Piston intended for fluid machine and provided with system for pressing seal, and fluid machine comprising such piston

Abstract

A piston for a fluid machine, intended to be mounted at least partially inside a bushing of the fluid machine in such a way as to be relatively reciprocally movable relative to the bushing, the piston extending in a main direction and comprising a head having a first end of the piston and a shaft having a second end of the piston, according to the invention, the first end is intended to define a fluid expansion and / or compression chamber together with a bushing of the machine, the shaft comprising a side wall provided with at least one annular groove defined between a first and a second castellated member, the groove being equipped with a gasket-type seal for cooperating in a sealing manner with the side wall of the bushing, the seal is provided with a through-hole allowing fluid flow from the expansion and / or compression chamber to the second end, the seal comprising a cavity separate from the through-hole, the cavity comprising a compression system for pressing the seal against the first and second castellated members in the main direction, the compression system being of mechanical and / or fluidic type. The invention further relates to a fluid machine.

Description

Technical Field

[0001] This invention relates to a piston intended for use in fluid machinery and equipped with a system for compressing a seal. The seal in question is a loose seal that includes at least one orifice for fluid flow.

[0002] The present invention also relates to a fluid machine including such a piston. The fluid machine may be a pump or a compressor. The fluid in question may be cryogenic.

[0003] A piston for fluid machinery is designed to be mounted at least partially within a bushing in such a way that it reciprocates relative to the bushing of the machinery.

[0004] The piston extends in the main direction and includes a head having a first end of the piston and a shaft having a second end of the piston. The first and second ends of the piston are defined according to the main direction.

[0005] The first end of the piston is designed to form a fluid expansion and / or compression chamber together with the bushing of the machine.

[0006] The shaft includes a sidewall having at least one annular groove defined between the first pheasant-shaped member and the second pheasant-shaped member.

[0007] Specifically, the annular groove is equipped with at least one gasket-type seal designed to mate with the sidewall of the bushing of the machine. The at least one gasket-type seal is provided with a through-hole designed to allow fluid flow from the expansion and / or compression chamber to a second end of the piston.

[0008] The one or more gasket-type seals primarily ensure a seal in the compression chamber without impeding the relative movement of the piston relative to the bushing. In other words, the one or more gasket-type seals allow the piston to move relative to the bushing with virtually no friction.

[0009] Furthermore, the one or more gasket-type seals ensure the proper functioning of the fluid machinery and greatly contribute to meeting the specifications of the fluid machinery, especially the pumped flow rate / velocity.

[0010] Finally, the one or more seals enable the reduction of leakage and BOG (boiled gas). Background Technology

[0011] Boiling gas (BOG) is an irreversible vaporized fluid that cannot be liquefied again without external cooling or extraction work. BOG may be caused by entropy resulting from the heat input to the expansion chamber (imperfect insulation mass), or by friction caused by leakage and / or enthalpy expansion such as Joule-Thomson expansion.

[0012] To perform the aforementioned functions, a sufficient number of gasket seals are required, depending on the performance of each seal, the pressure involved, and other factors such as the fluid itself. Furthermore, for optimal operation of the fluid machinery under high pressure and extremely low temperatures, the gasket seals need to possess good mechanical integrity.

[0013] In most cases, a pair of gasket-type seals are provided in each groove: a first gasket-type seal contacts the first crenellated part of the groove, and a second gasket-type seal contacts the second crenellated part of the groove. Starting from the piston head, the first gasket-type seal precedes the second gasket-type seal.

[0014] The first washer-type seal is fitted with a first through hole. The second washer-type seal is fitted with a second through hole. Furthermore, the first and second washer-type seals are arranged in a groove such that their respective through holes are angularly offset / misaligned with each other about the main axis of the piston.

[0015] Therefore, the fluid flow originating from the compression chamber flows along the leakage path, which passes through the first orifice of the first gasket seal, then flows along the interface between the two gasket seals, and then passes through the second orifice of the second gasket seal.

[0016] When an axial clearance (i.e., a clearance in the main direction of the piston) is formed between the first gasket seal and the first crenellated member, the fluid flow originating from the compression chamber no longer has to pass through the first orifice of the first gasket seal. A portion of the flow bypasses the first and second through orifices and flows into the gap between the seal and the piston sidewall and / or the gap between the seal and the bushing sidewall.

[0017] A change in the leakage path represents a loss of seal and a deterioration in the performance of the machine.

[0018] Therefore, there is a need to develop a new type of piston in which the flow originating from the compression chamber passes primarily through a through-hole designed for this purpose, without bypassing the gasket-type seal. Summary of the Invention

[0019] Therefore, a first aspect of the present invention relates to a piston that otherwise conforms to the general definition given in the foregoing preamble.

[0020] According to a first aspect of the invention, the at least one seal includes at least one cavity separate from the through hole, the cavity being configured to receive a compression system for pressing the gasket-type seal against a first crenellated member and against a second crenellated member in the main direction of the piston.

[0021] Therefore, the present invention provides the possibility of introducing a system for compressing the gasket seal in the main direction of the piston within a gasket seal. This compression eliminates, on the one hand, the risk of axial clearance arising between the gasket seal and the first crenellated member, and on the other hand, the risk of axial clearance arising between the gasket seal and the second crenellated member.

[0022] Other embodiments of the piston include the following features:

[0023] - The at least one gasket-type seal includes the following two side lips in a single piece: a first lip arranged facing the first crenellated member, and a second lip arranged facing the second crenellated member;

[0024] - The first lip and the second lip define a cavity therebetween designed to accommodate the extrusion system;

[0025] - The following two separate gasket-type seals are arranged facing each other in the at least one groove: a first gasket-type seal facing the first crenellated member, and a second gasket-type seal facing the second crenellated member;

[0026] - The two seals have opposing surfaces, each of which is provided with a notch;

[0027] - The corresponding notches of the seals are aligned to form a cavity designed to accommodate the extrusion system;

[0028] - The extrusion system is of mechanical and / or fluid type;

[0029] - An extrusion system is in the form of an insert permanently placed in a cavity;

[0030] - The extrusion system includes a certain mass of fluid from the compression chamber and stored in the cavity;

[0031] - The fluid of a certain mass is configured to press the first lip against the first crenellated member and the second lip against the second crenellated member in the main direction of the piston;

[0032] - The insert is configured to press the first lip against the first crenellated member in the main direction of the piston, and to press the second lip against the second crenellated member;

[0033] - The fluid of a certain mass is configured to press the first seal against the first crenellated member and the second seal against the second crenellated member in the main direction of the piston;

[0034] - The insert is configured to press the first seal against the first crenellated member in the main direction of the piston, and to press the second seal against the second crenellated member;

[0035] - The insert and the at least one seal are each made of materials with different coefficients of thermal expansion, with the coefficient of thermal expansion of the insert being greater than that of the seal.

[0036] According to a second aspect, the present invention relates to a fluid machine, particularly a cryogenic fluid machine, such as a pump for cryogenic fluids like hydrogen, comprising a bushing and a piston according to any one of the foregoing embodiments, the piston being at least partially inserted into the bushing to form a fluid expansion and / or compression chamber together with the bushing, the piston and the bushing being configured to move relative to each other in a reciprocating manner. Attached Figure Description

[0037] Other specific features and advantages will become apparent from the following description provided with reference to the accompanying figures, wherein:

[0038] Figure 1 This is a cross-sectional view illustrating a first embodiment of a fluid machine according to the invention, the machine including a bushing, a piston, a set of gasket-type seals and a removable system of crenellations along the piston, each gasket-type seal being provided with a cavity and a compression system, the piston including a single gasket-type seal located between two crenellations.

[0039] Figure 2 This is a partial cross-sectional view showing another example of the machine according to the first embodiment, in which a system consisting of crenellated members is fixed relative to a piston.

[0040] Figure 3 This is a partial cross-sectional view showing another example of fluid machinery according to the first embodiment, where the seal has a C-shaped shape that defines a cavity containing a compression system facing the bushing.

[0041] Figure 4 This is a partial cross-sectional view showing another example of fluid machinery according to the first embodiment, where the seal has a C-shaped shape that defines a cavity showing no compression system facing the bushing.

[0042] Figure 5 This is a partial cross-sectional view showing another example of a fluid machine according to the first embodiment, with the seal having a C-shaped shape and the seal and extrusion system facing the piston.

[0043] Figure 6 This is a partial cross-sectional view showing another example of fluid machinery according to the first embodiment, wherein the seal has a Z-shaped profile that forms two cavities configured to receive a compression system.

[0044] Figure 7This is a partial cross-sectional view illustrating an example of a fluid machine according to a second embodiment, wherein the piston includes two separate seals between two consecutive crenellated members, each seal having a recess forming a cavity designed to receive a compression system facing the bushing.

[0045] Figure 8 This is a partial cross-sectional view showing another example of the machine according to the second embodiment, with the cavity facing the piston.

[0046] Figure 9 This is a partial cross-sectional view showing another example of a machine according to the second embodiment, wherein the cavity is closed and located in the middle between the bushing and the piston.

[0047] Figure 10 This is a partial cross-sectional view illustrating a third embodiment of the machine according to the invention, in which the piston comprises two separate seals separated by a gap between two consecutive crenellated members, the gap being configured to receive a C-shaped compression system.

[0048] Figure 11 This is a partial cross-sectional view illustrating another example of a machine according to a third embodiment, the extrusion system comprising a series of V-shaped inserts. Detailed Implementation

[0049] like Figures 1 to 11 As shown, the present invention relates to a fluid machine 1, and more particularly to a cryogenic fluid machine. The fluid machine 1 can be a pump or compressor for conveying fluids. The fluid in question can be a cryogenic fluid with a temperature below -150°C. It can be hydrogen.

[0050] Reference Figure 1 The fluid machinery 1 extends along the main axis Y, which is also called the "longitudinal axis", "longitudinal direction" or "main direction".

[0051] The fluid machinery 1 also has a transverse axis X perpendicular to the main axis Y. The transverse axis X is also referred to below as the "radial axis" or "radial direction".

[0052] The fluid machinery 1 includes a bushing 2 and a piston 3, with the piston 3 at least partially disposed inside the bushing 2. In particular, the piston 3 and the bushing 2 are configured to move relative to each other in a reciprocating manner in the main direction Y.

[0053] The piston 3 and bushing 2 form an expansion and / or compression chamber 4, which is designed to receive and deliver fluid for expansion and / or compression in a cycle that includes a suction phase and a delivery phase of the fluid in the expansion and / or compression chamber 4.

[0054] In other words, the volume of the expansion and / or compression chamber 4 varies depending on the relative position of the piston 3 with respect to the bushing 2 and the stage (intake or delivery) of the fluid intake and delivery cycle in the expansion and / or compression chamber 4.

[0055] To allow one to move relative to the other, piston 3 or bushing 2 may be connected to a drive component (not shown).

[0056] More specifically, the piston 3 includes a head 31 inserted into the bushing 2 and a shaft 32 connected to the head 31. Together with the shaft 32, the head 31 forms a shoulder. The shaft 32 is connected to a rod-like member (not shown), which is intended to be arranged outside the bushing 2 and can be actuated by a drive member.

[0057] Specifically, the head 31 of the piston 3 has a first end 31a. The shaft 32 of the piston 3 has a second end 32a opposite to the first end 31a.

[0058] The bushing 2 includes a sidewall 21 and a bottom 22, which form a recess into which the head 31 of the piston 3 is inserted. Therefore, the bottom 22 and sidewall 21 of the bushing 2 and the first end 31a of the piston 3 define the expansion and / or compression chamber 4.

[0059] In addition, the sidewall 21 and / or bottom 22 of the bushing 2 are provided with at least one inlet orifice and at least one outlet orifice. These orifices communicate with the expansion and / or compression chamber 4.

[0060] Still refer to Figure 1 The machine 1 includes a system of crenellated members 5 arranged along the main direction Y on the side wall 34 of the piston 3. In particular, the system of crenellated members is arranged on a portion of the side wall 34 located in the region facing the shaft 32 of the piston 3.

[0061] Advantageously, the system consisting of the crenellated members 5 extends in an O-shape around the side wall 34 of the piston 3, that is, the system consisting of the crenellated members 5 is closed around the side wall 34 of the piston 3 shaft 32 in a plane perpendicular to the main direction Y.

[0062] Advantages, such as Figure 1 As shown, the system consisting of crenellated components 5 can be manufactured separately from the piston 3. Figure 2 In the alternative form shown, the system consisting of the crenellated member 5 can be integrally formed with the piston 3.

[0063] When manufactured separately from piston 3, the system consisting of crenellated members 5 can be reversibly assembled onto piston 3. For example, the system consisting of crenellated members 5 can be removably threaded onto piston 3, and more specifically, removably threaded onto piston 3 along the sidewall 34 of shaft 32.

[0064] In the configuration where the system consisting of crenellated members is removable relative to the piston, the system consisting of crenellated members 5 is designed to fit with the sidewall 34 of the piston 3 in an interference fit and sealing manner. This interference fit is achieved through the different thermal contractions of the system consisting of crenellated members 5 relative to the piston 3.

[0065] It should be noted that the interference fit and / or seal between the system consisting of the crenellated parts and the piston 3 can only be achieved through the different thermal contractions of the system consisting of the crenellated parts relative to the piston 3.

[0066] The system consisting of crenellated members 5 protrudes radially relative to the sidewall 34 of the piston 3. Therefore, the system consisting of crenellated members 5 defines a set of grooves, i.e., a set of recesses or cavities, which are designed to receive a set of gasket-type seals 6.

[0067] The set of gasket-type seals 6 is designed to mate with the bushing 2 to restrict the flow of fluid toward the outside of the expansion and / or compression chamber 4.

[0068] The statement "a system consisting of crenellated elements 5" (and / or a set of grooves or a set of gasket-type seals 6) means a system comprising one or more crenellated elements 5 (or a group comprising one or more grooves, or correspondingly a group comprising one or more gasket-type seals 6).

[0069] exist Figure 1 and Figure 2 In the example shown, the shoulder formed between the head 31 and the shaft 32 of the piston 3 cooperates with the first crenellation of the set of crenellations 5 to form the first groove of the set of grooves.

[0070] Figure 1 and Figure 2 All show a machine comprising multiple crenellations, multiple grooves and multiple gasket-type seals, wherein an enlarged view of the groove defined by the first crenellation 5a and the second crenellation 5b is shown.

[0071] exist Figures 1 to 6 In the first embodiment shown, each groove defined by the first crenellation 5a and the second crenellation 5b is provided with a single gasket-type seal 6. Specifically, Figure 1 and Figure 2 A groove with a single gasket-type seal 6 is shown.

[0072] The gasket-type seal 6 has an outer surface designed to mate with the sidewall 21 of the bushing 2 in an interference fit. The gasket-type seal 6 also has an inner surface designed to face the sidewall 34 of the piston 3. Finally, the gasket-type seal 6 has a first lateral surface and a second lateral surface extending between the outer and inner surfaces.

[0073] In the example shown, the first lateral surface of the seal 6 is arranged to face the first crenellation 5a. The second lateral surface of the seal 6 is arranged to face the second crenellation 5b.

[0074] Furthermore, the gasket-type seal 6 has a through-hole that allows fluid to flow from the expansion and / or compression chamber 4 to the second end 32a of the piston 3. The through-hole extends between the first and second lateral faces of the gasket-type seal 6.

[0075] Advantageously, the mechanism includes at least one expander 7 located between the gasket seal 6 and the shaft 32 of the piston 3. The at least one expander 7 is designed to press the gasket seal 6 radially (i.e., in the X direction) against the sidewall 21 of the bushing 2.

[0076] According to the present invention, such as Figures 3 to 6 As shown, the gasket-type seal 6 includes at least one cavity 8 separate from the through-hole. The cavity 8 is configured to accommodate a system 9 for pressing the gasket-type seal 6 in the main direction Y of the piston 3.

[0077] More specifically, the compression system is designed to press the seal 6 against the first crenellated member 5a and the second crenellated member 5b in the direction Y of the piston 3.

[0078] exist Figure 3 , Figure 4 and Figure 5 In the example shown, the gasket seal 6 has a C-shaped profile in the cross-section of the longitudinal plane.

[0079] In this cross-section, the gasket-type seal 6 includes two side lips: a first lip 62 facing the first crenellated member 5a, and a second lip 61 facing the second crenellated member 5b. The lips 61 and 62 define a cavity 8 between them designed to accommodate the compression system 9.

[0080] Advantageously, the cavity 8 designed to accommodate the extrusion system is annular.

[0081] Reference Figure 3 and Figure 4 Cavity 8 and extrusion system 9 face bushing 2. Figure 4 The image shows a gasket-type seal 6 without the compression system 9.

[0082] Reference Figure 5 The cavity 8 and the extrusion system 9 face the piston 3 and are in contact with the expander 7.

[0083] exist Figure 6In the example shown, the gasket seal 6 has a Z-shaped profile in its longitudinal plane section. In this case, the gasket seal 6 includes two horizontal branches 6a and 6b connected by an inclined branch 6c. Branches 6a, 6b, and 6c define two cavities 8a and 8b, each designed to receive a compression system.

[0084] exist Figures 7 to 11 In the second embodiment shown, each groove includes two separate gasket-type seals 6a, 6b arranged facing each other: a first seal 6a facing the first crenellated member 5a, and a second seal 6b facing the second crenellated member 5b.

[0085] More specifically, the first seal 6a has a first transverse surface arranged facing the first crenellated portion 5a. The second seal 6b has a second transverse surface arranged facing the second crenellated portion 5b.

[0086] Furthermore, the first seal 6a includes a first through-hole. The second seal includes a second through-hole. These two through-holes are angularly offset / displaced from each other about the principal direction Y of the machine 1. This angular offset between the through-holes creates a leakage path to the interface of the two seals 6a, 6b.

[0087] Reference Figure 7 , Figure 8 and Figure 9 The first sealing member 6a and the second sealing member 6b, arranged in a common groove, are respectively provided with at least one first notch 8a and at least one second notch 8b. The notches 8a and 8b are particularly... Figure 9 As can be seen in the text.

[0088] Specifically, notches 8a and 8b are formed on the opposite transverse surfaces of seals 6a and 6b, respectively. Thus, notches 8a and 8b face each other and form a cavity 8 designed to accommodate the compression system 9.

[0089] It should be noted that, in Figure 9 In the example shown, the first seal 6a and / or the second seal 6b may also be provided with at least one additional notch formed on the side surface of the seals 6a, 6b. The respective additional notches of the seals 6a, 6b are intended to accommodate a system for pressing the seals 6a, 6b in the radial direction X.

[0090] In this second embodiment, the cavity 8 (and the corresponding extrusion system 9) may occupy a position near the sidewall 21 of the bushing 2 (see...). Figure 7 ), or near the side wall 34 of piston 3 (see Figure 8 ), or located substantially equidistantly between the side wall 21 of bushing 2 and the side wall 34 of piston 3 at the midpoint (see Figure 9 ).

[0091] Reference Figure 10 and Figure 11 The first seal 6a and the second seal 6b are positioned a certain distance apart from each other. The first seal 6a and the second seal 6b form a gap between them, which constitutes a cavity 8 designed to accommodate the extrusion system 9.

[0092] In particular, Figure 11 In the example shown, the first seal 6a has a flat first transverse surface and a convex second transverse surface arranged facing the first crenellated member 5a. The convex second transverse surface has a V-shaped profile in the longitudinal section of the machine 1.

[0093] The second seal 6b has a flat first transverse surface and a concave second transverse surface arranged facing the second crenellated member 5b. The concave second transverse surface has a V-shaped profile in the longitudinal section of the machine 1.

[0094] Therefore, the convex transverse surface of the first seal 6a and the concave transverse surface of the second seal 6b are arranged facing each other and have complementary geometries.

[0095] The extrusion system 9 may consist of a large amount / a certain mass of fluid from the compression chamber 4 and stored in the cavity 8.

[0096] In this configuration, cavity 8 is in fluid communication with the through-hole of seal 6 (or the through-holes of both seals in the second embodiment). This is Figure 6 and Figure 9 The situation of the machine shown.

[0097] exist Figure 9 In the example shown, a large amount of fluid stored in cavity 8 presses the first seal 6a against the first crenellated member 5a and the second seal 6b against the second crenellated member 5b. This compression occurs in the main direction Y of piston 3.

[0098] In an alternative form, the extrusion system 9 may include a solid insert. This is Figures 3 to 5 , Figure 7 , Figure 8 , Figure 10 and Figure 11 The mechanical situation shown.

[0099] exist Figures 3 to 5 In the example shown, the insert 9 presses the first lip 61 of the seal 6 against the first crenellated member 5a and the second lip 62 of the seal 6 against the second crenellated member 5b. This pressing occurs in the main direction Y of the piston 3.

[0100] exist Figure 7 , Figure 8 , Figure 10and Figure 11 In the example shown, the insert 9 presses the first seal 6a against the first crenellated member 5a and the second seal 6b against the second crenellated member 5b. This pressing occurs in the main direction Y of the piston 3.

[0101] The insert forming the extrusion system is advantageously made of a material different from that of the seals 6a and 6b. The coefficient of thermal expansion of the insert is greater than that of the seals 6a and 6b.

[0102] It should be noted that the insert extends along the cavity 8 and may have different profiles in the longitudinal section of the machine 1.

[0103] Specifically, refer to Figure 3 , Figure 4 and Figure 5 The insert 9 may have a rectangular profile that is complementary to the rectangular profile of the cavity 8. In this case, the insert 9 is completely disposed within the cavity 8.

[0104] Reference Figure 8 The insert 9 has an inverted T-shaped profile in the longitudinal section of the machine 1. Therefore, in this longitudinal section, the insert 9 includes two branches: a first branch arranged in the cavity 8, and a second branch arranged against the expander 7.

[0105] See Figure 10 In the longitudinal section of the machine 1, the insert 9 may have a C-shaped profile that is complementary to the profile of the cavity 8 formed between the first seal 6a and the second seal 6b.

[0106] See Figure 11 The insert 9 has a V-shaped profile in the longitudinal section of the machine 1. This profile has a shape complementary to the profiles of the first seal 6a and the second seal 6b.

[0107] Advantageously, the system consisting of crenellated elements 5 forms a first group of elements, wherein all crenellated elements 5 are preferably substantially identical (particularly in terms of their physicochemical properties). Similarly, this group of gasket-type seals 6 forms a second group of elements, wherein all gasket-type seals 6 are preferably substantially identical (particularly in terms of their physicochemical properties).

[0108] Advantageously, in its removable configuration, the system consisting of the crenellated parts 5 is made of a different material than the piston 3.

[0109] Advantageously, the system consisting of the crenellated elements 5 and / or the set of seals 6 can be made of polymers (based on PTFE, PEEK, PAEK, PA, PAI, PI, PPS, PPA). The piston 3 and / or bushing 2 can be made of metal (e.g., steel, copper alloy, aluminum alloy, etc.).

[0110] This choice of material can limit the heating risk between the system consisting of the crenellated part 5 and the piston 3, and can also limit the heating risk between the sealing device 6 and the bushing 2.

[0111] Advantageously, piston 3 and bushing 2 are made of metal, and their coefficient of thermal expansion is 5.10. -6 m / (mK) to 30.10 -6 The system consisting of the crenellated element 5 and the set of seals 6 can be made of polymer. The coefficient of thermal expansion of the material of the system consisting of the crenellated element 5 and / or the material of the set of seals 6 can be greater than the coefficient of thermal expansion of the materials selected for the piston 3 and the bushing 2.

[0112] Regardless of the material chosen for piston 3, and regardless of the material chosen for the system composed of crenellated members 5, the coefficients of thermal expansion of these materials must differ sufficiently to ensure different contractions of the system composed of crenellated members relative to piston 3. Advantageously, this difference must be at least 2.10. -6 m / (mK), preferably 2.10 -6 m / (mK) to 3.10 -6 Within the range of m / (mK).

Claims

1. A piston (3) for a fluid machine (1), the piston (3) being intended to be at least partially mounted inside a liner (2) of the fluid machine (1) in a manner enabling relative reciprocating movement with respect to the liner (2) of the fluid machine (1), the piston (3) extending in a main direction (Y) and comprising a head (31) having a first end (31a) of the piston (3) intended to define, with the liner (2) of the fluid machine (1), a fluid expansion and / or compression chamber (4), and a shaft (32) having a second end (32a) of the piston (3), the shaft (32) comprising a lateral wall (34) provided with at least one annular groove defined between a first splined element (5a) and a second splined element (5b), the at least one annular groove being equipped with at least one gasket seal (6) intended to cooperate in a sealed manner with a lateral wall (21) of the liner (2) of the fluid machine (1), the at least one gasket seal (6) being provided with a through hole intended to allow fluid flow from the expansion and / or compression chamber (4) to the second end (32a) of the piston (3), characterized in that the at least one gasket seal (6) comprising at least one cavity (8) separate from the through hole, the cavity (8) comprising an extrusion system (9) for pressing the gasket seal (6) against the first splined element (5a) and the second splined element (5b) in the main direction (Y) of the piston (3), the extrusion system (9) being of a mechanical and / or fluid type.

2. The piston (3) according to claim 1, wherein the at least one gasket seal (6) comprising, in a single piece, the following two lateral lips: a first lip (61) arranged facing the first splined element (5a), and a second lip (62) arranged facing the second splined element (5b), the first lip (61) and the second lip (62) of the seal (6) defining, between them, the cavity (8) intended to accommodate the extrusion system (9).

3. The piston (3) according to claim 1, wherein the following two separate gasket seals (6a, 6b) are arranged facing each other in the at least one annular groove: a first seal (6a) facing the first splined element (5a), and a second seal (6b) facing the second splined element (5b).

4. The piston (3) according to claim 3, wherein the two separate gasket seals have facing surfaces, each of the facing surfaces being provided with a recess (8a, 8b), the respective recesses (8a, 8b) of the first seal (6a) and of the second seal (6b) being aligned to form the cavity (8) intended to accommodate the extrusion system (9).

5. The piston (3) according to any one of the preceding claims, wherein the extrusion system (9) is in the form of an insert permanently arranged in the cavity (8), and / or comprises a mass of fluid coming from the compression chamber and stored in the cavity (8).

6. The piston (3) according to claim 5, when dependent on claim 2, wherein said mass of fluid or said insert is configured to press a first lip (61) of said seal (6) against said first ratchet (5a) and a second lip (62) of said seal (6) against said second ratchet (5b) in the main direction (Y) of said piston (3).

7. The piston (3) according to claim 5, when dependent on claim 3, wherein said mass of fluid or said insert is configured to press a first lip (61) of said seal (6) against said first ratchet (5a) and a second lip (62) of said seal (6) against said second ratchet (5b) in the main direction (Y) of said piston (3).

8. The piston (3) according to any one of claims 5 to 7, wherein said insert and said at least one gasket seal (6) are respectively made of materials having different coefficients of thermal expansion, the coefficient of thermal expansion of said insert being greater than the coefficient of thermal expansion of said seal (6).

9. A fluid machine (1), in particular a cryogenic fluid machine, for example a pump for a cryogenic fluid such as hydrogen, comprising a bushing (2) and a piston (3) according to any one of the preceding claims, said piston (3) being at least partially inserted inside said bushing (2) so as to form, together with said bushing (2), a fluid expansion and / or compression chamber (4), said piston (3) and said bushing (2) being configured to be movable with respect to each other in a relative reciprocating movement.

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