DESCRIPTION

Field of the invention

The present invention refers in general to an improved sealing device for bores of a heat exchanger and, more specifically but not exclusively, to an improved sealing device designed for sealing the bores of the plug-type box header of an air-cooled heat exchanger.

Background of the invention

Typically, an air-cooled heat exchanger comprises a tube bundle with parallelepiped shaped headers on both ends of the tubes. Cooling air is provided by one or more fans. Usually, the tube bundle is horizontally disposed and the air blows upwards through the tube bundle. Headers have the purpose of distributing the fluid from the piping to the tubes of the heat exchanger. Almost all headers of air-cooled heat exchangers comprise welded parallelepiped boxes, also called box headers.

A vast majority of the box headers are of the plug type. This means that, for each tube connected to one wall or sheet (that is, the tube-sheet) of the box header there is a corresponding bore obtained on the opposite wall or sheet (that is, the plug-sheet) of said box header. The plug-sheet bores are used in the manufacturing process of the heat exchanger, for example to obtain the tube-to- tube-sheet joints by welding.

Once the tube-to-tube-sheet joints have been made, each plug-sheet bore is typically sealed with a respective sealing device comprising at least one plug and at least one gasket. If the sealing devices are removed from the box header, the respective plug-sheet bores therefore remain available for further inspection, maintenance and/or repair operations on the heat exchanger, for example to have access to the tube-sheet from the plug-sheet side for inspection and cleaning of individual tubes.

The plug-sheet bores and the respective sealing devices are usually the weakest point of the header of a heat exchanger. Traditionally, there are two standard configurations for these sealing devices, that is:

- single plug configuration;

- double plug configuration. A single plug configuration is shown in figure 1. In figure 1 a sealing device 100, comprising a plug 110 and a gasket 120, is inserted into a bore 130 of the plug-sheet 140 of a box header. The bore 130 is axially aligned with a tube 150 which is integrally joined with the tube-sheet 160 of the box header. The plug 110 has a bolt shape and is provided with a head 170, which protrudes from the bore 130 at the outer side of the box header plug-sheet 140, and with a threaded shank 180, which is inserted into the bore 130 in a threaded coupling. The annular shaped gasket 120 is arranged around the threaded shank 180 and is placed at the head 170 of the plug 110. This annular shaped gasket 120 is designed to be inserted into an enlarged portion 190 of the bore 130 when the plug 110 is in its operating or sealing position (that is, the position shown in figure 1), as well as to perform a sealing action due to the compression force exerted by the head 170 after the shank 180 has been screwed into the bore 130.

Therefore, in the single plug configuration shown in figure 1 there are two possible annular paths for the leakage, through the mating threads of the bore 130 and the shank 180 and downstream said threads, of the fluids contained in the box header. The first annular path is located between the radially oriented portion of the gasket 120 facing a corresponding radially oriented portion of the enlarged portion 190 of the bore 130. The second annular path, which follows the first one, is located between the axially oriented portion of the gasket 120 facing a corresponding axially oriented portion of the enlarged portion 190 of the bore 130. In other words, this second annular path is located around the circumferential edge of the gasket 120. Additionally, in the single plug configuration shown in figure 1 the annular shaped gasket 120 is subject to both frictional and torsional stresses when the shank 180 of the plug 110 is screwed into the bore 130, as well as to a compression stress which increase as the sealing capacity of said annular shaped gasket 120 increases, but which can also lead to the breakage of said annular shaped gasket 120 if the shank 180 of the plug 110 is subjected to excessive torque inside the bore 130. A double plug configuration is shown in figure 2. In figure 2 a sealing device

200, comprising a first plug 210A, a second plug 210B and a gasket 220, is inserted into a bore 230 of the plug-sheet 240 of a box header. The bore 230 is once again axially aligned with a tube 250 which is integrally joined with the tube- sheet 260 of the box header. The first plug 21 OA has a bolt shape and is provided with a head 270, which protrudes from the bore 230 at the outer side of the box header plug-sheet 240, and with a threaded shank 280, which is inserted into the bore 230 in a threaded coupling. The first plug 210A axially pushes the second plug 210B inside the bore 230. In other words, the second plug 210B does not rotate inside the bore 230, since said second plug 210B has no thread on its outer circumferential surface. The annular shaped gasket 220 is arranged around a circumferential surface portion of the second plug 210B having a reduced diameter and abuts against another circumferential surface portion of said second plug 210B having an enlarged diameter. This annular shaped gasket 220 is designed to be inserted into a corresponding shaped portion 290 of the bore 230 when both the first plug 210A and the second plug 210B are in their operating or sealing position (that is, the position shown in figure 2), as well as to perform a sealing action due to the compression force exerted by the second plug 210B against the shaped portion 290 of the bore 230 after the shank 280 of the first plug 210A has been screwed into the bore 230.

Therefore, in the double plug configuration shown in figure 2 there are once again two possible annular paths for the leakage of the fluids contained in the box header. These two possible annular paths are conceptually the same as those described above with reference to the single plug configuration. On the contrary, in the double plug configuration shown in figure 2 the annular shaped gasket 220 is subject to less frictional and torsional stresses with respect to those of the annular shaped gasket 120 described above, since the second plug 210B is simply pushed inside the bore 230 and does not rotate therein (or undergoes a very limited rotation). However, the compression stress on the annular shaped gasket 220 is more or less the same as that of the annular shaped gasket 120 described above with reference to the single plug configuration. Additionally, it should be noted that the double plug configuration shown in figure 2 is more complicated and more expensive than the single plug configuration shown in figure 1. Regardless of the plug configuration, all plug-type sealing devices assembled everywhere on the header of a heat exchanger are always possible points of leakage. These leakages, and leakage in general, are not due to a weak design of the sealing devices, but they are matter of imperfections, misalignments, fabrication tolerances, mounting tolerances, corrosion after operation, vibrations, and many other unpredictable reasons. In other words, the leakage of each sealing device is something related to probability and statistic. Actually, it should be kept in mind that in the header of a heat exchanger, except for welded joints, at least fugitive emissions are always present at any junction.

In general, during the design of a sealing device the solution is often to apply very close construction tolerance to the components of said sealing device, to issue proper assembly instruction and to prescribe some leakage test. However, in field the solution is often to increase the tightening load, but this could lead to an excessive mechanical stress to the components of the sealing device and smashing of the gasket.

Summary of the invention

One object of the present invention is therefore to provide an improved sealing device for bores of a heat exchanger which is capable of resolving the drawbacks of the prior art in a simple, inexpensive and particularly functional manner.

In detail, one object of the present invention is to provide an improved sealing device for bores of a heat exchanger which is capable of reducing leakages, with respect to the sealing devices according to the prior art, by modifying the design of the gasket and of the sealing device as a whole.

Another object of the present invention is to provide an improved sealing device for bores of a heat exchanger which is capable of reducing the stresses on the gasket while maintaining high sealing performances.

These objects are achieved according to the present invention by providing an improved sealing device for bores of a heat exchanger as set forth in the attached claims.

Further features of the invention are underlined by the dependent claims, which are an integral part of the present description.

The sealing device for bores according to the present invention is designed in particular for sealing bores obtained on a header portion of a heat exchanger. The sealing device comprises at least one bolt-type plug, which is provided with a head and with a substantially cylindrical shank. The shank has a threaded side surface, as well as a base surface which is substantially perpendicular to a central rotation axis of the plug. The plug is designed to be inserted into a corresponding bore in a threaded coupling. The sealing device also comprises at least one disk-shaped gasket having a predefined thickness, wherein said disk-shaped gasket is provided with a substantially flat and solid seal surface and with a substantially flat and solid contact surface, which is opposite to the seal surface. The sealing device further comprises at least one pusher assembly, which is interposed between the bolt-type plug and the disk-shaped gasket along the central rotation axis.

The pusher assembly comprises at least one disk-shaped anti-rotational pusher, which is provided with at least one first projection, having a first predefined thickness and comprising a pusher surface, and with at least one second projection, opposite the pusher surface and having a second predefined thickness. The second projection has the shape of any three-dimensional figure which is not axially symmetric around the central rotation axis. The pusher assembly also comprises at least one circumferentially threaded ring, having a predefined thickness which is smaller than the second predefined thickness of the second projection. The ring is provided with at least one through opening having a shape that is geometrically similar to the shape of the second projection.

In the assembled configuration of the sealing device, the second projection of the anti-rotational pusher is inserted into the through opening of the circumferentially threaded ring in a mating configuration, so that said second projection projects through said opening to adhere to the base surface of the plug shank. In this assembled configuration, the pusher surface of the anti-rotational pusher adheres to the contact surface of the disk-shaped gasket, so as to push said gasket into its sealing position in the bore. Preferably, the cross section of the second projection, i.e., a section which is orthogonal to the central rotation axis, is that of a two-dimensional closed geometric figure made of line segments. Preferably, at least one of the line segments is a straight-line segment.

Preferably, the through opening of the circumferentially threaded ring has a shape that is geometrically mating with the shape of the second projection of the anti-rotational pusher. More preferred, the through opening of the circumferentially threaded ring has a shape that is geometrically congruent with the shape of the second projection of the anti-rotational pusher. Also preferably, the shank of the plug has the same overall diameter as the diameter of the threaded ring. Even more preferably, the thread of the shank has the same pitch as the thread of the ring.

Preferably, the base surface of the shank has a circular surface and has a diameter which is smaller than the overall diameter of said shank. Also preferably, the pusher surface of the anti-rotational pusher has the same overall diameter as the diameter of the disk-shaped gasket, whereas the overall diameter of said pusher surface and of said disk-shaped gasket is smaller than the overall diameters of the shank and of the threaded ring. The disk-shaped gasket may be provided with a substantially flat and solid seal surface and with a substantially flat and solid contact surface, whereas the pusher surface of the anti-rotational pusher may also be provided with at least one circumferential groove which is capable of reducing the contact area between said pusher surface and the contact surface of the disk-shaped gasket. According to a preferred aspect of the present invention, the bolt-type plug may be provided with at least one through channel, which is oriented along the central rotation axis, for purging, venting and inspection purposes. Therefore, the anti-rotational pusher may be provided in turn with at least one through duct, which is aligned with a corresponding through channel of the bolt-type plug, for the same purging, venting and inspection purposes. Preferably, said through duct is internally threaded. More preferred, the through duct of the anti-rotational pusher has an internal diameter which is greater than the internal diameter of the through channel of the bolt-type plug and is internally threaded, so that the internal thread of said through duct makes it possible to at least partially insert a proper threaded extraction tool into said through duct for dismantling purposes.

The anti-rotational pusher, the threaded ring and the bolt-type plug may be preferably manufactured with the same material, so that said anti-rotational pusher, said threaded ring and said bolt-type plug have substantially the same hardness. The hardness of the disk-shaped gasket is instead lower than the hardness of the anti-rotational pusher, the threaded ring and the bolt-type plug. The bolt-type plug, the pusher assembly and the disk-shaped gasket are preferably made of metallic materials.

A method for assembling the sealing device described so far inside a bore obtained on a header portion of a heat exchanger is furthermore disclosed. The method comprises the steps of:

- providing a through hole in the header portion with multiple drilling operations, in order to obtain a bore comprising in sequence a first bore portion with a first predefined diameter, a second bore portion with a second predefined diameter and a third bore portion with a third predefined diameter. The bore should be made in such a way that:

- the first predefined diameter is smaller than the second predefined diameter,

- the second predefined diameter is smaller than the third predefined diameter, and

- the axial length of the second bore portion is greater than the sum of the predefined thickness of the disk-shaped gasket and the first predefined thickness of the first projection of the anti-rotational pusher;

- providing an internal thread in at least the third bore portion; - inserting the disk-shaped gasket into the second bore portion up to a first circumferential abutment wall of the bore, wherein the first circumferential abutment wall is located between the first bore portion and the second bore portion;

- inserting the second projection of the disk-shaped anti-rotational pusher into the through opening of the circumferentially threaded ring in a mating configuration, so as to form the pusher assembly in such a way that said second projection projects through said opening;

- inserting the pusher assembly into the bore by screwing the circumferentially threaded ring into the internal thread of the third bore portion, in such a way that the circumferentially threaded ring can no longer rotate by stopping against a second circumferential abutment wall of the bore, wherein said second circumferential abutment wall is located between the second bore portion and the third bore portion, and in such a way that the pusher surface of the anti- rotational pusher enters into the second bore portion to adhere to the contact surface of the gasket;

- inserting the bolt-type plug into the bore by screwing the shank of said bolt-type plug into the internal thread of the third bore portion, in such a way that the base surface of the shank faces the second projection of the disk-shaped anti- rotational pusher; and

- applying a tightening torque to the bolt-type plug, in such a way that the base surface of the shank adheres to the second projection of the disk-shaped anti- rotational pusher for pushing the gasket into its sealing position against the first circumferential abutment wall of the bore.

Brief description of the drawings

The features and advantages of an improved sealing device for bores of a heat exchanger according to the present invention will be clearer from the following exemplifying and non-limiting description, with reference to the enclosed schematic drawings, in which:

Figure 1 is a side sectional view of a sealing device for bores of a heat exchanger according to the prior art, wherein the sealing device is of the single plug type;

Figure 2 is a side sectional view of another sealing device for bores of a heat exchanger according to the prior art, wherein the sealing device is of the double plug type;

Figure 3 is a side sectional view of a preferred embodiment of the sealing device for bores of a heat exchanger according to the present invention;

Figure 4 is an enlarged view of the detail indicated with reference “IV” in figure 3;

Figure 5 is a side view of the components of the sealing device of figure 3; Figure 6 is a perspective view of the components of figure 5;

Figure 7 is another perspective view of the components of figure 5; and Figure 8 shows the sequential assembly steps of the components of figure 5 inside a corresponding bore of a heat exchanger.

Detailed description of the invention

With reference to the figures, a preferred embodiment of an improved sealing device for bores of a heat exchanger according to the present invention is shown. The sealing device is indicated as a whole with reference numeral 10. The sealing device 10 is designed to seal a corresponding bore, in particular a bore obtained on the header of a heat exchanger. More specifically but not exclusively, the sealing device 10 is designed to seal a corresponding bore 12 obtained on the plug-sheet 14 of the box header of an air-cooled heat exchanger, that is, a bore 12 which is axially aligned with a tube 16 which, in turn, is integrally joined with the tube-sheet 18 of the box header, as shown in figure 3. It should be noted that, in order to properly receive the sealing device 10, the bore 12 should be specifically machined, as will be better explained hereinafter with reference to the assembly method of said sealing device 10.

As shown in particular in figures 5 to 7, the sealing device 10 comprises at least one bolt-type plug 20, which is provided with a head 22 and with a substantially cylindrical shank 24. Preferably, the shank 24 is integrally formed in one piece with the head 22. The shank 24 has a threaded side surface 26, as well as a base surface 28 which is substantially perpendicular to a central rotation axis A of the plug 20. The plug 20 is thus designed to be inserted into a corresponding bore 12 in a threaded coupling.

The sealing device 10 also comprises at least one disk-shaped gasket 30 having a predefined thickness G. The disk-shaped gasket 30 is which is provided with a substantially flat, preferably solid, seal surface 32 and with a substantially flat, preferably solid, contact surface 34, which is opposite to said seal surface 32. The sealing device 10 further comprises at least one pusher assembly 36, 38, which is interposed between the bolt-type plug 20 and the disk-shaped gasket 30 along the central rotation axis A. The pusher assembly 36, 38 comprises two separate interlocking elements.

A first one of these interlocking elements is at least one disk-shaped anti-rotational pusher 36, which is provided with at least one first projection 42A, having a first predefined thickness C1 and comprising a pusher surface 40, and with at least one second projection 42B, opposite the pusher surface 40 and having a second predefined thickness C2. The second projection 42B may have the shape of any three-dimensional figure which is not axially symmetric around the central rotation axis A. Preferably, the cross section of the second projection 42B, i.e., a section which is orthogonal to the central rotation axis A, is that of a two-dimensional closed geometric shape made of line segments 44, 46, wherein at least one of these line segments 44, 46 is preferably a straight-line segment 44.

With the expression “two-dimensional closed geometric shape” it should be intended that the cross section of the second projection 42B is that of a closed geometrical figure made of line segments 44, 46, wherein at least one of these line segments is preferably a straight-line segment 44, whereas the other line segments 46 may also be curved segments. For example, as shown in the attached figures, the cross section of the second projection 42B is roughly that of a rectangle, wherein two opposite straight-line segments 44 are joined by two opposite curved-line segments 46. Further possible designs of the second projection 42B are possible, that is, triangular, square, rectangular, hexagonal, etc. cross sections of the second projection 42B, but also cross sections with one or more curved-line segments. Flowever, the presence of at least one straight-line segment 44 improves the anti-rotational capabilities of the pusher assembly, as will be better explained hereinafter.

The second interlocking element of the pusher assembly 36, 38 is at least one circumferentially threaded ring 38, having a predefined thickness B which is smaller than the second predefined thickness C2 of the second projection 42B of the anti-rotational pusher 36. The ring 38 is provided with at least one through opening 48 having a shape that is geometrically similar to the shape of said second projection 42B. More precisely, the through opening 48 should have a shape that is geometrically congruent with the shape of the second projection 42B of the anti-rotational pusher 3.

In the assembled configuration of the sealing device 10, as shown for example in figure 4, the second projection 42B of the anti-rotational pusher 36 is inserted into the through opening 48 of the ring 38 in a mating configuration, so that said second projection 42B projects through said opening 48 to adhere to the base surface 28 of the plug shank 24. Additionally, in this assembled configuration of the sealing device 10 the pusher surface 40 of the anti-rotational pusher 36 adheres to the contact surface 34 of the gasket 30, so as to push said gasket 30 into its sealing position in the bore 12.

In other words, thanks also to a particular shape of the bore 12, as will be better explained hereinafter with reference to the assembly method of the sealing device 10, when the plug 20 pushes against the pusher assembly 36, 38, by acting on the anti-rotational pusher 36, the mating shapes of the second projection 42B of said anti-rotational pusher 36 and the through opening 48 of the ring 38 prevent said anti-rotational pusher 36 from rotating, so that said anti-rotational pusher 36 may only move in the axial direction, that is, the direction of the central rotation axis A. This is due to the fact that the circumferentially threaded ring 38 is screwed and locked inside the bore 12 before the plug 20 is fully tightened inside said bore 12. Since the anti-rotational pusher 36 does not rotate anymore inside the bore 12 when the pusher surface 40 comes into contact with the contact surface 34 of the gasket 30, there is no twisting of said gasket 30 and thus no frictional and/or torsional stress on said gasket 30 when the plug 20 is tightened.

Preferably, as shown in the attached figures, the shank 24 of the plug 20 has the same overall diameter D as the diameter of the threaded ring 38. In other words, the thread 26 of the shank 24 has the same overall diameter D of the thread of the ring 38. Advantageously, the thread 26 of the shank 24 may also have the same pitch as the thread of the ring 38. These features allow to easily machine the bore 12 for an equally easy insertion of the sealing device 10 into said bore 12.

Preferably, the base surface 28 of the shank 24 has a circular surface and has a diameter E which is smaller than the overall diameter D of said shank 24. This feature allows to reduce the thrust and rotation surface of the plug 20 acting on the pusher assembly 36, 38, while maintaining the sealing capacity of the whole sealing device 10. For the same reason as above, the pusher surface 40 of the anti-rotational pusher 36 may also be provided with at least one circumferential groove 50 which is capable of reducing the contact area between said pusher surface 40 and the contact surface 34 of the disk-shaped gasket 30.

The pusher surface 40 of the anti-rotational pusher 36 preferably has the same overall diameter F as the diameter of the disk-shaped gasket 30. Advantageously, as will be better explained hereinafter with reference to the assembly method of the sealing device 10, the overall diameter F of said pusher surface 40 and of said disk-shaped gasket 30 is smaller than the overall diameter D of the shank 24 and of the threaded ring 38. The pusher surface 40 of the anti- rotational pusher 36 can be a flat surface or, alternatively, a convex surface.

Preferably, the anti-rotational pusher 36, the threaded ring 38 and the bolt- type plug 20 are manufactured with the same material, so that said anti-rotational pusher 36, said threaded ring 38 and said bolt-type plug 20 have substantially the same hardness. The hardness of the disk-shaped gasket 30 is instead lower than the hardness of the anti-rotational pusher 36, the threaded ring 38 and the bolt- type plug 20. Regardless of hardness, all the components of the sealing device 10, that is, the bolt-type plug 20, the pusher assembly 36, 38 and the disk-shaped gasket 30 are preferably made of metallic materials.

The bolt-type plug 20 may be provided with at least one through channel 52, which is oriented along the central rotation axis A and which has purging, venting and inspection purposes. Consequently, the anti-rotational pusher 36 may be provided with at least one through duct 54, which is aligned with a corresponding through channel 52 of the bolt-type plug 20 and which has the same purposes of said through channel 52. Additionally, the through duct 54 may be internally threaded, so as to make it possible to at least partially insert a proper threaded extraction tool into said through duct 54, so that the anti-rotational pusher 36 and thus the disk-shaped gasket 30 may be easily dismantled from the bore 12 if necessary. For this additional purpose, this through duct 54 preferably has an internal diameter which is greater than the internal diameter of the through channel 52 of the bolt-type plug 20.

With specific reference to figures 4 and 8, the method for assembling the sealing device 10 described so far inside a bore 12 obtained on a header of a heat exchanger is as follows. This assembling method initially requires a specific step of forming a proper bore 12, that is, a bore 12 with multiple internal diameters and with specific abutment walls designed to allow proper operation of the sealing device 10.

More specifically, the assembling method comprises a preliminary step of providing a through hole in the plug-sheet 14 of the box header with multiple drilling operations. These multiple drilling operations, carried out one after the other, allow to obtain a bore 12 comprising in sequence a first bore portion 56 with a first predefined diameter X, a second bore portion 58 with a second predefined diameter Y and a third bore portion 60 with a third predefined diameter Z. These bore portions 56, 58, 60 are visible in figure 4. The first predefined diameter X of the first bore portion 56 is smaller than the second predefined diameter Y of the second bore portion 58, whereas said second predefined diameter Y is smaller than the third predefined diameter Z of the third bore portion 60. In other words, with reference in particular to Figure 4:

X < Y < Z, in such a way that the first bore portion 56, which opens towards the tube-sheet 18 of the box header and is thus axially aligned with a corresponding tube 16, is narrower than the second bore portion 58. Additionally, the third bore portion 60, which opens from the opposite side of the plug-sheet 14 with respect to the first bore portion 56, is wider than the second bore portion 58, which is located between the first bore portion 56 and the third bore portion 60.

Furthermore, the bore 12 is designed in such a way that the axial length H of the second bore portion 58 is greater than the sum of the predefined thickness G of said disk-shaped gasket 30 and the first predefined thickness C1 of the first projection 42A of the anti-rotational pusher 36. In other words, with reference in particular to Figures 4 and 5:

H > G + C.

These dimensional features allow the pusher assembly 36, 38 to correctly perform its anti-rotational capabilities. Subsequently, at least the third bore portion 60 must be internally threaded, so as to allow the screwing of the threaded components of the sealing device 10, that is, the plug 20 and the circumferentially threaded ring 38, into the bore 12. The sequential assembly steps of the components of the sealing device 10 into the bore 12 are shown in figure 8. The first assembly step (step 8A, figure 8) comprises the insertion of the disk shaped gasket 30 into the bore 12, more specifically into the second bore portion 58, up to a first circumferential abutment wall 62 obtained in the bore 12. This first circumferential abutment wall 62 is located between the first bore portion 56 and said second bore portion 58 of the bore 12. The bore 12 is thus machined in such a way that the diameter F of the disk-shaped gasket 30 is greater than the first predefined diameter X of the first bore portion 56, whereas said diameter F of the disk-shaped gasket 30 is substantially equal (except for obvious construction tolerances) to the second predefined diameter Y of the second bore portion 58. In other words, with reference in particular to Figures 4 and 5: F > X; F = Y.

Therefore, since the disk-shaped gasket 30 is a solid gasket, that is, it has no through hole, in the sealing device 10 according to the present invention there is one single possible path for the leakage of the fluids contained in the header of the heat exchanger. This single possible leakage path can only occur through the annular-shaped contact area between the disk-shaped gasket 30 and the first circumferential abutment wall 62. The difference between the diameter F of the disk-shaped gasket 30 and the first predefined diameter X of the first bore portion 56 therefore determines the overall surface of this leakage path.

The second assembly step (step 8B, figure 8) comprises the insertion, preferably outside the bore 12, of the second projection 42B of the disk-shaped anti-rotational pusher 36 into the through opening 48 of the circumferentially threaded ring 38 in a mating configuration. The pusher assembly 36, 38 is thus formed, in such a way that the second projection 42B of the disk-shaped anti- rotational pusher 36 projects through the through opening 48 of the circumferentially threaded ring 38, since the second predefined thickness C2 of said second projection 42B is greater than the predefined thickness B of said ring 38. The third assembly step (step 8C, figure 8) comprises the insertion of the pusher assembly 36, 38 into the bore 12 by screwing, with a proper tool, the circumferentially threaded ring 38 into the internal thread of the third bore portion 60. This circumferentially threaded ring 38 is screwed up to a second circumferential abutment wall 64 of the bore 12, located between the second bore portion 58 and the third bore portion 60. In this way, this circumferentially threaded ring 38 can no longer rotate inside the bore 12, since it stops against the second circumferential abutment wall 64. However, due to the specific dimensions of the bore 12 described above, the pusher surface 40 of the anti-rotational pusher 36 always enter into the second bore portion 58 to adhere to the contact surface 34 of the gasket 30.

The fourth assembly step (step 8D, figure 8) comprises the insertion of the bolt-type plug 20 into the bore 12 by screwing the shank 24 of said bolt-type plug 20 into the internal thread of the third bore portion 60, in such a way that the base surface 28 of the shank 24 faces the second projection 42B of the disk-shaped anti-rotational pusher 36. At this point, a predefined tightening torque to the bolt- type plug 20 can be applied to perform the fifth and final assembly step (step 8E, figure 8) of the method for assembling the sealing device 10. In this way, the base surface 28 of the shank 24 adheres to the second projection 42B of the disk- shaped anti-rotational pusher 36. Simultaneously, the pusher surface 40 of the anti-rotational pusher 36, due to the fact that said anti-rotational pusher 36 cannot rotate, simply pushes (but does not twist) the gasket 30 into its sealing position against the first circumferential abutment wall 62 of the bore 12. It is thus seen that the improved sealing device for bores of a heat exchanger according to the present invention achieve the previously outlined objects, reducing the leakages of said sealing device with respect to prior art devices by modifying the design of the gasket (from ring-shape to solid disk-shape) and of the pusher assembly. In this way, the leakage can occur only through one path instead of two (length of leakage path is halved with respect to prior art devices). Additionally, the construction tolerance on the sealing device components became less important than in prior art devices, so that these components can be relaxed for longer life.

Finally, the adoption of an internal anti-rotational pusher assembly ensures that the gasket won’t be subjected to shear stress due to friction during tightening of the plug, which would lead to gasket disruption (for a single plug configuration such that of figure 1 this is an evidence, whereas for a double plug configuration such that of figure 2 this is a probability depending on several parameters). The following comparison table shows all the differences, and the consequent advantages, between the improved sealing device according to the present invention and the prior art devices. The improved sealing device for bores of a heat exchanger of the present invention thus conceived is susceptible in any case of numerous modifications and variants, all falling within the same inventive concept; in addition, all the details can be substituted by technically equivalent elements. In practice, the materials used, as well as the shapes and size, can be of any type according to the technical requirements.

The scope of protection of the invention is therefore defined by the enclosed claims.

List of references 10: sealing device;

12: bore;

14: plug-sheet of the box header;

16: tube;

18: tube-sheet of the box header; 20: bolt-type plug;

22: plug head;

24: plug shank;

26: shank threaded side surface;

28: shank base surface; 30: disk-shaped gasket;

32: gasket seal surface;

34: gasket contact surface;

36: anti-rotational pusher;

38: circumferentially threaded ring; 40: pusher surface;

42A: pusher first projection;

42B: pusher second projection;

44: second projection straight-line segments;

46: second projection curved-line segments; 48: ring through opening;

50: pusher surface circumferential groove;

52: plug through channel;

54: pusher through duct; 56: first bore portion;

58: second bore portion;

60: third bore portion;

62: first circumferential abutment wall; 64: second circumferential abutment wall;

A: plug central rotation axis;

B: ring thickness;

C1 : pusher first projection thickness;

C2: pusher second projection thickness; D: shank and ring diameter;

E: base surface diameter;

F: pusher surface and gasket diameter;

G: gasket thickness;

H: axial length of second bore portion; X: diameter of first bore portion;

Y: diameter of second bore portion;

Z: diameter of third bore portion.