Technical field

This invention relates to a reciprocating compressor.

This invention addresses the technical sector of fluid machines designed to generate power or, in this specific case, to transfer energy to a fluid. More specifically, a reciprocating compressor is a machine which transfers power from a motor to a fluid by pressurizing the fluid in a compression chamber. The term "reciprocating" denotes the presence of a part, generally a piston, which is slidable with alternating motion inside a cylinder. Background art

Reciprocating compressors may be single acting or double acting. Single- acting reciprocating compressors compress the fluid only in one direction of sliding of the piston. Double-acting reciprocating compressors compress the fluid in both directions of sliding of the piston.

This disclosure deals with the category of double-acting reciprocating compressors. In the latter, to allow compression in both directions, it is important that the piston is not connected directly to a connecting rod of a crank mechanism. In effect, the space inside the cylinder containing a piston rod must be hydraulically sealed. To allow hydraulic sealing, therefore, the piston rod is connected to a crosshead which is in turn connected to the connecting rod of the crank mechanism.

In industrial applications, high rotation speeds and compression ratios subject the crosshead to considerable stresses. In particular, in addition to stress in the sliding direction of the piston, the crosshead is also subjected to stresses in a transverse direction, perpendicular to the sliding direction. Furthermore, with alternating motion, these forces are variable in intensity, with all the consequences in terms of fatigue stress that this involves. To make up for the problems caused by these stresses, it is of fundamental importance to reduce crosshead wear caused by sliding along a guide.

In some prior art solutions, the transverse cross section of the crosshead was characterized by two circular arcs and two straight lines. The two circular arcs were shaped to match the circular arcs of the guide. To limit wear, however, a complex system for lubricating the walls was necessary. In particular, this solution was based on the gap theory whereby lubricating a micro gap generates a force at right angles to the walls which are sliding against each other, thus preventing contact between the walls and significantly reducing wear. Further, this solution suffered from hygiene problems which, in some cases, were extremely restrictive.

Reciprocating compressors of this kind are described in document US2016281707.

Lubrication, however, requires a number of additional components which may worsen the complexity of the system and, consequently, the probability of its failure. This applies in particular to oil collection systems and oil pumping systems. Additionally, the presence of a lubrication system inevitably leads to maintenance requirements which in turn increase variable costs.

It is these technical difficulties which have led to the now common need to dispense with the oil circuit by producing "oil free" reciprocating compressors, which do not require lubrication.

Disclosure of the invention

The aim of this disclosure is to provide a double-acting reciprocating compressor to overcome the above mentioned disadvantages of the prior art.

More specifically, the aim of this disclosure is to provide a double-acting reciprocating compressor capable of compressing a fluid without having to lubricate the crosshead in its guide. This aim is fully achieved by the double-acting reciprocating compressor of this disclosure as characterized in the appended claims.

In an embodiment, the reciprocating compressor comprises a cylinder defining an internal space therein. The reciprocating compressor comprises a piston which is slidable inside the internal space of the cylinder. The reciprocating compressor comprises a motor which includes a drive shaft.

In an embodiment, the compressor comprises a slider-crank mechanism which includes a connecting rod and a crank.

In an embodiment, the crank is connected to the drive shaft. In an embodiment, the crank is configured to rotate about a longitudinal axis. In an embodiment, the longitudinal axis is the axis about which the drive shaft rotates.

In an embodiment, the compressor comprises a crosshead. In an embodiment, the crosshead includes a body.

In an embodiment, the body is connected to the connecting rod of the slider-crank mechanism.

In an embodiment, the compressor comprises a guide. In an embodiment, the guide is coupled to the crosshead. This coupling allows the crosshead to slide in a sliding direction. In one embodiment in particular, the crosshead comprises a plurality of rolling elements. In an embodiment, the plurality of rolling elements are connected to the body. In an embodiment, each rolling element of the plurality of rolling elements is in contact with the guide.

In an embodiment, the guide includes a contact wall extending along the sliding direction. In an embodiment, the contact wall at least partly surrounds the crosshead. In one embodiment, the crosshead is coupled to the guide to slide therein.

In another embodiment, the crosshead is coupled to the guide to slide on the outside of the guide.

In an embodiment, the contact wall has an inside face facing towards the crosshead. In an embodiment, the contact wall has an outside face on the side opposite to the inside face.

In one embodiment, the rolling elements of the plurality are in contact with the inside face of the contact wall.

In another embodiment, in which the crosshead is coupled to the guide to slide on the outside of the guide, the rolling elements of the plurality are in contact with the outside face of the contact wall.

In an embodiment, at least a first and a second rolling element of the plurality of rolling elements are operatively subjected to a first and a second constraint force of the guide.

By constraint force is meant the force applied by any wall on any object in contact therewith. More specifically, therefore, it is specified that a surface applies a constraint force on any body when that body comes into contact with that surface.

In other words, therefore, in an embodiment, the first and the second rolling element of the plurality of rolling elements are operatively in contact with the guide.

In an embodiment, the constraint forces have at least some components which are oriented in a transverse direction. In an embodiment, the transversely oriented components of the first and second rolling elements are directed both ways. The transverse direction is perpendicular to the sliding direction and lies in a working plane perpendicular to the longitudinal axis. By working plane is meant the plane in which the crank rotates and the connecting rod performs its roto-translational movement. In an embodiment, the body lies between the first and the second rolling element of the plurality of rolling elements.

In an embodiment, the plurality of rolling elements includes a third rolling element which is spaced from the first rolling element along the sliding direction. In an embodiment, the third rolling element is positioned relative to the guide to generate a third constraint force. The third constraint force has at least one component oriented in the transverse direction. The transversely oriented component of the third constraint force is directed the same way as the respective component of the first constraint force of the first rolling element.

The first and second rolling elements allow us to define a subset of the rolling elements which we will call "supporting subset".

In an embodiment, the supporting subset is the subset including the rolling elements of the plurality of rolling elements having at least one component oriented in the transverse direction.

It is specified that in this disclosure, identifying something as first or second is totally arbitrary. Hereinafter in this disclosure, attributing certain features to the first or the second rolling element is the result of an arbitrary choice made for the purposes of description.

In an embodiment, the rolling elements of at least one subset of rolling elements of the plurality are positioned relative to the guide to generate at least a first and a second constraint force. The first and second constraint forces generated by the rolling elements belonging to the subset have respective centring components which are longitudinally oriented. In an embodiment, the respective centring components are directed both ways. This subset is the subset including the rolling elements of the plurality of rolling elements which have at least one longitudinally oriented centring component. For clarity, we will call this subset "centring subset" without in any way limiting the function of the elements contained in that subset solely to the function of centring.

In an embodiment, the intersection of the supporting subset and the centring subset includes the rolling elements which have both a transversely oriented component and a longitudinally oriented component. In an embodiment, the supporting subset and the centring subset are separate and do not intersect and contain rolling elements which have either only a transversely oriented component or a longitudinally oriented component.

In an embodiment, the supporting subset comprises the entire plurality of rolling elements and the centring subset is an empty set.

In an embodiment, the supporting subset comprises the entire plurality of rolling elements and coincides with the centring subset.

In an embodiment, the rolling elements of the centring subset of the rolling elements of the plurality are positioned relative to the guide to generate a third constraint force. The third constraint force has a longitudinally oriented centring component. The third constraint force is spaced from one of the centring components along the sliding direction and is directed the same way.

In an embodiment, the rolling elements of the plurality are positioned relative to the guide to generate at least two constraint forces oriented in the transverse direction. In an embodiment, the at least two transversely oriented constraint forces are directed in the same way and spaced along the longitudinal direction.

In an embodiment, the rolling elements of the plurality include rollers which are coupled to flat walls of the guide.

In an embodiment, the guide includes a first flat wall. The first flat wall is oriented parallel to the sliding direction and to the longitudinal axis. In an embodiment, the guide includes a second flat wall. The second flat wall is oriented parallel to the sliding direction and to the longitudinal axis.

In an embodiment, the guide includes a third wall. In an embodiment, the guide includes a fourth wall.

In an embodiment, the guide comprises a first centring element. The first centring element is slidably coupled to the third wall to move along the sliding direction while remaining in contact therewith.

In an embodiment, the guide comprises a second centring element. The second centring element is slidably coupled to the fourth wall to move along the sliding direction while remaining in contact therewith.

In an embodiment, the first and second centring elements are connected to the body of the crosshead. In an embodiment, the first and second centring elements are connected by an adjustment system configured to vary the position of the body relative to the first and second centring elements along the longitudinal direction.

In an embodiment, each adjustment system comprises an eccentric pin. In an embodiment, the eccentric pin is connected to the respective centring element and to the crosshead.

In an embodiment, each adjustment system comprises a blocking member configured to stop the eccentric pin rotating about an adjustment axis parallel to the transverse direction.

In an embodiment, the crosshead includes a preloading spring. In an embodiment, the preloading spring is connected to one or more rolling elements of the plurality of rolling elements. For clarity, we will call "preloaded rolling elements" the rolling elements of the plurality which are connected to the preloading spring.

In an embodiment, the preloaded rolling elements are less in number than the rest of the rolling elements of the plurality of rolling elements.

In an embodiment, the compressor comprises a regulating system configured to translate the guide at least in a direction parallel to the longitudinal axis. In an embodiment, the regulating system comprises a lead screw and a slide coupled to the lead screw. In an embodiment, the regulating system may be a rack and pinion assembly.

This disclosure is also intended to protect a method for compressing a fluid.

In an embodiment, the method comprises a step of providing a reciprocating compressor which includes a cylinder, a piston, a crosshead including a body, and a slider-crank mechanism including a connecting rod and a crank.

In an embodiment, the method comprises a step of taking in the fluid through an intake port and through an additional intake port.

In an embodiment, the method comprises a step of rotating the crank about a longitudinal axis.

In an embodiment, the method comprises a step of reciprocatingly sliding the crosshead and the piston as one therewith, along a sliding direction in a guide, to compress the fluid in the cylinder. In an embodiment, the method comprises a step of discharging the compressed fluid through a discharge port and through an additional discharge port.

In one embodiment, the method comprises a step of reciprocatingly sliding the crosshead along the guide. In an embodiment, the step of reciprocatingly sliding the crosshead along the guide comprises a step of rolling a plurality of rolling elements of the crosshead, which are in contact with the guide.

In an embodiment, the step of rolling, the plurality of rolling elements roll and remain in contact with an inside surface of the guide, facing the crosshead. In an embodiment, in the step of rolling, the crosshead slides inside the guide.

In an embodiment, the method comprises a step of adjusting. The step of adjusting varies the position of the body of the crosshead at least along a direction parallel to the longitudinal axis.

In an embodiment, the method comprises a step of regulating. The step of regulating varies the position of the guide at least along a direction parallel to the longitudinal axis. Brief description of the drawings

These and other features will become more apparent from the following detailed description of a preferred, non-limiting embodiment, with reference to the accompanying drawings, in which:

- Figure 1 illustrates a double-acting reciprocating compressor according to this disclosure;

- Figures 2 and 3 schematically illustrate the reciprocating compressor of Figure 1 in respective cross sections at right angles to each other;

- Figure 4 illustrates a crosshead of the reciprocating compressor of Figure 1 , in perspective views from different angles;

- Figure 5 illustrates the crosshead of Figure 4 in a perspective view from a different angle;

- Figures 6 to 9 are, respectively, a side view, a front view, a rear view and a top view of the crosshead of Figure 4;

- Figure 10 schematically illustrates the crosshead of Figure 4 in a front view;

- Figure 1 1 illustrates a variant embodiment of the crosshead of Figure 10;

- Figure 12 illustrates the crosshead of Figure 10 in a side view;

- Figure 13 schematically illustrates a variant of the crosshead of Figure 4 provided with a regulating system;

- Figure 14 schematically illustrates a detail of an adjustment system for adjusting the crosshead of Figure 4;

- Figure 15 illustrates a variant embodiment of the crosshead of Figure 1 1 ;

- Figure 16 illustrates a variant embodiment of the crosshead of Figure 13.

Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, the numeral 1 denotes a reciprocating compressor. In a preferred embodiment, the reciprocating compressor 1 is a double-acting compressor.

In an embodiment, the reciprocating compressor 1 comprises a motor. In an embodiment, the reciprocating compressor 1 comprises a bed 2.

In an embodiment, the motor comprises a drive shaft 3.

In an embodiment, the reciprocating compressor 1 comprises a slider- crank mechanism 4. The term "slider-crank mechanism 4" is used to denote a kinematic chain consisting of mechanical parts capable of converting the rotational motion of one part into translational motion of another part. In an embodiment, the slider-crank mechanism 4 comprises a connecting rod 4A. In an embodiment, the slider-crank mechanism 4 comprises a crank 4B. In an embodiment, the crank 4B is connected to the drive shaft 3 and to the connecting rod 4A. In an embodiment, the crank 4B is rotatable about a longitudinal axis L.

In an embodiment, the reciprocating compressor 1 comprises a cylinder 5. In an embodiment, the cylinder 5 has at least one intake valve 5A. In an embodiment, the cylinder 5 has at least one discharge valve 5B. In an embodiment in which the reciprocating compressor 1 is double acting, the reciprocating compressor 1 comprises an additional intake valve 5A' and an additional discharge valve 5B'.

In an embodiment, the reciprocating compressor 1 comprises a piston 6. In an embodiment, the piston 6 is slidable in the cylinder 5 along a sliding axis which is parallel to a sliding direction S. In an embodiment, the piston 6 is provided with a plurality of hydraulic seals on the wall of it which comes into contact with the cylinder 5. In an embodiment in which the reciprocating compressor 1 is double acting, the piston 6 is always at a position closer to the intake valve 5A or discharge valve 5B than the additional intake valve 5A' or additional discharge valve 5B'. In other words, the sliding of the piston 6 inside the cylinder 5 is included between the intake valve 5A and the additional intake valve 5A'. That way, during sliding in a going direction A, oriented from the additional intake valve 5A' to the intake valve 5A, the piston 6 compresses a gas in an above-piston chamber, which is the part of the cylinder 5 between the piston 6 and the intake valve 5A. On the other hand, during sliding in a return direction R, oriented from the intake valve 5A to the additional intake valve 5A', the piston 6 compresses a gas in an under-piston chamber, which is the part of the cylinder 5 between the piston 6 and the additional intake valve 5A'. For this to happen, the under-piston chamber must remain sealed during the sliding of the piston 6, hence during the compressing of the gas. The connecting rod 4A must not therefore be connected directly to the piston 6. In an embodiment, the reciprocating compressor 1 comprises a crosshead 10. A crosshead 10 is a mechanism used to keep the piston 6 free of the connecting rod 4A, allowing only parts which are movable with translational motion to be present in the space inside the cylinder 5.

In an embodiment, the crosshead 10 is connected to the connecting rod 4A and to the piston 6. In an embodiment, the reciprocating compressor 1 comprises a guide 7. In an embodiment, the guide 7 is connected to the bed 2 of the reciprocating compressor 1 . In an embodiment, the guide 7 is associated with the crosshead 10 and is configured to keep an axis of translation of the crosshead coincident with the sliding axis of the piston 6.

In an embodiment, the crosshead 10 of the reciprocating compressor 1 comprises a body 1 1 .

In an embodiment, the crosshead 10 of the reciprocating compressor 1 comprises a central body 1 1 A.

The central body 1 1 A of the crosshead 10 allows identifying six faces of the crosshead 10. In an embodiment, the central body 1 1 A comprises two lateral faces 1 10, perpendicular to a longitudinal direction L, at right angles to the sliding direction S and lying in a working plane PL at right angles to the longitudinal axis L.

In an embodiment, the central body 1 1 A comprises a front face 1 1 1 which faces towards the piston 6. In an embodiment, the central body 1 1 A comprises a rear face 1 12 which faces towards the connecting rod 4A.

In an embodiment, the central body 1 1 A comprises an underside face 1 13 which is parallel to the longitudinal direction L. In an embodiment, the central body 1 1 A comprises a top face 1 14 which is parallel to the longitudinal direction. In an embodiment, the top face 1 14 is further from the bed 2 of the reciprocating compressor 1 than the underside face 1 13.

In an embodiment, the lateral faces 1 10 are parallel to the sliding direction

S and to a transverse direction T, perpendicular to the longitudinal direction L.

In an embodiment, the guide 7 comprises an inside surface 7A.

In an embodiment, the guide 7 comprises an outside surface 7B.

In one embodiment in particular, the inside surface 7A comprises a plurality of faces facing towards the crosshead 10.

In an embodiment, the guide 7 comprises two side walls 70, each facing towards the respective lateral face of the central body 1 1 A. In an embodiment, the guide 7 comprises a top wall 71 , facing towards the top face 1 14 of the central body 1 1 A.

In an embodiment, the guide 7 comprises a bottom wall 72, facing towards the underside face 1 13 of the central body 1 1 A.

In an embodiment, the bottom wall 72 and the top wall 71 of the guide 7 are flat walls. In an embodiment the two side walls 70 of the guide 7 are smooth, flat walls.

In an embodiment, the top wall 71 and the top wall 72 are parallel to the sliding direction S and to the longitudinal direction L. In an embodiment, the side walls 70 are parallel to the sliding direction S and to the transverse direction T.

In an embodiment, the crosshead 10 comprises a hinge 8A disposed on the rear face 1 12 of the central body 1 1 A.

In an embodiment, the hinge 8A is a pin which is elongated along the longitudinal direction, at right angles to the sliding direction S, and to which one end of the connecting rod 4A is keyed.

In an embodiment, the crosshead 10 comprises a connecting member 8B disposed on the front face 1 1 1 of the central body 1 1 A. In an embodiment, the connecting member 8B is a rod with a variable circumferential profile configured to be coupled to the piston 6.

In an embodiment, the crosshead 10 of the reciprocating compressor 1 comprises a plurality of rolling elements 120. In an embodiment, the plurality of rolling elements 120 are coupled to the main body 1 1 of the crosshead 10. In an embodiment, the plurality of rolling elements 120 are coupled to the crosshead 10 by respective rotating pins.

In one embodiment, each rotating pin is connected to one of the two lateral faces 1 10. In another embodiment, each rotating pin is connected to one of the other four faces of the central body 1 1 A.

In an embodiment, the plurality of rolling elements 120 are configured to remain in contact with the guide 7. In an embodiment, the crosshead 10 comprises at least a first and a second rolling element disposed inside the guide 7 to generate a first and a second constraint force with at least one component that is oriented along the transverse direction T and directed both ways. This feature allows the crosshead 10 to have two supporting points on the guide 7 to generate opposite constraint forces that prevent the crosshead 10 from translating along the transverse direction T.

In a preferred embodiment, the crosshead 10 comprises a first supporting carriage 1 18A and a second supporting carriage 1 18B. By "supporting carriage" we mean a set of rolling elements of the plurality of rolling elements 120 operatively subjected to a respective constraint force with at least one component along the transverse direction T.

In an embodiment, the first and the second supporting carriage 1 18A and 1 18B are subjected to constraint forces directed entirely in the transverse direction T. In an embodiment, the first and the second supporting carriage 1 18A and 1 18B are subjected to constraint forces which have a component oriented along the longitudinal direction L, too.

In this embodiment, the first and second supporting carriage 1 18A and 1 18B may also perform a centring function. By "centring" we mean keeping the axis of translation of the crosshead 10 at a longitudinal design position along the longitudinal direction L.

In an embodiment, the crosshead 10 comprises a self-lubricating bearing for each rolling element.

It is understood that the choice of first and second supporting carriage 1 18A and 1 18B is purely arbitrary, meaning that all the features subsequently correlated with the first or the second supporting carriage 1 18A or 1 18B could be arbitrarily inverted.

In an embodiment, the first supporting carriage 1 18A is in contact with the bottom wall 72 of the guide 7. In an embodiment, the second supporting carriage 1 18B is in contact with the top wall 71 of the guide 7.

In an embodiment, the first supporting carriage 1 18A comprises one or more rolling elements of the plurality of rolling elements 120. In an embodiment, the second supporting carriage 1 18B comprises one or more rolling elements of the plurality of rolling elements 120.

In an embodiment, the rolling elements belonging to the first supporting carriage 1 18A are less in number than the rolling elements belonging to the second supporting carriage 1 18B.

In an embodiment, the first supporting carriage 1 18A comprises four rolling elements. In an embodiment, the second supporting carriage 1 18B comprises two rolling elements.

In an embodiment, the first supporting carriage 1 18A comprises a first pair of rollers 1 18A' and a second pair of rollers 1 18A".

In an embodiment, the first pair of rollers 1 18A' is spaced from the second pair of rollers 1 18A" along the sliding direction S. In an embodiment, each roller of the first pair of rollers 1 18A' is spaced from the other along the longitudinal direction L. In an embodiment, each roller of the second pair of rollers 1 18A" is spaced from the other along the longitudinal direction L. This prevents the body 1 1 of the crosshead 10 from rotating both about the sliding axis and about an axis parallel to the longitudinal direction L. In an embodiment, the crosshead 10 comprises an elastic element. In an embodiment, the elastic element is a leaf spring 122. In an embodiment, the leaf spring 122 is connected to the main body 1 1 . In an embodiment, the leaf spring 122 is connected to the plurality of rolling elements 120. In an embodiment, the leaf spring 122 is connected to the second supporting carriage 1 18B, which is in contact with the top wall 71 of the guide 7. In an embodiment, the leaf spring 122 is connected to the main body 1 1 A by a secondary body 1 1 B provided with a plurality of fasteners such as, for example, but not limited to, screws, bolts, rivets or the like. In an embodiment, the leaf spring 122 is connected directly to the main body 1 1 A by the plurality of fasteners such as, for example, but not limited to, screws, bolts, rivets or the like.

In an embodiment, the leaf spring 122 is connected to the top face 1 14 of the main body 1 1 .

The leaf spring 122 allows keeping the plurality of rolling elements 120 in contact with the respective walls of the guide 7. More specifically, the leaf spring 122 allows maintaining contact between the respective walls of the guide 7 and the rolling elements the guide is connected to and the rolling elements disposed on the face of the main body 1 1 A opposite to the one the leaf spring 122 is connected to. In one embodiment, therefore, the leaf spring 122 allows the first and the second supporting carriage 1 18A and 1 18B to remain in contact with the top wall 71 and the bottom wall 72 of the guide 7 during use of the compressor.

In effect, the leaf spring 122 is preloaded and is configured to apply an elastic force on the plurality of rolling elements 120 along a preloading direction.

In an embodiment, the connecting rod 4A is configured to apply a working force on the crosshead 10, at the hinge.

The elastic force is added to the working force. In particular, the direction of the working force varies with the rotation of the drive shaft 3. That means the working force is towards the bottom wall 72 and the top wall 71 alternately.

The elastic force, on the other hand, remains constant until the preloading value is exceeded. When the working force is directed towards the bottom wall 72 of the guide 7, it is added to the elastic force. Instead, when it is directed towards the top wall 71 of the guide 7, it is subtracted from the elastic force. That accounts for the presence of four rolling elements in the first supporting carriage 1 18A and only two rolling elements in the second supporting carriage 1 18B.

In an embodiment, the plurality of rolling elements 120 of the crosshead 10 comprises at least two rolling elements which are operatively subjected to a first and a second centring constraint force having at least one centring component that is oriented along the longitudinal direction and directed both ways.

In an embodiment, the at least two rolling elements may belong to the first supporting carriage 1 18A or to the second supporting carriage 1 18B or one to the first supporting carriage 1 18A and one to the second supporting carriage 1 18B.

In an embodiment, the respective centring constraint force of the at least two rolling elements has only one centring component oriented along the longitudinal direction L and no component oriented along the transverse direction T.

In an embodiment, the crosshead 10 comprises a centring unit 1 18C. In an embodiment, the centring unit 1 18C comprises a plurality of centring elements 121 . In an embodiment, the plurality of centring elements 121 comprises two or more rolling elements of the plurality of rolling elements 120. In an embodiment, the plurality of centring elements 121 comprises a plurality of wear pads 121 '.

In this embodiment, the centring elements 121 work by sliding against the respective side wall of the guide 7. This solution is possible because the direction of the working force is never perpendicular to the side wall of the guide 7 and the forces applied on the wear pads are small and are the result of possible misalignments between the connecting rod 4A, the crosshead 10 and the piston 6.

In an embodiment, the centring unit 1 18C comprises a first centring element 121 A and a second centring element 121 B. In an embodiment, the first centring element 121 A is in contact with one of the two side walls 70 of the guide 7. In an embodiment, the second centring element 121 B is in contact with the side wall 70 on the side opposite the one the first centring element is in contact with.

In an embodiment, the centring unit 1 18C comprises a third centring element disposed in contact with the same wall as the first centring element 121 A and subjected to a centring constraint force having a centring component along the longitudinal direction L directed the same way as the centring constraint force the first centring element 121 A. is subjected to.

In an embodiment, the plurality of centring elements 121 of the centring unit 1 18C are connected to the main body 1 1 A of the crosshead 10. In an embodiment, the plurality of centring elements 121 are connected to the secondary body 1 1 B of the crosshead 10, integral with the main body 1 1 A. In an embodiment, the crosshead 10 comprises an adjustment system 125 for each centring element 121 . The adjustment system 125 allows translating the main body 1 1 A of the crosshead 10 at least along the longitudinal direction L so as to align it with the sliding direction S of the piston 6. In other words, the adjustment system 125 allows varying the position of the body 1 1 of the crosshead 10 at least along the longitudinal direction L relative to the position of the first and second centring elements 121 A, 121 B.

In an embodiment, the adjustment system 125 comprises an eccentric pin 125A. In an embodiment, the eccentric pin 125A is connected to the secondary body 1 1 B. In an embodiment, the eccentric pin 125A is connected to the main body 1 1 A.

In an embodiment, the eccentric pin 125A has an adjustment axis R. The eccentric pin 125A is configured to rotate about the adjustment axis R, modifying the distance of a working axis of the centring element from the respective side wall 70 of the guide 7.

In an embodiment in which the centring element 121 is a rolling element of the plurality of rolling elements 120, the working axis of the centring element 121 is a transverse axis of rotation parallel to the transverse direction T. In an embodiment in which the centring element 121 is a wear pad 121 ', the working axis of the centring element 121 is a transverse axis of symmetry of the wear pad 121 '.

In an embodiment, the adjustment system 125 comprises a blocking member 125B. In an embodiment, the blocking member 125B is associated with the eccentric pin 125A. In an embodiment, the blocking member 125B has two operating configurations. In the first operating configuration, which we will call "working position", the blocking member 125B is configured to prevent the eccentric pin 125A from rotating about the adjustment axis R. In the second operating configuration, which we will call "adjustment position", the blocking member 125B is configured to allow the eccentric pin 125A to rotate about the adjustment axis R.

In an embodiment, the reciprocating compressor 1 comprises a regulating system 126. The regulating system 126 allows the guide 7, and the crosshead 10 associated therewith to be translated at least along the longitudinal direction L. In other words, the regulating system 126 allows the crosshead 10-guide 7 assembly to slide along the longitudinal direction L relative to the bed 2 of the reciprocating compressor 1 .

In an embodiment, the regulating system 126 comprises a rack 126A. In an embodiment, the regulating system 126 comprises a pinion 126B. In an embodiment, the pinion 126B is connected to the bed 2 of the reciprocating compressor 1 . In an embodiment, the rack 126A is connected to the guide 7 on an outside wall of the guide 7 corresponding to the bottom wall 72 of the guide 7. In an embodiment, the rack 126A is connected to the guide 7 on an outside wall of the guide 7 corresponding to the bottom wall 71 of the guide 7.

In an embodiment, the pinion 126B is configured to rotate and to allow translating the rack 126A it is coupled to, in turn causing the guide 7 to be translated.

In an embodiment, the regulating system 126 comprises a lead screw 126A'. In an embodiment, the regulating system 126 comprises a coupling profile 126B' formed on the guide 7 and configured to be coupled to the lead screw 126A'. In an embodiment, the regulating system 126 comprises a prismatic guide formed on the bed 2 of the reciprocating compressor 1 . The lead screw 126A' is configured to rotate on the coupling profile 126B' to move the guide 7 according to the pitch of the lead screw 126A' and the degrees of rotation. The prismatic guide 7, on the other hand, is configured to allow the guide 7 to be translated only along the longitudinal direction.

According to one aspect of this disclosure, this invention also provides a method for compressing a fluid.

In an embodiment, the method comprises providing a reciprocating compressor 1 which includes a cylinder 5, a piston 6, a crosshead 10, a guide 7, and a slider-crank mechanism 4 including a connecting rod 4A and a crank 4B.

The method comprises a step of taking in through an intake port. The step of taking in through an intake port fills an above-piston chamber with fluid, this chamber being the part of the cylinder 5 between the piston 6 and the intake valve 5A.

During this step, the piston 6 slides in a return direction R.

In an embodiment, the method comprises a step of taking in through an additional intake valve 5A'. In an embodiment, during this step of taking in through the additional intake valve 5A', the piston 6 slides in a going direction A.

In an embodiment, during the step of taking in through the additional intake valve 5A', the reciprocating compressor 1 compresses a fluid contained in an above-piston chamber, the part of the cylinder 5 between the piston 6 and the intake valve 5A.

In an embodiment, during the step of taking in through the intake valve 5A, the reciprocating compressor 1 compresses a fluid contained in an under- piston chamber, the part of the cylinder 5 between the piston 6 and the additional intake valve 5A'.

In an embodiment, the method comprises, at the end of the step of compressing, a step of discharging through a discharge valve 5B and an additional discharge valve 5B', respectively.

Hereinafter, we will use the terms "step of compressing" to denote, without distinction, the step of compressing the fluid contained in the chamber above piston and the step of compressing the fluid contained in the chamber under piston.

In an embodiment, the step of compressing comprises a step of reciprocatingly sliding the crosshead 10. The connecting rod 4A associated with the drive shaft 3 imparts translational motion to the crosshead 10 which causes the latter to move along the guide 7.

By its translation the crosshead 10 in turn drives the piston 6 to perform the function of compressing the fluid in the cylinder 5.

In an embodiment, the step of reciprocatingly sliding the crosshead 10 is carried out in a sliding direction S on a guide 7.

In an embodiment, sliding reciprocatingly occurs between two operating positions: a distal position of maximum distance between the crosshead 10 and the cylinder 5; and a proximal position of minimum distance between the crosshead 10 and the cylinder 5.

In an embodiment, the step of reciprocatingly sliding the crosshead 10 along the guide 7 comprises a step of rolling a plurality of rolling elements 120 of the crosshead 10.

In an embodiment, the crosshead slides reciprocatingly in the guide 7 while keeping the plurality of rolling elements 120 in contact with an inside surface 7A of the guide 7 itself. During the step of sliding, the guide 7 subjects a first and a second rolling element to a first and a second constraint force, each having at least one component that is oriented along the transverse direction T and directed both ways.

In an embodiment, during the step of rolling, the plurality of rolling elements 120 remain in contact with a bottom wall 72 and a top wall 71 of the guide 7.

In an embodiment, during the step of rolling, a first supporting carriage 1 18A, which comprises four rolling elements of the plurality of rolling elements 120, remains in contact with the bottom wall 72 of the guide 7 as it rolls.

In an embodiment, during the step of rolling, a second supporting carriage 1 18B, which comprises two rolling elements of the plurality of rolling elements 120, remains in contact with the top wall 71 of the guide 7 as it rolls. In an embodiment, the method comprises a step of transversely guiding, performed by a centring unit 1 18C. In an embodiment, during the step of transversely guiding, a first and a second centring element 121 A and 121 B are subjected to a first and a second centring constraint force, each having at least one component that is oriented along the longitudinal direction L and directed both ways.

This prevents translation of the crosshead 10 in the longitudinal direction L during the reciprocating sliding thereof.

In an embodiment in which the crosshead 10 comprises a plurality of centring elements 121 , the step of transversely guiding comprises rolling a plurality of rolling elements of the plurality of rolling elements 120.

In an embodiment, the plurality of centring elements 121 remain in contact with the side walls 70 of the guide 7.

In an embodiment in which the plurality of centring elements 121 is a plurality of wear pads 121 ', during the step of transversely guiding, each wear pad 121 ' of the plurality of wear pads 121 ' slides against the side walls 70 of the guide 7.

In an embodiment, the method comprises a step of longitudinal adjustment.

In an embodiment, during the step of longitudinal adjustment, a central body 1 1 A of the crosshead 10, to which the connecting rod 4A and the piston 6 are connected, moves translationally at least along the longitudinal direction L relative to the first and second centring elements 121 A and 121 B.

More specifically, the step of longitudinal adjustment may include a step of adjusting each centring element 121 of the plurality of centring elements 121 .

The step of adjusting each centring element 121 modifies the distance of the working axis of that centring element 121 from the respective side wall 70 along which the centring element rolls.

Further, the step of adjusting each centring element 121 is not independent of the step of adjusting the other centring elements 121 . In effect, when the working axis of a centring element 121 is moved towards or away from the respective side wall, considering the guide 7 to be equal in size, it is necessary to also move the working axis of the centring element 121 rolling on the opposite side wall 70 towards or away.

In an embodiment, the method comprises a step of providing an eccentric pin 125A connected to the crosshead 10 and to the respective centring element 121 .

In an embodiment, the step of longitudinal adjustment comprises a step of releasing in which a blocking member 125B is slackened to move it from a working position to an adjustment position.

In an embodiment, the step of longitudinal adjustment comprises a step of rotating the eccentric pin 125A. In an embodiment, the step of rotating the eccentric pin 125A is carried out about an axis of adjustment R.

In an embodiment, the step of longitudinal adjustment comprises a step of blocking, in which the blocking member 125B is tightened to move it from the adjustment position to the working position.

In an embodiment, the method comprises a step of preloading.

In an embodiment, during the step of preloading, a preloading spring connected to the crosshead 10 applies an elastic force on the plurality of rolling elements 120 of the crosshead 10. In an embodiment, during the step of preloading, the preloading spring is connected only to a plurality of preloaded rolling elements 120, forming part of the plurality of rolling elements 120.

In an embodiment, during the step of preloading, the spring applies an elastic force on the second supporting carriage 1 18B.

In an embodiment, the step of preloading allows the plurality of rolling elements 120 to remain in contact with the top wall 71 or the bottom wall 72 of the guide 7.

In an embodiment, during reciprocating compression operations, the step of preloading determines a stress overload of part of the plurality of rolling elements 120 in contact with the bottom wall 72 of the guide 7.

In an embodiment, during reciprocating compression operations, the step of preloading determines a stress overload of the first supporting carriage 1 18A which is in contact with the bottom wall of the guide 7.

In an embodiment, the method comprises a step of longitudinal regulation. In an embodiment, during the step of longitudinal regulation, the guide 7 of the crosshead 10 is translated at least along the longitudinal direction L. In an embodiment, during the step of longitudinal regulation, a pinion 126B attached to a bed 2 of the reciprocating compressor 1 rotates along a rack 126A attached to the guide 7 of the crosshead 10. As the pinion 126B rotates, the rack 126A is translated along the longitudinal direction L and the guide 7 of the crosshead 10 is translated with it.

In an embodiment, during the step of longitudinal regulation, a lead screw 126A' attached to a bed 2 of the reciprocating compressor 1 rotates about an axis of regulation parallel to the longitudinal direction L.

In an embodiment, during the step of longitudinal regulation, the lead screw 126A' is engaged in a coupling profile integral with the guide 7 of the crosshead 10.

When the lead screw 126A' rotates, the guide 7 is translated along the longitudinal direction L according to the screw pitch and the degrees of rotation.

The paragraphs listed below, labelled with alphanumeric references, are non-limiting example modes of describing this invention.

A) A double-acting, reciprocating compressor 1 , comprising:

- a cylinder 5 defining an internal space;

- a piston 6 slidable inside the internal space of the cylinder 5;

- a motor including a drive shaft 3;

- a slider-crank mechanism 4 including a connecting rod 4A and a crank 4B connected to the drive shaft 3 and configured to rotate about a longitudinal axis L;

- a crosshead 10 including a body 1 1 connected to the connecting rod 4A of the slider-crank mechanism 4;

- a guide 7 coupled to the crosshead 10 to allow the crosshead to slide in a sliding direction S,

wherein the crosshead 10 comprises a plurality of rolling elements 120, connected to the body 1 1 and each in contact with the guide 7.

A1 ) The compressor of paragraph A, wherein the guide 7 includes a contact wall extending along the sliding direction S and at least partly surrounding the crosshead 10, wherein the crosshead 10 is coupled to the guide 7 to slide therein.

A2) The compressor of paragraph A1 , wherein the contact wall has an inside face facing towards the crosshead 10 and an outside face on the side opposite to the inside face, and wherein the rolling elements 120 of the plurality of rolling elements are in contact with the inside face of the contact wall..

A3) The compressor of any one of the preceding paragraphs, wherein at least a first and a second rolling element of the plurality of rolling elements 120 are operatively subjected to a first and a second constraint force of the guide 7, respectively, the constraint forces having at least respective components oriented in a transverse direction T, which is perpendicular to the sliding direction S and is contained in a working plane PL perpendicular to the longitudinal axis L and directed in opposite ways. A4) The compressor of paragraph A3, wherein the plurality of rolling elements 120 includes a third rolling element, spaced from the rolling element along the sliding direction S and positioned relative to the guide 7 to generate a third constraint force having at least one component which is oriented in a transverse direction T and directed in the same way as the respective component of the constraint force of the first rolling element. A5) The compressor of paragraph A3 or A4, wherein the rolling elements 120 of at least one subset of rolling elements of the plurality are positioned relative to the guide 7 to generate at least a first and a second constraint force having respective centring components which are oriented along a longitudinal direction parallel to the longitudinal axis L and directed in opposite ways.

A6) The compressor of paragraph A5, wherein the rolling elements 120 of the subset of rolling elements 120 of the plurality are positioned relative to the guide 7 to generate a third constraint force reaction having a centring component which is oriented along the longitudinal direction L and spaced, along the sliding direction S, relative to one of the centring components directed the same way.

A7) The compressor of any one paragraphs A3 to A6, wherein rolling elements 120 of the plurality are positioned relative to the guide 7 to generate at least two constraint forces oriented in the transverse direction T and directed in the same way and spaced along the longitudinal direction L.

A8) The compressor of any one of the preceding paragraphs, wherein the rolling elements 120 of the plurality include rollers which are coupled to flat walls of the guide 7.

A9) The compressor of any one of the preceding paragraphs, wherein the guide 7 includes:

- a first and a second flat wall 71 and 72 oriented parallel to the sliding direction S and to the longitudinal axis L;

- a third and a fourth wall connecting the first wall 71 to the second wall 72;

- a first centring element 121 A slidably coupled to the third wall to move along the sliding direction S while remaining in contact therewith;

- a second centring element 121 B slidably coupled to the fourth wall to move along the sliding direction S while remaining in contact therewith; wherein the first and the second centring element 121 A and 121 B are connected to the body 1 1 of the crosshead 10 by an adjustment system 125 configured to vary the position of the body 1 1 relative to the first and second centring elements 121 A, 121 B along the longitudinal direction L. A10) The compressor of paragraph A9, wherein each adjustment system 125 comprises: - an eccentric pin 125A connected to the respective centring element 121 and to the crosshead 10;

- a blocking member 125B configured to prevent rotation of the eccentric pin 125A about an axis of adjustment R parallel to a transverse direction T, perpendicular to the sliding direction S contained in a working plane PL perpendicular to the longitudinal axis L.

A1 1 ) The compressor of any one of the preceding paragraphs, wherein the crosshead 10 comprises a preloading spring 122, connected to one or more rolling elements of the plurality of rolling elements 120.

A12) The compressor of paragraph A1 1 , wherein the rolling elements connected to the preloading spring 122 are less in number than the rest of the rolling elements of the plurality of rolling elements 120.

A13) The compressor of any one of the preceding paragraphs, comprising a regulating system 126 configured to translate the guide 7 at least in a direction parallel to the longitudinal axis L.

B) A method for compressing a fluid, comprising the following steps:

- providing a reciprocating compressor 1 which includes a cylinder 5, a piston 6, a crosshead 10 including a body 1 1 , and a slider-crank mechanism 4 including a connecting rod 4A and a crank 4B;

- taking in the fluid through an intake port 5A and through an additional intake port 5A';

- rotating the crank 4B about a longitudinal axis L;

- reciprocatingly sliding the crosshead 10, and the piston 6 as one therewith, along a sliding direction S in a guide 7, to compress the fluid in the cylinder 5;

- discharging the compressed fluid through a discharge port 5B and through an additional discharge port 5B';

characterized in that the step of reciprocatingly sliding the crosshead 10 along the guide 7 comprises a step of rolling a plurality of rolling elements 120 of the crosshead 10, which are in contact with the guide 7.

B1 ) The method of paragraph B, wherein, in the step of rolling, the plurality of rolling elements 120 roll and remain in contact with an inside surface 7A of the guide 7, facing the crosshead, and wherein, in the step of rolling, the crosshead 10 slides inside the guide 7.

B2) The method of paragraph B or B1 , comprising a step of adjustment, in which the position of the body 1 1 of the crosshead 10 varies at least along a direction parallel to the longitudinal axis L.

B3) The method of paragraph B or B1 or B2, comprising a step of adjustment, in which the position of the guide 7 varies at least along a direction parallel to the longitudinal axis L.