DK2466148T3 - Centrifugal pump sealing device. - Google Patents

Description

Sealing system for centrifugal pumps Description [0001] The invention concerns a sealing arrangement for maintaining the smallest gaps between rotor and casing of a liquid-delivering fluid work machine, especially a centrifugal pump.

[0002] In fluid work machines, the leakage flow through gaps between rotating and stationary parts with different pressures upstream and downstream from the gaps constitute a significant loss factor. Such gaps are used at various places in fluid work machines. They might be the places for installation of split rings, wear rings, piston and/or disk-shaped relief devices, step seals in the feedthrough area of shaft wheels and/or rotors or parts thereof. Since the size of such gaps greatly influences the efficiency of the machines, one endeavours to keep them as narrow and long as possible, in order to avoid an excessive leakage flow. Many variants are known in the literature for the sealing of such gaps and their configuration. The minimum gap which can be achieved in such designs is limited, since one must always allow for manufacturing and installation tolerances to enable a mobility between the parts. A low-friction relative movement in the area of such a sealing gap is of advantage, especially for the rotor and for the casing.

[0003] It is known from EP 1 365 156 B1 how to maintain close tolerances for gap seals in the area of the seal. When using plastic as sealing material in a water pump, however, there is the drawback that the plastic will swell up under the action of the water and result in a narrowing of the sealing diameter. This increases the friction between seal and rotor, which increases the power consumption of the pump. In order to decrease the power loss of a pump unit in the region of the gap seal, an additional stiffening element is proposed for the gap seal, which is surrounded at least in part by a sealing material. The materials of the stiffening element and the sealing material are chosen such that at least one sealing dimension of the gap seal remains essentially constant under the action of a fluid. For this, the shrinkage or swelling of the one material counterbalances the shrinkage or swelling of the other material in the desired direction, so that an essentially constant dimension of the seal should be achieved. This requires the use of materials for stiffening element and sealing material which swell up differently under the influence of the fluid. The stiffnesses of sealing material and stiffening material should be attuned to each other so that even an increasing of the diameter of the stiffening ring due the force produced by the swelling of the sealing material is compensated and the sealing dimension remains constant.

[0004] From US 4913619 A there is known a device of this kind for a ceramic seal in a pump, in which the two sealing components are press fitted in the casing.

[0005] From EP 0 480 261 B1 there is known a multiple-part guiding device transporting a flow for centrifugal pumps, whose parts alternately lie against a fitting site thanks to the use of different materials in dependence on the particular temperature. This prevents a striking of the pump shaft against bearing locations or seal bushings and a contact between stationary and rotating parts.

[0006] EP 2 148 096 A1 shows a multiple-part sealing arrangement that is placed between a wall of the pump casing and the impeller of a centrifugal pump and seals it off into a shell-shaped section. In this kind of split ring seal, additional complex parts have to be built onto impeller and casing, which involves considerable expense and results in larger size of structural parts and larger volume.

[0007] DE 10 2008 001 814 A1 likewise shows a very complex multiple-part impeller seal in a centrifugal pump, consisting of a rigid pressure ring and an elastic sealing ring. In operation of the centrifugal pump, the sealing ring thrusts against a sliding surface to provide a seal, while the sliding ring is biased against the sliding surface. The drawback here is that the biasing has to be precisely adjusted or else the better sealing result will come at the cost of an increased frictional power.

[0008] The problem which the invention proposes to solve is to create a device for controlling the gap width between rotor and casing of a fluid work machine, in particular a centrifugal pump, guiding liquid and/or steam, which enables an automatic adjusting of the gap width without enlarging the structural part and which can also be used as a replacement for existing gap seals .

[0009] The solution calls for a device made of a composite material for controlling the gap width between rotor and casing of a fluid work machine, in particular a centrifugal pump, wherein at least a first material component of the composite material is designed as a form-giving stabilization component and a second material component of the composite material is designed as a swelling material producing under the influence of moisture a change in volume, and wherein at least one gap-limiting wall surface of the device can be spatially altered by means of the swelling material.

[0010] A device according to the invention, especially a split ring, swells up upon first contact with the delivered fluid until the gap between rotor and casing is minimized. The dimensions of a new, nonswollen split ring are less than required for operation. This affords the advantage, when installing the new split ring, that it is easy to mount. In operation, the split ring part made from swelling material swells up due to contact with the transported fluid, so that it takes on the optimal dimensions for the operation and minimizes the gap bounded by the device. The device according to the invention consists of at least two different material components, wherein at least one first material component predefines the geometric form of the device and one second material component is designed as a swelling material with gap width-changing properties. Advantageously, the swelling material is arranged in the composite material over the entire surface of the latter, in layers, points and/or segments. Thus, a precise changing of the gap can occur for a design model and/or a loading condition. The pointlike and/or segmented arrangement in the composite material also include the so-called gradient materials or graded structural parts made from them. Their texture design enables an adapting or adjusting of those wall surfaces which delimit a sealing gap, border on it, or have an effect of changing it.

[0011] According to other embodiments, the material components have different swelling behaviour and/or different fluid permeability. It is likewise possible for the first material component to be designed as a protective layer which temporarily or partially shields the second material component. In this way, a controlled swelling behaviour can be achieved. A device used as a gap seal can be installed with minimal tolerances, and the swelling material is protected by a shielding against contact with the liquid. If a change in the gap occurs in the course of the operating life, for example due to wear and tear, this will occur at the first material component. The swelling process at the second material component will occur depending on its degree of wear or liquid permeability. Thus, longer operating times with minimal sealing gaps can be accomplished without overhauling work interrupting the operation .

[0012] In one advantageous embodiment, the device consists of a composite material, especially a layered composite material, wherein at least one of the layers consists of a material which swells upon contact with a transported fluid. The layering makes it possible to increase the stability of the device. In particular, a laminated layering thanks to a combination of stabilizing layers and swelling layers makes it possible to reduce the effect of abrasion. If a nonswelling layer is gradually worn down in the course of the operating life, the next swelling layer is freed up and swells until the gap is once again reduced to a necessary minimum. The separation of the individual swelling layers allows for an adapting of the seal as needed to the different operating conditions.

[0013] In traditional split rings, when the rotor strikes against the split ring the result is a permanent widening of the gap, and in the worst case a blockage. In the case of the invention, however, only the impermeable first material is damaged, so that the second material freed up in this way once more readjusts the gap thanks to its swelling.

[0014] In another embodiment, in the case of alternating layer position of the composite material, the layer thickness of the second material increases toward the side away from the gap. When the split ring is gradually worn down during operation, the sealing element will swell up more in order to close the widening gap. This is accomplished if the layer thickness of the swelling material increases.

[0015] The second material for use in a sealing arrangement according to the invention is a biogenic material, in particular wood or thermally treated wood. This allows the use of a simple and cost-effective material which is available in large volume and with different material properties.

[0016] Furthermore, the first material can be a polymer material based on renewable raw materials. It is advantageous for the material to be exactly adjustable to the needs of the gap seal and for the necessary raw materials to be available with almost no limit.

[0017] In the use of the device according to the invention, such as a split ring, it is advantageous for the materials used to have different strengths with respect to the mating friction partner. Since the split ring is easily biased by the swelling, a friction arising during operation between split ring and casing or between split ring and rotor can result in abrasion of material. This is dependent on the choice of the material of the friction partner. As a result of the abrasion, the split ring is soon ground down, until the biasing of the split ring due to swelling no longer results in friction between the individual structural parts. In addition, one must take into account the typical overload scenarios for the particular application, and the time course of the swelling should be optimally adjusted to them.

[0018] The layers are tribologically adjusted to the individual case of usually high relative velocities and different pressing forces from radial deflection of the rotor, so that in event of contact the efficiency is not reduced by the friction losses outweighing the gain from the sealing effect.

[0019] In order to measure the material abrasion, in another embodiment there is provided a sensor for detecting when the device is worn down. Thanks to this sensor, it is possible to detect the inherent wear on the device. If the device is entirely worn down, an evaluating device of the sensor will send a signal that the device has to be replaced soon.

[0020] In an especially preferred embodiment, a moisture sensor is integrated in the gap at the furthest removed swelling region, which responds to the moisture initiating the swelling and thus indicates that the last swelling region is being utilized.

[0021] For use in rotational fluid work machines, the device is configured as a split ring. Split rings of the most diverse kind are customary for reducing the gap between the rotor and the casing of a fluid work machine. The split ring according to the invention can be designed in its geometry and its automatically adjusting properties so that it can be retrofitted without problem in already existing fluid work machines .

[0022] Furthermore, the invention describes a method of constructing a device for maintaining the smallest gap width between rotor and casing of a fluid work machine, wherein the material pairing of the gapforming surfaces of device and casing or rotor is chosen such that wear occurs only at the device, and the at least one swelling layer of the device is chosen in dependence on the transported fluid so that a swelling of this layer brings about an automatic adjustment of the gap width to a minimum gap. This method ensures that an excessive swelling and thus a loss through friction and wear of the device are prevented.

[0023] In one embodiment of the method, the material pairing when designing the device is chosen such that wear is minimized. The choice of the materials takes into account different factors of influence, such as the area of application of the fluid work machine, the transported fluid and the transport conditions such as pressure and temperature. If all factors are attuned to each other, it is possible to keep down the wear on the gap-forming surfaces.

[0024] Further embodiments will emerge from the combination of those presented thus far and therefore are not further indicated here.

[0025] Sample embodiments of the invention are presented in the drawings and shall be described more closely below. There are shown

Fig. 1, a perspective view of a device according to the invention

Fig. 2, a section along plane A of Fig. 1,

Fig. 3, a section along plane B of Fig. 1 for a first sample embodiment

Fig. 4, a section along plane B of Fig. 1 for a second sample embodiment,

Fig. 5, a section along plane B of Fig. 1 for a third sample embodiment,

Fig. 6, a section along plane B of Fig. 1 for a fourth sample embodiment,

Fig. 7, a variant of the device of Fig. 2 in sectional view along plane A of Fig. 1,

Fig. 8, another variant of the device of Fig. 2 in sectional view along plane A of Fig. 1 and Fig. 9, another variant of the device of Fig. 2 in sectional view along plane A of Fig. 1.

[0026] Fig. 1 shows a perspective view of a device according to the invention. The device is configured as an annular gap seal 1. In this representation, only a first material 2 can be seen, forming the surface of the gap seal 1.

[0027] The gap seal 1 can either be connected on the outer surface 3 firmly and statically sealing to another structural part, for example a pump casing, in which case a gap to be sealed is present at the inner surface 4. A neck or hub part of a rotating pump impeller, not shown here for reasons of clarity, would be inserted into the space enclosed by the inner surface 4, here shown in the form of an annular internal circumferential surface. Between these two parts, a sealing gap would be formed to ensure the relative movement of the impeller. On the other hand, the gap seal 1 can also be firmly connected on the inner surface 4 to a rotating impeller. The sealing gap would then be formed between the outer surface 3, in this case in the form of an annular rotating outer circumferential surface, and a stationary opening (not shown) of a pump casing accommodating the gap seal. In order to produce a rotationally firm connection to the particular structural part, the gap seal 1 can be further provided with grooves, toothings, or other twist prevention designs. These are familiar items and therefore are not otherwise shown in the present representation. The end face 6 lies each time against the structural part holding the device. Generally speaking, the surface of the gap seal facing the particular gap shall be designated and represented as the gap wall 7. The sectional planes A and B have been drawn to further explain the following figures.

[0028] Fig. 2 shows a section through the gap seal 1 along section plane A shown in Fig. 1. It is clearly seen that the overall device has a layered construction, where one layer of a first material 2 is followed in alternating fashion by a layer of a second material 5. The form-giving first material 2 completely encloses the layers of the swelling second material 5. In a device consisting of several layers in succession, this prevents those layers which consist of the second material 5 from coming into direct contact with a transported fluid. This dependably prevents a swelling of the layers 5. In the installed state of the gap seal 1 and in an operative connection with a casing and/or an impeller, the outer surface 3 and/or the inner surface 4 are exposed to a wear-producing loading, especially in the case of the pump under stress outside of the design range, such as a partial load or an excess load. In this way, during the course of the operating period a material abrasion from the first material 2 would occur, and the sealing gap bounded by it would increase. If this material abrasion exposes the layer of the second material 5, its swelling property would then cause a change in shape of the inner surface 4 and/or outer surface 3. In the annular configuration shown here, the swelling would result in a corresponding change in the diameter, so that the gap-bounding wall surface decreases the sealing gap.

[0029] Fig. 3 shows a longitudinal section through a split ring according to the invention along plane B in Fig. 1. The encapsulation of the second material 5 an at the outer surfaces of the device is clearly seen in the figure at left. Both the end faces 6 and the gap wall 7 as well as the side lying opposite it are made of the first material 2. Upon wearing of the gap wall 7, material abrasion occurs on this surface bounding the gap, so that a gap cross section is increased, similar to wear. If, thanks to the wear, a gap wall 7' indicated by broken line is exposed, the swelling second material 5 is then in direct contact with the fluid being sealed off. Consequently, the volume of the second material 5 increases, thereby forming here a new gap wall 7" of smaller diameter, as shown in Fig. 3 at right. The radial position of this new self-adjusting gap wall 7" causes a reduction of the gaps being sealed and reducing the flow passage, which improves the efficiency of a fluid machine. The influence of the shorter gap length, which is minimal here thanks to the slightly shorter length or width of the newly formed gap wall 7" with no material abrasion at the end face, is negligible.

[0030] Fig. 4 shows a longitudinal section through a second sample embodiment of the split ring according to the invention along plane B of Fig. 1. The end faces 6 consist of a first material 2, the gap wall 7 consists of the second material 5 and in the starting condition it is not encapsulated in the direction of the gap. Upon first contact with the fluid, a swelling occurs, which narrows the gap. The figure shows two additional layers of the swelling material 5, which are entirely encapsulated by the first material 2. These are exposed only upon continuing wear and begin to swell later on.

[0031] Fig. 5 and Fig.6 show longitudinal sections along plane B of Fig. 1 for two further sample embodiments of the split ring according to the invention. In there embodiments the gap wall 7 is provided in the axial direction, i.e., at one of the end faces 6. The outer surface 3 and the inner surface 4 are firmly joined to the neighbouring structural part.

[0032] The embodiment in Fig. 5 shows a split ring in which the swelling second material 5 is completely encapsulated by the first material 2. Only when the first material 2 is worn down by friction at the gap wall 7 can fluid penetrate into the second material 5 a cause it to swell, thereby further reducing the gap.

[0033] The embodiment in Fig. 6 is comparable to the split ring shown in Fig. 4. The second material 5 at the gap wall 7 is exposed to the fluid from the outset and can immediately begin swelling, which lets the gap be reduced to a minimum.

[0034] Fig. 7 shows a variant of the device according to the invention in a sectional view in the plane A of Fig. 1, in which the thickness of the swelling layer, consisting of the second material 5, increases. In the figure, at the centre of the ring, is shown the region of the gap wall 7 at the inner surface 4 in which the device makes contact with the mating movable part. In the case of the rotor seal, the rotor is arranged here. Thanks to the swelling, the device is pressed against the rotor. Due to the resulting friction, the device is gradually worn down. The continuing swelling of the second material 5 closes the gap during the operation. When the first layer of the second material 5 is completely worn down, an increased swelling is needed in order to close the enlarged gap. This is made possible by the thicker layer of second material 5.

[0035] Fig. 8 shows in a sectional view along plane A of Fig. 1 a variant in which the swelling layer of the second material 5 is arranged in individual segments. These segments are each time completely encapsulated by the first material 2, so that each segment can swell separately. Thanks to this arrangement, one can specifically compensate for differences in the gap width depending on local wearing sites, without letting the entire circumference of the split ring swell up. In this way, one can prevent the second material from swelling in areas where it is again removed at once by abrasion, which might needlessly increase the friction. A segmenting of the second material 5 is also possible in the axial direction, which is not shown in Fig. 8 for technical reasons.

[0036] Another variant of this segmented arrangement of the second material 5 within a closed matrix formed by the first material 2 is shown in Fig. 9. In the cutout detail of Fig. 10, lenses of the second material 5 are shown, having a gradation, i.e., a steady increase in volume. With increasing abrasion, an ever increasing swelling is needed to close the gap. This circumstance is handled by the increasing size of the lenses of the second material. A similar arrangement has already been shown in Fig. 7.

[0037] The lenses in Fig. 10 are shown in orderly arrangement. Also advisable are split rings in which the lenses of the second material 5 are statistically distributed in the first material. Likewise, the size relations in the example shown are only exemplary, since the swelling lenses can also be provided as microparticles. The effects made possible by the gradation can also be obtained when the lenses are in a radially disorderly arrangement.

[0038] For simplicity, the individual layers are shown here in parallel. Geometries are also conceivable in which identical layers are interconnected by spine-like deformations. This achieves an increased stability or a specific swelling in the entire device. One can also use split ring forms which mimic the geometry of the gap space.

List of reference symbols: [0039] 1 Gap seal 2 First material 3 Outer surface 4 Inner surface 5 Second material 6 End face 7 Gap wall A Sectional plane B Sectional plane

Claims (13)

An arrangement of a composite material for gap width control between the rotor and housing of a flow machine which conducts a fluid in the form of liquid and / or steam, in particular a centrifugal pump, wherein a first material component (2) of the composite material is designed as a shaping stabilizer component, and characterized in that another material component of the composite material is formed as a swelling material (5), where this under humidity influence a volume change and where at least one gap-limiting wall surface of the device is spatially variable by means of the swelling material (5). Device according to claim 1, characterized in that the device consists of at least two different material components, wherein at least one first material component (2) determines the geometric configuration of the device and at least a second material component is designed as a swelling material (5). ) with gap width changing properties. Device according to claim 1 or 2, characterized in that the swelling material is arranged over the entire surface, layer-shaped, point-wise and / or segmented in the composite material. Device according to claim 1, 2 or 3, characterized in that the material components (2, 5) comprise a different swelling ratio and / or a different fluid permeability. Device according to one of claims 1 to 4, characterized in that the first material component (2) is formed as a protective layer which temporarily, if applicable, partially shields the second material component (5). Device according to one of claims 1 to 5, characterized in that it consists of a layered composite material, wherein at least one of the layers consists of a material (5) which swells upon contact with a transport fluid. Device according to one of claims 1 or 6, characterized in that the layering of the composite material is laminated. Device according to one of claims 1 to 7, characterized in that, with alternating layer position of the composite material, the layer thickness of the second material (5) increases in the direction towards the side distant from the gap. Device according to one of claims 1 to 8, characterized in that the second material (5) is a biogenic material, in particular wood or thermally treated wood. Device according to one of claims 1 to 9, characterized in that at least one of the materials (2, 5) is a polymeric material based on renewable raw materials. Device according to one of claims 1 to 10, characterized in that the materials (2, 5) used can be worn off. Device according to one of claims 1 to 11, characterized in that a sensor is provided for recording the wear of the device. Device according to one of claims 1 to 12, characterized in that the device is designed as a ring with slot (s).