Pump for cryogenic liquid

Abstract

The invention relates to a pump (1) for cryogenic liquids, comprising at least one static seal (2) able to provide sealing between a first mechanical component (3) and a second mechanical component (8), the first mechanical component (3) having a duct (4) intended to contain a cryogenic liquid, with an opening (5) in one end (6) of the first mechanical component, said end (6) of the first mechanical component having a contact surface (7), the seal having a first face (9) bearing against the contact surface (7) of the first mechanical component (3) and a second face (10) bearing against a contact surface (11) of the second mechanical component (8) located at one end (15) of the second mechanical component, characterized in that the contact surface (7) of the first mechanical component (3) comprises at least one closed groove (12) surrounding the opening (5) in the end (6) of the first mechanical component.

Description

CRYOGENIC LIQUID PUMP Designation of the technical field concerned

[0001] The present invention relates to cryogenic installations for the production, storage or use of a cryogenic liquid. It relates more particularly to pumps which ensure the flow of cryogenic liquid in said installations. The invention is particularly suitable for pumps for liquid hydrogen. Technical problems addressed by the invention

[0002] A cryogenic liquid pump includes several static seals that ensure the pump is sealed against its external environment, or between compartments internal to the pump. These seals are generally toric in shape, inside which cryogenic liquid may be found. They are held between contact surfaces, two or more depending on the nature of the seal, that of its housing and the location of the seal in the pump. For example, a seal can be placed between two parallel surfaces with only two contact surfaces on either side of it, it can be placed in a triangular section groove with 3 contact surfaces, or it can be placed in a rectangular section groove, with 4 contact surfaces.

[0003] In state-of-the-art pumps for cryogenic liquids, copper seals or energized seals, e.g. lip seals with springs, are usually found between two parallel contact surfaces.

[0004] The bearing surfaces for static seals of cryogenic pumps according to the state of the art can be smooth surfaces but with machining grooves. These surfaces are generally obtained by turning or milling. The advance of the cutting tool during machining forms spiral-shaped grooves, thus creating a leak path for the cryogenic liquid.

[0005] The contact surfaces for static seals of cryogenic pumps according to the state of the art can also have smooth surfaces, without visible machining grooves. They are obtained, for example, by an initial turning or milling step followed by grinding. This type of surface finish is advantageous due to the absence of machining grooves, but the presence of an impurity between the surface and the static seal can create a leak path. Similarly, marking the surface by an object, a scratch, for example during assembly of the pump, handling or maintenance, can also create a leak path for the cryogenic liquid. These surfaces can thus be altered over time. Thus, the slightest imperfection can lead to a significant leak rate.

[0006] These small leak paths may not be a problem for some cryogenic liquids but they are for hydrogen due to the small size of the hydrogen molecule.

[0007] Seals used in cryogenic pumps are usually made of copper. Due to the low yield strength of copper, the presence of an impurity between the seal and a contact surface can increase the risk of leakage.

[0008] The invention provides a new solution to this problem.

[0009] According to the invention, there is provided a pump for cryogenic liquids comprising at least one static seal capable of ensuring a seal between a first mechanical part and a second mechanical part, the first mechanical part having a conduit intended to contain a cryogenic liquid with an opening in one end of the first mechanical part, said end of the first mechanical part having a contact surface, the seal having a first face bearing on the contact surface of the first mechanical part and a second face bearing on a contact surface of the second mechanical part arranged at one end of said second mechanical part, characterized in that the contact surface of the first mechanical part comprises at least one closed groove surrounding the opening in the end of the first mechanical part,and in that the second mechanical part has a conduit for containing a cryogenic liquid with an opening in the end of the second mechanical part, the seal having an opening connecting the openings of the first and second mechanical parts, and in that the contact surface of the second mechanical part comprises at least one closed groove surrounding the opening in the end of the second mechanical part.,

[0010] Advantageously according to the invention, the contact surface of the first mechanical part comprises a plurality of successive closed grooves starting from the opening of the conduit of the first mechanical part, a first groove being closest to the opening, the second groove and the following ones surrounding the groove(s) arranged closer to the opening of the conduit of the first mechanical part.

[0011] The closed groove(s) have for example been formed by a cutting tool during a machining operation. For example, closed grooves are formed by a cutting tool during turning machining of the contact surface. To obtain closed grooves, the tool is advanced towards the duct, or from the duct, while the cutting tool is retracted from the surface. Machining is thus carried out by a succession of successive machining steps. Let us take the example where the machining of the bearing surface is carried out from the outside thereof, that is to say from a point furthest radially from the duct. While it is in a position retracted from the surface to be machined, the cutting tool is positioned radially at a first position. The tool is then advanced towards the surface to carry out a first machining operation.Once this is done, the tool is withdrawn from the support surface and then moved radially to a second position, closer to the duct. The tool is then advanced towards the surface to carry out a second machining operation. The operation is repeated as many times as necessary to machine the entire support surface. The amount of radial movement of the tool between two machining operations, and the depth of penetration of the tool during machining, are adapted according to the shape and dimensions of the cutting surface of the tool so as to obtain machining of the entire support surface. This will include as many closed grooves as there are operations of radial movement of the tool in the withdrawal position followed by machining.

[0012] Advantageously, the contact surface of the second mechanical part comprises a plurality of successive closed grooves starting from the opening of the second mechanical part, a first groove being closest to the opening, the second and subsequent grooves of the contact surface of the second mechanical part surrounding the groove(s) of the surface of the contact surface of the second mechanical part arranged closer to the opening in the end of the second mechanical part.

[0013] The presence of closed grooves according to the invention on the two opposite contact surfaces between which the static seal is positioned ensures a seal on either side of the seal.

[0014] Advantageously, the closed grooves are concentric. They can also be circular. The distance between two neighboring closed grooves can be the same for all the closed grooves present on a bearing surface.

[0015] Advantageously, the closed grooves form closed furrows delimited by projecting edges. These are imprinted in the seal by a local deformation of the latter due to the compression of the seal which results from the clamping force exerted by the two bearing surfaces. The edges thus form successive barriers which block the escape of the cryogenic liquid.

[0016] Advantageously, the static seal also ensures a seal with a third mechanical part, the seal having a third face bearing on a contact surface of the third mechanical part, characterized in that the contact surface of the third mechanical part is free of grooves.

[0017] Depending on its nature and location in the pump, the static seal can also provide a seal with a third mechanical part, the seal having a third face resting on a contact surface of the third mechanical part, the pump then being characterized in that the contact surface of the third mechanical part is without a groove. This type of seal is found in particular between the cylinder head and the sleeve, and the sleeve and the cylinder of the pump. The housing in which the seal is placed, formed by the three mechanical parts, is advantageously of triangular section, just like the seal. In this case, the static seal advantageously forms a torus of triangular section.

[0018] Advantageously, the static seal is made of polymer. Polymers have a yield strength that is higher than that of copper. In addition, they are highly resistant to cryogenic temperatures. They have superior sealing characteristics to metals. They withstand traction and creep well. The use of a polymer also makes it possible to overcome any imperfections that may be present on the bearing surfaces of the static seals. The polymer has plasticity and mechanical properties that allow it to better conform to these imperfections than copper, which improves the seal at the static seal.

[0019] Advantageously, the static seal can be made of polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), or polyimide. These materials are advantageous in particular because their coefficients of expansion are low compared to other polymers. The static seal is therefore better able to maintain good dimensional stability even when subjected to temperatures ranging from cryogenic to ambient temperatures.

[0020] A pump according to the invention is particularly suitable for pumping liquid hydrogen. Brief description of the figures

[0021] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0022] is a schematic and partial view, in section, of a pump at the level of a static seal placed between two contact surfaces in which the static seal makes it possible to obstruct a conduit, the seal being in the working position;

[0023] is a schematic and partial view of a pump at a static seal according to the, in exploded view at the seal for better visualization of the seal contact surfaces;

[0024] is a schematic and partial view, in section, of a pump at the level of a static seal placed between two contact surfaces according to an exemplary embodiment of the invention in which the static seal ensures sealing during the continuity of a conduit between two parts, the seal being in the working position;

[0025] is a schematic and partial view of a pump at a static seal according to the, in exploded view at the seal for better visualization of the seal contact surfaces;

[0026] is a schematic and partial view, in section, of a pump at the level of a static seal placed between three contact surfaces according to an exemplary embodiment of the invention in which the static seal ensures sealing during the continuity of a conduit between two parts, the seal being in the working position;

[0027] is a schematic and partial view of a pump at a static seal according to the, in exploded view at the seal for better visualization of the seal contact surfaces;

[0028] is a schematic and partial view, seen from above, of a contact surface comprising grooves according to an exemplary embodiment of the invention; and

[0029] is a schematic and partial view, in section, of the contact surface of according to the. Detailed description

[0030] Referring to the, we can see a static flat seal 2 placed between a first mechanical part 3 and a second mechanical part 8, in which the static seal makes it possible to obstruct a conduit 4 having an axis A, intended to receive a cryogenic liquid, from the first part 3, the seal being shown in the working position.

[0031] Referring to the, the same static flat seal 2 can be seen as in, but in a mounting position facilitating the description of the invention. The conduit 4 has an opening 5 in one end 6 of the first mechanical part, said end 6 of the first mechanical part having a contact surface 7, the seal having a first face 9 bearing on the contact surface 7 of the first mechanical part 3 and a second face 10 bearing on a contact surface 11 of the second mechanical part 8 arranged at one end 15 of said second mechanical part.

[0032] The seal comprises a first face 9 intended to bear on a contact surface 7 of the first part 3. It also comprises a second face 10 intended to bear on a contact surface 11 of the second part 8. The contact surface 7 of the first mechanical part comprises closed grooves according to the invention. The contact surface 11 of the second mechanical part does not need to have closed grooves according to the invention because it does not have to provide a sealing function. After positioning the seal between the two mechanical parts, a clamping force is applied by the two mechanical parts so as to compress the seal. Since the seal is made of polymer, it deforms during compression. As illustrated in, the closed grooves present on the contact surface 7 comprise a closed projecting edge forming a crest 18 between two closed grooves 17.The compression of the seal and its elastic material allow the face 9 of the seal to perfectly match the contact surface of the first mechanical part 3. Thus, the seal fills the grooves 17 and the projecting edges are imprinted in the seal, forming successive barriers, these being as many obstacles to the flow of liquid between the face 9 of the seal and the contact surface 7 of the first mechanical part. The seal thus makes it possible to completely obstruct the opening 5 of the conduit 4 of the first mechanical part.

[0033] Referring to the, we can see a static flat seal 2 placed between a first mechanical part 3 and a second mechanical part 8, according to an exemplary embodiment of the invention in which the static seal makes it possible to ensure the sealing of the fluidic continuity between a conduit 4 of the first part 3 and a conduit 13 of the second part 8, intended to receive a cryogenic liquid, the seal being shown in the working position.

[0034] Referring to the, the same static flat seal 2 can be seen as in, but in a mounting position facilitating the description of the invention. The second mechanical part 8 has a conduit 13 with an opening 14 in one end 15 of the second mechanical part. The seal has an opening 16 connecting the openings 5, 14 of the first and second mechanical parts. The seal comprises a first face 9 intended to bear on a contact surface 7 of the first part 3. It also comprises a second face 10 intended to bear on a contact surface 11 of the second part 8. In this example, the seal must ensure sealing on its two opposite faces 9, 10. The two contact surfaces 7, 11 thus comprise closed grooves according to the invention.As in the example illustrated in, after positioning the seal between the two mechanical parts, a clamping force is applied by the two mechanical parts so as to compress the seal. The compression of the seal and its elastic material allow the two bearing faces of the seal to perfectly match the contact surfaces of the mechanical parts. Thus, the seal fills the grooves 17 of the two contact surfaces and the projecting edges of these are imprinted in the seal, forming successive barriers, preventing the flow of liquid between the two faces of the seal and the contact surfaces of the mechanical parts. Sealing during the passage of a cryogenic liquid from conduit 4 to conduit 13 is thus ensured.

[0035] Referring to the, we can see a static seal 2 of triangular section placed between a first mechanical part 3, a second mechanical part 8, and a third mechanical part 19 according to an exemplary embodiment of the invention in which the static seal makes it possible to ensure a sealed fluid continuity between a conduit 4 of the first part 3 and a conduit 13 of the second part 8, the seal being shown in the working position. The housing in which the seal is placed, formed by the three mechanical parts, is of triangular section.

[0036] Referring to the, we can see the same static seal 2 as in, but in a mounting position facilitating the description of the invention. The seal comprises a first face 9 intended to bear on a contact surface 7 of the first part 3. It comprises a second face 10 intended to bear on a contact surface 11 of the second part 8. It also comprises a third face 20 intended to bear on a contact surface 21 of the third part 19. In this example, the seal must ensure a seal on its two opposite faces 9, 10. This function being ensured on these two faces, the third face 20 of the seal does not need to ensure a seal. It is nevertheless advantageous that it also ensures a seal to reinforce the overall seal obtained by the seal. Only the two opposite contact surfaces 7, 11 comprise closed grooves according to the invention.The third contact surface 21 is perfectly smooth and therefore has no grooves.

[0037] The third contact surface serves in particular as a guide during the installation of the seal. Thus, the third face 20 of the seal slides on the contact surface 21 of the third mechanical part when the seal is installed during assembly of the pump. A sliding of the third face of the seal on the contact surface of the third mechanical part can also result from a differential expansion of the third mechanical part relative to the other two. If grooves were present on the third mechanical part, they would have the effect of damaging the seal, by an effect similar to planing.

[0038] Advantageously, the seal has a triangular section slightly larger than that of the housing in which it is placed. Thus, when the seal is compressed by tightening the first two parts 3, 8, the force exerted by the first two contact surfaces, those which comprise closed grooves according to the invention, causes a deformation of the seal towards the third contact surface. This configuration makes it possible to best fill the volume in which the seal is placed and maximizes the extent of the surfaces of the seal bearing on the contact surfaces.

[0039] Referring to the, one can see represented, in top view, the contact surface 7 of a mechanical part 3 comprising a plurality of closed grooves 12 according to an exemplary embodiment of the invention.

[0040] The contact surface surrounds a conduit 4 intended to receive a cryogenic liquid. In this example, the closed grooves are circular and concentric around the axis A of the conduit 4, with a constant distance between two grooves along the length of the grooves and a constant distance between two successive grooves. The grooves could be non-circular, of any shape. Thus, the distance from a groove to the axis of the conduit 4 can vary along the length of the groove. Similarly, the distance between two grooves can vary along the length of the grooves, these being able to be closer in places and being further apart in other places. The distance between two successive grooves can also be different, these being able, for example, to be closer in the vicinity of the conduit 4 and being further apart on the outside of the contact surface. The only constraint is that the grooves are closed to block the flow of the cryogenic liquid.

[0041] Referring to the, the contact surface of the can be partially shown, in section along the section plane CC shown in the. The closed grooves 12 present on the contact surface 7 comprise a closed projecting edge forming a crest 18 between two closed grooves 17.

Claims

Pump (1) for cryogenic liquids comprising at least one static seal (2) capable of ensuring a seal between a first mechanical part (3) and a second mechanical part (8), the first mechanical part (3) having a conduit (4) intended to contain a cryogenic liquid with an opening (5) in one end (6) of the first mechanical part, said end (6) of the first mechanical part having a contact surface (7), the seal having a first face (9) bearing on the contact surface (7) of the first mechanical part (3) and a second face (10) bearing on a contact surface (11) of the second mechanical part (8) arranged at one end (15) of said second mechanical part, characterized in that the contact surface (7) of the first mechanical part (3) comprises at least one closed groove (12) surrounding the opening (5) in the end (6) of the first mechanical part,in that the second mechanical part (8) has a conduit (13) intended to contain a cryogenic liquid with an opening (14) in the end (15) of the second mechanical part, the seal (2) having an opening (16) connecting the openings (5, 14) of the first and second mechanical parts, and in that the contact surface (11) of the second mechanical part (8) comprises at least one closed groove (12) surrounding the opening (14) in the end (15) of the second mechanical part., Pump according to claim 1, characterized in that the contact surface (7) of the first mechanical part (3) comprises a plurality of successive closed grooves (12) starting from the opening (5) of the conduit (4) of the first mechanical part, a first groove being closest to the opening (5), the second and subsequent grooves surrounding the groove(s) arranged closer to the opening (5) of the conduit (4) of the first mechanical part. Pump according to claim 1, characterized in that the contact surface (11) of the second mechanical part (8) comprises a plurality of successive closed grooves (12) starting from the opening (14) of the second mechanical part, a first groove being closest to the opening (14), the second and subsequent grooves of the contact surface (11) of the second mechanical part (8) surrounding the groove(s) of the surface (11) of the contact surface of the second mechanical part (8) arranged closer to the opening (14) in the end (15) of the second mechanical part. Pump according to one of claims 2 or 3, characterized in that the closed grooves (12) are concentric. Pump according to one of the preceding claims, characterized in that the closed grooves (12) form closed furrows (17) delimited by projecting edges (18). Pump according to one of the preceding claims, the static seal (2) also ensures a seal with a third mechanical part (19), the seal having a third face (20) bearing on a contact surface (21) of the third mechanical part (19), characterized in that the contact surface (21) of the third mechanical part (19) is devoid of a groove (12). Pump according to claim 6, characterized in that the static seal (2) forms a torus of triangular section. Pump according to one of the preceding claims, characterized in that the static seal (2) is made of polymer. Pump according to claim 8, characterized in that the static seal (2) is made of polytetrafluoroethylene (PTFE). Pump according to claim 8, characterized in that the static seal (2) is made of Polychlorotrifluoroethylene (PCTFE). Pump according to claim 8, characterized in that the static seal (2) is made of polyimide. Pump according to one of the preceding claims, characterized in that it is capable of pumping liquid hydrogen.

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