US3516757A - Labyrinth seal for a hydraulic rotary machine - Google Patents

Description

. K. BAUMANN June 23, 1970 LABYRINTH SEAL FOR A HYDRAULIC ROTARY MACHINE 2 SheetsSheet 1 Filed June 24. 1968 June 23, 1970 K. BAUMANN 1 3,516,757

LABYRINTH SEAL FOR A HYDRAULIC ROTARY MACHINE Filed June 24. less 2 Sheets-Sheet 2 United States Patent 8 Claims ABSTRACT OF THE DISCLOSURE A hydraulic rotary machine, the runner of which runs sometimes in water and sometimes in air has a labyrinth seal in which the relative position of the parts bounding the sealing gap on either side is variable from the position intended for rotation of the runner in water, in which the width of the sealing gap is comparatively small to a position with increased gap width intended for rota tion of the runner in air.

BACKGROUND OF THE INVENTION In hydraulic rotary machines, the runners of which rotate sometimes in water and sometimes in air, for example in Francis turbines, storage system pumps or reversible pump turbines, it has been necessary hitherto to cool the existing labyrinth seals, which usually have very narrow gaps, during operation in air in order thereby to prevent excessive heating of the interengaging parts. During operation in water, this cooling occurs directly through the working water flowing through the gaps, so that additional precautions are not necessary.

The simplest and most obvious method of cooling the labyrinth seals during operation in air, namely to lead water into the labyrinth gaps, has the disadvantage of resulting in considerable losses which may be between 1 and 2% of the nominal power of the hydraulic machine, depending on the gap width and the quantity of water admitted. Despite these high losses, however, the admission of water has been absolutely necessary in the hitherto known embodiments of labyrinth seals, especially since, owing to practically unavoidable alignment errors, and furthermore owing to the necessary bearing play, possible deformation and displacement of the housing and so forth, there was a danger that the stationary and rotating parts of the labyrinth could come into contact with each other and therefore seize up.

SUMMARY OF THE INVENTION In a labyrinth seal of a hydraulic rotary machine, the runner of which rotates sometimes in water and sometimes in air, the invention is now based on the problem of taking steps to prevent metallic contact between the parts bounding the sealing gap and excessive heating during rotation in air, while dispensing with additional cooling.

This problem is solved according to the invention in that the relative position of the parts bounding the sealing gap on either side is variable from a position intended for rotation of the runner in water, in which the width of the sealing gap is comparatively small, to a position with increased gap width intended for rotation of the runner in air. This may be eifected by the non-rotating part bounding the sealing gap being displaceable in the machine housing and being connected to one or more servomotors by intermediate members, for example shift rods. It is possible in this way to advance this part to the working position for rotation of the runner in water "ice and to form the necessary narrow gap in this way. If the machine is to be operated in air, the displaceable part is moved by means of the servomotors until the sealing gap is sufficiently wide. Additionally, by suitable configuration of the parts concerned, for example by the provision of stops or the like, precautions may be taken to ensure that the parts may be moved together only to an extent such that the predetermined working position is observed. At the same time, owing to the small gap width, it is advantageous if the displaceable part in the working position always assumes the same position and is held firmly immovable in the machine housing. This may be done, for example, by means of a conical stop limiting the adjustment distance in the gap direction.

The servomotors necessary for actuating the slidable part of the labyrinth seal may be of any desired and known form. Thus, for example, hydraulically or pneumatically operated servomotors or even simple lever mechanisms or spindles driven by electric motor may be used.

In the operation of a hydraulic rotary machine with the labyrinth seal according to the invention, it is essential to provide the sealing gap with water during the varia tion of the relative position of the parts bounding the sealing gap on either side. Flooding of the sealing gap with water and hence any cooling which may be necessary should be interrupted only when the parts bounding the sealing gap on either side are in a position relative to each other such that the width of the sealing gap is large enough to prevent with certainty these parts from coming into contact with each other.

With the construction of the labyrinth seal according to the invention, it is possible substantially to reduce the power losses of the hydraulic machine during operation in the emptied condition, that is to say, therefore, during rotation of the runner in air. This is attributable to the fact that the said power losses mainly occur owing to the hitherto necessary supply of water to the gaps, as well as to rotor disc friction. In the application of the concept according to the invention, the only power loss remaining, apart from friction losses in the bearings, is the driving power necessary to overcome windage losses.

In addition to the reduction in the power losses, the construction of the labyrinth seal according to the invention is also accompanied by yet other advantages. Machine sets of usual type of storage pump installations comprise, as a rule, an electrical machine, which may be operated as generator and as motor, as well as a turbine and storage pump. During turbine operation, that is to say during peak current generation, the storage pump is as a rule uncoupled, because the power losses of the storage pump rotating in air with labyrinth seals supplied with water are so high that economic operation is frequently doubtful. In addition, cases are known in which obviously for the same reason the turbine is uncoupled during operation of the pump. In the case of reactive power operation (phase shifter operation), the storage pump is frequently uncoupled also for reducing the losses, the runner of the turbine rotating in air or being also uncoupled according to the type. The mechanical and constructional outlay as well as the outlay necessary for the control of the couplings or clutches is considerable. Apart from this, however, it is still necessary to provide each of the three machines of the pumped storage set with two bearings. Furthermore, if very short change-over times between the individual methods of operation are desired, it is necessary to provide a starting turbine or a hydraulic coupling between the electrical machine and storage pump for rapid acceleration of the storage pump. These devices, the couplings, starting turbines, hydraulic couplings and a certain number of bearings, may be dispensed with if the conception according a to the invention is used. The machine set of the storage pump installation may thus be limited to the three "principal machines, namely the electrical machine, turbine and storage pump. If the most rational arrangement is considered, a common shaft and two bearings suffice for three machine units. As a further consequence of the simplification, compared with the conventional construction, the substantially small space requirement must be mentioned, accompanied by correspondingly lower building costs.

A storage pump installation in which the rotary hydraulic machine or machines are provided with the labyrinth seals constructed according to the invention furthermore permits shorter change-over times between the individual methods of operation than can be realised with the conventional construction. This results from the following:

During turbine operation, the storage pump runs in air; I

during pump operation, the turbine runs in air; the change-over from turbine operation to pump operation and vice versa can only be done by the alternate filling and emptying of the hydraulic machine concerned.

In phase-shifter operation, both hydraulic machines are empty. The storage pump may be accelerated directly from stoppage in the water-filled condition or in the empty condition by putting the turbine into operation.

The subject of the invention may also be used advantageously in the case in which the machine set comprises a reversible pump turbine. Acceleration to pump operation is eifected as a rule in known manner by means of a separate rigidly coupled electric starting motor with the pump turbine empty, the runner rotating in air. The size or design of the starting motor depends, among other things, also on the power loss of the runner rotating in air. With the conception of the labyrinth seal according to the invention, these losses may be substantially reduced, so that the starting motor may be designed for a lower power. This is particularly important if suflicient time is available for acceleration in pump operation, so that starting motor torque to be applied may be relatively small. In addition, the losses occurring during phase-shifter operation, which occur as is known in the empty pump turbine, are also substantially reduced.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiment examples of a labyrinth seal according to the invention for a hydraulic rotary machine are represented in the drawings, in which FIG. 1 shows a diagrammatic longitudinal section through the rotary machine in the region of the labyrinth seals, the parts bounding the sealing gaps being in the position intended for rotation of the runner in water, and

FIG. 2 shows the same longitudinal section, in which, however, the parts bounding the sealing gaps are in the position intended for rotation of the runner in air.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The rotary machine, shown only partly in the drawings, may be a Francis turbine, a centrifugal pump or a reversible pump turbine. On the hub side, the runner 1 is sealed by means of a comb-like labyrinth seal 2, and on the rim side by means of a stepped labyrinth seal 3 relative to the stationary parts 4, 5 and 6, 7, respectively, of the housing. The comb-like seal 2 has a sealing gap 8 on one side only of the combs, while a larger gap 8' is provided on the other side. At 9 is shown the sealing gap of the labyrinth seal 3.

On the housing side, the sealing gaps 8 and 9 are bounded by nonrotating annular parts 10 and 11, axially displaceable in the housing parts 5 and 7, respectively, and connected by intermediate members 12 to one or more hydraulic or pneumatic servomotors 13. At 14 are shown seals on the guide surfaces, denoted by 16, of the housing parts 5 and 7. On the runner side, the bounda- .ries of the sealing gaps 8 and 9 are formed directly by corresponding coaxial annular parts 15 of the runner hub and runner rim, respectively."

Each of the servomotors 13 consists of a housing 17 and a piston 18 slidable therein and rigidly connected to the corresponding intermediate member 12. In the housing 17, chambers 19 and 20 are provided on either side of the piston 18 and are adapted to be connected by ducts 21 and 22 via control valves, not shown, to a pressure fluid source. The parts 10 and 11 may be moved by means of the servomotors 13 in the axial direction of the machine between two end positions, one of which is shown in FIG. 1 and the other in FIG.

The end position according to FIG. 1 is intended for normal operation of the machine, in which the runner 1 rotates in water, the width of the sealing gaps 8 and 9 being then comparatively small. To ensure that, at each of the seals 2 and 3, the displaceable parts 10 and'11 always assume the same position in both axial and radial directions, each of these parts is equipped with a centering stop, provided with a conical surface 24, which in the position according to FIG. 1 bears on a corresponding conical surface 23 of the housing parts 4 and 6, respectively, thus ensuring non-play connection with the machine housing.

The parts 10 and 11 are constructed as annular pistons, and in the position according to FIG. 1 bound with the housing 4, 5 and 6, 7, respectively, an annular chamber 25 communicating via one or more ducts 26 with the pressure water space 27 of the machine. The effect of this step is that during operation with water in the position according to FIG. 1, the parts 10 and 11 are forced automatically by the water pressure in the annular chambers 25 against the stop surfaces 23 of the housing. The servomotors 13 have then only to be designed for producing the forces necessary for the displacement of the parts 10 and 11.

For the operation with rotation of the runner 1 in air', the parts 10 and 11 are brought into the position shown in FIG. 2 by means of the servomotors 13. As will be seen, the sealing gaps 8 and 9 are bounded by stepped cylindrical surfaces. In the position according to FIG. 2, the parts 10 and 11, with reference to the position according to FIG. 1, have been moved in the axial direction away from the runner 1 by an amount corresponding substantially to the axial length of a step. The gap width has thus been increased in each case by the amount of one step height. The riskv of the sealing parts 15 ofthe rotor 1 coming into contact with the non-rotating sealing parts 10 and 11 is thus precluded in any case, and there also occurs substantially less heating of the air in the gaps than would be obtained with the narrow sealing gaps in the position according to FIG. 1.

To permit supply of water to the sealing gaps 8 and 9 during sliding of the parts 10 and 11, ducts 28 leading respectively to the sealing gaps 8 and 9 are provided, these ducts being in communication with a longitudinal bore passing through the intermediate member 12. The longitudinal bore of the member 12 in turn is connected to a chamber 29, recessed in the servomotor housing 17 and adapted to be charged from outside with pressure water.

The pressure water supplied passes through the bore in the intermediate member 12 and the duct 28 as coolant to the sealing gaps 8 and 9, respectively. During the movement of the displaceable parts 10, 11 away from the runner 1, the water supply should continue until the position shown in FIG. 2 is reached, that is to say, until the gap has been increased. Conversely, on the return of the parts 10, 11 to the position shown in FIG. 1, the pressure'water supply should be interrupted only when the hydraulic rotary machine has been filled with water for actualoperation.

A variation in the width of the sealing gaps 8 and 9 on displacement of the parts 10 and 11 would also be obtained if the sealing gaps 8 and 9 were to be bounded by conical surfaces instead of stepped cylindrical surfaces. A width of sealing gap, sufiicient for operation of the runner in air, would then possibly be obtained even for a smaller variation in position of the displaceable part than in the case of the stepped boundary surfaces.

Labyrinth seals with sealing gaps bounded by conical surfaces, however, have been found to be particularly disadvantagous in practice, especially in the case of large hydraulic machines, because their sealing efrect varies appreciably even with slight axial displacement of the runner. Continuous variation of the width of the sealing gap and therefore also of the efiiciency of the machine and of the axial thrust may occur in operation. For this reason, in a labyrinth seal according to the invention, stepped cylindrical boundary surfaces are to be preferred for the sealing gap.

I claim:

1. In a hydraulic rotary machine operable in either of two conditions, namely a water-filled condition and an air-filled condition, said machine comprising a housing; a runner arranged for rotation in said housing; means defining a water fiow path leading through said housing and said runner; at least one labyrinth, seal formed by a annular part of said runner and a coaxial non-rotating annular part of said housing arranged to bound a gap between one another; said annular parts of the runner and the housing being shiftable axially relatively to one another; and stop means preventing axial movement of said annular parts into contact with each other and effective in the water-filled condition of the machine to establish a predetermined minimum sealing gap between said annular parts, and effective in the air-filled condition of the machine to establish a predetermined larger gap.

2. The machine defined in claim 1 in which said nonrotating part is mounted in the machine housing so as to be displaceable in the axial direction of the machine between said stop means; and servo means for the displacement'of said non-rotating part.

3. The machine defined in claim 1 in which said parts bounding the gap have stepped cylindrical surfaces and are axially shiftable between the stop means a distance exceeding the axial length of one step.

4. The machine defined in claim 2; and a centering stop provided for ensuring play-free connection of the displaceable non-rotating part to the machine housing in the position intended for rotation of the runner in water.

5. The machine defined in claim 2 in which said displaceable non-rotating part is formed as an annular piston, and in the position intended for rotation of the runner in water bounds with the housing an annular space supplied with pressure water and holding the non-rotating part against the then effective stop means.

6. The machine defined in claim 5 in which said annular space communicates with the high-pressure side of the water flow path of the machine.

7. The'method of operating a hydraulic rotary machine of the type including a housing, a runner arranged for rotation in the housing, a water flow path through said housing and runner, a labyrinth seal formed by an annular part of the runner and a coaxial non-rotating annular part of the housing which bound a sealing gap therebetween, said annular parts being axially shiftable relatively to one another to vary the radial width'of said gap, which method comprises (a) operating said machine water-filled with a predetermined sealing gap between said annular parts and with the gap water-filled; and

(b) operating said machine air-filled with a larger gap between said annular parts and with the gap air-filled.

8. The method of operating the hydraulic rotary machine defined in claim 7 which comprises supplying water to said sealing gap during variation of the relative position of said two parts bounding the sealing gap.

References Cited UNITED STATES PATENTS 1,823,702 9/1931 Ring. 3,174,719 3/1965 Sproule et al. 253-26 3,226,083 12/1965 Braikevitch et a1. 2 53-26 3,330,532 7/1967 Willi 253-26 FOREIGN PATENTS 599,264 10/1925 France. 1,074,886 4/1954 France.

EVERE'ITE A. POWELL, JR., Primary Examiner US. Cl. X.R. 415-1, 171

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