Reciprocating compressor with improved sealing for low molecular weight gases

Abstract

A compressor for compressing low molecular weight gases in which an annular gap (50) is defined to have a predetermined thickness (G) between a central part (13) of a cylinder (10) of a compression unit (1, 2) and a central part (33) of a head portion (30) of a slidable member (20), such as a pressure or plunger, slidably disposed within the cylinder (10), and wherein the central part (33) of the head portion (30) comprises an inlet opening (17) for an isolation fluid (9) available at a predetermined isolation pressure higher than the delivery pressure of the compression unit. The cylinder-piston unit may be a single-action unit (1, 2, 3) having a compression chamber (12) defined in the cylinder (10) by a compression face (36) at an end of the head portion (30) opposite the rod portion (39); the cylinder (10) has a head portion (30) having a compression surface (32) at one end thereof, or a double-acting unit in which the head portion (30) has another compression surface (32) at the other end thereof, thereby defining a second compression chamber (22) in the cylinder (10), along which the rod portion (39) is arranged longitudinally and within the second compression chamber. In an advantageous embodiment, the central member (33) of the head portion (30) has a diameter (D1) that decreases from the proximal member (31) of the head portion (30) towards the distal member (35). A second isolation chamber may also be defined around the rod portion (39), in particular arranged to be supplied with the same isolation fluid (9) as the head portion (30) of the slidable member (20).

Description

[0001] Scope of the Invention

[0002] The present invention relates to a reciprocating compressor comprising at least one compression unit, such as a cylinder-piston unit or a plunger unit, the at least one compression unit comprising a slidable member movably arranged in a cylinder to define compression chambers, providing an improved sealing system between the compression chambers to prevent low molecular weight and / or high pressure gases, in particular hydrogen or hydrogen-containing gas mixtures, from leaking from the compression chambers.

[0003] Existing Technology-Technical Problems

[0004] As is well known, hydrogen has been attracting increasing attention as a possible energy carrier for decades to limit the widespread use of fossil fuels. From this perspective, it is necessary to build hydrogen generation plants, as well as hydrogen distribution networks and hydrogen storage systems. To be economically viable, they must operate at high pressures, even in the order of hundreds of bars, which can be achieved by using reciprocating compressors.

[0005] It is also known how difficult it is to provide a hermetic seal for low-molecular-weight gases, particularly for hydrogen-containing gases, due to their tendency to leak through conventional sealing systems. A small amount of hydrogen normally leaking from equipment into the atmosphere is an undesirable event. Besides the value of the lost product, the high cost of protective measures necessary to comply with regulations for potentially explosive atmospheres must also be considered.

[0006] One possible solution to the hydrogen leakage problem from reciprocating machines is to provide the piston with a large number of piston rings as sealing elements around the piston end portion facing the machine's compression chamber. However, this would require a longer piston-cylinder unit, thereby increasing the manufacturing cost of the compressor. Similarly, plunger compressors should be equipped with a sufficiently long plunger to act as a sealing element and prevent gas leakage.

[0007] Another problem with reciprocating compressors is uneven wear of the connecting rod bearings, particularly at high compression ratios. As is well known, when the slidable member passes top dead center, i.e., when the thrust direction reverses after the compression stroke, the upper half of the connecting rod bearing remains fully loaded, while the lower half remains unloaded, leading to uneven wear of the bearings. Single-acting compressors (including plunger compressors) are particularly susceptible to this problem because the thrust acting on the connecting rod due to the gas pressure in the only compression chamber being compressed is not counteracted by the counterpressure generated by the gas present in the second, opposing compression chamber, as is the case with double-acting compressors.

[0008] EP2796719 A1, US 4,174,929 and US2018 / 051684A1 relate to specific compressor unit arrangements. Summary of the Invention

[0009] It is therefore an object of the present invention to provide a reciprocating compressor which, for the same type of gas and a given operating pressure, provides an improved seal to prevent leakage and outward loss of low molecular weight gases, in particular hydrogen-containing gases, relative to the most commonly used reciprocating compressors.

[0010] Another object of the present invention is to provide a high pressure reciprocating compressor, i.e. a compressor operating at a delivery pressure of 100 bar or more, which provides improved sealing to prevent gas leakage and outward loss relative to the most commonly used reciprocating compressors for the same type of gas.

[0011] A particular object of the present invention is to provide a reciprocating compressor comprising at least one piston-cylinder unit which, for the same type of gas and / or given operating pressure, allows a certain degree of tightness while comprising a relatively small number of piston rings arranged around the end portion of the piston facing the compression chamber or while having a relatively short piston sealing area of ​​its own piston unit.

[0012] Another specific object of the present invention is to provide a reciprocating compressor that overcomes the problem of differential rod bearing wear caused by the failure of the upper half rod bearing to disengage during thrust reversal at top dead center.

[0013] Furthermore, it is an object of the present invention to provide a compressor capable of achieving better compression efficiency than conventional reciprocating compressors when the latter is used to process low molecular weight gases.

[0014] These and other objects are achieved by a compressor configured to compress a low molecular weight gas to a predetermined delivery pressure as claimed in claim 1. Advantageous embodiments of the compressor are defined in the dependent claims.

[0015] The compressor comprises at least one compression unit including a cylinder and a slidable member arranged in the cylinder, the slidable member having a head portion and a rod portion, the rod portion being integral with the head portion and arranged so that the head portion performs a stroke in the cylinder,

[0016] The cylinder has a cylinder proximal part relative to the rod portion, a cylinder central part and a cylinder distal part, the cylinder proximal part and the cylinder distal part having a first inner diameter of the cylinder,

[0017] The head portion has a head portion proximal component, a head portion central component, and a head portion distal component relative to the shaft portion, the head portion proximal component and the head portion distal component having a first outer diameter of the head portion,

[0018] wherein the first inner diameter of the cylinder and the first outer diameter of the head portion are equal to a common nominal diameter of the cylinder and the head portion, apart from a predetermined coupling tolerance,

[0019] The cylinder center member has a second inner diameter,

[0020] The head portion center member has a second outer diameter,

[0021] The distal member of the head portion includes a compression surface on an opposite side relative to the central member of the head portion,

[0022] The compression surface defines a compression chamber within the cylinder having an intake port and a delivery port for low molecular weight gas.

[0023] wherein, according to the present invention, the second inner diameter of the cylinder center part is greater than the second outer diameter of the head portion center part by a predetermined amount, i.e., by a predetermined gap thickness, so that an annular gap having a thickness equal to said predetermined amount is defined between the head portion center part and the cylinder center part,

[0024] and wherein the cylinder center member has at least one inlet opening for an isolation fluid, wherein the inlet opening is in fluid communication with a source of said isolation fluid, the isolation fluid source being configured to supply isolation fluid into the annular gap at a predetermined isolation pressure such that the isolation fluid occupies the annular gap and the annular gap forms an isolation chamber between the compression chamber and a space opposite the compression chamber relative to the head portion of the slidable member.

[0025] In the case of a compressor equipped with a single-acting compression unit, such as a single-acting cylinder-piston unit or plunger unit, there is a sealing chamber between the compression chamber and the outside of the compressor, and such compression chamber is configured to contain an isolation fluid at a pressure that is always higher than or at least equal to the pressure in the compression chamber. This sealing chamber provides an additional sealing effect between the compression chamber and the outside, i.e. the proximal space adjacent to the proximal part of the head portion. In the case of a cylinder-piston unit 1 or 2, this additional sealing effect is superimposed on the sealing effect provided by the piston rings 41, 45 of the cylinder-piston units 1 and 2. In the case of the plunger unit 3, on the other hand, this additional effect is superimposed on the sealing effect provided by the corresponding mutual contact surfaces of the proximal part 11 and the distal part 15 of the cylinder 10 on the one hand and by the corresponding mutual contact surfaces of the proximal part 31 and the distal part 35 of the plunger 20 on the other hand.

[0026] In other words, in the case of a single-acting cylinder-piston unit, the isolation chamber cooperates with the piston rings, or in the case of a plunger unit, the isolation chamber cooperates with the sealing portion of the cylinder-plunger coupling to contain the gas compressed in the compression chamber. Since the isolation fluid is less prone to leakage than low-molecular-weight gases, a given sealing performance can be ensured with a smaller number of piston rings in the case of a cylinder-piston unit, or with a shorter sealing portion of the cylinder-plunger coupling in the case of a plunger unit. By means of a smaller number of piston rings, or by means of a shorter length of the sealing portion, the length and therefore the overall dimensions of the compressor unit and of the compressor itself can be reduced, which simplifies the compressor construction and allows to control manufacturing costs.

[0027] The present invention provides a space-saving and cost-effective compressor that limits the loss of compressed gas to the environment and, in the case of a double-acting compressor unit as described below, limits gas leakage between opposing compression chambers, thereby improving compression efficiency. This reduces economic losses due to compressed gas leakage. Furthermore, in the case of flammable gases such as hydrogen or certain mixtures thereof, the risk of an explosive atmosphere forming around the compressor can be limited.

[0028] In this specification, expressions such as "pneumatic communication" and "hydraulic communication" between two spaces indicate that there is a connection device between these spaces, such as a pipe, a pipe element, etc., through which a gas or a liquid can flow, respectively. In addition, these gases and liquids are not limited to air and water, respectively, contrary to the common meanings of "pneumatic" and "hydraulic".

[0029] Preferably, the annular gap between the cylinder center part and the head part center part of the compression unit has a thickness of at least 1 mm, in particular, the thickness is at least 5 mm, more in particular, the thickness is at least 10 mm.

[0030] In some embodiments of the present invention,

[0031] - the second inner diameter of the central part of the cylinder is equal to the first inner diameters of the distal and proximal parts of the cylinder and is therefore equal to the common nominal diameter;

[0032] the second outer diameter of the central part of the head portion of the slidable member is smaller than the common nominal diameter by the predetermined gap thickness, i.e. the difference between the common nominal diameter and the second outer diameter of the central part of the head portion is equal to the gap thickness;

[0033] - The length of the central part of the head portion is at least equal to the stroke of the slidable member.

[0034] In other words, the annular gap and the sealing chamber can be made by using a cylinder having an intermediate portion whose diameter is greater than the nominal diameter, which can be obtained, for example, by removing material only from a conventional cylinder having the same internal diameter over its entire length. In this case, the sealing chamber is defined between the intermediate portion of the cylinder and the head portion of the slidable member.

[0035] In this case, the isolation chamber moves integrally with the slidable member when the latter performs its stroke within the cylinder.

[0036] However, in other embodiments of the application, the annular gap and the sealing chamber can be made by using a cylinder having an intermediate portion whose diameter is greater than the nominal diameter, which can be obtained, for example, by removing material only from a conventional cylinder having the same internal diameter over its entire length. In other words, in this case:

[0037] - the second external diameter of the head portion central component is equal to the first internal diameter of the distal and proximal components of the cylinder, and therefore to the common nominal diameter;

[0038] - the second internal diameter of the cylinder central component is greater than the common nominal diameter by the above-mentioned predetermined gap thickness, i.e. the difference between the second internal diameter of the cylinder central component and the common nominal diameter is equal to the gap thickness;

[0039] - the length of the central component of the cylinder is at most equal to the difference between the length of the head portion central component and the stroke of the slidable member.

[0040] In particular, the compression unit is a cylinder-piston unit, in which the slidable member is a piston,

[0041] wherein the head portion proximal and distal components each comprise at least two elastic piston rings, which are at a distance from each other and are arranged to slide within the cylinder, and

[0042] wherein the head portion central component is located between the elastic piston rings of the head portion proximal component and the elastic piston rings of the head portion distal component.

[0043] In one embodiment of the application, the cylinder-piston unit is a double-acting cylinder-piston unit, i.e. the compression face of the head portion is a first compression face, the compression chamber is a first compression chamber, and the proximal component of the head portion comprises a second compression face opposite the first compression face with respect to the central component of the head portion, wherein the second compression face and the cylinder define a second compression chamber through which the rod portion is arranged to pass over its entire length.

[0044] In this case, an isolation chamber remains defined between the two compression chambers, which always operate at different pressures. The isolation chamber contains a fluid at a pressure that is constantly higher than, or even at least equal to, the maximum pressure reached in each compression chamber. Thus, together with the piston rings, the isolation chamber contributes to sealing the compression chambers relative to one another, even in this case with a limited number of piston rings and, therefore, a limited length of the piston head portion.

[0045] This makes it possible to significantly limit gas leakage between one compression chamber and another using a limited number of piston rings and therefore a limited length of the piston head portion, thereby maintaining a high compression efficiency of the compressor.

[0046] Advantageously, the head portion center part of the slidable member has a shape whose diameter decreases from the proximal part towards the distal part of the head portion, in particular, the shape is a frustoconical shape.

[0047] In this way, the resultant force of the pressure acting on the central part of the head section due to the isolation fluid contained in the isolation chamber has a component directed away from the single compression surface in the case of a single-acting unit, or away from the compression surface opposite the rod section. This component helps to position the connecting rod bearing in its seat in such a way that once the sliding element has entered the top dead center, that is, during the subsequent stroke of the sliding element, the lower part of the bearing is compressed, that is, the lower part of its bearing surface is engaged. "Bottom dead center" is understood to be the extreme position of the sliding element, which corresponds to the minimum size of the compression chamber defined by the single compression surface of the sliding element, or in any case, in a double-acting cylinder-piston unit, the minimum size of the compression chamber defined by the compression surface opposite the piston rod relative to the piston head itself.

[0048] In some embodiments, the cylinder core has at least one isolation fluid outlet opening in its middle portion. In this case, preferably, the inlet opening and the outlet opening are realized in the same cross-section of the cylinder, and the cylinder has a circumferential recess, i.e., a circumferential groove, in said cross-section, which communicates with the isolation fluid inlet opening and with the isolation fluid outlet opening. This allows for a uniform distribution of the isolation fluid within the isolation chamber.

[0049] In some embodiments of a compressor including a cylinder-piston unit, the annular gap providing the isolation chamber is a first annular gap providing a head section annular chamber, and the rod section is provided with a proximal seal and a distal seal, defining a second annular gap therebetween, the second annular gap being arranged to be supplied with a rod section isolation fluid to provide the rod section isolation chamber. In addition to the improved sealing provided by the head section isolation chamber between the two compression chambers and the associated aforementioned performance advantages, this is a further improvement in the sealing system of the double-acting cylinder-piston unit with respect to gas leakage into the environment.

[0050] In these cases, the rod section isolation fluid may be the same as the piston head section isolation fluid, and the head section isolation chamber and the rod section isolation chamber may be supplied by the same circuit.

[0051] In particular, the head portion isolation chamber and the stem portion isolation chamber, i.e. the first annular gap and the second annular gap, have a mutual connection selected between:

[0052] - interconnected in parallel, wherein the first annular gap and the second annular gap are both arranged to receive a common isolation fluid directly from an isolation fluid source;

[0053] - connected to one another in series, wherein the cylinder and the second annular gap also have corresponding insulating fluid outlet openings, wherein the outlet opening of the cylinder is hydraulically connected to the inlet opening of the second annular gap or insulating chamber.

[0054] In a variation of the above embodiment, the compressor unit may include a closed isolation fluid supply circuit including a source of isolation fluid.

[0055] In one embodiment, such a supply circuit comprises a compensation vessel in which a deformable diaphragm or membrane is arranged to define a first variable-volume chamber and a second variable-volume chamber, the first variable-volume chamber and the second variable-volume chamber being pneumatically connected to the compression chamber delivery port and the cylinder inlet opening, respectively, and the second variable-volume chamber being configured to accommodate a predetermined amount of isolation fluid, whereby the isolation fluid can be supplied into the annular gap at a pressure that depends on the pressure of the low-molecular-weight gas at the delivery port.

[0056] In this way, a closed circuit containing a predetermined amount of barrier fluid is used to isolate the chamber, requiring only minimal or no barrier fluid to be supplied, while maintaining the pressure in the isolation chamber using the compressor's own compression power. The sealed circuit is completely isolated from the process by a deformable membrane, ensuring that gas cannot leak to the outside.

[0057] In an alternative embodiment, the compressor unit may include a cooling circuit configured to deliver cooling fluid at a predetermined cooling fluid pressure that is higher than the delivery pressure. In this case, the inlet opening of the cylinder is advantageously in hydraulic communication with the cooling circuit, whereby the barrier fluid comprises a portion of the cooling fluid. In other words, the source of the barrier fluid is the cooling circuit of the compressor.

[0058] Also in this case, it is possible to produce a sealing system without introducing fluids and supply circuits other than those already present “naturally” in the compressor, thus limiting the manufacturing and operating costs of the system.

[0059] In one embodiment, the compressor comprises a plurality of compression stages, i.e., a plurality of compression units, which are arranged to operate at a continuous suction-delivery pressure range relative to each other. In this case, the inlet opening of the isolation chamber of the compression unit arranged to perform the earlier compression stage can be pneumatically connected to the delivery port of the compression chamber of the compression unit arranged to perform the later compression stage, whereby the isolation fluid comprises the low molecular weight gas itself. A pressure reducing device can be provided along the pipeline arranged to allow said pneumatic connection so as to reduce the gas extracted from the delivery port of the unit performing the subsequent high pressure stage to a sufficiently low value to be properly used as isolation fluid in one or more previous subsequent stages without entering the isolation fluid. In this way, no fluid unrelated to the process is introduced into the isolation chamber, which prevents the risk of contamination of the process itself by foreign fluids. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The invention will hereinafter be illustrated by the description of some embodiments, by way of non-limiting examples, with reference to the accompanying drawings, in which:

[0061] - Figure 1 and Figure 2 A single-acting cylinder of a reciprocating compressor according to an embodiment of the present invention

[0062] - a schematic partial longitudinal sectional view of a piston unit, wherein the piston is at the top dead center and the bottom dead center respectively;

[0063] - Figure 3 yes Figure 1 and Figure 2 A schematic side view of the piston head portion of the cylinder-piston unit;

[0064] - Figure 4 and Figure 5 is a schematic partial longitudinal sectional view of a single-acting cylinder-piston unit of a reciprocating compressor according to another embodiment of the present invention, wherein the pistons are at the top dead center and the bottom dead center, respectively;

[0065] - Figure 6yes Figure 4 and Figure 5 A schematic longitudinal sectional view of a cylinder of a cylinder-piston unit in FIG.

[0066] - Figure 7 and Figure 8 is a schematic partial longitudinal sectional view of a plunger unit of a reciprocating compressor according to another embodiment of the present invention, wherein the plungers are at the top dead center and the bottom dead center, respectively.

[0067] - Figure 9 yes Figure 7 and Figure 8 A schematic side view of the plunger in FIG;

[0068] - Figure 10 and Figure 11 are schematic partial longitudinal cross-sectional views of a double-acting cylinder-piston unit of a reciprocating compressor according to two alternative embodiments of the present invention, wherein the isolation chamber has a single isolation fluid inlet-outlet opening and is internally defined by a cylindrical surface and a frustoconical surface, respectively;

[0069] - Figure 12 and Figure 13 are schematic partial longitudinal cross-sectional views of a double-acting cylinder-piston unit of a reciprocating compressor according to two further alternative embodiments of the present invention, wherein an isolation chamber has an isolation fluid inlet opening and an isolation fluid outlet opening different from the isolation fluid inlet opening and is internally defined by a cylindrical surface and a frustoconical surface, respectively;

[0070] - Figure 14 is shown in more detail Figure 12 A schematic longitudinal sectional view of a double-acting cylinder-piston unit;

[0071] - Figure 15 and Figure 16 They are Figure 14 A longitudinal sectional perspective view of a cylinder-piston unit and a cylinder;

[0072] - Figure 17 Yes Figure 2 A partial longitudinal sectional view of the cylinder-piston unit in FIG. 1 , wherein an isolation chamber is further provided on the piston rod portion;

[0073] - Figure 18 and Figure 19 Shown Figure 17 A supply diagram of a head portion isolation chamber and a rod portion isolation chamber, wherein the two isolation chambers are respectively arranged in parallel and in series with each other to be supplied with the same isolation fluid;

[0074] - Figure 20 Yes Figure 12Schematic partial longitudinal sectional view of a cylinder-piston unit in, wherein the head portion insulating chamber and the rod portion insulating chamber are arranged to receive a cooling fluid of the cylinder-piston unit as insulating fluid;

[0075] - Figure 21 Yes Figure 10 A schematic partial longitudinal sectional view of a cylinder-piston unit in FIG.

[0076] An isolated fluid supply circuit including a compensation container is provided. DETAILED DESCRIPTION

[0077] refer to Figures 1 to 9 , depicts three compression units 1, 2, and 3 of a compressor configured to compress a low molecular weight gas to a predetermined delivery pressure. Compression units 1, 2, and 3 include a cylinder 10 and a slidable member 20. Slidable member 20 includes a head portion 30 slidably coupled within cylinder 10 in the direction of a common longitudinal axis 5, along which cylinder 10 and head portion 30 extend.

[0078] The cylinder 10 and the head portion 30 comprise respective components in sliding contact with each other and have a common tolerance diameter D and a respective predetermined coupling tolerance which can be determined in a manner known to a person skilled in the art according to the operating conditions of the compression unit.

[0079] In particular, compression units 1 and 2 consist of cylinder-piston units ( Figures 1 to 3 and Figures 4 to 6 ) is composed of a piston unit ( Figures 7 to 9 ) is composed of, wherein the slidable member 20 is a plunger.

[0080] In addition to the head portion 30, the slidable member 20 also comprises a rod portion 39 which is integrally connected to the head portion 30 and is arranged so that the head portion 30 performs a stroke of length C in the cylinder 10. The rod portion 39 is typically a connecting rod which is connected in a manner not shown to a crankshaft which may be common to several compression units 1, 2 or 3 and their respective variants.

[0081] The rod portion 39 has a diameter D3, which is Figures 1 to 6 ), this diameter is smaller than the nominal diameter D of the head portion 30 and is therefore the maximum diameter of the rod portion 39. In contrast, in the plunger unit 3 ( Figures 7 to 9 ), the rod portion diameter D3 is substantially equal to the nominal diameter D of the head portion 30, in other words, the rod portion 39 forms an extension member having the same nominal diameter D as the head portion 39, which is oriented toward a transmission device (not shown) of the compressor.

[0082] The head portion 30 includes a proximal portion 31, a central portion 33 and a distal portion 35 ( Figure 1 and Figure 3 ). Similarly, the cylinder 10 has a proximal part 11, a central part 13 and a distal part 15 ( Figure 2 ). The words "proximal" and "distal" indicate the positions of the head portion components 31, 35 and the cylinder components 11, 15 relative to the rod portion 39. Furthermore, as expected, the diameters of the proximal components 11, 31 and the distal components 15, 35 of the cylinder 10 and the head portion 30, respectively, are equal to the nominal diameter D, in addition to corresponding coupling tolerances that allow the proximal components 11, 31 and the distal components 15, 35 to slide in contact with each other.

[0083] Opposite the head portion central part 33 , the distal part 35 of the head portion 30 comprises a compression face 36 which defines a compression chamber 12 in the cylinder 10 provided with an intake port 14 for the gas to be compressed and a delivery port 16 for the compressed gas.

[0084] In particular, Figures 1 to 6 In the cylinder-piston unit, at least two piston rings 41, 45 are arranged on the proximal part 31 and the distal part 35 of the head portion 30 of the piston 20 to be in sliding contact with the inner surface of the cylinder 10. Figures 7 to 9 In the plunger unit 3 , the proximal part 31 and the distal part 33 of the head portion 30 are smooth sealing portions that are arranged to be in sliding contact with the inner surface of the cylinder 10 .

[0085] As shown in the figure, the cylinder center part 13 has a second inner diameter D2 ( Figure 1 、 Figure 2 and Figure 6 ), and the piston head portion center part 33 has a second outer diameter D1 ( Figure 3 、 Figure 4 and Figure 5 The second inner diameter D2 of the cylinder center part 13 and the second outer diameter D1 of the head part center part 33 differ by a predetermined amount G=D2-D1. More precisely, the second inner diameter D2 of the cylinder is larger than the second outer diameter D1 of the head part by the predetermined amount G ( Figure 1 and Figure 4 ).

[0086] Thus, an annular gap or chamber 50 is defined between the cylinder centerpiece 13 and the head portion centerpiece 33. The annular gap 50 has a major diameter equal to the cylinder second inner diameter D2 and a minor diameter equal to the head portion second outer diameter D1.

[0087] A hole 17 is drilled through the wall of the cylinder central part 13 to provide an inlet opening for the fluid into the annular gap 50. The hole 17 is preferably arranged to be located at a first axial end 51 of the annular gap 50 when the slidable member 20 is at top dead centre Figure 1 , Figure 4 and Figure 7 ) and at a second axial end 52 of the annular gap 50 opposite the first axial end 51 when the slidable member 20 is at bottom dead centre Figure 2 , Figure 5 and Figure 8 . The inlet opening 17 is in fluid communication with the source 8 of isolation fluid 9 Figure 7 and Figure 8 and is configured to feed the isolation fluid 9 into the annular gap 50 at a predetermined isolation pressure.

[0088] The isolation fluid 9 thus fills and occupies the annular gap 50, thus forming an isolation chamber 50 between the compression chamber 12 and the space 22 opposite the compression chamber 12 with respect to the head portion 30 of the slidable member 20. In addition to the sealing effect provided by the piston rings 41, 45 of the cylinder-piston units 1 and 2, and in the case of the plunger unit 3, by the respective surfaces of the proximal part 1115 and the distal part of the cylinder 10 and the proximal part 31 and the distal part 35 of the head portion 30 of the plunger 20 in contact with each other, the isolation fluid 9 and the isolation chamber 50 provide an additional sealing effect between the compression chamber 12 and the space 22.

[0089] In the figures, for the sake of clarity, the difference between the common nominal diameter D and the second outer diameter D1 of the head portion central part 33 and the difference between the second inner diameter D2 of the cylinder and the common nominal diameter D (nominal) are exaggerated, in other words, the thickness G of the annular gap 50 is represented as being independent of scale. The thickness G is preferably at least 1 mm, more particularly it is at least 5 mm, more particularly it is at least 10 mm, depending on the operating pressure of the compression units 1 to 3, in a manner that can be easily understood by the skilled person.

[0090] Figures 1 to 3 and Figures 7 to 9 relate to an embodiment of the application in which the second inner diameter D2 of the cylinder is equal to the first inner diameter of the proximal part 11 and the distal part 15 of the cylinder 10 and thus to the common nominal diameter D of the cylinder 10 and the head portion 30, and in which the second outer diameter D1 of the head portion central part 33 of the slidable member 20 is smaller than the first outer diameter of the proximal part 31 and the distal part 35 and thus smaller than the common nominal diameter D by a gap thickness G. The annular gap 50 is thus included in the profile of the head portion 30.

[0091] In this case, the annular gap 50 can be obtained, for example, by removing a portion of material of a given length L1 from the central part 33 of the head portion 30 of the slidable member 20. In particular, Figures 1 to 3 In the case of the cylinder-piston unit 1, the central part 33 is located between the piston rings 41 and 45 of the head portion 30 of the piston 20 ( Figure 3 ), so that the length L1 of the central part 33 having the reduced (second) outer diameter D1 is less than the distance between the innermost piston rings 41 and 45 of the head portion 30. In addition, as Figure 1 and Figure 2 As shown, during the stroke C of the slidable member 20, the annular gap 50 moves together with the head portion 30, and the length L1 of the head portion central part 33 is preferably equal to or at least not shorter than the stroke C of the piston 20. In this way, when the slidable member 30 is at the top dead center ( Figure 1 and Figure 7 ) and bottom dead center ( Figure 2 and Figure 8 ), the inlet opening 17 is longitudinally located at the first axial end 51 and the second axial end 52 of the annular gap 50 and, in any case, is always longitudinally located within the length L1 of the annular gap 50 .

[0092] on the other hand, Figures 4 to 6 Concerning an embodiment of the present invention, the second outer diameter D1 of the head portion central part 33 is equal to the first outer diameters of the corresponding proximal part 31 and distal part 35 of the head portion 30 and is therefore equal to the common nominal diameter D of the cylinder 10 and the head portion 30 , and the second inner diameter D2 of the cylinder central part 13 is greater than the first inner diameters of the corresponding proximal part 11 and distal part 15 and is therefore greater than the common nominal diameter D by a gap thickness G. Thus, the annular gap 50 is included in the profile of the cylinder 10 .

[0093] In this case, the annular gap 50 can be obtained, for example, by removing a portion of material of a given length L2 from the central part 13 of the cylinder 10. In any case, the cylinder central part 13 with the increased (second) inner diameter has a length L2 that is at most equal to the difference LC between the length L of the head part central part 33 and the stroke C of the slidable member 20, wherein the head part central part 33 is understood to be the area of ​​the central part 33 between the innermost piston rings 41, 45. During the stroke C of the slidable member 20, a fixed annular gap 50 always exists between the cylinder central part 13 and the head part and central part 33.

[0094] Similar considerations apply to compression units consisting of a plunger unit in which the diameter of the plunger centerpiece is larger than the nominal common diameter of the plunger and cylinder.

[0095] Figures 10 to 14 and Figures 17 to 21 Involved basis Figure 1 and Figure 2 Advantageous embodiments of the piston-cylinder unit 1 are double-acting piston-cylinder units 1a-1i, which, on the other hand, may also be single-acting embodiments. In double-acting piston-cylinder units 1a-1i, the proximal portion 31 of the head portion 30 includes a second compression surface 32, opposite the first compression surface 36, relative to the central portion 33 of the head portion. The cylinder 10 and the second compression surface 32 define a second compression chamber 22, through which the rod portion 39 is arranged to extend. The second compression chamber 22 is provided with an intake port 24 for the gas to be compressed and a delivery port 26 for the compressed gas.

[0096] exist Figure 10 and Figure 12 In both embodiments shown, the head portion center part 33 of the piston-cylinder unit 1a and 1c has a cylindrical shape with a diameter D1. Figure 11 and Figure 13 In the two advantageous embodiments shown, the head part central part 33 of the piston-cylinder unit 1b and 1d has a frustoconical shape, or more generally, a shape with a diameter D1 that decreases from a maximum value D1" next to the proximal part 31 of the head part to a minimum value D1' next to the distal part 33 of the head part.

[0097] Figure 14 and partially Figure 15 and Figure 16 Shown in more detail Figure 12 The piston-cylinder unit 1c, in particular Figure 16 In FIG. 1 , the cylinder 10 of the piston-cylinder unit 1 c is represented without the head portion 30 of the piston 20 in order to illustrate the interior of the cylinder 10 .

[0098] refer to Figures 12 to 16 In addition to the inlet opening 17, the cylinder center part 13 of the piston-cylinder unit 1c is also provided with an outlet hole or opening 18 for the insulating fluid 9. The outlet opening 18 is arranged along the cylinder 10 so as to be located at the first axial end 51 of the head part center part 33 when the piston 20 is at top dead center (e.g., Figure 1 ), and is located at the second axial end 52 of the head portion center member 33 when the piston 20 is at the bottom dead center (as shown in FIG. Figure 2 Thus, in addition to pressurizing the annular gap 50, the isolation fluid 9 can also pass through the annular gap. This feature can obviously be extended to Figures 1 to 3 In the case of a single-acting cylinder-piston unit 20, and Figures 7 to 9 The case of the plunger unit 3.

[0099] In particular, if Figure 16 As shown, the cylinder 10 has a recess or circumferential groove 19 at a cross section, preferably at a cross section forming the input opening 17 and the output opening 18 , and the circumferential groove 19 communicates with the input opening and the output opening.

[0100] Figures 17 to 19 The invention relates to three double-acting cylinder-piston units 1e, 1f and 1g according to respective variants of an advantageous embodiment of the invention, wherein the rod portion 39 is provided with a proximal seal and a distal seal (not shown) defining a second annular gap between the proximal seal and the distal seal, thereby providing a rod portion isolation chamber, i.e. a chamber arranged to be supplied with a rod portion isolation fluid 9 or 9'. Figure 18 and Figure 19 In the cylinder-piston units 1f and 1g, the two annular gaps (i.e., the head portion isolation chamber 50 and the rod portion isolation chamber) are arranged to receive the same isolation fluid 9 from a common isolation fluid source 8. In particular, the piston-cylinder unit 1g ( Figure 19 ) has an inlet opening 67 which is in hydraulic communication with the isolation fluid source 8, whereby the two isolation chambers are arranged to receive a common isolation fluid 9 directly from the isolation fluid source 8, i.e. they are arranged in parallel with respect to the isolation fluid source 8. Alternatively, the piston-cylinder unit 1f ( Figure 18 )'s cylinder 10 and the second annular gap have corresponding outlet openings 18, 68 for a common insulating fluid 9, wherein the outlet opening 18 of the head part insulating chamber 50 is hydraulically connected to the inlet opening 67 of the rod part insulating chamber, in other words, the two insulating chambers are arranged in series relative to the common insulating fluid source 8.

[0101] even though Figures 17 to 19 Only double-acting cylinder-piston units 1e-g are shown, in which the isolation chambers are provided with different inlet openings 17, 67 and outlet openings 18, 68, the scope of the invention also includes single-acting cylinder-piston compression units or double-acting cylinder-piston compression units, in which, in addition to the head section isolation chamber 50, a rod section isolation chamber is provided, and each isolation chamber has one inlet / outlet opening, or different inlet and outlet openings, which can be modified in a manner obvious to the skilled person. Figures 17 to 19 to obtain the content shown in .

[0102] Figure 20A cylinder-piston unit 1h according to an embodiment of the present invention is shown, wherein a cooling circuit 70 is configured to deliver a cooling fluid 7 that is available at a cooling fluid pressure that is higher than the delivery pressure of the compressor comprising the cylinder-piston unit 1h. Furthermore, as shown, the rod section isolation chamber and the head section isolation chamber are hydraulically connected to the cooling circuit 70 in parallel with each other, or, in an alternative, not shown, variation of this embodiment, they can be connected in series with each other. Thus, a portion of the cooling fluid 7 contained in the cooling circuit 70 supplies the isolation fluid 9 to both the rod section isolation chamber and the head section isolation chamber, and the inlet opening 17 of the isolation chamber 50 is hydraulically connected to the cooling circuit 70.

[0103] even though Figure 20 Only a double-acting cylinder-piston unit 1h is shown, comprising both a head part isolating chamber and a rod part isolating chamber, and wherein the isolating chamber is provided with both an inlet opening 17, 67 and an outlet opening 18, 68, the scope of the present invention also includes a compressor comprising a single-acting cylinder-piston unit or a double-acting cylinder-piston unit, which is provided with only a head part isolating chamber, and a compressor comprising a single-acting cylinder-piston unit or a double-acting cylinder-piston unit, which has a head part isolating chamber and possibly a rod part isolating chamber, one or more chambers having (each) a single inlet / opening 17 or different inlet and outlet openings 17, 18 and an outlet opening, wherein one or more chambers or isolating chambers are hydraulically connected to the cooling circuit of the cylinder-piston unit, wherein the Figure 20 Modifications will be apparent to those skilled in the art.

[0104] refer to Figure 21 In a piston-cylinder unit 1i of a compressor according to an embodiment of the present invention, the supply circuit 4 includes a compensator box 40, within which a deformable membrane 45 defines a first chamber 41 and a second chamber 42 having variable volumes. The first chamber 41 of the compensator box 40 is in pneumatic communication with the delivery ports 16, 26 of the compression chambers 12, 22, thereby containing a variable volume of low-molecular-weight gas processed by the compressor unit 1i at the delivery pressure of the compressor unit 1i during operation of the compressor unit 1i. The second chamber 42 is in communication with the suction ports 17, 67 of the annular gap or isolation chamber between the head portion 30 and the piston rod portion 39 of the piston 20, and contains a predetermined amount of isolation fluid 9 at a pressure that depends on the pressure in the first chamber 41, i.e., the delivery pressure of the compressor unit 1i.

[0105] even though Figure 21Only a double-acting cylinder-piston unit 1h comprising both a head part isolation chamber and a rod part isolation chamber is shown, the scope of the present invention also includes a compressor of a single-acting cylinder-piston unit or a double-acting cylinder-piston unit provided with only a head part isolation chamber, as well as a compressor comprising a single-acting cylinder-piston unit or a double-acting cylinder-piston unit comprising a single-acting or double-acting cylinder-piston unit having a head part isolation chamber and possibly a rod part isolation chamber, wherein a first chamber of the compensating container is pneumatically connected to the delivery port of one or more compression chambers and a second chamber is connected to the suction port of the isolation chamber, wherein Figure 21 Modifications will be apparent to those skilled in the art.

[0106] In an embodiment not shown, the compressor has a plurality of compression stages, ie it comprises Figures 1 to 21 A plurality of compression units 1 or 1a-g or 2 or 3 are shown arranged in series, operating within a continuous suction-delivery pressure range. In this case, the inlet opening 17 of the isolation chamber 50 of the upstream compressor unit arranged to perform a lower-pressure compression stage can be pneumatically connected to the delivery ports 16, 26 of the compression chamber of the downstream compressor unit arranged to perform a higher-pressure compression stage, whereby the isolation chamber 50 of the upstream lower-pressure compression unit is supplied with an isolation fluid 9 comprising a low-molecular-weight gas processed by the downstream higher-pressure compression unit.

[0107] The foregoing description of the embodiments of the present invention is able to illustrate the present invention from a conceptual perspective, and others using known technology will be able to modify and / or adjust such specific embodiments in various applications without further research and without departing from the concept of the present invention in this way, and therefore, it should be understood that such adjustments and modifications will be regarded as equivalent to modifications and specific embodiments. The devices and materials used to implement the various functions described can be of various types and therefore do not depart from the scope of the present invention. It should be understood that the expressions or terms used are purely descriptive and therefore not restrictive.

Claims

1. A compressor configured to compress a low molecular weight gas to a predetermined delivery pressure, wherein at least one compression unit (1, 1a-i, 2, 3) is provided, the at least one compression unit comprising a cylinder (10) and a slidable member (20) arranged in the cylinder (10), the slidable member (20) having a head portion (30) and a rod portion (39), the rod portion being integral with the head portion (30) and being arranged so that the head portion (30) performs a stroke (C) in the cylinder (10), The cylinder (10) has a proximal part (11), a central part (13) and a distal part (15) relative to the rod portion (39), the proximal part (11) and the distal part (15) of the cylinder (10) having a first inner diameter, The head portion (30) has a proximal part (31), a central part (33) and a distal part (35) relative to the stem portion (39), the proximal part (31) and the distal part (35) of the head portion (30) having a first outer diameter, wherein, apart from a predetermined coupling tolerance, the first inner diameter of the cylinder (10) and the first outer diameter of the head portion (30) are equal to a common nominal diameter (D) of the cylinder (10) and the head portion (30), The central part (13) of the cylinder (10) has a second inner diameter (D2), The central part (33) of the head portion (30) has a second outer diameter (D1), The distal part (35) of the head portion (30) includes a compression surface (36) on the opposite side relative to the central part (33) of the head portion (30), The compression surface (36) defines a compression chamber (12) within the cylinder (10), the compression chamber having an intake port (14) and a delivery port (16) for the low molecular weight gas, It is characterized by The second inner diameter (D2) is greater than the second outer diameter (D1) by a predetermined amount (G), so that an annular gap (50) having a thickness (G) equal to the predetermined amount is defined between the central part (33) of the head portion (30) and the central part (13) of the cylinder (10), And in that the central part (13) of the cylinder (10) has at least one inlet opening (17) for an isolation fluid (9), wherein the inlet opening (17) is in fluid communication with a source (8) of the isolation fluid (9), the source being configured to supply the isolation fluid (9) into the annular gap (50) at a predetermined isolation pressure so that the isolation fluid occupies the annular gap (50), and the annular gap (50) forms an isolation chamber between the compression chamber (12) and a space (22) opposite the compression chamber (12) relative to the head portion (30) of the slidable member (20).

2. The compressor according to claim 1, wherein the thickness (G) of the annular gap (50) between the central part (13) of the cylinder (10) and the central part (33) of the head part (30) of the compressor unit (1, 1a-i, 2, 3) is at least 1 mm, in particular at least 5 mm, more in particular at least 10 mm.

3. The compressor according to claim 1, wherein: - the second inner diameter (D2) of the central part (13) of the cylinder (10) of the compression unit (1, 1a-i, 2) is equal to the common nominal diameter (D); - said second outer diameter (D1) of said central part (33) of said head portion (30) is smaller than said common nominal diameter (D) by said predetermined amount (G); - said central part (33) of said head portion (30) has a length (L1) at least equal to said stroke (C).

4. The compressor according to claim 1, wherein: - said second outer diameter (D1) of said central part (33) of said head portion (30) of said compression unit (3) is equal to said common nominal diameter (D); - said second inner diameter (D2) of said central part (13) of said cylinder (10) is greater than said common nominal diameter (D) by said predetermined amount (G); - the central part (13) of the cylinder (10) has a length (L2) that is at most equal to the difference between the length (L1) of the central part (33) of the head portion (30) and the stroke (C).

5. The compressor according to claim 1, wherein the compression unit (1a-i) is a cylinder-piston unit and the slidable member is a piston (20), wherein the proximal part (31) and the distal part (35) of the head portion (30) each comprise at least two elastic piston rings (41, 45) at a distance from each other, the elastic piston rings (41, 45) being arranged to slide within the cylinder (10), and The central part (33) of the head part (30) is located between the elastic piston ring (41) of the proximal part (31) of the head part (30) and the elastic piston ring (45) of the distal part (35) of the head part (30).

6. A compressor according to claim 5, wherein the cylinder-piston unit (1a-i) is a double-acting cylinder-piston unit, wherein the compression surface (36) of the head portion (30) is a first compression surface, the compression chamber (12) is a first compression chamber, and the proximal part (31) of the head portion (30) includes a second compression surface (32) on the opposite side of the first compression surface relative to the central part (33) of the head portion (30), wherein the second compression surface and the cylinder (10) define a second compression chamber (22), and the rod portion (39) is arranged to pass through the entire length of the second compression chamber.

7. The compressor according to claim 1, wherein the second diameter (D1) of the central part (33) of the head part (30) of the compression unit (1b, 1d) decreases from the proximal part (31) toward the distal part (35) of the head part (30).

8. The compressor according to claim 1, wherein the central part (13) of the cylinder (10) of the slidable member (20) of the compressor unit (1c-h, 2, 3) has at least one outlet opening (18) for the isolation fluid (9).

9. The compressor according to claim 8, wherein the inlet opening (17) and the outlet opening (18) are formed at the same cross section of the cylinder (10), and the cylinder (10) has a circumferential groove (19) at the cross section, the circumferential groove communicating with the inlet opening (17) and communicating with the outlet opening (18).

10. A compressor according to claim 6, wherein the annular gap (50) is a first annular gap, and the rod portion (39) of the slidable member (20) of the compressor unit (1e-i) is provided with a proximal seal and a distal seal, defining a second annular gap of the rod portion (39) between the proximal seal and the distal seal, the second annular gap having at least one inlet opening (67), the at least one inlet opening being arranged to be supplied by a rod portion isolation fluid (9, 9').

11. The compressor according to claim 10, wherein the first annular gap (50) and the second annular gap of the compressor unit (1f-i) are arranged to receive a common insulating fluid (9) and have a mutual connection selected between: - parallel interconnection, wherein the first annular gap and the second annular gap are arranged parallel to each other, i.e. they are both arranged to receive the common isolation fluid (9) directly from the source (8); - are connected to each other in series, wherein the cylinder (10) and the second annular gap also have respective outlet openings (18, 68) for the common insulating fluid (9), the outlet opening (18) of the cylinder being hydraulically connected to the inlet opening (67) of the second annular gap.

12. The compressor according to claim 1, wherein the compressor unit (1h) comprises a cooling circuit (70) for the cylinder (10) and the slidable member (20), the cooling circuit being configured to deliver a cooling fluid (7) at a predetermined cooling fluid pressure higher than the delivery pressure, wherein the inlet opening (17) of the cylinder (10) is hydraulically connected to the cooling circuit (70).

13. The compressor according to claim 10, wherein the compression unit (1i) comprises a supply circuit (4), in which a compensation container (40) is provided, and within which a deformable membrane is arranged to define a first variable-volume chamber (41) and a second variable-volume chamber (42), wherein the first variable-volume chamber (41) and the second variable-volume chamber (42) are in fluid communication with the delivery port (16) of the compression chamber (12) and the inlet opening (17) of the cylinder (10), respectively, wherein the second variable-volume chamber (42) is configured to accommodate a predetermined amount of the isolation fluid (9), The isolation fluid can be fed into the annular gap (50) at a pressure that depends on the pressure of the low molecular weight gas at the delivery port (16).

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