Positive displacement pump with mechanical seal

Abstract

Positive displacement pump (1) with a rotatingly driven displacement body (10, 11) which is mounted on an associated shaft (12, 13) in a product chamber (51) through which the product to be pumped flows, wherein the shaft (12, 13) enters the product chamber (51) through an end wall (50) of a pumping section (5) of the pump (1), and the passage of the shaft (12, 13) through the end wall (50) is sealed by means of a mechanical seal (52), wherein the mechanical seal (52) - a first stationary ring (53) and - has a second ring (54) that moves with the displacer body (10, 11); characterized in that the stationary ring (53) is inserted into the shaft passage from the direction of the product space (51) and is directly supported on a spring element (56), wherein the spring element (56) is inserted into the shaft passage from outside the product space (51).

Description

[0001] Rotary positive displacement pumps have been known in the form of primitive gear pumps since the early 17th century. In modern pumps, displacer bodies are mounted on shafts, which are preferably located outside the product chamber through which the product to be pumped flows.

[0002] To prevent the product from unintentionally escaping the product chamber and to protect the product from external contamination, the passage of the shaft into the product chamber must be sealed.

[0003] A well-known method for sealing the shaft against the wall is, for example, the use of shaft seals. However, these are only conditionally reliable and have a severe pressure limit, and are particularly unsuitable when the type of product being conveyed requires a particularly secure seal, such as when conveying toxic substances or in hygienic areas, e.g., in the food, cosmetics, and / or pharmaceutical industries.

[0004] In these areas, the use of mechanical seals has become established, as they ensure a very safe and reliable seal. However, this comes at the cost of a complex seal design. The seal typically has at least one rotating section connected to the shaft and a stationary section mounted in the wall.

[0005] For the seal to function reliably, the stationary section must be axially secured. This section typically has a flange that is bolted to the wall with several screws.

[0006] In many cases, it is undesirable or simply impossible to position the flange within the product chamber, as this would impede product flow and make the corresponding contours difficult to clean. Therefore, the flange must be mounted from outside the product chamber.

[0007] This is disadvantageous for several reasons. To mount the flange, the shaft must be completely removed from the product chamber, or the pump housing, including all product-contacting components, must be detached from the shaft. For many pumps, this requires complete disassembly of the pump drive. Furthermore, since the rotating section of the mechanical seal can only be installed from the product side, the pump must always be completely disassembled for maintenance of the seal, for example.

[0008] Known solutions where the stationary section can also be mounted from the product chamber are usually complex in design, as fixing the stationary section is not trivial. For example, DE 10 2016 100 959 A1 describes a pump in which the sealing rings are arranged in a separate sleeve, which is secured against displacement in a complex manner. This complex design is particularly problematic for small pumps.

[0009] DE 93 18 143 U1 shows a shaft exit from a pump housing sealed by means of a mechanical seal installed on the product side. The stationary counter-ring holder, inserted in a receptacle of a housing part, is supported therein by a helical spring.

[0010] Publication CH 697 353 B1 concerns the sealing of the shaft of a gear pump against the fluids flowing through the pumping chamber. Counter rings are inserted on both sides into a gear fixed to the shaft. The corresponding stationary sliding rings are each preloaded against the counter rings by a spring inserted from the pumping chamber side.

[0011] US Patent 3,599,990 A discusses the sealing of a shaft passage for a ship's propeller. The document discloses spring elements that are supported against an externally mounted housing and clamp a sealing ring mounted on the sea side against its counterpart.

[0012] A pump arrangement disclosed in DE 18 00 888 A shows a spring element which is inserted into a bore during assembly and secured with a sliding ring before the entire arrangement including the shaft is then guided through the shaft passage from the product side.

[0013] From DE 20 2016 100 655 U1 a magnetic coupling pump with a mechanical seal is known in which a sliding ring rotating with a drive shaft is pressed against a stationary counter ring by means of a spring.

[0014] From DE 20 2018 105 090 U1, a sealing device for sealing a gap between a stationary and a moving element is known, which does not require a spring element. In this device, a clamping element is designed to press a sealing section of a sealing element against a sealing surface of the stationary element.

[0015] It is also known from DE 10 2018 129 054 A1 to secure a mechanical seal by means of a locking element running approximately perpendicular to an axial direction of the shaft through the wall of the product space.

[0016] The task is therefore to provide a positive displacement pump with a mechanical seal that is improved with regard to the problems described.

[0017] This problem is solved according to the invention by a positive displacement pump with a rotatingly driven displacement body, which is mounted on an associated shaft in a product chamber through which the product to be pumped flows, wherein the shaft enters the product chamber through an end wall of a pumping section of the pump, and the passage of the shaft through the end wall is sealed by means of a mechanical seal, wherein the mechanical seal has a first stationary ring and a second ring that rotates with the displacement body; which is further developed in that the stationary ring is inserted into the shaft passage from the direction of the product chamber and is directly supported on a spring element.

[0018] With the appropriate design, a highly effective and durable seal can be provided with a very simple construction.

[0019] The spring element can be inserted into the shaft passage from outside the product chamber. The shaft passage may have an internal projection that prevents the spring element from entering the product chamber. Additionally, the spring element can be axially supported by a snap ring that is inserted into a groove in the shaft passage.

[0020] The stationary ring and / or the projection can have alignment elements that prevent the stationary ring from rotating in the shaft passage. Several radial surfaces, e.g., three, can be provided for this purpose.

[0021] The spring element can comprise one or more disc springs, sinusoidal springs, wave springs, or similar spring elements. The spring element can be positioned between flat support rings. The use of appropriate spring elements ensures uniform support of the stationary ring across its entire circumference.

[0022] The stationary ring can be sealed against shaft penetration by an elastomer seal.

[0023] In one possible embodiment of a positive displacement pump according to the invention, the rotating ring can be received in a receiving bushing which is mounted on the shaft. For this purpose, the receiving bushing can be fixed between a stop shoulder of the shaft and the displacement body.

[0024] The rotating ring and / or the receiving bushing can in turn have alignment elements that prevent the rotating ring from twisting relative to the shaft. For this purpose, one or more radial surfaces can be provided.

[0025] The rotating ring can be sealed against the receiving bushing by an additional elastomer seal.

[0026] In a preferred embodiment of the invention, the positive displacement pump is a screw spindle pump.

[0027] The invention will now be explained in more detail with reference to some exemplary illustrations. The embodiments shown in the figures serve only to better understand the invention, without limiting it.

[0028] They show: Fig. 1: a positive displacement pump with attached drive motor; Fig. 2: the internal structure of the positive displacement pump Fig. 1 in a sectional view; Fig. 3: the internal structure of the positive displacement pump Fig. 1 in another sectional view.

[0029] Fig. Figure 1 shows a positive displacement pump 1 with a connected drive motor 2 in a perspective view. The motor 2 is a standard electric motor, the construction of which will not be discussed further here. The pump 1 comprises a coupling section 3, in which a shaft (not shown) of the pump 1 is detachably connected to the drive motor 2, a gearbox section 4, and a delivery section 5. Displacement elements (not shown) are arranged in the delivery section 5, which, when the pump is running, convey a liquid or pasty product from an inlet nozzle 6 to an outlet nozzle 7. The gearbox section has an inspection opening 8, which is closed with a cover.

[0030] Fig. Figure 2 shows the internal structure of the pump 1 in a horizontal longitudinal section, in which the coupling section 3, the gearbox section 4, and the conveying section 5 are recognizable.

[0031] In the conveying section 5, two cooperating displacement bodies 10, 11 are arranged, which in this case are conveying screws whose flanks mesh with minimal play. The displacement bodies 10, 11 are mounted at their ends on shafts 12, 13, which extend parallel to each other from the conveying section 5 through the gearbox section 4 to the coupling section 3.

[0032] Shaft 12 acts as a drive shaft and is equipped with a coupling in coupling section 3 to connect to an output shaft of the motor (not shown). The type of coupling can vary according to the requirements of the respective application. Rigid couplings are suitable for larger pumps, while bellows couplings, for example, are suitable for smaller pumps. The pump shown in this embodiment is designed for very small flow rates; here, a sliding jaw coupling 15 is provided, of which in Fig. 2 Only a hub 16 and a damping element 17 are visible. The illustrated coupling section 3 also has a flange 18 for connection to the motor 1. In other versions, the flange 18 can be omitted. A shaft seal 19 prevents oil from entering the coupling section 3.

[0033] Shaft 13 acts as the driven shaft and ends at the transition between gearbox section 4 and clutch section 3.

[0034] The shafts 12, 13 are each supported in the gearbox section by a first, radially acting bearing 20, 21 and by a second, radially and axially acting bearing 22, 23. The first bearings 20, 21 are designed as needle bearings and ensure precise radial guidance of the displacement bodies 10, 11 in the conveying section 5 of the pump 1. The second bearings 22, 23 are designed as double angular contact ball bearings in this example and, in addition to providing precise positional guidance of the shafts 12, 13, also serve to absorb axial forces generated by the conveying principle of the pump 1.

[0035] A synchronous gear 30 is arranged between the first and second bearings 20, 21, 22, 23 to drive the shaft 13. The synchronous gear 30 comprises a first pinion 31, which is fixed on the first shaft 12, and a second pinion 32, which is fixed on the second shaft 13.

[0036] To align the displacement bodies 10, 11 with each other so that their flanks do not touch, a rotational alignment of the shafts 12, 13 with each other is required. For this purpose, the synchronous gear is designed to be adjustable, which will be described in more detail below.

[0037] The pinions 31 and 32 are helical in the illustrated embodiment. The first pinion 31 is mounted on the shaft 12 such that a Fig. The first pinion 31 engages via a key 35 (not shown) on its inner circumferential surface. This key is inserted into the shaft 12. Towards the coupling section 3, the first pinion 31 rests against a stop shoulder 36 of the shaft 12. From the conveying section 5, a first stop nut 38 is screwed onto an external thread 39 of the shaft 12 and secures the first pinion 31 to the stop shoulder 36. The first stop nut 38 has a threaded section that engages the external thread 39 of the shaft 12. A locking section adjoins this threaded section. A setscrew 40 is provided in the locking section, which acts on the shaft 12 outside the external thread 39 to secure the first stop nut 38 and prevent it from loosening.

[0038] The second pinion 32 is fixed to the shaft 13 in a similar manner to the first pinion 31 being fixed to the shaft 12. The second pinion also has a Fig. 2. An axial groove (not shown) engages the shaft 13 via a key 42. However, the pinion 12 does not rest against a fixed stop shoulder in the direction of the contact section 3, but against a second stop nut 44, which is screwed onto a first external thread 45 of the shaft 13. A third stop nut 48 is screwed onto a second external thread 49 of the shaft 13, so that the second pinion 32 is axially fixed between the second stop nut 44 and the third stop nut 48.

[0039] The second and third stop nuts 44, 48, like the first stop nut 38, each have a threaded section and a fixing section. Threaded pins in the fixing sections serve to fix the stop nuts 44, 48 to the shaft 13.

[0040] Since there is only limited installation space available between shafts 12 and 13, the threaded section and the fixing section of the first stop nut 38 and the third stop nut 48 are axially interchanged. This allows the respective fixing section to have a larger diameter to provide sufficient thread depth for the set screws, while the respective threaded section has a smaller outer diameter.

[0041] To align the conveying flanks of the displacement bodies 10, 11, the second pinion 32 can now be axially displaced relative to the first pinion 31 by rotating the second and third stop nuts 44, 48. The helical gearing of the pinions 31, 32 causes a rotation of the shaft 13 relative to the shaft 12. In this way, the conveying flanks of the displacement bodies 10, 11 can be aligned so that they do not touch during operation of the pump 1.

[0042] In the example shown, the second pinion 32 is slightly shorter than the first pinion 31, so that it completely overlaps with the first pinion 31 over the entire axial adjustment range. Alternatively, the second pinion 32 can also be longer than the first pinion. In this case, the length difference between the pinions corresponds at least to the axial adjustment range of the second pinion 32.

[0043] The external threads 39, 45, 49 of the shafts 12, 13 are preferably designed such that the stop nuts 38, 44, 48 cannot loosen even without the action of the grub screws in the usual direction of rotation of the pump.

[0044] In alternative designs, not shown here, the axial groove of the second pinion can be slightly helical. In such cases, the shaft 13 is also slightly rotated during axial displacement. The total rotation of the shaft 13 during displacement of the second pinion then results, depending on the orientation of the helical groove, either from the sum or the difference of the pitches of the groove on the one hand and the tooth flanks of the pinion on the other. A helical groove can also be used in conjunction with straight-cut pinions. In another alternative design, both pinions can be axially adjustable. If the pinions have axial grooves with different pitches, adjustment of the synchronous gear can be achieved by simultaneously displacing both pinions. This can be advantageous if uneven wear of the tooth flanks of the pinions causes problems.

[0045] The assembly of shafts 12, 13 and the synchronous gear 30 in the gear section 4 of pump 1 is carried out as follows: First, the inner rings of the needle bearings 20, 21 are attached to shafts 12, 13. In addition, the second stop nut 44 is screwed onto shaft 13.

[0046] Then, the shafts 12, 13 are inserted from the side of the still unassembled coupling section 3 through the bearing bores of the ball bearings 22, 23 into the bearing housing of the gear section 4. Simultaneously, the pinions 31, 32 and the first and third stop nuts 38, 48 are inserted through the inspection opening 8 into the bearing housing, so that the first pinion 31 and then the first stop nut 38 slide over the shaft 12, and the second pinion 32 and the third stop nut 38 slide over the shaft 13.

[0047] The outer rings and cages of the needle bearings 20, 21 and the ball bearings 22, 23 are then inserted from the outside into their respective bearing bores to support the shafts 12, 13. Finally, the bearings 20, 21, 22, 23 are fixed and, if necessary, sealed using standard methods.

[0048] Fig. Figure 3 shows pump 1 in a vertical longitudinal section in the axial plane of shaft 12. A further description of elements already described above follows. Fig. Two of them will be presented, but for the sake of clarity, they will not be presented here.

[0049] In Fig.Figure 3 shows how the shaft 12 passes through an end wall 50 of the conveying section 5 into a product chamber 51. The shaft passage is sealed by a mechanical seal 52, which comprises a stationary ring 53 and a ring 54 that rotates with the shaft 12. The stationary ring 53 is axially supported by a spring assembly 56, which is inserted into the passage bore through the end wall 50 from the direction of the gear section 4 and is held axially by a snap ring 57. A projection 58 in the passage bore prevents the spring assembly 56 from falling out of the shaft passage when the mechanical seal 52 is replaced in the direction of the conveying section 5. The stationary ring 53 has a smaller diameter at its end facing away from the conveying section than the projection 58 and thus rests directly against the spring assembly 56. In the example shown, the spring assembly 56 consists of a sinusoidal spring or...A wave spring held between two flat support rings. Such springs are known, for example, as "crest-to-crest". ® The wave spring can be obtained from the company Smalley.

[0050] The stationary ring 53 can have a raised area (not shown) that interacts with a notch (not shown) on the projection 58 to prevent the stationary ring 53 from rotating unintentionally with the shaft 12. Alternatively, several, e.g., three, interacting radial surfaces can be provided on both the stationary ring 53 and the projection 58. A sealing ring 59 provides a seal between the stationary ring 53 and the through-bore.

[0051] In an alternative embodiment not shown, the projection 58 can be formed by a further snap ring.

[0052] The rotating ring 54 is received in a receiving bushing 60, which is fixed between the displacer body 10 and a stop shoulder of the shaft 12. Similar to the stationary ring 53, the rotating ring 54 can also be secured against rotation on the shaft 12 by suitable contours. A sealing ring 61 prevents the product from penetrating behind the rotating ring 54.

[0053] In the area where the stationary ring 53 and the rotating ring 54 meet, they are lapped with high precision to ensure a good seal. The diameter of rings 53 and 54 is increased in the contact area. This improves heat dissipation to the product being conveyed, thus increasing the service life of the seal 52. It also reduces the influence of the internal pressure of the product being conveyed on the contact force of rings 53 and 54. In the example shown, the stationary ring 53 and the rotating ring have different contours. In principle, both rings 53 and 54 can also be manufactured as identical parts to further reduce the number of different components.

[0054] The sealing of the shaft 11 against the end wall 51 is carried out in an analogous manner by a mechanical seal, which is not shown for the sake of clarity, but corresponds in structure and function to the mechanical seal 52.

[0055] In addition to the mechanical seals shown, a second seal can be provided for each of the shafts 11, 12, which is located downstream of the respective mechanical seal. A space between the mechanical seal and the additional seal can be filled with a barrier or flushing fluid.

[0056] The design of the mechanical seal 52 described here is particularly advantageous for compact pumps, as it comprises only a minimal number of components and is therefore easy to manufacture, assemble, and replace. During initial assembly, the spring assembly can be pushed into the shaft passage from the side of the gearbox section 4 so that it rests against the projection 56. The snap ring 57 is then inserted into the shaft passage to hold the spring assembly 56 in place.

[0057] The snap ring 57 and the spring assembly 56 have a free inner diameter that is larger than the outer diameter of the shaft 12 in the area that projects into the product chamber 51 of the pump 1. This allows the spring assembly 57 and snap ring 56 to be installed before the shaft 12 is inserted through the shaft bore.

[0058] The stationary ring 53 can then be pushed over the shaft 12 from the direction of the product chamber 51 until it abuts the spring assembly 56. Then the receiving bushing 60 with the inserted rotating ring 54 is pushed over the shaft 12 before the displacer body is placed on it and presses the receiving bushing 60 against the stop shoulder of the shaft 12.

[0059] In the illustrated embodiment, the inlet nozzle 6 is screwed into the body of the pumping section 5. For this purpose, the inlet nozzle is composed of a threaded section 61 and a connecting section 62. The threaded section 61 and the connecting section 62 can be made of different materials. In the illustrated embodiment, the outlet nozzle 7 is formed integrally with an outlet-side end plate 70 of the pumping section 5. In other embodiments, the outlet nozzle 7 can be screwed to the pumping section 5 in a similar manner to the inlet nozzle 6. A height-adjustable support foot 71 is mounted under the pump 1.

Claims

[1] Positive displacement pump (1) with a rotatingly driven displacement body (10, 11) which is mounted on an associated shaft (12, 13) in a product chamber (51) through which the product to be pumped flows, wherein the shaft (12, 13) enters the product chamber (51) through an end wall (50) of a pumping section (5) of the pump (1), and the passage of the shaft (12, 13) through the end wall (50) is sealed by means of a mechanical seal (52), wherein the mechanical seal (52) - a first stationary ring (53) and - has a second ring (54) that moves along with the displacer body (10, 11); characterized by , that the stationary ring (53) is inserted into the shaft passage from the direction of the product space (51) and is directly supported on a spring element (56), wherein the spring element (56) is inserted into the shaft passage from outside the product space (51). [2] Positive displacement pump according to claim 1, wherein the shaft passage has an inner projection (58) which prevents the spring element (56) from entering the product space (51). [3] Positive displacement pump according to claim 1 or 2, characterized by , wherein the spring element (56) is axially supported on a snap ring (57) which is inserted into a groove of the shaft passage. [4] Positive displacement pump according to claim 2 or 3, wherein the stationary ring (53) and / or the projection (58) have alignment elements which prevent the stationary ring (53) from twisting in the shaft passage. [5] Positive displacement pump according to one of the preceding claims, wherein the spring element (56) comprises one or more disc springs, sinusoidal springs, wave springs or similar spring elements. [6] Positive displacement pump according to one of the preceding claims, wherein the stationary ring (53) is sealed against the shaft passage by an elastomer seal (59). [7] Positive displacement pump according to one of the preceding claims, wherein the rotating ring (54) is received in a receiving bushing (60) which is mounted on the shaft (12, 13). [8] Positive displacement pump according to claim 7, wherein the receiving bushing (60) is fixed between a stop shoulder of the shaft (12, 13) and the displacer body (10, 11). [9] Positive displacement pump according to claim 7 or 8, wherein the rotating ring (54) and / or the receiving bushing (60) have alignment elements which prevent the rotating ring (54) from rotating relative to the shaft (12,13). [10] Positive displacement pump according to one of claims 7 to 9, wherein the rotating ring (54) is sealed against the receiving bushing (60) by an elastomer seal (61). [11] Positive displacement pump according to any of the preceding claims, characterized by that the pump is a screw pump.

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