 
against the first clamping ring 13 by means of the second clamping ring 
35. The internal space 42 is defined as in the previous examples between 
the internal and external surfaces 41, 17 of the receptacle 4 and of the 
end-piece 3 from the bottom endwall 9 of the receptacle 4 up to the first 
extremity 18 of the annular recess 16. The recess 16 is located in the 
line of extension of the internal space 42 and its length L1 is disposed 
in a direction parallel to the axis of symmetry 7. The recess 16 is formed 
between the external surface 17 of the body 28 of the end-piece 3 and an 
internal wall 66 of the receptacle 4 at which said receptacle has a fifth 
internal diameter D5 of greater length than a sixth diameter D6 measured 
across the internal space 42 of said receptacle. In consequence, the first 
extremity 18 of the annular recess 16 has the shape and function of an 
abutment shoulder against which the seal 30 can be applied in the first 
position P1. The seal 30 is placed within the recess 16 and constitutes a 
ring around the body 28 of the end-piece 3, the plane of said ring being 
normal to the axis of symmetry 7. In the non-compressed state (not shown), 
the seal 30 has a diameter which is slightly longer than the third 
distance d3 between the walls 66, 17 of the recess 16. In the 
nonlimitative example herein described, the first ring 13 has the same 
internal diameter (not shown) as the sixth diameter D6 in order to close 
the recess 16 to a partial extent at its second extremity 23. 
The enclosure 42 is filled with insulating fluid. When the insulating fluid 
48 expands, it thrusts the seal 30 into the recess 16 towards the second 
extremity 23 of this latter, with the result that the seal 30 occupies 
another position P2, Pn located nearer to the second extremity 23 of the 
recess 16 as the insulating fluid has expanded to a greater extent. Since 
the first side 47 of the seal 30 is in free air or at atmospheric 
pressure, the seal 30 is thrust back to the first position P1 when the 
fluid 48 decreases in volume. In this embodiment of the invention in which 
the length L1 of the recess 16 is substantially parallel to the axis of 
symmetry 7 along which the seal 13 also moves, the seal 30 does not 
undergo any deformation which would result in modification of the radius 
of its section S2. In consequence, the walls 66, 17 of the recess 16 can 
be parallel or in other words at a constant distance d3 from each other. 
In order to assist the return of the seal 30 to the first position P1, it 
is nevertheless possible to provide the annular recess 16 with walls 66, 
17 which are not parallel to each other in order to ensure that the 
distance from one wall to the other decreases progressively towards the 
second extremity 23 of the recess 16 with a fairly low angle of slope. 
In this configuration as in the preceding configurations, the seal 30 does 
not need to be powerfully clamped within the recess 16 since it is not 
required to afford resistance to very high pressures of the expanded fluid 
by reason of the fact that it is displaced and increases the useful volume 
of the enclosure 42 as a function of the expansion of fluid. In 
consequence, assuming that the reserve volume constituted by the recess 16 
is insufficient to compensate for expansion of the fluid, the seal 30 sets 
up only a relatively low resistance to the fluid which is permitted to 
pass out of the electrical connection assembly 1, thus preventing 
breakdown of this latter. 
The invention is applicable to enclosures containing an expandable fluid 
and is particularly wellsuited to high-voltage electrical connection 
assemblies for ensuring leak-tightness with respect to the fluid which 
serves to provide enhanced electrical insulation.