Piston for a fluid machine and equipped with a sealing system; fluid machine comprising such a piston

Abstract

Piston (3) for a fluid machine (1), the piston (3) being intended to be mounted at least partially inside a sleeve (2) of the machine (1), the piston (3) comprising a head (31) intended to delimit with the sleeve (2) an expansion chamber (4), and a shaft (33) having at least one annular groove provided with at least one sealing gasket (6) intended to cooperate hermetically with the sleeve (2), the gasket (6) having a flow orifice for a flow of fluid from the expansion chamber (4), characterized in that the gasket (6) comprises at least one cavity (8) distinct from the flow orifice, the cavity (8) being configured to house a system (9) configured to press the gasket (6) against a first notch (5a) and against a second notch (5b) forming the annular groove. (See abstract figure: Figure 1)

Description

Title of the invention: Piston for a fluid machine and equipped with a gasket sealing system, fluid machine comprising such a piston

[0001] The invention relates to a piston for a fluid machine and provided with a sealing system. These are leaky seals comprising at least one fluid flow orifice.

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

[0003] A piston for a fluid machine is intended to be mounted at least partly inside a sleeve of the machine, according to a relative back-and-forth movement with respect to the sleeve.

[0004] The piston extends along a principal direction and comprises a head having a first end of the piston, and a handle having a second end of the piston. The first end and the second end of the piston are defined along the principal direction.

[0005] The first end of the piston is intended to form with the machine's liner a chamber for expanding and / or compressing the fluid.

[0006] The handle includes a side wall which is provided with at least one annular groove defined between a first notch and a second notch.

[0007] In particular, the annular groove is provided with at least one sealing gasket intended to cooperate with a side wall of the machine's cylinder liner. This at least one sealing gasket is provided with a passage orifice intended to allow a flow of fluid from the expansion and / or compression chamber to the second end of the piston.

[0008] The seal(s) primarily ensure the sealing of the compression chamber without hindering the relative movement of the piston with respect to the cylinder liner. In other words, the seal(s) allow the piston to move relative to the cylinder liner with virtually no friction.

[0009] In addition, the seal(s) ensure proper operation of the fluid machine, and contribute to a large part to achieving its specifications, in particular the pumped flow rate.

[0010] Finally, the seal(s) help to reduce leaks and BOG (Boil off Gas).

[0011] BOG represents a fluid that has vaporized irreversibly and cannot be reliquefied without any external cold exchange or work extraction. BOG can be the result of entropy generation due to heat ingress (imperfect insulation quality) in the expansion chamber, or result from friction and / or isenthalpic Joule-Thomson expansion due to leaks.

[0012] To ensure the various functions described above, a sufficient number of seals must be present, the number of which depends on the performance of each seal, the pressure involved, and other factors such as the fluid itself. Furthermore, for optimal operation of the fluid machine at high pressures and extremely low temperatures, the seals must have good mechanical integrity.

[0013] In most cases, a pair of seals is provided in each groove: a first seal in contact with the first notch of the groove, and a second seal in contact with the second notch of the groove. The first seal precedes the second seal from the piston head.

[0014] The first sealing ring has a first passage orifice. The second sealing ring has a second passage orifice. Furthermore, the first and second sealing rings are arranged in the groove such that their respective passage orifices are angularly offset from each other around the main axis of the piston.

[0015] Thus, the fluid flow from the compression chamber follows a leakage path which passes through the first orifice of the first sealing joint, then to the interface between the two sealing joints, before passing through the second orifice of the second sealing joint.

[0016] When axial play (i.e., play along the main direction of the piston) develops between the first seal and the first notch, the fluid flow from the compression chamber no longer necessarily passes through the first orifice of the first seal. Part of the flow bypasses the first and second passage orifices to flow into the gap between the seals and the piston side wall and / or into the gap between the seals and the cylinder liner side wall.

[0017] The modification of the leakage path means a loss of sealing and a degradation of machine performance.

[0018] Thus, there appears a need to develop new pistons in which the flow from the compression chamber passes essentially only through the passage orifices provided for this purpose without bypassing the sealing joints.

[0019] To this end, according to a first aspect, the invention relates to a piston, moreover conforming to the generic definition given in the preamble above.

[0020] According to this first aspect of the invention, at least one seal comprises at least one cavity distinct from the passage orifice, the cavity being configured to house a system for pressing the sealing seal against the first slot and against the second slot along the main direction of the piston.

[0021] Thus, the invention makes it possible to introduce into the seal a system for clamping it along the main direction of the piston. This clamping eliminates the risk of axial play appearing between the seal and the first notch on the one hand, and between the seal and the second notch on the other.

[0022] Other embodiments of the piston include the following features: - at least one sealing ring comprises, in a single piece, two lateral lips: a first lip positioned opposite the first slot, and a second lip positioned opposite the second slot, - the lips define between them the cavity intended to house the clamping system, - two separate sealing rings are arranged opposite each other in at least one groove: a first seal opposite the first slot and a second seal opposite the second slot, - the two seals have facing faces, each of which is provided with a notch, - the respective notches of the seals are aligned to form the cavity intended to house the clamping system, - the clamping system is of the mechanical and / or fluidic type, - the clamping system is in the form of an insert permanently disposed in the cavity.- The pressing system comprises a mass of fluid from the compression chamber, stored in the cavity; - the mass of fluid is configured to press, along the main direction of the piston, the first lip against the first slot and the second lip against the second slot. -1'insert is configured to press, along the main direction of the piston, the first lip against the first slot and the second lip against the second slot. - the fluid mass is configured to press, along the main direction of the piston, the first seal against the first slot, and the second seal against the second slot. -1'insert is configured to press the first seal against the first slot, and the second seal against the second slot, following the main direction of the piston. - the insert and at least one seal are made of materials with different coefficients of thermal expansion, the coefficient of thermal expansion of the insert being greater than the coefficient of thermal expansion of the seal.

[0023] According to a second aspect, the invention relates to a fluid machine, and in particular to a cryogenic fluid, for example a pump for cryogenic fluid such as hydrogen, comprising a sleeve and a piston according to any one of the preceding embodiments, the piston being inserted at least in part inside the sleeve so as to form with the sleeve a chamber for expansion and / or compression of the fluid, the piston and the sleeve being configured to be mobile relative to each other in a reciprocating motion.

[0024] Other features and advantages will become apparent from the description below, made with reference to the following figures in which:

[0025] [Fig. 1] is a cross-sectional view illustrating a first embodiment of the fluid machine according to the invention, the machine comprising a sleeve, a piston, a set of sealing gasket(s), and a removable slot system along the piston, the sealing gaskets each being provided with a cavity and a plating system, the piston comprising between two slots a single sealing gasket.

[0026] [Fig.2] is a partial sectional view illustrating another example of the machine according to the first embodiment, the slot system(s) being fixed relative to the piston.

[0027] [Fig.3] is a partial sectional view illustrating another example of the fluid machine according to the first embodiment, the seal having a C-shape which delimits a cavity containing the plating system, the cavity being turned towards the liner.

[0028] [Fig.4] is a partial sectional view illustrating another example of the fluid machine according to the first embodiment, the seal having a C-shaped form which delimits a cavity shown without the plating system, the cavity being turned towards the sleeve.

[0029] [Fig.5] is a partial sectional view illustrating another example of the fluid machine according to the first embodiment, the seal having a C-shape, the seal and the plating system being turned towards the piston.

[0030] [Fig.6] is a partial sectional view illustrating another example of the fluid machine according to the first embodiment, the joint having a Z-profile which forms two cavities configured to receive the plating system.

[0031] [Fig. 7] is a partial cross-sectional view illustrating an example of the fluid machine according to a second embodiment, the piston comprising between two consecutive slots two separate seals each having a housing, the housings respective joints forming the cavity intended to receive the plating system, the cavity being turned towards the sleeve.

[0032] [Fig.8] is a partial sectional view illustrating another example of the machine according to the second embodiment, with the cavity facing the piston.

[0033] [Fig.9] is a partial sectional view illustrating another example of the machine according to the second embodiment, the cavity being closed and located in a median position between the sleeve and the piston.

[0034] [Fig. 10] is a partial sectional view illustrating a third embodiment of the machine according to the invention, the piston comprising between two consecutive slots two distinct seals separated by an interval configured to receive the C-shaped plating system.

[0035] [Fig. 11] is a partial sectional view illustrating another example of the machine according to the third embodiment, the plating system comprising a series of V-shaped inserts.

[0036] As illustrated in [Fig. 1] to [Fig. 11], the invention relates to a fluid machine 1, and in particular a cryogenic fluid machine. The fluid machine 1 may be a pump or a compressor for transferring a fluid. The fluid in question may be cryogenic at a temperature below 150°C. It may be hydrogen.

[0037] With reference to [Fig.1], the fluid machine 1 extends along a principal axis Y, also designated by the expressions “longitudinal axis” or “longitudinal direction” or even “principal direction”.

[0038] The fluid machine 1 also has a transverse axis X which is perpendicular to the main axis Y. The transverse axis X is also referred to hereafter by the expressions "radial axis" or "radial direction".

[0039] The fluid machine 1 comprises a sleeve 2 and a piston 3 which is disposed at least partly inside the sleeve 2. In particular, the piston 3 and the sleeve 2 are configured to be mounted movable relative to each other in a reciprocating relative motion along the principal direction Y.

[0040] The piston 3 and the liner 2 form a compression and / or expansion chamber 4 intended to receive and expel a fluid for expansion and / or compression according to a cycle comprising an intake phase and a discharge phase of the fluid in the compression and / or expansion chamber 4.

[0041] In other words, the compression and / or expansion chamber 4 has a volume which varies according to the relative position of the piston 3 with respect to the sleeve 2, and according to the phase (admission or discharge) of the intake and discharge cycle of the fluid in the chamber 4.

[0042] To ensure their relative movement with respect to each other, the piston 3 or the liner 2 can be connected to a driving element (not illustrated).

[0043] In more detail, the piston 3 comprises a head 31 which engages inside the cylinder liner 2, and a shaft 32 which is connected to the head 31. The head 31 forms a shoulder with the shaft 32. The shaft 32 is connected to a rod (not shown) intended to be positioned outside the cylinder liner 2 and can be actuated by the drive mechanism.

[0044] In particular, the head 31 of the piston 3 has a first end 31a. The handle 32 of the piston 3 has a second end 32a, opposite the first end 31a.

[0045] The sleeve 2 includes a side wall 21 and a bottom 22 which form a housing into which the head 31 of the piston 3 engages. Thus, the bottom 22 and the side wall 21 of the sleeve 2, as well as the first end 31a of the piston 3, delimit the expansion and / or compression chamber 4.

[0046] Furthermore, the side wall 21 and / or the bottom 22 of the sleeve 2 are provided with at least one inlet port and at least one outlet port. These ports communicate with the compression and / or expansion chamber 4.

[0047] Still with reference to [Fig.1], the machine 1 includes a slot system(s) 5 arranged on a side wall 34 of the piston 3, along the main direction Y. In particular, the slot system(s) is arranged on a portion of the side wall 34 located at the level of the handle 32 of the piston 3.

[0048] Advantageously, the slot system(s) 5 extends in O around the side wall 34 of the piston 3, that is to say, the slot system(s) 5 is closed around the side wall 34 of the head 31 of the piston 3, in a plane perpendicular to the main Y direction.

[0049] Advantageously, as illustrated in [Fig.1], the slot system(X) 5 can be made separately from the piston 3. In an alternative illustrated in [Fig.2], the slot system(X) 5 can form a single body with the piston 3.

[0050] When manufactured separately from the piston 3, the slot system(s) 5 can be assembled to it reversibly. For example, the slot system(s) 5 can be removably threaded along the piston 3, and more specifically along the side wall 34 of the handle 32.

[0051] In its removable configuration relative to the piston, the slot system(s) 5 is designed to cooperate with the side wall 34 of the piston 3 in a tight and sealing manner. Such a tight fit is achieved through differential thermal contraction of the slot system(s) (5) relative to the piston 3.

[0052] It should be noted that the tight fit and / or sealing between the slot system(s) and the piston 3 can be obtained exclusively by the differential thermal contraction of the slot system(s) with respect to the piston 3.

[0053] The slot system(s) 5 extends radially from the lateral wall 34 of the piston 3. Thus, the slot system(s) 5 delimits a set of groove(s), that is- to say a set of housing(s) or hollow, intended to receive a set of sealing joint(s) 6.

[0054] The set of sealing gaskets 6 is intended to cooperate with the sleeve 2 to limit fluid flow out of the expansion and / or compression chamber 4.

[0055] The expression “slot system(s) 5” (respectively set of groove(s) or set of seal(s) 6) designates a system comprising one or more slots 5 (respectively a set comprising one or more grooves, or a set comprising one or more seal(s) 6).

[0056] In the example illustrated in [Fig.1] and [Fig.2], the shoulder formed between the head 31 and the handle 32 of the piston 3 cooperates with a first slot of the set of slots 5 to form a first groove of the set of grooves.

[0057] Fig. 1 and Fig. 2 each illustrate a machine comprising a plurality of slots, grooves and sealing joints, with an enlarged view of a groove which is delimited by a first slot 5a and a second slot 5b.

[0058] In a first embodiment illustrated in [Fig.1] to [Fig.6], each groove delimited by a first notch 5a and a second notch 5b is provided with a single sealing gasket 6. In particular in [Fig.1] and [Fig.2], a groove is highlighted with a single sealing gasket 6.

[0059] The sealing ring 6 has an outer lateral face designed to cooperate with the lateral wall 21 of the sleeve 2 in a tight fit. The sealing ring 6 also has an inner lateral face designed to be opposite the lateral wall 34 of the piston 3. Finally, the sealing ring 6 has a first transverse face and a second transverse face extending between the outer lateral face and the inner lateral face.

[0060] In the illustrated example, the first transverse face of the joint 6 is positioned opposite the first slot 5a. The second transverse face of the joint 6 is positioned opposite the second slot 5b.

[0061] In addition, the sealing seal 6 has a passage orifice allowing a flow of fluid from the expansion and / or compression chamber 4 to the second end 32a of the piston 3. The passage orifice extends between the first transverse face and the second transverse face of the sealing seal 6.

[0062] Advantageously, the machine includes at least one expander 7 which is positioned between the sealing gasket 6 and the sleeve 32 of the piston 3. The at least one expander 7 is intended to press the sealing gasket 6 radially (i.e. in the direction X) against the side wall 21 of the sleeve 2.

[0063] According to the invention, as illustrated in [Fig. 3] to [Fig. 6], the sealing gasket 6 comprises at least one cavity 8 distinct from the passage orifice. The cavity 8 is configured to house a sealing system 9 for the sealing gasket 6 along the main direction Y of the piston 3.

[0064] More specifically, the clamping system is intended to clamp the seal 6 against the first slot 5a and against the second slot 5b along the Y direction of the piston 3.

[0065] In the examples illustrated in [Fig.3], [Fig.4] and [Fig.5], the sealing joint 6 has a C-shaped profile in a cross-section in a longitudinal plane.

[0066] According to this cross-section, the sealing gasket 6 comprises two lateral lips: a first lip 62 positioned opposite the first slot 5a, and a second lip 61 positioned opposite the second slot 5b. The lips 61, 62 define between them the cavity 8 intended to house the plating system 9.

[0067] Advantageously, the cavity 8 intended to house the plating system has an annular shape.

[0068] With reference to [Fig.3] and [Fig.4], the cavity 8 and the plating system 9 are turned towards the sleeve 2. In [Fig.4], the sealing gasket 6 is shown without the plating system 9.

[0069] With reference to [Fig.5], the cavity 8 and the plating system 9 are turned towards the piston 3, in contact with the expander 7.

[0070] In the example illustrated in [Fig. 6], the sealing gasket 6 has a Z-shaped profile when viewed in a longitudinal plane. The sealing gasket 6 then comprises two horizontal branches 6a, 6b connected by an oblique branch 6c. The branches 6a, 6b, 6c define two cavities 8a, 8b, each intended to receive a sealing system.

[0071] In a second embodiment illustrated in [Fig.7] to [Fig.11], each groove contains two separate sealing gaskets 6a, 6b which are arranged opposite each other: a first gasket 6a which is arranged opposite the first slot 5a, and a second gasket 6b which is arranged opposite the second slot 5b.

[0072] More specifically, the first joint 6a has a first transverse face which is arranged opposite the first slot 5a. The second joint 6b has a second transverse face which is arranged opposite the second slot 5b.

[0073] Furthermore, the first seal 6a includes a first passage orifice. The second seal includes a second passage orifice. The two passage orifices are angularly offset from each other around the principal Y direction of the machine 1. This angular offset between the passage orifices creates a leakage path that passes through the interface of the two seals 6a, 6b.

[0074] With reference to [Fig.7], [Fig.8] and [Fig.9], the first seal 6a and the second seal 6b arranged in a common groove are provided respectively with at least one first notch 8a and at least one second notch 8b. The notches 8a, 8b are visible in particular in [Fig.9].

[0075] In particular, the notches 8a, 8b are formed respectively on the transverse faces opposite the joints 6a, 6b. The notches 8a, 8b are therefore opposite and form the cavity 8 intended to house the plating system 9.

[0076] It should be noted that in the example illustrated in [Fig. 9], the first seal 6a, respectively the second seal 6b, may also be provided with at least one additional notch formed on a lateral face of said seal 6a, 6b. The respective additional notches of the seals 6a, 6b are intended to house a clamping system for said seals 6a, 6b in the radial direction X.

[0077] In this second embodiment, the cavity 8 (and consequently the clamping system 9) can occupy a position close to the lateral wall 21 of the sleeve 2 (see [Fig.7]), or a position close to the lateral wall 34 of the piston 3 (see [Fig.8]), or even a median position, substantially equidistant between the lateral wall 21 of the sleeve 2 and the lateral wall 34 of the piston 3 (see [Fig.9]).

[0078] With reference to [Fig. 10] and [Fig. 11], the first seal 6a and the second seal 6b are positioned at a certain distance from each other. The first seal 6a and the second seal 6b form a gap between them which constitutes the cavity 8 intended to house the plating system 9.

[0079] In particular, in the example illustrated in [Fig. 11], the first joint 6a has a first flat transverse face positioned opposite the first slot 5a and a second convex transverse face. The second convex face, viewed longitudinally from the machine 1, has a V-shaped profile.

[0080] The second joint 6b has a first flat transverse face positioned opposite the second slot 5b and a second concave transverse face. The second concave face has a V-shaped profile in a longitudinal section of the machine 1.

[0081] Thus, the convex transverse face of the first joint 6a and the concave transverse face of the second joint 6b are arranged opposite each other and have complementary geometries.

[0082] The plating system 9 can consist of a mass of fluid coming from the compression chamber 4 and stored in the cavity 8.

[0083] In this case, the cavity 8 is in fluidic communication with the passage orifice of the seal 6 (or the passage orifices of the seals for the second embodiment). This is the case of the machine illustrated in [Fig. 6] and [Fig. 9].

[0084] In the example illustrated in [Fig.9], the mass of fluid stored in the cavity 8 presses the first seal 6a against the first slot 5a, and the second seal 6b against the second slot 5b. This pressing occurs along the principal direction Y of the piston 3.

[0085] Alternatively, the plating system 9 may include a solid insert. This is the case for the machine illustrated in [Fig.3] to [Fig.5], [Fig.7], [Fig.8], [Fig.10] and [Fig.11].

[0086] In the examples illustrated in [Fig.3] to [Fig.5], the insert 9 presses the first lip 61 of the seal 6 against the first slot 5a, and the second lip 62 of the seal 6 against the second slot 5b. This pressing takes place along the main direction Y of the piston 3.

[0087] In the examples illustrated in [Fig.7], [Fig.8], [Fig.10] and [Fig.11], the insert 9 presses the first seal 6a against the first slot 5a, and the second seal 6b against the second slot 5b. This pressing takes place along the main direction Y of the piston 3.

[0088] The insert forming the plating system is advantageously made from a different material than that of the joints 6a, 6b. The coefficient of thermal expansion of the insert is greater than the coefficient of thermal expansion of the joints 6a, 6b.

[0089] It should be noted that the insert extends along the cavity 8 and can present different profiles depending on a longitudinal section of the machine 1.

[0090] In particular, with reference to [Fig.3], [Fig.4] and [Fig.5], the insert 9 may have a rectangular profile, complementary to the rectangular profile of the cavity 8. In this case, the insert 9 is entirely disposed in the cavity 8.

[0091] With reference to [Fig. 8], the insert 9 may have an inverted T-shaped profile along a longitudinal cutting plane of the machine 1. The insert 9 therefore comprises, along this longitudinal cutting plane, two branches: a first branch which is disposed in cavity 8, and a second branch which is disposed against the expander 7.

[0092] With reference to [Fig. 10], the insert 9 may have, according to a longitudinal section plane of the machine 1, a C-shaped profile, complementary to the profile of the cavity 8 formed between the first seal 6a and the second seal 6b.

[0093] With reference to [Fig. 11], the insert 9 can have a V-shaped profile along a longitudinal cutting plane of the machine 1. This profile has a shape complementary to that of the profile of the first seal 6a and the second seal 6b.

[0094] Advantageously, the slot system(s) 5 forms a first group of elements in which all the slots 5 are preferably substantially identical (in particular from the point of view of their physicochemical properties). Similarly, the set of sealing gasket(s) 6 forms a second group of elements in which all the gaskets 6 are preferably substantially identical (in particular from the point of view of their physicochemical properties).

[0095] Advantageously, the slot system(s) 5 in its removable configuration is made of a different material from the material of the piston 3.

[0096] Advantageously, the slot system(s) 5 and / or the joint assembly(ies) (6) can be made of polymer (based on PTFE, PEEK, PAEK, PA, PAI, PI, PPS, PPA). The piston 3 and / or the liner 2 can be made of metal (for example, steel, copper alloy, aluminum alloy, etc.).

[0097] Such a choice of materials makes it possible to limit the risk of overheating, on the one hand, between the slot system(s) 5 and the piston 3; and on the other hand, between the seal assembly(ies) 6 and the sleeve 2.

[0098] Advantageously, the piston 3 and the cylinder liner 2 are made of metal and may have a coefficient of thermal expansion between 5 x 10⁶ m / (mK) and 30 x 10⁶ m / (mK). The slot system(s) 5 and the seal assembly(ies) 6 may be made of polymer. The material of the slot system(s) 5 and / or the material of the seal assembly(ies) 6 may have a coefficient of thermal expansion higher than that of the material selected for the piston 3 and the cylinder liner 2.

[0099] Regardless of the material chosen for the piston 3, and regardless of the material chosen for the slot system(s) 5, a sufficient difference between the respective coefficients of thermal expansion of these materials is necessary to guarantee a differential contraction of the slot system(s) with respect to the piston 3. Advantageously, this difference is at least 2.106 m / (mK), and preferably, between 2.106 and 3.106 m / (mK).

Claims

Demands

1. Piston (3) for a fluid machine (1), the piston (3) being intended to be mounted at least partially inside a sleeve (2) of the machine (1) in a reciprocating motion relative to the sleeve (2), the piston (3) extending in a principal direction (Y) and comprising a head (31) having a first end (31a) of the piston (3), and a shaft (32) having a second end (32a) of the piston (3), the first end (31a) of the piston (3) being intended to delimit with the sleeve (2) of the machine (1) a chamber (4) for the expansion and / or compression of the fluid, the shaft (32) comprising a side wall (34) having at least one annular groove defined between a first slot (5a) and a second slot (5b), the at least one annular groove being provided with at least one sealing gasket (6) intended to cooperate in a sealed manner with a side wall (21) of the jacket (2) of the machine (1),at least one sealing gasket (6) being provided with a passage orifice intended to allow a flow of fluid from the expansion and / or compression chamber (4) to the second end (32a) of the piston (3), characterized in that the at least one sealing gasket (6) comprises at least one cavity (8) distinct from the passage orifice, the cavity (8) being configured to house a clamping system (9) for clamping the sealing gasket (6) against the first slot (5a) and against the second slot (5b), along the principal direction (Y) of the piston (3).

2. Piston (3) according to the preceding claim, wherein the at least one sealing joint (6) comprises in one piece two lateral lips: a first lip (61) disposed opposite the first slot (5a), and a second lip (62) disposed opposite the second slot (5b), the lips (61, 62) of the joint (6) defining between them the cavity (8) intended to house the plating system (9).

3. Piston (3) according to claim 1, in which two separate seals (6a, 6b) are arranged opposite each other in at least one groove: a first seal (6a) opposite the first slot (5a) and a second seal (6b) opposite the second slot (5b).

4. Piston (3) according to the preceding claim, in which the two seals have facing faces, each of which is provided with notch (8a, 8b), the respective notches (8a, 8b) of the joints (6a, 6b) being aligned to form the cavity (8) intended to house the plating system (9).

5. Piston (3) according to any one of the preceding claims, wherein the shim system (9) is of the mechanical and / or fluidic type.

6. Piston (3) according to the preceding claim, wherein the plating system (9) is in the form of an insert permanently disposed in the cavity (8), and / or comprises a mass of fluid from the compression chamber and stored in the cavity (8).

7. Piston (3) according to the preceding claim taken in its connection with claim 2, wherein the mass of fluid (respectively the insert) is configured to press along the principal direction (Y) of the piston (3) the first lip (61) of the seal (6) against the first slot (5a) and the second lip (62) of the seal (6) against the second slot (5b).

8. Piston (3) according to claim 6 taken in its attachment to claim 3, wherein the mass of fluid (respectively the insert) is configured to press along the principal direction (Y) of the piston (3) the first seal (6a) against the first slot (5a), and the second seal (6b) against the second slot (5b).

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

10. Fluid machine (1), and in particular cryogenic fluid machine, for example pump for cryogenic fluid such as hydrogen, comprising a sleeve (2) and a piston (3) according to any one of the preceding claims, the piston (3) being inserted at least in part inside the sleeve (2) so as to form with the sleeve (2) a chamber (4) for expanding and / or compressing the fluid, the piston (3) and the sleeve (2) being configured to be mobile relative to each other in a reciprocating motion.

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