Sealing device for piston rod of reciprocating compressor

Abstract

To provide a sealing device (15) for sealing a piston rod (8) of a reciprocating compressor (1) during a compressor rest state that improves operational safety, the sealing device (15) includes a plurality of first packing retainers (18), each having a retaining opening (18a) in which a first packing ring (19) is disposed, and a second packing retainer (20a) having a retaining opening (20a) in which a second packing ring (21) is disposed. and a second retainer (20) located closer to the second axial device end (15a) than the plurality of first packing retainers (18) in the axial direction of the sealing device (15). The second packing ring (21) is an unbroken ring having a continuous inner circumferential sealing surface (21a), the second packing ring (21) configured to seal the piston rod (8) when the compressor (1) is at rest. The sealing device (15) includes a support passage (28). the support passage (28) has a first support passage end (28a), a second support passage end (28b), and a valve (29) for opening and closing the support passage (28), and the support passage (28) vents gas leaking through at least one of the plurality of first packing rings (19) in at least a direction from the first axial device end (15a) to the second axial device end (15b) from the first support passage end (28a) to the second support passage end (28b). the sealing device (15) further having an unobstructed vent passage (31), the vent passage (31) having a first vent passage end (31a) and a second vent passage end (31b), the vent passage (31) being configured to vent gas leaking past the second packing ring (21) in a direction from the first axial device end (15a) to the second axial device end (15b) from the first vent passage end (31a) to the second vent passage end (31b).

Description

[Technical field]

[0001] The present invention provides a sealing apparatus for sealing a piston rod of a reciprocating compressor, the sealing apparatus comprising a first axial device end configured to face a cylinder of the compressor, an opposing second axial device end configured to face a crankcase of the compressor, and a plurality of first packing retainers, each retainer having a retention opening in which a first packing ring is disposed, and a second packing retainer having a retention opening in which a second packing ring is disposed, the second packing retainer being disposed axially closer to the second axial end than the plurality of first packing retainers. The present invention further relates to a reciprocating compressor including such a sealing arrangement, the reciprocating compressor including a piston rod having a first packing ring and a second packing ring configured to seal against the piston rod when the compressor is at rest, the sealing arrangement further including a support passage having a first support passage end, a second support passage end, and a valve for opening and closing the support passage, the support passage configured to vent gas leaking past at least one of the plurality of first packing rings in a direction from the first axial device end to the second axial device end from the first support passage end to the second support passage end. The present invention further relates to a reciprocating compressor including such a sealing arrangement, as well as a method for operating such a piston compressor.

[0002] In reciprocating piston compressors, a sealing device is used to seal the compression chamber in the cylinder against the crankcase or spacer, respectively. Such a sealing device often has a plurality of packing retainers formed in the shape of a circular plate, each of which has a retaining opening disposed therein. A packing ring is disposed in each of the retaining openings, and the packing rings cooperate with the outer peripheral surface of the piston rod to form a sealing barrier during operation of the compressor. During operation of the compressor, the piston rod primarily reciprocates relative to the sealing device in the axial direction of the cylinder. In many cases, a packing ring made of a plurality of segments is used. However, such a segmented packing ring is typically activated only during operation by a pressure difference between a high pressure in the compression chamber and a low pressure in the crankcase to form a sealing barrier.

[0003] However, at rest of the compressor, these segmented rings are typically not (at least partially) activated. This is due to the fact that when the piston rod cools down after stopping, the sealing surface of the segmented rings no longer conforms to the outer surface of the piston rod, even though a certain pressure difference still exists. This essentially occurs as a result of the segmented rings and the piston rod having different thermal expansions. Therefore, at low temperatures, e.g. at ambient temperature, a certain gap forms between the segmented rings and the piston rod, which gap constitutes a leakage path.

[0004] In the rest state, such a segmented packing ring therefore does not establish a sufficient sealing barrier. This is, however, disadvantageous, since in the rest state, gas trapped inside the compression chamber can leak from the compression chamber in the axial direction past the sealing device in the direction of the crankcase, for example into the spacer. In some cases, for example when air is used as the compressed gas, such leakage is not a problem, but when other gases, such as flammable or toxic gases, are used, it can lead to various problems. When a flammable gas, such as natural gas, is compressed, on the one hand, leakage must be prevented for safety reasons in order to avoid a flammable atmosphere that may form in the spacer or in the environment surrounding the compressor. On the other hand, leakage must also be prevented for environmental reasons, since the leakage of any greenhouse gases into the environment is undesirable and in some cases prohibited or at least limited.

[0005] In the past, several different approaches have been developed to solve this particular leakage problem when the compressor is shut down. US Patent No. 10,883,483, for example, discloses a sealing device using a non-segmented sealing ring, which is activated by the residual pressure difference after shut down when the valve in the vent line is closed. During operation of the compressor, the valve is opened and the sealing ring is relieved by the absence of a pressure difference across the ring. However, when the sealing action of the non-segmented seal is reduced, for example due to wear or breakage of the non-segmented sealing ring, venting through the vent line is not possible due to the closed valve, and unwanted gas leakage passes through the worn or broken sealing ring to the crankcase or spacer. While gas from the vent line can be safely treated, for example by sending it to a combustion device, gas accumulating in the spacer is often untreated and may form an explosive atmosphere and / or cause environmental damage by releasing greenhouse gases into the air.

[0006] It was therefore an object of the present invention to provide a sealing device for sealing the piston rod of a reciprocating compressor in the compressor's rest state, which improves operational safety.

[0007] This object is achieved by a sealing device as described above, further comprising an unobstructed ventilation path, the ventilation path having a first ventilation path end and a second ventilation path end, the ventilation path being configured to vent gas leaking through the second packing ring in a direction from the first axial device end to the second axial device end from the first ventilation path end to the second ventilation path end, thereby improving operational safety by preventing gas from entering, for example, a compressor spacer, which may create a dangerous environment, such as a flammable atmosphere, even in the event of malfunction or breakage of the second packing ring.

[0008] According to a preferred embodiment, the first support passage end is connected to the retaining opening of the second packing retainer, preferably in a region radially outside the second packing ring, or the first support passage end is located between the second packing ring and the first packing ring of the adjacent first packing retainer in the axial direction of the sealing device, or the plurality of first packing retainers has at least two first packing retainers, and the first support passage end is located in the region of the first packing ring adjacent to the second packing ring, or between the first packing ring adjacent to the second packing ring and the first sealing device end in the axial direction of the sealing device. The first two options increase the design flexibility and are substantially similar in function. The third option can be advantageous in two ways. On the one hand, this arrangement allows the first packing ring adjacent to the second packing ring to be provided with additional sealing during the period between compressor shutdown and activation of the second packing ring, which is delayed due to the time required for thermal activation. On the other hand, the pressure drop across the first packing ring adjacent to the second packing ring can be utilized to cool the second packing ring, thereby facilitating thermal activation. In this case, it is particularly preferred if each first packing ring comprises a metallic material.

[0009] Preferably, the sealing device further comprises at least one third packing retainer, the third packing retainer having a retaining opening in which the third packing ring is disposed, the at least one third packing retainer being disposed closer to the second axial device end of the sealing device than the second packing retainer, the first vent passage end being connected to the retaining opening of the third packing retainer, preferably radially outside the at least one third packing ring, or the first vent passage end being located between the second and third packing rings in the axial direction of the sealing device. The third packing ring can further improve safety, since an additional seal barrier is created behind the second seal ring.

[0010] Preferably, the second vent end of the unblocked vent and the second support end of the support are connected to one common exhaust passage that can be connected to the exhaust space, preferably to a waste system. This allows a single disposable system to be used for the gas coming from the support and the gas coming from the vent. In this case, the valve of the support can of course only open and close the support, while the vent remains unblocked.

[0011] Preferably, the valve comprises an electrically controllable actuator which can be controlled by a control unit to open and close the valve, e.g. via the compressor control unit, thereby opening and closing the support passage.

[0012] Preferably, the valve further comprises a sensor configured to generate a sensor value representative of the open state of the valve, thereby forming a closed control loop, which makes it possible, for example, not to start the compressor if the valve is still closed.

[0013] In a preferred embodiment, the second packing ring is formed from a material including a polymer, the material having a coefficient of thermal expansion at least twice that of steel, and below a predetermined activation temperature, the inner diameter of the second packing ring is smaller than the outer diameter of the piston rod to be sealed, so that when the sealing device is installed in the compressor, the second packing ring is radially preloaded to provide a tight seal between the continuous inner circumferential sealing surface of the second packing ring and the outer circumferential surface of the piston rod, and at a given operating temperature, the inner diameter of the second packing ring is larger than the outer diameter of the piston rod, so that when the sealing device is installed in the compressor, the continuous inner circumferential sealing surface is spaced from the outer circumferential surface of the piston rod to provide an axial leakage path between the inner circumferential surface of the second packing ring and the outer circumferential surface of the piston rod, thereby allowing automatic heat-dependent activation and deactivation of the sealing action of the second packing ring. By reducing the contact pressure between the second packing ring and the piston rod to zero during compressor operation, wear of the second packing ring is also minimized. Moreover, due to the thermal activation of the second packing ring, no predetermined residual pressure needs to be present in the compression chamber when the compressor is shut down. This allows the sealing device of the present invention to be applied to virtually all compressor applications, regardless of the cylinder suction pressure. Thus, the sealing device will also operate with a suction pressure substantially less than ambient air (as in vacuum compressors). On the other hand, the sealing device of US Pat. No. 10,883,483 cannot function in compressors whose suction pressure is equal to or less than ambient pressure, since it necessarily requires a predetermined cylinder pressure to activate the non-segmented sealing ring.

[0014] In a preferred embodiment, the material of the second packing ring has a coefficient of thermal expansion of at least 30×10 -6 K -1 , preferably at least 60×10 -6 K -1 , especially at least 90×10 -6 K -1 It is 30×10 -6 K-1 The above ranges have been found to provide adequate expansion.

[0015] The operating temperature is preferably above 90° C. and / or the activation temperature is preferably below 80° C., the operating temperature and the activation temperature being the temperatures in the area of ​​the piston rod, in particular the temperature of the outer circumferential surface of the piston rod, which allows a good sealing action at rest and sufficient expansion to separate the second packing ring from the piston rod.

[0016] In a preferred embodiment, the second packing ring has a first axial end and an opposite second axial end, the second packing ring is disposed in the retaining opening of the second packing retainer with the first axial end facing the first axial end of the sealing arrangement, the second packing ring having a U-shaped cross section with radially spaced apart inner and outer legs, the inner leg providing the second packing ring inner peripheral sealing surface and the outer leg providing the second packing ring outer peripheral surface, the open side of the U-shape axially extending from the first axial end of the second packing ring. the second packing ring has one of a U-shaped cross section facing the opposite end, an L-shaped cross section having an axial leg and a radial leg, the axial leg providing an inner circumferential sealing surface of the second packing ring and the radial leg providing an outer radial surface of the second packing ring, the radial leg being disposed at the second axial end of the second packing ring, or a rectangular cross section, the second packing ring having a plurality of openings therein, each opening connecting the first axial end of the second packing ring to the outer circumferential surface of the second packing ring, thereby providing a variety of preferred shapes for the second packing ring to be flexibly adapted to a variety of applications.

[0017] If the second packing ring has a U-shaped profile, then a plurality of openings are preferably provided on the outer leg, each of the plurality of openings connecting the interior space of the U-shaped packing ring to the radially outer surface of the second packing ring, the interior space being located radially between the inner leg and the outer leg, and the openings being located away from the opposite axial ends of the second packing ring. If openings are provided, then the plurality of openings preferably comprises a plurality of elongated or elliptical holes, each elongated or elliptical hole preferably having a longitudinal axis, a first hole end and a second hole end opposite in the direction of the longitudinal axis, the first hole end being located closer to the first ring end than the second hole end. Preferably, in the unassembled state of the second packing ring, the axial length of the inner leg is less than the axial length of the outer leg. The openings allow gas to flow through the second packing ring. Additionally, the openings provide the second packing ring with a predetermined amount of axial flexibility, which allows for a close fit of the second packing ring in the retention openings of the second packing retainer that is substantially independent of axial thermal expansion.

[0018] The material of the second packing ring is preferably a fiber-reinforced composite material, which improves the mechanical strength of the second packing ring. Additionally or alternatively, the polymer of the material of the second packing ring preferably includes at least one of polytetrafluoroethylene, polyphenylene sulfide, polyetheretherketone, polyimide, polyamide. These polymers provide sufficient rigidity and have favorable tribological properties.

[0019] In a preferred application, at least one sealing device according to the invention is preferably used in a reciprocating piston compressor, which has a number of cylinders, in each of which a reciprocatingly movable piston is arranged, each piston being connected to a piston rod, and for at least one of the cylinders a sealing device according to the invention is arranged to seal the corresponding piston rod, the sealing device being arranged such that a first axial device end faces the cylinder and a second axial device end faces the crankcase of the compressor. If the compressor has more than one cylinder, preferably a sealing device according to the invention is arranged in each cylinder.

[0020] The compressor preferably has a compressor control unit for controlling operation of the compressor, the control unit being further configured to control the electrically controllable actuator of the valve of the support passage in response to an operating condition of the compressor, such that opening and closing of the valve can be linked to the operating condition of the compressor.

[0021] In a preferred embodiment, the compressor comprises an operating condition sensor, preferably a temperature sensor or a motion sensor, configured to detect a sensor value representative of an operating condition of the compressor, and an electrically controllable actuator of a valve of the support passage is configured to control the valve depending on the sensor value, or the control unit is configured to control the electrically controllable actuator of the valve depending on the sensor value, so that the valve can be opened or closed depending on a preferred condition of the compressor.

[0022] Preferably, the compressor also has a drive unit for driving the compressor, and the compressor control unit is configured to send a start signal to the drive unit to start the operation of the compressor, and to send an open signal to the actuator of the valve of the support passage to open the valve simultaneously with the start signal or before the start signal with a predetermined or adjustable opening lead time, the opening lead time preferably being in the range of 0 to 60 seconds. Additionally or alternatively, the control unit is preferably configured to send a stop signal to the drive unit to stop the operation of the compressor, and to send a close signal to the actuator of the valve of the support passage to close the valve simultaneously with the stop signal or after a predetermined or adjustable closing delay time after the stop signal, the closing delay time preferably being in the range of 0 to 120 seconds. In this way, the opening and closing of the valve can be directly linked to the starting / stopping of the drive unit.

[0023] The object of the invention is to provide a method for operating a reciprocating piston compressor, the compressor having a plurality of cylinders, in each of which a reciprocatingly movable piston is arranged, each piston being connected to a piston rod, and for each cylinder of the plurality of cylinders a sealing device is provided for sealing the corresponding piston rod, the sealing device having a first axial device end facing the corresponding cylinder and an opposite second axial device end facing a crankcase of the compressor, at least one sealing device of the plurality of sealing devices comprising a plurality of first packing retainers, each retainer having a retaining opening in which a first packing ring is located, and a second packing retainer having a retaining opening in which a second packing ring is located, the second retainer being located closer to the second axial device end than the plurality of first packing retainers in the axial direction of the sealing device, the second packing ring being an uncut ring with a continuous inner circumferential sealing surface, the sealing device further having a support passage and a support passage for supporting the second packing ring. The passage has a first support passage end and a second support passage end and a valve for opening and closing the support passage, and the sealing arrangement further has an unobstructed vent passage, the vent passage having a first vent passage end and a second vent passage end, and the method includes, during operation of the compressor, inactivating a seal between the piston rod and an inner peripheral sealing surface of the second packing ring, opening the valve of the support passage, and directing gas leaking past at least one of the plurality of first packing rings in a direction from the cylinder to the crankcase from the first support passage end to the second support passage end. or, during idle time of the compressor, activating a seal between the piston rod and an inner sealing surface of the second packing ring, closing a valve of the support passage, and venting gas that may leak past the second packing ring in the direction from the cylinder to the crankcase from the first vent passage end to the second vent passage end of the unobstructed vent passage.

[0024] The invention will now be explained in more detail with reference to the figures 1 to 4c which show exemplary, schematic and non-limiting advantageous embodiments of the invention. [Brief description of the drawings]

[0025] [Figure 1] 1 shows a reciprocating piston compressor with a sealing device according to an advantageous embodiment of the invention; [Figure 2a] 1 is a cross-sectional view showing a sealing device according to a preferred embodiment of the present invention. [Figure 2b] 1 is a cross-sectional view showing a sealing device according to a preferred embodiment of the present invention. [Figure 2c] 1 is a cross-sectional view showing a sealing device according to a preferred embodiment of the present invention. [Figure 2d] 1 is a cross-sectional view showing a sealing device according to a preferred embodiment of the present invention. [Figure 3a] FIG. 13 illustrates a second packing ring in an advantageous embodiment; [Figure 3b] FIG. 13 illustrates a second packing ring in an advantageous embodiment; [Figure 3c] FIG. 13 illustrates a second packing ring in an advantageous embodiment; [Figure 4a] FIG. 13 illustrates another preferred embodiment of the second packing ring. [Figure 4b] FIG. 13 illustrates another preferred embodiment of the second packing ring. [Figure 4c] FIG. 13 illustrates another preferred embodiment of the second packing ring.

[0026] In FIG. 1, an exemplary reciprocating piston compressor 1 is shown. In the following, for the sake of simplicity, the term compressor is used. The compressor 1 has a compressor casing, which in this example includes a crankcase 2, a spacer 3 and a cylinder housing 4. However, the spacer 3 is merely optional, and the compressor 1 can also be designed without the spacer 3. In the crankcase 2, a crankshaft 5 is arranged, which can rotate about an axis of rotation. The crankshaft 5 is connected to a connecting rod 6, which is itself connected to a crosshead 7. The crosshead 7 is attached to the crankcase 2 via suitable bearings so that the crosshead 7 can perform an axial movement. The crosshead 7 is connected to a piston rod 8, which extends through the spacer 3 into a cylinder 9 arranged in the cylinder housing 4. In the cylinder 9, a piston 10 connected to the piston rod 8 is arranged. The illustrated compressor 1 is designed as a single-cylinder compressor. However, the compressor 1 may of course have several cylinders 9, each of which is provided with a piston connected via a piston rod 8 to a common crankshaft 5. For simplicity's sake, the invention will be described with reference to only one cylinder 9.

[0027] The compressor 1 is designed as a double-acting compressor, the piston dividing the cylinder 9 into a first compression chamber 11a, facing away from the crankshaft 5, and a second compression chamber 11b, facing the crankshaft 5. The first compression chamber 11a is closed axially by a first cylinder head 12a, and the second compression chamber 11b is closed axially by a second cylinder head 12b. For each compression chamber 11a, 11b, at least one inlet valve 13 and at least one outlet valve 14 are provided in the cylinder housing 4. The inlet valves 13 and the outlet valves are shown only in a simplified manner. The valves 13, 14 may, for example, be designed as automatic valves or may be provided with electrically controllable actuators for opening and closing. If the inlet valves are designed as automatic valves, a valve unloader (not shown) may additionally be provided, which is arranged to keep the corresponding valve open independently of the pressure differential acting on the valve. The valve unloader may have an electrically controllable actuator for actuating the valve unloader.

[0028] A suitable drive unit 16 is further provided for driving the crankshaft 5 of the compressor 1. For the sake of simplicity, the drive unit 16 is shown only in schematic form. The drive unit 16 can, for example, comprise a suitable electric motor, a combustion engine or another suitable drive. In the case of an electric motor, of course, a power supply is also provided (not shown) for supplying the electric energy. The compressor 1 further comprises a compressor control unit 17 arranged to control various functions of the compressor 1. In the following, for the sake of simplicity, the abbreviation "control unit" is used. Via the control unit 17, the drive unit 16 can be controlled to start or stop the operation of the compressor 1 or to control the operating speed of the compressor 1. The control unit 17 can comprise suitable hardware and / or software. The control unit 17 can, for example, be arranged to control the above-mentioned actuators of the inlet valve 13 and the outlet valve 14 or the actuators of the valve unloader. Of course, other available functions of the compressor 1, such as the oil supply to the cylinders, can also be controlled by the control unit 17. Also monitoring functions, such as the processing of sensor values, can be controlled.

[0029] Furthermore, the compressor 1 comprises a sealing device 15 for sealing the piston rod 8. If the compressor 1 comprises several cylinders 9, then of course a sealing device 15 is provided for the piston rod 8 of each cylinder 9. The sealing device 15 has a first axial device end 15a facing the cylinder 9 and an opposite second axial device end 15b facing the crankcase 2. In the example shown, the first device end 15a is arranged on the second cylinder head 12b and the second device end 15b on the spacer 3. Of course, the position can be varied depending on the design of the compressor 1. The sealing device 15 is substantially cylindrically shaped and comprises a number of substantially disk-shaped packing retainers. Each packing retainer can have a retaining opening in which a packing ring can be arranged (not shown in FIG. 1). The packing ring surrounds the piston rod 8 to form a sealing barrier. The sealing device 15 according to the invention is explained in more detail below with reference to FIGS. 2a to 2d.

[0030] FIG. 2a shows a cross-sectional view of the sealing device 15 of FIG. 1 according to an exemplary embodiment of the invention. The sealing device 15 has a first axial device end 15a configured to face the cylinder 9 of the compressor 1, representing the high pressure side HP. The sealing device 15 has an opposite second axial device end 15b configured to face the crankcase 2 or the spacer 3 of the compressor 1, respectively. The sealing device 15 has a plurality of first packing retainers 18, each having a retaining opening 18a in which a first packing ring 19 is disposed. Each of the first packing rings is configured to seal against the piston rod 8 during operation of the compressor 1. The retaining opening 18a is shown for only one packing retainer 18 in FIG. 2a. The first packing retainers 18 may have the shape of a cylindrical disk and may be made of a suitable material, such as steel or a steel alloy.

[0031] Each of the first packing rings 19 may have, for example, multiple ring segments in the axial direction (as shown in FIG. 2a) and / or multiple ring segments in the circumferential direction (not shown). The first packing rings 19 may have, for example, a tangentially cut sealing ring and a radially cut sealing ring. The tangentially cut sealing ring may have multiple ring segments in the circumferential direction that abut at cooperating sealing surfaces in the circumferential direction to form a radial seal. The radially cut sealing ring may have multiple ring segments in the circumferential direction that are configured to overlap the tangential cuts of the tangentially cut ring to form a seal in the axial direction. Combination rings having both tangential and radial cuts are also known. Furthermore, a so-called "back-up ring" may be arranged in the retaining opening 18a adjacent to the first packing ring 19, which is not cut and is configured to prevent the ring segments of the first packing ring 19, which are usually made of plastic, from being pushed out. However, the backup ring is typically made of metal and does not function to seal the piston rod. Because these various packing rings are known to those skilled in the art, a detailed description will not be provided at this time. Of course, the first packing rings 19 disposed within the first packing retainers 18 do not necessarily have to be identical.

[0032] The sealing device 15 further includes a second packing retainer 20 having a retaining opening 20a in which a second packing ring 21 is disposed. The second packing ring 21 is an unbroken ring having a circumferentially continuous inner sealing surface 21a. The second packing ring 21 is configured to be activated to seal against the piston rod 8 during rest of the compressor 1 and to be deactivated during operation of the compressor 1. The sealing action of the second packing ring 21 can be activated by pressure, for example, similar to that disclosed in U.S. Pat. No. 1,088,343. Alternatively, however, and preferably, the sealing action of the second packing ring 21 during rest of the compressor 1 can be thermally activated, as will be described in more detail below. The second packing ring 21 has a different design from the plurality of first packing rings 19. As can be seen from FIG. 2a, in the axial direction of the sealing arrangement (corresponding to the axial direction of the piston rod 8), the second packing retainer 20 is located closer to the second axial arrangement end 15b than the plurality of first packing retainers 18.

[0033] In the illustrated example, an intermediate plate 27 is disposed between the second packing retainer 20 and the first subsequent first packing retainer 18. The intermediate plate 27 axially defines the retention opening 20a of the second packing retainer 20 and also the retention opening 18a of the subsequent first packing retainer 18, which are opposite each other. Thus, the intermediate plate 27 separates the second packing ring 21 disposed in the retention opening 20a of the second packing retainer 20 from the first packing ring 19 disposed in the retention opening 18a of the adjacent first packing retainer 18. However, the location of the intermediate plate 27 is merely optional and may be omitted if the first packing retainers 18 are arranged in a mirror image.

[0034] As shown in FIG. 2a, the second packing ring 21 may, for example, have a U-shaped cross section, the open side of the U facing the first axial device end 15a of the sealing device 15. The U-shape aids the deformation of the ring under pressure load. For the same reason, the second packing ring 21 may also be L-shaped. In general, however, a ring with a solid cross section can also be used as the second packing ring 21. A preferred embodiment of the second packing ring 21 is described below in connection with FIGS. 3a to 4c.

[0035] According to a preferred and optional embodiment of the present invention, the second packing ring 21 has a thermal expansion coefficient of iron, α FE In a preferred embodiment, the second packing ring 21 may be made of a material including a polymer having a thermal expansion coefficient α of at least α=30×10. -6 K -1 , preferably at least α=60×10 -6 K -1 , especially at least α=90×10 -6 K -1 According to a preferred embodiment, the polymer comprises at least one of polytetrafluoroethylene (known as PTFE), polyphenylene sulfide (known as PPS), polyetheretherketone (known as PEEK), polyimide (known as PI) or polyamide (known as PA). Of course, combinations of different polymers are also conceivable.

[0036] The second packing ring 21 is preferably designed such that at (or below) a given activation temperature, the inner diameter d_i of the second packing ring 21 is smaller than the outer diameter D_a of the piston rod 8, such that the second packing ring 21 is radially preloaded to form a tight seal between the continuous inner circumferential sealing surface 21a of the second packing ring 21 and the outer circumferential surface 8a of the piston rod 8. The second packing ring 21 is further designed such that at a given operating temperature, the inner diameter d_i of the second packing ring 21 is larger than the outer diameter D_a of the piston rod 8, such that the continuous inner circumferential sealing surface 21a is spaced from the outer circumferential surface 8a of the piston rod 8, providing an axial leakage path between the inner circumferential surface 21a of the second packing ring 21 and the outer circumferential surface 8a of the piston rod 8. The cold condition at ambient temperature is shown in FIG. 2a. Of course, when the second packing ring 21 is installed, the inner diameter d_i of the second packing ring 21 corresponds to the outer diameter D_a of the piston rod 8. However, when not installed, at ambient temperature, the inner diameter d_i of the second packing ring 21 is smaller than the outer diameter D_a of the piston rod 8, so that there is an interference similar to that of a press fit.

[0037] The activation temperature at which the second packing ring 21 is in the contracted state and seals against the piston rod 8 is typically below 80° C. The operating temperature at which the second packing ring 21 is in the expanded state and does not seal against the piston rod 8 is typically in the range of 90° C. or higher. However, the activation temperature is highly dependent on the operating temperature of the compressor 1, which itself may vary depending on the particular design and application of the compressor 1. Thus, if the expected operating temperature is known, the design of the second packing ring 21 can be adapted to the desired activation temperature. The operating temperature and activation temperature are preferably the temperatures in the area of ​​the piston rod 8, in particular the temperature of the surface 8a of the piston rod 8.

[0038] Due to the above mentioned features, during (sufficiently long) rest of the compressor 1, the temperature of the second packing ring 21 as well as the temperature of the piston rod 8 drops from the operating temperature to a temperature below the activation temperature, for example the ambient temperature or a temperature between the activation temperature and the ambient temperature, so that the second packing ring 21 forms a tight sealing barrier on the surface 8a of the piston rod 8. This ensures that gas still contained in the cylinder 9 cannot escape from the cylinder 9 in the axial direction into the spacer 3 and possibly further into the crankcase 5 or into the surrounding environment.

[0039] After starting the compressor 1, during operation of the compressor 1, the components of the compressor 1 start to heat up due to the compression work and due to friction. In particular, the second packing ring 21 and the piston rod 8 are heated by friction resulting from the reciprocating motion of the piston rod 8 relative to the second packing ring 21 and also relative to the plurality of first packing rings 19. After a certain period of operation, an operating temperature is reached, which temperature remains substantially constant during further operation. Within the scope of the present invention, "substantially constant" can mean that the operating temperature includes a certain fluctuation that may be in the range of ±10°C. Due to the above-mentioned characteristics, when the operating temperature is reached, the continuous inner peripheral sealing surface 21a of the second packing ring 21 moves away from the outer peripheral surface 8a of the piston rod 8, thereby forming a leakage path in the axial direction between the inner peripheral surface 21a of the second packing ring 21 and the outer peripheral surface 8a of the piston rod 8.

[0040] When the compressor 1 is stopped again, the reverse effect occurs: the components of the compressor 1 are gradually cooled down until the activation temperature is reached. Once the activation temperature is reached, the second packing ring 21 contracts back onto the rod (d_i≦D_a), whereby a tight sealing barrier is re-established. It can thus be seen that a substantially temperature-dependent sealing action is achieved automatically, without the need for any control intervention. However, as will be explained in more detail below, the sealing device can be provided with further advantageous features to improve its performance.

[0041] As shown in Fig. 2a, the second packing ring 21 preferably has a U-shaped cross section with radially spaced apart inner and outer legs 24 and 25. A preferred embodiment of such a U-shaped second packing ring 21 is shown in detail in Figs. 3a-3c, where Fig. 3a shows a cross-sectional view of the second packing ring 21, Fig. 3b shows a plan view of the second packing ring 21, and Fig. 3c shows an isometric view of the second packing ring 21. The second packing ring 21 has an outer diameter d_a, as can be seen in Fig. 2a, which is smaller than the diameter of the retaining opening 20a of the second packing retainer 20 in which the second packing ring 21 is to be placed. Thus, a ring-shaped space is formed between the outer peripheral surface 21b of the second packing ring 21 and the inner peripheral surface of the cylindrical retaining opening 20a.

[0042] Furthermore, in the example shown in Figs. 3a-3c, a plurality of openings 22 are provided on the outer leg 25 of the second packing ring 21, each of the plurality of openings 22 connecting the interior space 23 of the U-shaped packing ring 21 to the radially outer peripheral surface 21b of the second packing ring 21. The interior space 23 is formed between the radially opposed legs 24, 25 of the U-shape. The openings 22 thus extend through the outer leg 25 and are located at a distance from the opposed axial ends 21c, 21d of the second packing ring 21. The plurality of openings 22 may have substantially any suitable shape, for example cylindrical drillings or groove millings. More complex shapes may also be used if the second packing ring 21 is formed, for example, by 3D printing.

[0043] Preferably, the openings 22 are shaped as elongated or elliptical holes, with elongated holes being shown in FIG. 3c. Each elongated hole has a longitudinal axis L, a first hole end 22a and an opposite second hole end 22b in the direction of the longitudinal axis L, the first hole end 22a being preferably located closer to the first ring end 21c than the second hole end 22b, which is located closer to the second axial ring end 21d. Thus, the elongated holes 22 are substantially inclined relative to the front faces of the second packing ring 21 formed at the axial ring ends 21c, 21d. Such a shape is advantageous as it makes the second packing ring 21 more flexible in the axial direction.

[0044] Furthermore, the U-shaped outer leg 25 has an axial length b_a, which is longer than the axial length b_i of the inner leg 24. In the unmounted state, the length b_a of the outer leg 25 is preferably slightly longer than the axial length of the retaining opening 20a of the second packing retainer 20. In the example according to FIG. 2a, the axial length of the retaining opening 20a of the second packing retainer 20 is formed by the distance between the axial end face of the retaining opening 20a and the opposite axial end face of the intermediate plate 27, as can be seen in FIG. 2a. Due to the openings 22, the outer leg 25 has a certain structural elasticity, which allows the outer leg 25 to be elastically deformable in the axial direction and, as a result, fits tightly inside the retaining opening 20a. The number of openings 22 in the second packing ring 21 and the arrangement of the openings 22 can be varied depending on the size of the ring. In order to provide as uniform elasticity as possible in the circumferential direction, the openings 22 are preferably equally distributed in the circumferential direction.

[0045] In the radial direction, however, the second packing ring 21 does not have such structural elasticity but is particularly rigid, so that even in the heated state at operating temperature, the pressure difference causes practically no elastic deformation (or only very little). At operating temperature, it is therefore ensured, as mentioned above, that the inner diameter d_i of the second packing ring 21 is always larger than the outer diameter D_a of the piston rod 8 as a result of thermal expansion. In order to improve the structural rigidity also at higher temperatures, the material of the second packing ring 21 is advantageously a fiber-reinforced composite material.

[0046] The embodiment according to figures 3a to 3c is of course non-limiting, and as mentioned above, other embodiments are possible, some of which are described below in conjunction with figures 4a to 4c.

[0047] FIG. 4a shows a U-shaped second packing ring 21, which is substantially similar to the ring shown in FIGS. 3a-3c. Therefore, only the differences will be described in detail. The second packing ring 21 according to FIG. 4a additionally has an O-ring 37, which has a relatively high elasticity, in particular a significantly higher elasticity than the material of the second packing ring 21. The O-ring is arranged on a shoulder formed by a circumferential groove 38. The circumferential groove 38 is located adjacent to the outer peripheral surface 21b and adjacent to the surface of the second packing ring 21 at the second axial end 21d. As can be seen from FIG. 4a, the diameter of the O-ring 37 in the unmounted state is slightly larger than the axial depth of the groove 38. In the mounted state of the second packing ring 21, the O-ring 37 acts substantially like a spring. Since the axial length of the second packing ring 21 is smaller in the cold state than in the hot state due to thermal expansion acting in the axial direction, the O-ring 37 assists in radial sealing (between the second axial end 21d of the second packing ring 21 and the axial wall of the retaining opening 20a, see FIG. 2a) when the second packing ring 21 is in the cold state. In the hot state, when the second packing ring 21 thermally expands in the axial direction, the O-ring 37 is compressed to compensate for the axial length change. Thus, the mechanical stress in the outer leg 25 of the second packing ring 21 can be reduced.

[0048] FIG. 4b shows a cross-sectional view of another preferred embodiment of the second packing ring 21. It can be seen that the second packing ring 21 has an L-shaped cross section. This allows a very simple manufacture, since the openings 22 are not mandatory in this embodiment. Similar to the U-shaped rings of FIGS. 3a-3c and 4a, the second axial end 21d of the L-shaped second packing ring 21 of FIG. 4b also faces the first axial device end 15a of the sealing device 15 (or the cylinder 9, respectively, see FIG. 1) or the high pressure side HP, respectively (see FIG. 2a). Of course, an O-ring (not shown) may additionally be provided on the L-shaped packing ring 21 of FIG. 4b, similarly to FIG. 4a.

[0049] Fig. 4c shows a cross-sectional view of another preferred embodiment of the second packing ring 21. In this embodiment, the second packing ring 21 has a rectangular cross-section. To allow gas to flow from the first axial end 21c (cylinder side) to the outer peripheral surface 21b of the ring, a number of openings 41 are provided, which connect the first axial end 21c of the second packing ring 21 to the outer peripheral surface 21b of the second packing ring 21. The openings 41 may have substantially any suitable shape, for example, as shown in Fig. 4c, they may be inclined drillings or intersecting, preferably orthogonal, axial and radial openings.

[0050] According to the invention, the sealing device 15 further comprises a support passage 28, which, as shown in FIG. 2a, has a first support passage end 28a and a second support passage end 28b. For the sake of simplicity, a part of the support passage 28 is only shown diagrammatically in FIG. 2a. In the illustrated embodiment, the first support passage end 28a of the support passage 28 is connected to the retaining opening 20a of the second packing retainer 20 in a region radially outside the second packing ring 21. In particular, the first support passage end 28a opens into a space formed between the outer peripheral surface 21b of the second packing ring 21 and the inner peripheral surface of the retaining opening 20a in which the second packing ring 21 is located. However, this is merely one exemplary embodiment, and the first support passage end 28a of the support passage 28 does not necessarily have to be connected to the retaining opening 20a. The first support passage end of the support passage may be located between the second packing ring 21 and the subsequent first packing ring 19, for example, on the inner circumferential surface of the intermediate plate 27. However, if the second packing retainer 20 is designed in a different manner, the first support passage end 28a of the support passage 28 may be located, for example, on the inner circumferential surface of the second packing retainer 20, adjacent to the retaining opening 20a, toward the first axial device end 15a. Furthermore, a valve 29 for opening and closing the support passage 28 is provided between the first support passage end 28a and the second support passage end 28b.

[0051] As shown in Fig. 2a, a first portion of the support passage 28 is integrally formed with the second packing retainer 20, whereas a second portion of the support passage 28 is located outside the second packing retainer 20. The second portion of the support passage 28 may be implemented, for example, as a conduit connected to the second packing retainer 20 by a suitable connector. In the illustrated embodiment, the connector is arranged on the axial surface of the second packing retainer 20 facing the second device end 15b of the sealing device 15. However, other locations, for example on the radially outer surface, are also possible, provided that sufficient space is provided for connecting the second portion of the support passage 28.

[0052] In the illustrated example, the second packing retainer 20 also serves as a mounting flange for mounting the sealing device 15 on the compressor 1. For simplicity, mounting elements such as screws or the like are not shown in FIG. 2a. Of course, this is not necessary and the second packing retainer 20 may be provided as an additional separate component in addition to the mounting flange, in particular adjacent to the mounting flange in the direction of the first axial device end 15a. In this case, a first portion of the support passage 28 (adjacent to the first passage end 28a) may be integrally formed with the second packing retainer 20, a second (middle) portion of the support passage 28 may be integrally formed with the flange and a third portion of the support passage 28 (adjacent to the second passage end 28b) may again be implemented as a conduit. Of course, a suitable sealing element, such as an O-ring, may be disposed between the flange and second packing retainer 20 to provide a seal between a first portion of support passage 28 (inside second packing retainer 20) and a second portion of support passage 28 (inside the flange).

[0053] The support passage 28 has essentially two functions. During operation of the compressor 1 (e.g. when operating temperature is reached and the second packing ring 21 is disengaged from the piston rod 8 due to thermal activation as described above), the function of the support passage 28 is to provide a substantially free leakage path for gas flowing from the cylinder 9 through the plurality of first packing rings 19 in the direction of the second device end 15b of the sealing arrangement 15. In the disengaged state, the support passage 28 thereby substantially prevents an undesirable relatively large pressure drop across the second packing ring 21 due to the relatively small (throttle-like) clearance that would otherwise exist (without the passage 28) between the inner peripheral sealing surface 21a of the second packing ring 21 and the outer peripheral surface 8a of the piston rod 8. The valve 29 is, of course, open during operation of the compressor 1.

[0054] On the other hand, when the compressor 1 is at rest (e.g. below the activation temperature), in the activated sealing state of the second packing ring 21, a tight sealing barrier is formed between the second packing ring 21 and the piston rod 8. In order for the second packing ring 21 to develop its desired sealing action, the valve 29 of the support passage must of course be in the closed position, since otherwise gas would not be retained but would flow through the support passage 28 in the direction of the second support passage end 28b. For automatic control of the opening and closing of the valve 29, it is advantageous if the valve 29 has an electrically controllable actuator 30, which can be controlled by a control unit (e.g. the compressor control unit 17 as shown in FIG. 2a) in order to open and close the valve 29.

[0055] According to the invention, the sealing device 15 further comprises an unobstructed ventilation passage 31, which has a first ventilation passage end 31a and an opposite second ventilation passage end 31b. The ventilation passage 31 is configured to vent gas leaking from the first ventilation passage end 31a to the second ventilation passage end 31b, passing through the first packing rings 19 and through the second packing ring 21 (in particular between the inner peripheral surface 21a of the second packing ring 21 and the outer peripheral surface 8a of the piston rod 8) in the direction from the first axial device end 15a (or each of the cylinders 9) to the second axial device end 15b (or each of the spacers 3). This improves safety when the compressor is idle, since gas that leaks past the second packing ring 21, for example because the second packing ring 21 is worn, damaged, or completely broken, can always be safely vented through the unobstructed vent path 31.

[0056] Preferably, the sealing device 15 further comprises at least one third packing retainer 32, as shown in FIG. 2a, having a retaining opening 32a in which a third packing ring 33 is disposed. The at least one third packing retainer 32 may be designed substantially similarly to the plurality of first packing retainers 18. However, as can be seen in FIG. 2a, different types of packing rings may be used for the third packing ring 33 and for the first packing ring 19. Thus, the size of the retaining opening 32a of the third packing retainer 32 may differ from the size of the retaining opening 18a of the first packing retainer 18.

[0057] The third packing retainer 32 is arranged closer to the second axial device end 15b of the sealing device 15 than the second packing retainer 20. As described above in relation to the intermediate plate 27, the retaining opening 32a of the third packing retainer 32 is defined by the axial front surface of the second packing retainer 20, which faces the second device end 15b of the sealing device 15. As with the first packing ring 19, the at least one third packing ring 33 may have, for example, multiple ring segments in the axial direction and / or multiple ring segments in the circumferential direction. In the example shown in FIG. 2a, a single third packing retainer 32 is provided, and the third packing ring 33 arranged in the retaining opening 32a of the third packing retainer 32 has three sealing rings arranged in succession in the axial direction, each sealing ring having multiple ring segments in the circumferential direction. As already described above in relation to the first packing ring 19, such rings are known.

[0058] Similar to first packing retainer 18 and second packing retainer 20, third packing retainer 32 may be formed from a single piece, e.g., milled, into which retention openings 32a are located, or may be assembled from two or more pieces. For example, third packing retainer 32 may have a faceplate and an adjacent piece in which third packing ring 33 is located. The faceplate may be a cylindrical plate, e.g., intermediate plate 27, and the adjacent piece may be a hollow cylinder, for example.

[0059] If the third packing retainer 32 is provided in the sealing device 15, the first air passage end 31a of the unobstructed air passage 31 may be directly connected to the retaining opening 32a of the third packing retainer 32, preferably to a space formed radially outside the third packing ring 33, as shown in the example according to Fig. 2a. Also, as explained in connection with the support passage 28, a first part of the air passage 31 adjacent to the first air passage end 31a may be formed integrally with the third packing retainer 32, and a second part of the air passage 31 adjacent to the second air passage end 31b may be formed by a conduit. However, Fig. 2a only shows an exemplary embodiment, and the first air passage end 31a of the air passage 31, as well as the first support passage end 28a of the support passage 28, may also be arranged in different positions. For example, the first air passage end 31a may be located between the third packing ring 33 and the second packing ring 21 in the axial direction of the seal device 15, for example, on the inner circumferential surface of the second packing retainer 20.

[0060] As can be seen in FIG. 2a, the second vent end 31b of the unblocked vent passage 31 and the second support passage end 28b of the support passage 28 are preferably connected to one common discharge passage 34 which can be connected to a discharge space 35. Due to the vent passage 31 being unblocked, gas leaking through the second packing ring 21 can be safely discharged at any time into the discharge space 35. The discharge space 35 can be, for example, a reservoir for storing gas, for example a tank, or a disposal system for disposing of the gas, such as a flare device for burning the gas. This allows a very safe operation, since even in the event of a break in the second packing ring 21, the gas can be safely discharged via the vent passage 31 and therefore cannot enter the spacer 3 when the compressor 1 is at rest with the valve 29 in the closed position.

[0061] In the illustrated example, where the valve 29 of the support passage 28 can be actuated (opened or closed) by an electrically controllable actuator 30, the actuator 30 can preferably be controlled depending on the operating conditions of the compressor 1. For example, logic for controlling the actuator 30 of the valve 29 depending on a start signal S_start and / or a stop signal S_stop for the drive unit 16 can be implemented in the control unit 17. The control unit 17 can be configured to send a start signal S_start to the drive unit 16 to start the operation of the compressor 1, as shown in FIG. 2a. Additionally, the control unit 17 can send an opening signal S_open to the actuator 30 of the valve 29 of the support passage 28 to open the valve 29. The opening signal S_open can be sent simultaneously with the start signal S_start, whereby the valve 29 is opened immediately on start-up. Alternatively, the opening signal S_open can be sent with a predetermined or adjustable opening lead time before the start signal S_start is sent, whereby the valve 29 is opened at a predetermined time before start-up. The start lead time can preferably be in the range of 0 to 60 seconds. This ensures that the valve 29 is open at the moment the compressor starts.

[0062] The control unit 16 may be configured to send a stop signal S_stop to the drive unit 16 in order to stop the operation of the compressor 1, and furthermore can send a close signal S_close to the actuator 30 of the valve 29 in the support passage 28 in order to close the valve 29. Also, the close signal S_close can be sent simultaneously with the stop signal S_stop or after a predetermined or adjustable close delay time after the stop signal S_stop has been sent. The close delay time is also preferably in the range of 0 to 120 seconds. Simultaneous sending is possible, but this is not essential, since according to the invention the second packing ring 21 is thermally activated and not activated by differential pressure. A predetermined close delay time is advantageous, for example, to make sure that the piston rod 8 is completely at rest before the valve 29 is closed, so that contact and possible wear of the second packing ring 21 can be avoided in any case.

[0063] The valve 29 preferably also comprises a sensor 36 for detecting the open state of the valve 29. The sensor 36 is arranged to transmit a sensor value X representative of the open state (e.g. open or closed position) to the control unit 17. The control unit 17 can then process the sensor value X and can transmit, for example, a start signal S_start to the drive unit 16 only if a sensor signal X representative of the open state of the valve 29 is received. This allows the compressor 1 to be started only if the valve 29 is open and to be prevented from starting as long as the valve 29 is closed. This prevents the compressor 1 from starting with the valve 29 closed and thus a high differential pressure acting on the second packing ring 21. A high differential pressure could press the packing ring 21 too hard against the piston rod 8, which could result in overheating, excessive wear or possibly mechanical failure.

[0064] According to another preferred embodiment, the compressor 1 may comprise a suitable operating condition sensor (not shown) configured to detect sensor values ​​representative of the operating conditions of the compressor 1. The operating condition sensor may for example be a temperature sensor configured to detect the operating temperature. The temperature sensor may be arranged at a suitable position for detecting the operating temperature, for example in the area of ​​the second packing ring 21 and / or in the area of ​​the piston rod 8. The operating condition sensor may be connected to the control unit 17 in order to present the sensor values ​​to the control unit 17. The control unit 17 may further be configured to control a valve 29 of the support passage 28 depending on the sensor values, in particular the operating temperature. On the other hand, the valve 29 may also be directly controlled by the operating condition sensor, whereby no control by the control unit 17 is necessary. In this case, for example, a thermally operated valve may be used as the valve 29, which valve is essentially a combination of the valve 29, the actuator 30 and the operating condition sensor. The actuator 30 of the valve 29 may therefore automatically open or close the valve 29 depending on the detected sensor values, without a control intervention of the control unit 17 being required.

[0065] According to an alternative embodiment, the operating condition sensor may be, for example, a motion sensor arranged to detect sensor values ​​representative of the motion of a moving part of the compressor 1. The motion sensor may be, for example, a speed sensor for detecting the rotational speed of the crankshaft or the translational speed of the piston rod 8, etc. The motion sensor may also be connected to the control unit 17, which is arranged to control the actuator 30 of the valve 29 depending on the sensor value of the motion sensor. On the other hand, the motion sensor may also be implemented in the valve 29 together with the actuator 30, whereby the valve 29 is directly operated independently of the compressor control unit 17. Of course, the temperature sensor and the motion sensor are merely examples, and other sensors suitable for detecting the relevant sensor values ​​representative of the operating conditions of the compressor 1 may also be used. In a preferred embodiment, the actuation value of the measured sensor values, e.g. temperature, rotational speed, etc., at which the valve 29 should be closed or opened, can be adjusted, for example, via the control unit 17 or directly at the valve 29 or at the actuator 30.

[0066] Although not shown in the example according to FIG. 2a, further packing retainers may additionally be arranged in the sealing device 15. For example, it is conceivable to add a fourth packing retainer 42 adjacent to the third packing retainer 32, which is arranged closer to the second axial device end 15b than the third packing retainer 32. An exemplary embodiment is shown in FIG. 2b. The fourth packing retainer 42 has a retaining opening 42a in which a wiping ring 43 is arranged, which serves to wipe residual oil from the outer peripheral surface 8a of the piston rod 8. The wiping ring 43 may have one or more wiping edges 43a on its inner peripheral surface. The wiping ring 43 may further have one or more drainage passages 43b connecting the inner peripheral surface of the wiping ring 43 to the outer peripheral surface. The wiped off oil can be conveyed via a discharge passage 43b to an oil collecting space arranged radially outside the wiping ring 43 and inside the retaining opening 42a. The discharge space can be connected to an oil reservoir 44 by a suitable oil return line 45. Such wiping rings 43 are known, so a detailed description will not be given at the moment. Such an embodiment of the sealing device 15 including a wiping ring 43 can be used, for example, in compressors 1 that do not have a spacer 3 as the compressor 1 shown in FIG. 1 has. Such a sealing device 15 is often referred to as a so-called combined sealing device.

[0067] Like the embodiment according to FIG. 2a, the sealing device 15 according to FIG. 2b also has a support passage 28 with a valve 29 and an unobstructed ventilation passage 31. The function of the support passage 28 and the function of the ventilation passage 31 have already been described in detail in connection with FIG. 2a, so that only the differences between the two embodiments are described below. In contrast to FIG. 2a, in the embodiment according to FIG. 2b, the first ventilation passage end 31a of the ventilation passage 31 is located between the third packing ring 33 and the second packing ring 21 in the axial direction of the sealing device 15 (or of the piston rod 8, respectively). A first part of the ventilation passage 31 is formed integrally with the second packing retainer 20, in which the second packing ring 21 is arranged. The first ventilation passage end 31a is located in this case on the inner circumferential surface of the second packing retainer 20. In the illustrated example, the second packing retainer 20 also serves as a mounting flange for mounting the sealing device 15 on the compressor 1. Of course, the flanges can be provided with suitable attachment means (not shown), such as bolts or screws. However, the function of the vent passage 31 remains the same as in Figure 2a. Such a design is advantageous because it allows a standardized packing retainer (without built-in passages) to be used as the third packing retainer 32.

[0068] In the embodiment of FIG. 2b, the position of the first support passage end 28a of the support passage 28 also differs from the embodiment according to FIG. 2a. In FIG. 2a, the first support passage end 28a is directly connected to the retaining opening 20a of the second packing retainer 20. In contrast to this, in FIG. 2b, the first support passage end 28a is located between the first packing ring 19_1 arranged adjacent to the second packing ring 21 and the first packing ring 19_2 following it in the direction of the first axial device end 15a of the sealing device 15. This design has essentially two advantages over the preferred embodiment with a thermally activated second packing ring 21. On the one hand, this configuration allows the first packing ring 19_1 adjacent to the second packing ring 21 to provide additional sealing during the period between the shutdown of the compressor 1 and the thermal activation of the second packing ring 21, which is delayed due to the time required for cooling and shrinkage. Thus, until the point where the sealing action of the second packing ring 21 is fully deployed, the first packing ring 19_1 can provide additional sealing action due to the residual pressure within the cylinder 9 (FIG. 1).

[0069] To provide such an additional sealing effect, the first packing ring 19_1 adjacent to the second packing ring 21 is advantageously designed differently from the subsequent first packing ring 19_2 (and differently from the further first packing ring 19_3 arranged adjacent to the first packing ring 19_2 towards the first axial device end 15a in FIG. 2b). In particular, the first packing ring 19_1 is preferably designed as a so-called "double-acting" ring and is configured to provide a sealing effect even when there is no pressure difference across the ring. A double-acting ring can, for example, have a ring assembly with two tangential cutting rings, for example two identical tangential cutting rings. Another suitable ring can, for example, be a so-called "tangential to the rod" ring. Such rings are known. The first sealing ring 19_2 and the following first sealing ring 19_3 may, for example, be identical and may each have a ring assembly with a radial cut ring and a tangential cut ring, as already mentioned in FIG. 2a in connection with the first packing ring 19. On the other hand, the pressure drop occurring across the first packing ring 19_1 adjacent to the second packing ring 21 can be used for cooling the second packing ring 21, which accelerates the cooling and thus the thermal activation. In this case, it is particularly preferred if the corresponding first packing ring 19_1 contains a metallic material. For example, the above-mentioned backup ring made of metal can be used as part of the first packing ring 19_1.

[0070] Another preferred embodiment of the sealing device 15 of the present invention is described in relation to Fig. 2c. The plurality of first packing retainers 18 of the sealing device 15 of the illustrated embodiment includes two first packing retainers 18, each having a retaining opening 18a in which a first packing ring 19 is arranged. The first packing rings 19 may also be designed as described above. Of course, a larger number of first packing retainers 18 may be provided, similar to Figs. 2a and 2b. The sealing device 15 further includes a second packing retainer 20, which has a retaining opening 20a in which a second packing ring 21 is arranged. The second packing retainer 20 is arranged closer to the second device end 15b than the first packing retainers 18. An exemplary U-shaped second packing ring 21 is shown. However, the second packing ring 21 may have a different design, as explained in connection with Figures 3a-4c. Arranged adjacent to the second packing retainer 20 is an intermediate plate 27, in which a first part of an unobstructed vent passage 31 is arranged. As can be seen, similar to the embodiment according to Figure 2b, the first vent passage end 31a of the vent passage 31 is located between the second packing ring 21 and the first packing ring 19 following it in the direction of the second device end 15b.

[0071] The sealing device 15 further includes a fifth packing retainer 46 having a T-shaped cross section, which has two retaining openings 46a separated in the axial direction by a central portion of the T-shaped cross section. A fifth packing ring 47 is arranged in each of the retaining openings 46a. Each of the fifth packing rings 47 is formed as a so-called single-acting SLP ring assembly having three consecutive rings in the axial direction, each of the three rings being a cut ring and having a plurality of ring segments in the circumferential direction. The central ring and one of the outer rings each include a chamfer, the chamfer of the central ring being directed radially outward and the chamfer of the outer ring being directed radially inward. The chamfers face each other and are in contact.

[0072] As shown in FIG. 2c, the two fifth packing rings 47 are arranged in a mirror image, with the outer chamfered rings facing each other in the axial direction and in contact with the central part of the T-shaped cross section of the fifth packing retainer 46. With the sealing device 15 mounted on the compressor 1, a pressure chamber 46b is formed in the space located axially between the two fifth packing rings 47 and radially between the central part of the T-shaped cross section of the fifth packing retainer 46 and the piston rod 8. Furthermore, a flange F for mounting the sealing device 15 on the compressor 1 is arranged on the sealing device 15. The flange F is arranged on the extreme left side and has a second axial device end 15b of the sealing device 15, which is arranged to face the crankcase 2 (FIG. 1). As can be seen in FIG. 2c, flange F defines a retention opening 46a on a left side of fifth packing retainer 46 closer to second device end 15b, and intermediate plate 27 defines a retention opening 46a on a right side of fifth packing retainer 46 closer to first device end 15a.

[0073] The sealing device 15 further includes a purge passage 48 having a first purge passage end 48a and a second purge passage end 48b. The first purge passage end 48a is located on the inner peripheral surface of the central portion of the T-shaped cross section of the fifth packing retainer 46, axially between the two fifth packing rings 47. A first portion of the purge passage 48 adjacent the first purge passage end 48a is integrally formed with the fifth packing retainer 46, a second intermediate portion of the purge passage 48 is integrally formed with the flange F, and a third portion of the purge passage 48 adjacent the second purge passage end 48b is formed as a conduit suitably connected to the flange F. The second purge passage end 48b is connected to a pressurized gas source 49, preferably including nitrogen. A valve (not shown) for opening and closing the purge passage 48 may also be provided.

[0074] When pressurized gas from a pressurized gas source 49 is introduced into the pressure chamber 46b, a pressure is generated in the pressure chamber 46b, which presses the corresponding outer chamfered ring of each fifth packing ring 47 axially against the corresponding central ring. Due to the interacting chamfers, the central chamfered ring is pressed radially against the piston rod 8, forming a tight seal. Thus, gas leaking from the first device end 15a (or the compression chamber 9, respectively, FIG. 1) through the first packing ring 19 and through the second packing ring 21 in the direction of the second device end 15b can be safely vented through the unobstructed vent path 31. This is due not only to the sealing action of the fifth packing ring 47, but also to the pressure in the pressure chamber 46b, which is preferably higher than the pressure in the region of the first vent path end 31a.

[0075] FIG. 2d shows a different design of the sealing device 15, including a fifth packing retainer 46. In this case, the fifth packing retainer 46 has an L-shaped cross section and only a single retaining opening 46a. The retaining opening 46a faces towards the second axial device end 15b of the sealing device 15 and is axially bounded by a flange F. In the retaining opening 46a, only one fifth packing ring 47 is arranged, which is of a different design to the fifth packing ring 47 of FIG. 2c. In this case, the fifth packing ring 47 is a so-called double-acting DSLP ring assembly. The DSLP ring assembly is essentially a combination of the above-mentioned SLP ring assemblies, in which each outer chamfered ring is combined with a single central ring that has chamfers on both sides in the axial direction. The fifth packing ring 47 of FIG. 2c therefore has five axially consecutive rings, each of which has several ring segments in the circumferential direction.

[0076] The first purge passage end 48a of the purge passage 48 is connected to a space forming a pressure chamber 46b inside the retaining opening 46a, which is located radially outside the fifth packing ring 47. The axial location of the first purge passage end 48a is preferably in the center of the retaining opening 46a, but other locations are also possible. Also, a first part of the purge passage 48 adjacent to the first purge passage end 48a is integrally formed in the fifth packing retainer 46, and a second intermediate part of the purge passage 48 is integrally formed in the flange F. A third part of the purge passage 48 adjacent to the second purge passage end 48b is located outside the flange F and may be implemented as a conduit. The conduit is connected to a pressurized gas source (not shown). Furthermore, in the embodiment according to FIG. 2d, an unobstructed vent passage 31 also passes through the fifth packing retainer 46 and the flange F.

[0077] The purge passage 48 is circumferentially spaced apart from the ventilation passage 31 so as not to interfere with the latter. Analogous to FIG. 2c, the first ventilation passage end 31a of the ventilation passage 31 is located between the second packing ring 21 and the fifth packing ring 47 in the axial direction of the sealing device 15. However, an intermediate plate 27 as in FIG. 2c is not necessary in the embodiment of FIG. 2d. The total axial length of the sealing device 15 according to FIG. 2d may therefore be slightly less than the length of the sealing device according to FIG. 2c. The second packing ring 21 is designed according to the embodiment of FIG. 4c. However, of course, any of the other designs described are also possible.

[0078] When pressurized gas from a pressurized gas source (not shown in FIG. 2d) is introduced into the pressure chamber 46b, a pressure is generated in the pressure chamber 46b. This pressure radially presses the central double-chamfered ring of the fifth packing ring 47 against the two adjacent single-chamfered rings. Due to the interacting chamfers, the single-chamfered ring is radially pressed against the piston rod 8 and axially pressed against the non-chamfered rings, forming a tight seal in the axial and radial directions. Thus, gas leaking from the first axial device end 15a (or the compression chamber 9, respectively, FIG. 1) through the first packing ring 19 (not shown) and through the second packing ring 21 in the direction of the second axial device end 15b can be safely vented through the unobstructed vent path 31. This is again not only due to the sealing action of the fifth packing ring 47, but also due to the pressure in the pressure chamber 46b, which is preferably higher than the pressure in the area of ​​the first vent path end 31a.

Claims

1. A sealing device (15) for sealing a piston rod (8) of a reciprocating compressor (1), said sealing device (15) having a first axial device end (15a) configured to face a cylinder (9) of said compressor (1) and an opposite second axial device end (15b) configured to face a crankcase (2) of said compressor (1); a plurality of first packing retainers (18), each retainer having a retaining opening (18a) in which a first packing ring (19) is disposed; and a second packing retainer (19b) configured to receive a first packing ring (19c) and a second packing ring (19d) disposed in said first packing retainer (19e). a second packing retainer (20) having a retaining opening (20a) in which a packing ring (21) is disposed, the second retainer (20) being located closer to the second axial device end (15b) than the plurality of first packing retainers (18) in the axial direction of the sealing device (15), the second packing ring (21) being an unbroken ring having a continuous inner circumferential sealing surface (21a), the second packing ring (21) being configured to seal the piston rod (8) when the compressor (1) is at rest. The seal device (15) further includes a support passage (28), the support passage (28) having a first support passage end (28a), a second support passage end (28b), and a valve (29) for opening and closing the support passage (28), and the support passage (28) is configured to direct gas leaking through at least one of the plurality of first packing rings (19) in a direction from the first axial device end (15a) to the second axial device end (15b) from the first support passage end (28a) to the second support passage end (28b). ), the sealing device (15) further having an unobstructed ventilation path (31), the ventilation path (31) having a first ventilation path end (31 a) and a second ventilation path end (31 b), the ventilation path (31) being configured to vent gas leaking past the second packing ring (21) in a direction from the first axial device end (15 a) to the second axial device end (15 b) from the first ventilation path end (31 a) to the second ventilation path end (31 b).

2. The first support passage end (28a) is connected to the retaining opening (20a) of the second packing retainer (20), preferably in a radially outer region of the second packing ring (21), or the first support passage end (28a) is located between the second packing ring (21) and the first packing ring (19) of the adjacent first packing retainer (18) in the axial direction of the sealing device (15), or the first support passage end (28a) is located between the second packing ring (21) and the first packing ring (19) of the adjacent first packing retainer (18) in the axial direction of the sealing device (15).

2. The sealing device (15) of claim 1, wherein the packing retainer (18) has at least two first packing retainers (18), and the first support passage end (28a) is located in the region of the first packing ring (19) adjacent to the second packing ring (21) or between the first packing ring (19) adjacent to the second packing ring (21) in the axial direction of the sealing device (15) and the first axial device end (15a).

3. 3. The sealing device (15) according to claim 1 or 2, further comprising at least one third packing retainer (32), the third packing retainer (32) having a retaining opening (32a) in which a third packing ring (33) is disposed, the at least one third packing retainer (32) being disposed closer to the second axial device end (15b) of the sealing device (15) than the second packing retainer (20), and the first air passage end (31a) being connected to the retaining opening (32a) of the third packing retainer (32), preferably radially outside the at least one third packing ring (33), or the first air passage end (31a) being located between the second packing ring (21) and the third packing ring (33) in the axial direction of the sealing device (15).

4. 4. The sealing device (15) according to claim 1, wherein the second ventilation passage end (31b) of the unblocked ventilation passage (31) and the second support passage end (18b) of the support passage (28) are connected to a discharge space (35), preferably to a common discharge passage (34) which can be connected to a waste system.

5. 5. The sealing device (15) according to claim 1, wherein the valve (29) has an electrically controllable actuator (30) that can be controlled by a control unit (17) to open and close the valve (29).

6. The sealing device (15) according to any one of the preceding claims, wherein the valve (29) comprises a sensor (36) configured to generate a sensor value (X) representative of an open state of the valve (29).

7. The second packing ring (21) is formed from a material including a polymer, the material having a thermal expansion coefficient (α) that is at least twice the thermal expansion coefficient (αFE) of iron, and below a predetermined activation temperature, an inner diameter (d_i) of the second packing ring (21) is smaller than an outer diameter (D_a) of the piston rod (8) to be sealed, so that when the sealing device (15) is installed in the compressor (1), the second packing ring (21) is radially preloaded to allow the continuous inner circumferential sealing surface (21a) of the second packing ring (21) to contact the outer diameter (D_a) of the piston rod (8) to be sealed.

7. The sealing device (15) according to claim 1, wherein a tight seal is formed between the second packing ring (21) and the outer peripheral surface (8a) of the piston rod (8), and at a given operating temperature, the inner diameter (d_i) of the second packing ring (21) is greater than the outer diameter (D_a) of the piston rod (8), such that, when the sealing device (15) is installed in the compressor (1), the continuous inner circumferential sealing surface (21a) of the second seal ring (21) is spaced from the outer peripheral surface (8a) of the piston rod (8) to provide a leakage path axially through the second packing ring (21).

8. The thermal expansion coefficient (α) of the material of the second packing ring (21) is at least 30×10 －６ K －１ , preferably at least 60×10 －６ K －１ , especially at least 90×10 －６ K －１ The sealing device (15) according to claim 7,

9. 9. The sealing device (15) according to claim 7 or 8, wherein the operating temperature is 90° C. or higher and / or the activation temperature is 80° C. or lower, the operating temperature and the activation temperature being temperatures in the region of the piston rod (8), in particular the temperatures of the outer peripheral surface (8a) of the piston rod (8).

10. The second packing ring (21) has a first axial end (21c) and an opposite second axial end (21d), and the second packing ring (21) is disposed in the retaining opening (20a) of the second packing retainer (20) such that the first axial end (21c) faces the first axial device end (15a) of the sealing device (15), and the second packing ring (21) is a U-shaped cross-section having a radially spaced inner leg (24) and an outer leg (25), said inner leg (24) being provided with the inner circumferential sealing surface (21a) of said second packing ring (21) and said outer leg (25) of said second packing ring (21) being provided with a radially outer circumferential surface (21b), the open side of said U-shape facing axially towards said first axial end (21c) of said second packing ring (21); an L-shaped cross section having an axial leg (39) and a radial leg (40), the axial leg (39) being provided with the inner circumferential sealing surface (21a) of the second packing ring (21) and the radial leg (40) being provided with the radially outer circumferential surface (21b) of the second packing ring (21), the radial leg (40) being arranged at the second axial end (21d) of the second packing ring (21); a rectangular cross-section, said second packing ring (21) being provided with a plurality of openings (41), each of said openings (41) connecting said first axial end (21c) of said second packing ring (21) to its outer circumferential surface (21b), The sealing device (15) according to any one of claims 1 to 9, further comprising one of:

11. 11. The sealing device (15) of claim 10, further comprising a plurality of openings (22) on the outer leg (25), each of the plurality of openings (22) connecting an internal space (23) of the U-shaped packing ring (21) to the radially outer peripheral surface (21 b) of the second packing ring (21), the internal space (23) being located radially between the inner leg (24) and the outer leg (25), and the openings (22) being located spaced apart from the opposing axial ends (21 c, 21 d) of the second packing ring (21).

12. The sealing arrangement (15) of claim 11, wherein the plurality of openings (22) comprise a plurality of elongated or elliptical holes.

13. 13. The sealing device (15) of claim 12, wherein each elongated or elliptical hole has a longitudinal axis (L), a first hole end (22a) and an opposite second hole end (22b) in the direction of the longitudinal axis (L), the first hole end (22a) being located closer to the first ring end (21c) than the second hole end (22b).

14. The sealing device (15) according to any one of claims 10 to 13, wherein in an unassembled state of the second packing ring (21), the axial length (b_i) of the inner leg (24) is smaller than the axial length (b_a) of the outer leg (25).

15. 15. The sealing device (15) according to any one of claims 1 to 14, wherein the material of the second packing ring (21) is a fiber reinforced composite material and / or the polymer of the material of the second packing ring (21) comprises at least one of polytetrafluoroethylene, polyphenylene sulfide, polyether ether ketone, polyimide, polyamide.

16. 1. A reciprocating piston compressor (1), comprising a plurality of cylinders (9), in each of which a reciprocatingly movable piston (10) is arranged, each piston (10) being connected to a piston rod (8), and for at least one cylinder (9) of the plurality of cylinders (9), a sealing device (15) according to any one of claims 1 to 15 is provided for sealing the corresponding piston rod (8), the sealing device (15) being arranged such that a first axial device end (15a) faces the cylinder (9) and a second axial device end (15b) faces a crankcase (2) of the compressor (1).

17. 17. A reciprocating piston compressor (1) according to claim 16, comprising a sealing device (15) according to any one of claims 5 to 15, the compressor (1) having a compressor control unit (17) for controlling the operation of the compressor (1), the control unit (17) being configured to control an electrically controllable actuator (30) of a valve (29) of a support passage (28) depending on an operating condition of the compressor (1).

18. 18. The reciprocating piston compressor (1) according to claim 16 or 17, wherein the compressor (1) comprises an operating condition sensor, preferably a temperature sensor or a motion sensor, configured to detect a sensor value representative of an operating condition of the compressor (1), and wherein the electrically controllable actuator (30) of the valve (29) of the support passage (28) is configured to control the valve (29) depending on the sensor value, or the control unit (17) is configured to control the electrically controllable actuator (30) of the valve (29) depending on the sensor value.

19. The compressor (1) has a drive unit (16) for driving the compressor (1), and the compressor control unit (17) is configured to send a start signal (S_start) to the drive unit (16) to initiate operation of the compressor (1) and to send an open signal (S_open) to the actuator (30) of the valve (29) of the support passage (28) to open the valve (29) simultaneously with the start signal (S_start) or before the start signal (S_start) with a predetermined or adjustable opening lead time, the opening lead time being preferably between 0 and 60 19. The reciprocating piston compressor (1) according to claim 17 or 18, wherein a delay time in the range of 0 to 120 seconds and / or the control unit is configured to send a stop signal (S_stop) to the drive unit (16) to stop operation of the compressor (1) and to send a close signal (S_close) to the actuator (31) of the valve (29) of the support passage (28) to close the valve (29) simultaneously with the stop signal (S_stop) or after a predetermined or adjustable closing delay time after the stop signal (S_stop), the closing delay time being preferably in the range of 0 to 120 seconds.

20. A method for operating a reciprocating piston compressor (1), the compressor (1) having a plurality of cylinders (9), each of which has a reciprocatingly movable piston (10) arranged therein, each piston (10) being connected to a piston rod (8), and for each cylinder (9) of the plurality of cylinders (9), a sealing device (15) is provided for sealing the corresponding piston rod (8), the sealing device (15) having a first axial device end (15a) facing the corresponding cylinder (9) and an opposite second axial device end (15b) facing a crankcase (2) of the compressor (1), and at least one sealing device (15) of the plurality of sealing devices is a plurality of first packing retainers (18), each retainer having a retaining opening (18a) in which a first packing ring (19) is arranged. a first packing retainer (18) and a second packing retainer (20) having a retention opening (20a) in which a second packing ring (21) is disposed, the second retainer (20a) being located closer to the second axial device end (15b) than the plurality of first packing retainers (18) in the axial direction of the seal device (15), the second packing ring (21) being a cut packing ring having a continuous inner peripheral sealing surface (21a). the sealing device (15) further comprises a support passage (28) having a first support passage end (28a) and a second support passage end (28b) and a valve (29) for opening and closing the support passage (28); the sealing device (15) further comprises an unobstructed vent passage (31) having a first vent passage end (31a) and a second vent passage end (31b); and the method comprises: during operation of the compressor (1), inactivating the seal between the piston rod (8) and the inner peripheral sealing surface (21a) of the second packing ring (21), opening the valve (2) of the support passage (28) and venting gas leaking past at least one of the first packing rings (19) in the direction from the cylinder (9) to the crankcase (2) from the first support passage end (28a) to the second support passage end (28b) of the support passage (28) and venting gas leaking past the second packing ring (21) in the direction from the cylinder (9) to the crankcase (2) from the first vent passage end (31a) to the second vent passage end (31b) of the unblocked vent passage (31); or - activating the seal between the piston rod (8) and the inner peripheral sealing surface (21a) of the second packing ring (21) during a shutdown of the compressor (1) and closing the valve (29) of the support passage (28) to vent gas that may leak past the second packing ring (21) in the direction from the cylinder (9) to the crankcase (2) from the first vent end (31a) to the second vent end (31b) of the unobstructed vent path (31); The method includes:

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