EP2912311B1

EP2912311B1 - Simplified construction multistage reciprocating volumetric compressor

Info

Publication number: EP2912311B1
Application number: EP13747505.9A
Authority: EP
Inventors: Marco Ghiotto
Original assignee: Nardi Compressori SRL
Current assignee: Nardi Compressori SRL
Priority date: 2012-08-28
Filing date: 2013-06-13
Publication date: 2017-04-26
Anticipated expiration: 2033-06-13
Also published as: EP2912311A2; WO2014033563A2; WO2014033563A3; ITPD20120250A1

Description

The present invention refers to a multistage (multi-phase or high pressure, for instance and typically 30 bar, suitable for high compression ratios) reciprocating volumetric compressor with simplified construction and high functional efficiency, related to the prior art.
Notoriously, compressors are operating machines of pneumatic type used from several time to increase the pressure of a fluid (generally a gas, such as for example air) through the use of mechanical energy. Prior art documents published as US4,518,328 A , US5,016,524 A and US2,862,736 A disclose examples of known compressors.
Compressors are mainly classified into two large families, the first one of which includes the volumetric compressors, in which the compression of the gas is given by well defined mechanical movements, the second one of which includes, instead, the dynamic compressors, in which the compression of the gas is a direct consequence of the speed which is possible to impart on the body.
The volumetric compressors cause a reduction of the volume of the fluid on which they operate, thus providing an immediate increase in pressure of the latter; they are particularly suitable to be used to process small flows of fluid and give high lifts to the latter.
Moreover, reciprocating volumetric compressors can be further divided into single-stage (or single-phase or low pressure) volumetric compressors and multistage (or multi-phase or high pressure) volumetric compressors which differ from the first ones in relation to the possibility of achieving high compression ratios.
The reasons why the compression ratios achieved by a single-stage reciprocating volumetric compressor are not high primarily depend on the action of obnoxious volume (generally equal to 2÷5% of the volume or displacement of the compressor) and on the final high temperature of the compressed fluid, to the point of excessively overheating some component organs (typically cylinder, piston or plunger, valves) of the compressor.
Therefore it appears immediate as overheating of the component organs is an aspect of crucial and fundamental importance in a not only single-stage but also, obviously, multistage reciprocating volumetric compressor, depending on its constructive composition and type of component organs used.
In its elementary conformation, a common multistage reciprocating volumetric compressor, which the present invention is specifically oriented to, firstly comprises a plurality of compression stages, each of which includes, in turn, a movable piston slidingly coupled with reciprocating linear motion into a compression chamber of a fluid defined inside an outer cylinder.
A multistage reciprocating volumetric compressor of known type also includes motorization means, operatively connected with the movable piston of each of the aforementioned compression stages through transmission means, for example, and typically a crank-connecting rod mechanism.
Finally, a conventional multistage reciprocating volumetric compressor of the known technique comprises sealing means interposed between the movable piston and the outer cylinder with the inner wall of which cooperate by sliding contact.
The multistage reciprocating volumetric compressors are able to achieve high compression ratios and adapt themselves to many uses in industrial field: purely by way of example, it is indicated that a multistage reciprocating volumetric compressor, operating at 30 bar, is used in the building field for the actuation of nailers that, by means of the compressed air, stick nails or similar into a reinforced cement structure.
However, even the most modern and sophisticated multistage reciprocating volumetric compressors of the prior art present some recognized drawbacks.
In particular, a first drawback of the typical multistage reciprocating volumetric compressors of known type derives from the fact that the sealing means have a construction rather complex and articulated, above all due to the high number of components that distinguishes it: this inevitably affects at a considerable extent cost and price of the finished product.
Furthermore, the type of transmission or motion transformation means used nowadays in high pressure reciprocating volumetric compressors - based on a mechanism of the crank-connecting rod type which imparts a reciprocating floating motion to the movable piston-imposes, on one hand, very tight dimensional tolerances between the movable piston and the outer cylinder which further complicate construction and cost of the machine concerned and, on the other hand, long strokes of the movable piston and high extension of the surfaces of the sliding organs responsible for compression (piston itself and related sealing means) which cause inevitable problems of overheating to be considered and solved with consequent additional and expensive design features, such as a special carefully designed ventilation system, sudden decay of the performance of the compressor otherwise taking place.
To the high cost of the multistage reciprocating volumetric compressors of the current state of the art also contributes the fact that many of the components of the sealing means and transmission means, because of their functional purpose, must be obtained with mechanical precision operation, aspect that, as widely known, is source of a significant increase in costs.
A last but not least drawback of the known multistage reciprocating volumetric compressors is constituted by their noise level during operation, determined in large measure by the high number of components which form it, especially in reference to the sealing means interposed between the movable piston and the outer cylinder.
Prior art document US3,518,030 A which is considered to be the closest prior art shows a reciprocating volumetric compressor of the two stages type, one of which comprises a fixed piston and the other a movable piston that is moved with strictly linear reciprocating motion by means of a flexible membrane (or diaphragm) to which the movable piston is made integral and which is moved by actuation means such as a pressurized gas.
In particular, the sealing means of the compression system of the document US3,518,030 A include an annular seal made of Teflon® which is radially press outwardly against a bushing by a radially inwardly compressed O-ring: providing a double seal fulfills a safety function to avoid mixing between the pressurized implementation gas and compression gas.
Prior art document GB1,493,450 A shows a reciprocating volumetric compressor, in this case, however, of the single-stage type, in which the movable piston is moved with strictly linear reciprocating motion and the sealing means include a first cup-shaped ring, made in simple polytetrafluoroethylene (PTFE, also known as Teflon®), and a second metallic ring inserted by pressure between an upper hub of the movable piston and an annular wall projecting upwardly of the first ring: this second ring has only the function to stably connect the first ring with the movable piston pushing downwardly, axially, the annular radial flange of the first ring itself.
Starting therefore from the knowledge of the aboventioned drawbacks of the current state of the art, the present invention intends to give them accomplished remedy.
In particular, main purpose of the present invention is to conceive a multistage reciprocating volumetric compressor which presents a construction simpler than equivalent compressors of known type, comparable for performance.
Otherwise said, prevailing purpose of the present invention is to devise a simplified construction multistage reciprocating volumetric compressor which presents, on one hand, a number of components, especially in relation to the sealing means interposed between the movable piston and the outer cylinder, lower than that one of similar compressors of known type and, on the other hand, component organs which, despite their effectiveness and efficiency, are simpler in concept and construction than the prior art concerned, if not even also commercially available on a large scale.
In the context of the just stated purposes, it is a first task of the present invention to provide a simplified construction multistage reciprocating volumetric compressor which presents a production cost lower than known multistage reciprocating volumetric compressors, manpower and materials used being equal.
It is another task of the invention to give substance to a simplified construction multistage reciprocating volumetric compressor which, during operation, is particularly silent or, in any case, possesses a noise level much lower than that one of comparable prior art compressors.
It is a further purpose of the invention to provide a simplified construction multistage reciprocating volumetric compressor whose sealing means retain their structural and functional integrity for a life comparable if not superior to that one of the sealing means used in the multistage compressors of the state of the art.
It is a last but not least purpose of the present invention to make available a simplified construction multistage reciprocating volumetric compressor which still possesses a high compression efficiency and which keeps unchanged over time its functional capacity at least as much as the equivalent compressors of known type.
The aforesaid purposes are achieved by means of a simplified construction multistage (or high pressure) reciprocating volumetric compressor according to claim 1 attached hereto, as hereinafter referred for the sake of brevity of exhibition.
Further technical features of detail of the multistage reciprocating volumetric compressor of the present invention are indicated in the corresponding dependent claims.
The above-mentioned claims, hereinafter specifically and concretely defined, are considered an integral part of the present description.
Advantageously, the multistage reciprocating volumetric compressor of the invention presents a construction simpler than that one of the equivalent compressors of the prior art.
This especially concerns the composition of the sealing means that, in the invention, simply include an elastic memory or elastically yielding main ring which is coupled with the outer wall of the movable piston and cooperates with an auxiliary radial thrust ring, interposed between the elastic memory main ring itself and the outer wall of the movable piston in such a way as to oppose the structural deformations due to overheating suffered by the elastic memory main ring during operation, preventing these deformations become dangerously permanent and are thus able to adversely affect on the compressor performance.
Given such a composition of the sealing means, which the reduced number of components which can be easily assembled together by an operator is highlighted here of, the simplification made by the invention compared to the current state of the art appears immediately recognizable by a person skilled in the art.
The presence of the auxiliary thrust radial ring also allows the elastic memory main ring to retain long its original structural and functional capacity in such a way that the sealing means of the compressor of the invention have a life if not superior at least comparable to that one of the sealing means used in known multistage compressors.
Still advantageously, the multistage reciprocating volumetric compressor, which is the object of the present invention, has a production cost lower than that one of equivalent compressors of known type, which reflects in the possibility of practicing prices of sale to the public more competitive and attractive, despite the guarantee of achieving high performances.
Equally advantageously, the reduction in the number of components of the sealing means obtained with the invention compared to the prior art allows the multistage reciprocating volumetric compressor herein claimed to be less noisy than equivalent known compressors, with all the advantages that this entails, especially in conditions of use both for the people's health and the environmental impact.
In an advantageous way, moreover, the multistage reciprocating volumetric compressor of the invention has largely satisfactory compression efficiency, in any case comparable to that one of the most modem prior art multistage reciprocating volumetric compressors.
Said purposes and advantages, as well as other ones that will emerge hereinafter in the elaborate, will become apparent from the description which follows, relating to a preferred embodiment of the simplified construction multistage reciprocating volumetric compressor of the invention, given by exemplifying and illustrative, but not limitative, way with reference to the accompanying drawings, in which:

figure 1 is an assonometric view of the multistage reciprocating volumetric compressor of the invention;
figure 2 is an assonometric exploded view of figure 1;
figure 3 is a simplified and partial assonometric view of figure 1;
figure 4 is a side view of figure 3;
figure 5 is an enlarged and partly cutaway assonometric view of a constructive detail of figure 3.

The simplified construction multistage reciprocating volumetric compressor, object of the invention and used, for example, for actuating by means of compressed air machines so-called "nailers" in the building field, is shown in figure 1 where it is globally indicated with 1. As it can be seen, the multistage reciprocating volumetric compressor 1 of the invention includes in this specific case:

two compression stages 2, 3, each of which includes a movable piston 4 slidingly coupled with reciprocating swinging motion into a compression chamber of a fluid, typically a gas such as air, defined inside an outer cylinder 5;
motorization means, overall indicated with 6, operatively connected with the movable piston 4 of each of the aforesaid compression stages 2, 3 through transmission means, as a whole reported with 7;
sealing means, generally indicated with 8 and better seen starting from figure 2, interposed between the movable piston 4 and the outer cylinder 5 with the inner wall of which cooperate by sliding contact.

In accordance with the invention, the sealing means 8 comprise an elastic memory main ring 9 coupled with the outer wall 4a of the movable piston 4 through joint means, overall indicated with 10 and mostly visible in figure 5, and cooperating with an auxiliary radial thrust ring 11, interposed between the elastic memory main ring 9 and the outer wall 4a of the movable piston 4 in such a way as to:

oppose the structural deformations due to overheating suffered by the elastic memory main ring 9 itself during the operation, preventing these deformations become permanent and thus compromise the structural integrity (and, in turn, sealing capacity) of the elastic memory main ring 9;
increase, in this way, the fluid pressure inside the compression chamber, finally providing an improvement of the efficiency of the volumetric compressor 1 as a whole compared to the equivalent compressors of the prior art.

Figure 1 shows how, according to an established practice in the technical field concerned, the multistage reciprocating volumetric compressor 1 also includes, preferably, a support frame 12 suitable to insist on a reference surface (not shown for the sake of simplicity) and coupled below with the motorization means 6.
Furthermore, it is highlighted that the multistage reciprocating volumetric compressor 1 of the invention is, suitably although not necessarily, of the dry type, i.e. without oil lubrication and, even in combination of the fact that, in this case, is constructed with only two compression stages 2, 3, it presents features of lightness, small sizes, limited bulk, therefore resulting easy to be handled and transported.
Preferably but not necessarily, the elastic memory main ring 9, commonly referred to in the jargon of the field of compressors also with the term "segment", presents in cross section a profile substantially shaped as a bench, being composed of an annular base block 13, coupled with the movable piston 4 by means of the joint means 10 previously introduced, and an annular laminar lip 14 projecting upwardly from the base block 13 so as to define with the latter an intermediate plane 15 which the auxiliary thrust radial ring 11 is partially arranged in, as well shown in figure 5.
More in detail, the annular laminar lip 14 protrudes from the base block 13 at the outer side surface 13a of the annular base block 13 itself.
In preferred, advantageous but not binding, manner the elastic memory main ring 9 is a commercially available component made of composite material; more specifically, the composite material comprises polytetrafluoroethylene (PTFE, also known under the trademark Teflon®), in an appropriate and innovative way loaded with carbon, graphite, glass fibre and/or cast iron, in such a way that the composite material presents, at the same time, a low friction coefficient, resulting self-lubricating, and a good mechanical strength.
These mechanical properties make the elastic memory main ring 9 particularly suited to mechanically interfere with the inner wall of the outer cylinder 5 while the movable piston 4 that supports it flows inside the compression chamber with reciprocating swinging motion, however performing a consequent short linear straight stroke, as it will be explained shortly. Providing the auxiliary thrust radial ring 11 allows to keep the elastic memory main ring 9 in the original shape even and especially in presence of its overheating, which can be widely conceived or however not averted, until over the temperature of its formation, during the operation of the multistage volumetric compressor 1: if, indeed, the main ring 9 overheated beyond its temperature of formation (which in the case of the composite material described above is equal to about 180°C), it would irretrievably lose its elastic memory and it would therefore not be able to assume its original shape when the volumetric compressor 1 is stopped, thus being unusable for a subsequent operational phase of the latter.
This negative circumstance is averted by the presence of the auxiliary thrust radial ring 11 which keeps the elastic memory main ring 9 in the correct position and shape even in presence of the above critical conditions of temperature, so that it can still be reused in a subsequent phase of operation.
Preferably, the auxiliary thrust radial ring 11 presents in cross section a circular profile, as it may be still observed in figure 5, and is made of soft plastic material, actually constituting an O-ring.
With reference to the joint means 10, by purely preferred and non-exclusive title they comprise a first annular undercut 16 made in the central part of the outer wall 4a of the movable piston 4 and an inner appendix 17 of the annular base block 13: this inner appendix 17 is snap grafted into the aforementioned first annular undercut 16.
Again figure 5 shows, also, that, preferably but not exclusively, the outer wall 4a of the movable piston 4 has a second annular undercut 18 which the auxiliary thrust radial ring 11 is only partially housed and retained into: basically, therefore, the auxiliary thrust radial ring 11 contrasts against the intermediate plane 15, the inner surfaces orthogonal each other which define the second annular undercut 18 and the inner face of the annular laminar lip 14.
The second annular undercut 18 is adjacent to the first annular undercut 16 and is positioned between the first annular undercut 16 itself and the upper surface 4b of the movable piston 4. The second annular undercut 18 ensures retention capacity of the auxiliary thrust radial ring 11 in its normal constructive position illustrated in figure 5, providing, consequently, high structural and functional stability to the assembly that includes it.
As far as the transmission means 7 are concerned, in preferred but not binding way they comprise a monobloc connecting rod 19, advantageously obtained through die casting (and therefore not susceptible to further processing) and connected, on one side, with the drive shaft 20 of the motorization means 6 and, on the other side, with the movable piston 4 in such a way that the movable piston 4 itself slides with a reciprocating swinging motion into the compression chamber of the outer cylinder 5.
In particular, the drive shaft 20 of the motorization means 6 defines a linear rotation axis Z around which the monobloc connecting rod 19 is pivoted.
It is also highlighted that, in the specific case described herein, a first portion 36 of the movable piston 4 is made of one piece with the monobloc connecting rod 19, resulting in single piece with the latter; a second portion 37 of the movable piston 4 is arranged above close to the sealing means 8, particularly the main ring 9 and the auxiliary ring 11, and firmly kept in position by locking means, as a whole numbered with 38, in order to close the structural assembly formed by the movable piston 4 and sealing means 8.
The multistage reciprocating volumetric compressor 1 may also comprise a plurality of shaped counterweights 21, 22, 23, rigidly coupled with the motorization means 6 through motion gripping means, on the whole numbered with 24.
Each of the shaped counterweights 21, 22, 23 is provided with free surfaces (opposite faces 25, 26 and side edge 27) widely protruding cantilevered from the motorization means 6 (in particular from its drive shaft 20) in such a manner that the shaped counterweights 21, 22, 23, when the motorization means 6 are operated, move a given and non-negligible air flow and thus advantageously contribute to discharge heat produced by the compression stages 2, 3 during operation.
In the specific case, each of the shaped counterweights 21, 22, 23 takes the shape of a laminar plate having a substantially semicircular or half-moon profile, as well illustrated in figures 3 and 4, thus able to handle a relatively high amount of air that contributes to the cooling of the compressor 1.
With reference to the motion gripping means 24, in this case, they preferably include:

a flat lobe 28 (or key or shoulder, in more properly technical jargon) made in an end portion 29 of the outer surface 20a of the drive shaft 20 of the motorization means 6, better visible in particular in figure 3;
an as much corresponding linear portion 30 of the perimetrical wall delimiting a through hole 31 made in each of the shaped counterweights 21, 22, 23, particularly visible in figures 3 and 4.

More precisely, figure 4 shows that the through hole 31 is made at the midpoint M of the diameter D of the substantially semicircular profile of each of the shaped counterweights 21, 22,23.
In figure 4 it can be also observed that, in preferred but not limiting way, at the middle point M of the diameter D of the substantially semicircular profile, each of the shaped counterweights 21, 22, 23 is provided with a semi-annular reinforcement protrusion 32, monolithic with the shaped counterweights 21, 22, 23 and partly concerned by the through hole 31 in such a manner that the through hole 31 itself is substantially arranged for a first half in the semi-annular reinforcement protrusion 32 and for a second half in the faces of the shaped counterweights 21, 22, 23.
It is understood that in other examples of a multistage reciprocating volumetric compressor not illustrated, the motion gripping means could comprise more than one single flat lobe (or shoulder) made in a portion of the outer surface of the drive shaft of the motorization means and, in turn, more than one corresponding linear portion of the perimetrical wall which delimits a through hole made in each of the aforementioned shaped counterweights.
Also, in other examples of a multistage reciprocating volumetric compressor, yet not illustrated, the motion gripping means could include one or more flat lobes made in the entire outer surface of the drive shaft of the motorization means, and not only in a limited portion of such an outer surface, as just, described.
It is also understood that in further optional examples of a multistage reciprocating volumetric compressor, here not accompanied by reference drawings, the motion gripping means could be of other type compared to those ones just described.
In an example described herein, the compression stages are two in number (numbered with 2 and 3) and the shaped counterweights are three in number (numbered with 21, 22, 23) so as to take a disposition, better obtainable from the attached figure 2, such that:

a first shaped counterweight 21 and a second shaped counterweight 23 are facing from opposite sides to the transmission means 7 of the second compression stage 3 and coupled with the drive shaft 20 of the motorization means 6 in such a way as to be symmetrically opposed each other with respect to the rotation axis Z defined by the drive shaft 20 in order to represent a stabilizing flywheel for the multistage reciprocating volumetric compressor 1 as a whole;
the second shaped counterweight 22 and a third shaped counterweight 23 are facing from opposite sides to the transmission means 7 of the first compression stage 2 and coupled with the drive shaft 20 of the motorization means 6 in such a way as to be facing each other and asymmetrically arranged with respect to the rotation axis Z of the drive shaft 20 in order to balance the greater thrust produced by the second compression stage 3 with respect to the first compression stage 2 during operation.

Basically, then, effects and weights of the first two shaped counterweights 21 and 22 associated with the second compression stage 3 substantially cancel each other, while the third shaped counterweight 23 is opposed to the greater thrust exerted by the movable piston 4 of the second compression stage 3, by virtue of the higher pressure at which it operates, thereby balancing the operation of the multistage reciprocating volumetric compressor 1 described herein.
More specifically, the first shaped counterweight 21 is placed between the transmission means 7 of the second compression stage 3 and an outer locking flange 33, while the second shaped counterweight 22 is placed between the transmission means 7 of the two compression stages 2, 3 and the third shaped counterweight 23 is placed between the transmission means 7 of the first compression stage 2 and an inner locking counter-flange 34 coupled with the outer locking flange 33 through fastening means, generally indicated with 35 and of the type per se known to the person skilled in the art.
Operatively, and in particular in the installation phase of the multistage reciprocating volumetric compressor 1 of the invention, the elastic memory main ring 9 is firmly but removably coupled, by means of the joint means 10, with the movable piston (or plunger) 4 of each of the compression stages 2, 3 of the reciprocating volumetric compressor 1.
Afterwards, the auxiliary thrust radial ring 11 is interposed between the elastic memory main ring 9 and the outer wall 4a of the movable piston 4 in such a manner as to be at least partially arranged close to the intermediate plane 15 of the elastic memory main ring 9 and moreover partially restrained by the second annular undercut 18 defined in such an outer wall 4a.
During the operation of the reciprocating volumetric compressor 1 of the invention, as a result of the specific constructive composition of the transmission (or motion transformation) means 7 of which such a volumetric compressor 1 is, preferentially, provided with, the movable piston 4 moves with reciprocating swinging motion inside the compression chamber of the outer cylinder 5 of each of the compression stages 2, 3, however performing a net linear stroke which produces the predetermined delivery of compressed air.
Yet these last technical considerations allow to state that the preferred embodiment described herein advantageously contributes to the achievement by the invention of the initially prefixed purposes in respect of the known technique in the sector of multistage volumetric compressors, known technique which provides transmission means capable of determining a linear reciprocating floating motion for the movable piston inside the compression chamber of the outer cylinder, with all the problems and limitations that result and which have been widely mentioned before.
Unlike the prior art concerned, the multistage reciprocating volumetric compressor of the present invention does not require a large number of components, many of which are already commercially available: for example, it does not require of the connecting elements between the sealing means and piston, such as the so-called piston-pins, typical of the prior art, with the obvious economic savings - both of production cost and sale price - that this entails.
A possible overheating of the elastic memory main ring 9, which cannot be averted due to the, generally composite, material which is made of, as well as the high temperatures which are released within a multistage volumetric compressor, however, does not affect the structural nature of the main ring 9 itself thanks to the presence of the auxiliary thrust or reinforcement radial ring 11.
If necessary, indeed, the auxiliary thrust radial ring 11 suitably contrasts the assumption by the elastic memory main ring 9 of an inadequate and wrong structural position that, under the intrinsic elastic recovery of which it enjoys, wouldn't allow the recovery of the correct and operative original structural position and which would otherwise irreversibly caused by the excessively high or still above the temperature of formation of the main ring 9 itself temperatures, which inevitably develop in one or more of the compression stages 2, 3.
In this way, the elastic memory main ring 9 retains its structural integrity over time and, consequently, its precise functional sealing capacity, with the obvious advantages resulting therefrom for the performance of the multistage reciprocating volumetric compressor 1 object of the present invention.
The multistage reciprocating volumetric compressor which is exclusively claimed herein differs significantly from the known art, in particular from the prior documents US3,518,030 and GB1,493,450 cited before which concern compressors constructively very different from the compressor of the invention (for example, in the first ones the reciprocating motion of the movable piston is purely linear and floating, in the second one the reciprocating motion of the piston is swinging) and in which the related sealing means perform a different function from that one provided by the innovative design of the sealing means of the compressor of the invention.
On the basis of the above, it is understood, therefore, that the simplified construction multistage (or high pressure) reciprocating volumetric compressor, object of the present invention, achieves the purposes and reaches the advantages previously mentioned.
In execution phase, changes could be made to the multistage reciprocating volumetric compressor of the invention, consisting, for example, in a number of compression stages greater than two.
In such a specific case, the number of shaped heat disposal and, in addition, stages balance counterweights will vary accordingly, according to appropriate design arrangements of their dimensions and positions.
In addition, other examples of a multistage reciprocating volumetric compressor, not shown, could provide transmission means different from those ones previously described in reference to the figures that follow, which does not affect the advantage brought by the present invention.
Besides that, in additional and alternative examples of a multistage reciprocating volumetric compressor not yet represented in the drawings that follow, the joint means by which the elastic memory or elastically yielding main ring is coupled with the outer wall of the movable piston could differ from those ones described above.

Claims

Multistage reciprocating volumetric compressor (1) having a simplified construction comprising:
- at least two compression stages (2, 3), each of which includes a movable piston (4) slidingly coupled into a compression chamber of a fluid defined inside an outer cylinder (5);

- motorization means (6), operatively connected with a movable piston (4) of each of said compression stages (2, 3) through transmission means (7);

- a sealing means (8) interposed between said movable piston (4) and said outer cylinder (5) with which an outer wall of said movable piston cooperates by contact,
characterized in that said sealing means (8) comprise an elastic memory main ring (9), coupled with the outer wall (4a) of said movable piston (4) through a joint means (10) and cooperating with an auxiliary radial thrust ring (11), said auxiliary radial thrust ring (11) being interposed between said elastic memory main ring (9) and a part of said outer wall (4a) of said movable piston (4) which is slidingly coupled with a reciprocating swinging motion into said compression chamber, wherein said sealing means (8) is adapted to:
• oppose and prevent structural deformations of said elastic memory main ring (9) becoming permanent due to overheating suffered by said elastic memory main ring (9) during operation;

• keep structural integrity of said elastic memory main ring (9) unchanged, thereby increasing a fluid pressure inside said compression chamber.
Compressor (1) according to claim 1 characterized in that said elastic memory main ring (9) presents in cross section a bench-shaped profile being composed of an annular base block (13), coupled with said movable piston (4) by means of said joint means (10), and of an annular laminar lip (14) projecting upwardly from said base block (13) so as to define with said base block (13) an intermediate plane (15) which said auxiliary radial thrust ring (11) is partly arranged in.
Compressor (1) according to claim 2 characterized in that said annular laminar lip (14) protrudes from said annular base block (13) at the outer side surface (13a) of said annular base block (13).
Compressor (1) according to any of the preceding claims characterized in that said elastic memory main ring (9) is made of composite material.
Compressor (1) according to claim 4 characterized in that said composite material includes polytetrafluoroethylene (PTFE) loaded with carbon, graphite, glass fibre and/or cast iron.
Compressor (1) according to any of the preceding claims characterized in that said auxiliary radial thrust ring (11) presents in cross section a circular profile.
Compressor (1) according to any of the claims 2 to 6 characterized in that said joint means (10) comprise a first annular undercut (16) made in the central part of said outer wall (4a) of said movable piston (4) and an inner appendix (17) of said annular base block (13) which is snap grafted into said first annular undercut (16).
Compressor (1) according to any of the preceding claims characterized in that said outer wall (4a) of said movable piston (4) has a second annular undercut (18) which said auxiliary radial thrust ring (11) is partially housed into.
Compressor (1) according to claims 8 and 7 characterized in that said second annular undercut (18) is adjacent to said first annular undercut (16) and is placed between said first annular undercut (16) and the upper surface (4b) of said movable piston (4).
Compressor (1) according to any of the preceding claims characterized in that said transmission means (7) comprise a monobloc connecting rod (19) connected, on one side, with the drive shaft (20) of said motorization means (6) and, on the other side, with said movable piston (4) in such a manner that said movable piston (4) slides with a reciprocating swinging motion into said compression chamber of said outer cylinder (5).
Compressor (1) according to claim 10 characterized in that said drive shaft (20) of said motorization means (6) defines a linear rotation axis (Z) around which said monobloc connecting rod (19) is pivoted.