Steam turbine control diaphragm

Abstract

Steam turbine control diaphragm having a fixed part formed by fixed parts (1) of vanes arranged at a pitch (t), while the channels between fixed parts (1) of the vanes have a width (c) at the inlet into the fixed part, and a rotatable part of the diaphragm formed by the leading edges (2) of the vanes, while the rotatable part of the diaphragm is rotatable with respect to the fixed part of the diaphragm for the gradual closing of the channels between the fixed parts (1) of the vanes, whereby the width of the fixed parts (1) of the vanes at the inlet into the fixed part is n times the width (c) of the channels plus eventual overlap (p), where n is a natural number greater than 1, and the leading edges (2) of the vanes of the rotating part are of n types: the first type, having a width that is the same as the width of the fixed parts (1) of the vanes at the inlet into the fixed part, the second type, having a width of (n-l)-multiple of the width (c) of the channels between the fixed parts (1) of the vanes plus eventual overlap (p), and so on, up to the nth type, having a width equal to the width (c) of the channels between the fixed parts (1) of the vanes plus eventual overlap (p). The leading edges (2) of the vanes of the rotatable part are spaced so that - in the fully open state all the leading edges (2) are, with their sides that are backward in the direction of rotation of the rotatable part during closing, in alignment with the edges of the corresponding fixed parts (1) and all the channels are open,- in the state after turning by the width (c) of the channels between the fixed parts (1) of the vanes in the direction of rotation of the rotatable part during closing- the leading edges of the first type close the channels adjacent in the direction of rotation and remaining channels are open, and- the leading edges of the second type are, with their sides that are frontal in the direction of rotation, in alignment with the edges of the corresponding fixed parts (1)- in the state after turning by the double width (c) of the channels between the fixed parts (1) of the vanes in the direction of rotation of the rotatable part during closing- the leading edges of the first and second type close the channels adjacent in the direction of rotation and remaining channels are open, and- the leading edges of the possible third type are, with their sides that are frontal in the direction of rotation, in alignment with the edges of the corresponding fixed parts (1), and so on, until- in the state after turning by n times the width (c) of the channels between the fixed parts (1) of the vanes in the direction of rotation of the rotatable part during closing, all channels are closed.

Description

[0001] Steam turbine control diaphragm

[0002] Technical field

[0003] This invention relates to a control diaphragm of a steam turbine. The control diaphragm is a device used to control the pressure in a controlled extraction. Its task is to maintain the pressure in the wide range of operating modes when the amount of extracted steam and thus the amount of steam passing through the flow path of the turbine downstream of the extraction also changes. Controlled extraction, i.e. the extraction of steam from the flow path of the turbine, is carried out e.g. in district heating plant turbines where the extraction heats the heating water heaters. The outlet temperature from the heater is dependent on the extraction pressure and must be maintained even with a very variable amount of heated water and thus also the amount of steam taken from the turbine. There are also various industrial processes that need constant extraction parameters with a variable amount of steam into the extraction.

[0004] Background Art

[0005] Maintaining the desired pressure in the extraction with changing flow rate is a technical problem. With the change of the extracted amount, the amount of medium flowing into the flow path in the direction of the main flow downstream of the extraction also changes, which leads to the fact that, according to the laws of physics, the pressure in the extraction changes, and therefore it is necessary to add a control body for the extraction, which will limit pressure fluctuations in the extraction. This is achieved by adapting the flow area of the control body to the residual flow downstream of the extraction. For example, a control seat valve or seat valves, that can be closed and opened as needed, can be used. Other possible solutions are control flaps or slide valves.

[0006] A special case of a rotary slide valve is the control diaphragm. Like any rotary valve, the control diaphragm is also made up of a fixed and a rotatable part. Here, however, the fixed and rotatable part are formed by parts of the stage stator blade row, the blades of which are cut into two parts:

[0007] 1) parts of the blades at the trailing edges firmly connected to the stator, as in conventional (non-control) stages, also referred to as fixed parts, and

[0008] 2) parts containing leading edges connected by two rings at the hub and tip into a grid allowing rotational movement with respect to the stator (and thus with respect to the fixed parts) around the axis of the diaphragm. This rotatable part is controlled by a control mechanism.

[0009] Control diaphragms are known for both axial and radial, and also for radial-axial stages. In the case of the stator guiding blade row of the axial stage of the steam turbine, the blades are cut by a plane perpendicular to the axis of the diaphragm. In the case of a stage with a radial or radial-axial stator blade row, the blade row is cut into two parts by a cylindrical surface with an axis identical to the axis of the diaphragm.

[0010] By changing the mutual position of these two parts, the channels between the blades close or open, which changes the flow area of the diaphragm. As a result, it is possible to maintain the required pressure in the space upstream of the diaphragm even if a large amount of steam is taken from it and only a small remaining amount of steam flows through this diaphragm.

[0011] When the flow area in the control body is reduced due to pressure control in the extraction, the medium must accelerate significantly in the reduced cross-section. In most control bodies, a large cross-section dimensioned for maximum flow follows further downstream (e.g. a pipe downstream of a seat valve or flap). In it, the flow slows down again, which usually means the conversion of a large part of the kinetic energy into heat, which can no longer be used for mechanical work. This process is called throttling and the loss associated with it is called throttling loss. However, the control diaphragm has a narrowed area in the stator blade row, which is very close to the rotor blade row. The steam flow thus loses only a small part of its kinetic energy, and it is immediately directed in the required circumferential direction by the trough side (pressure side) of the fixed part of the stator. Due to inertia, it then reaches the rotor blades, which convert the kinetic energy into mechanical work. Thus the control diaphragms have better efficiency than other throttling control bodies. Compared to other control bodies, the control diaphragm also takes up less space in the axial direction, because it connects directly to the flow path at its inlet and outlet and it also functions as a part of the turbine stage itself. If the pressure at the extraction point is controlled by a seat valve or flap, there must be space to bring the steam to the seat valve / flap and then to take it back to the flow path.

[0012] The usual and most frequently used control diaphragm is described, for example, in the document US 5799927. When moving the leading edges from a completely open position, the channels between the blades are gradually closed, and it is thus possible to continuously control the steam flow through the diaphragm until the channels are completely closed, and the leading edges completely close the inter-blade channels.

[0013] Such a standard design of the diaphragm has a minimal loss at full opening, when the rotatable and the fixed part of the stator grid connect to each other. However, with partial opening, losses occur on the route between throttling and the rotor blades. In the partially open state, the flow separates downstream of the leading edge, and the resulting vortices are then transferred to the rotor blade row and to other stages and significantly reduce the efficiency of the turbine, see e.g. Lampart P., Puzyrewski R., Numerical analysis of adaptive control in LP turbines, TASK Quarterly, vol. 9, No. 2, pp. 211 - 234, 2005.

[0014] For example, in the case of cogeneration turbines, the most important operation is just in the partially open state.

[0015] In some cases, higher efficiency can be achieved by using a common control stage with several seat valves, each of which is connected to a group of inter-blade channels (or nozzles), while the individual groups are separated from each other. The gradual opening of seat valves also changes the flow area of the stage and creates the effect of the so-called nozzle governing, i.e. governing by groups of inter-blade channels (or nozzles), when it is possible to achieve the elimination of losses by throttling at the so-called valve points in which part of seat valves are fully open and remaining seat valves are completely closed and thus do not generate any losses. With such an arrangement, the control stage connected to the seat valves has a higher efficiency under partial load in the vicinity of the valve points than a partially open control diaphragm. Thus, for turbines where partial operation is of great importance, a multivalve arrangement may be more advantageous than the known control diaphragm.

[0016] Another solution is known from document EP2014876. According to this solution, the channel, which is divided by the blade 14 into two parts, is partially covered, so that in the partially closed state one of these two parts is covered and one is open.

[0017] In this solution, however, it is not a classic control diaphragm formed by a cut stator blade row, but rather a control slide valve formed by a wall without flow-optimized trailing profiles (it is only supplemented with blades 14). As such, this solution is flow inefficient in both fully open and partially open states. In addition, it is difficult to be designed to achieve the required parameters, and it is complicated to manufacture.

[0018] Another major disadvantage of this solution is that it does not control continuously along the entire travel path of the rotatable part: in the part of the movement where the edge of the rotatable part passes over the intermediate profile 14, the flow through the diaphragm does not change, and the diaphragm therefore does not control at all in this portion. This is a very unpleasant feature from the point of view of controlling the machine.

[0019] Other known solutions (various mechanical tilting or turning of individual blades, etc.) are far more complicated and expensive not only for manufacturing, but especially for maintenance. Due to their complexity, such solutions also have a very high failure rate.

[0020] Disclosure of the invention

[0021] The aim of this invention is therefore to improve the design of the control diaphragm in such a way as to improve its efficiency in a partially open state, to also enable nozzle governing if possible, and at the same time to make its design simple and trouble-free.

[0022] This goal is achieved by the control diaphragm according to claim 1. Advantageous embodiments are the subject of dependent patent claims. According to the invention, the circumferential width of the fixed parts of the blades is n times the width (c) of the channels plus eventual overlap (p), where n is a natural number greater than 1. The width (c) of the channels in this text will always denote the width of the channel at the fixed part inlet. According to the invention, the leading edges of the blades of the rotatable part are of n different types, while the leading edges of all following types are arranged: the first type, having a width (bi) which is the same as the width of the fixed parts of the blades, the second type (b?), having a width (n-1) times the width (c) of the channels between the fixed parts of the blades plus eventual overlap (p), and so on, up to the nth type, having a width (bn) equal to the width (c) of the channels between the fixed parts of the blades plus eventual overlap (p). Thus: bi = n * c + p b? = (n-1) * c + p bn- (n-(n-l)) * c + p - c + p.

[0023] At the same time, the width of the fixed parts of the blades plus the width of the inter-blade channel together gives the pitch (t) of the blades, i.e. t = bi + c.

[0024] Therefore, if we start from the pitch (t) of the blades, for example when designing such a control diaphragm, it is possible to derive the width (c) of the channels, for a selected natural number n > 1, according to the relationship: c = (t - p) / (n + 1)

[0025] It is obvious that, in order to completely close the diaphragm, the width of all leading edges (even the narrowest ones) must be at least as wide as the width of the respective interblade channel, and must not be smaller. This fact is described using parameter (p), indicating eventual overlap. The situation where the narrowest leading edge is exactly the same as the width of the corresponding inter-blade channel, and the overlap is therefore zero, is described by the value of the parameter p = 0. From the point of view of tightness of the control diaphragm in the closed state, however, it is advantageous if the overlap is non-zero, i.e. p > 0. Optimal closure will thus occur in the state after turning in the direction of rotation of the rotatable part when closing by n*c+p / 2, however, the diaphragm is fully closed at any turning from n*c to n*c+p. The overlap p thus represents a kind of dimensional margin preventing leaky closure in case of inaccurate turning of the rotatable part of the control diaphragm or in case of its inaccurate misalignment with respect to the fixed part.

[0026] At the same time, however, it is advantageous that this overlap is not too large, because from an aerodynamic point of view it should be as small as possible so as not to unnecessarily reduce the width of the channels.

[0027] Values of overlap (p) around 3 mm have proven to be particularly advantageous. An overlap of 1.5 mm (=3 mm / 2) on both sides of the leading edge is such that, with sufficient margin, a tight seal is reliably ensured when fully closed.

[0028] With larger profile dimensions, the optimal value of the overlap (p) can reach up to 6 mm, for the largest profiles up to 8 mm. However, larger overlaps are also possible.

[0029] At the same time, the leading edges of the blades of the rotatable part according to the invention are distributed in such a way that

[0030] - in the fully open state, all the leading edges (2) are, with their sides that are backward in the direction of rotation of the rotatable part during closing, in alignment with the edges of the respective fixed parts (1) (i.e. they align smoothly with them) and all channels are open,

[0031] - in the state after turning by the width (c) of the channels between the fixed parts (1) of the blades in the direction of rotation of the rotatable part during closing

[0032] - the leading edges of the first type close the channels adjacent in the direction of rotation and remaining channels are open, and

[0033] - the leading edges of the second type are, with their sides that are frontal in the direction of rotation, in alignment with the edges of the corresponding fixed parts (1),

[0034] - in the state after turning by twice the width (c) of the channels between the fixed parts (1) of the blades in the direction of rotation of the rotatable part during closing - the leading edges of the first and second type close the channels adjacent in the direction of rotation and remaining channels are open, and

[0035] - the leading edges of the possible third type are, with their sides that are frontal in the direction of rotation, in alignment with the edges of the corresponding fixed parts (1), and so on, until

[0036] - in the state after turning by n times the width (c) of the channels between the fixed parts (1) of the blades in the direction of rotation of the rotatable part during closing, all channels are closed.

[0037] Opening takes place analogously gradually in the opposite order when turning in the opposite direction.

[0038] This solution makes it possible to achieve the effect of nozzle governing even for the control diaphragm and to optimize its efficiency for partial opening.

[0039] By appropriately choosing the number n and the number of leading edges of each of these n different types and by grouping them, it is possible to set the governing characteristics in order to optimize the expected most probable operating modes according to the specific use of the steam turbine, in particular the optimization of the flow at the assumed most frequent operating flow rates, which may for example correspond to the positions, when a part of the channels is fully open and the remaining part of the channels is fully closed - this eliminates the disadvantages associated with flow separation downstream of the edge of the leading part when the channels are only partially opened.

[0040] With different ratios of the number of leading edges of different widths, the diaphragm can be adjusted to the flow rate at which the highest efficiency is needed. Different leading edges can advantageously be arranged alternately, for example one by one of each type, or with different numbers of leading edges of different types, or they can be arranged in larger groups, which makes it possible to have undisturbed flow and smaller losses at least in part of the stage circumference (then it is necessary to create a sufficiently large gap between the stage with the diaphragm and the stage downstream of it in the direction of the steam flow, so that, when partially opened, the steam flow from the group of open channels can flow into space downstream of closed channel groups). This de facto makes it possible to use the advantages of nozzle or group governing even in the case of a control diaphragm, and the solution according to the present invention thus combines the advantages of these two known solutions.

[0041] In one advantageous embodiment, n=2, i.e. the width of the fixed parts of the blades is twice the width of the channels between these blades (plus eventual overlap p), the leading edges of the first type have the width of the fixed parts of the blades and the leading edges of the second type have the width of the channels (plus eventual overlap p). This embodiment has, while maintaining the advantages of the solution according to the present invention, the largest channel width.

[0042] In another advantageous embodiment, n=3, i.e. the width of the fixed parts of the blades is three times the width of the channels between these blades (plus eventual overlap p), the leading edges of the first type have the width of the fixed parts of the blades, the leading edges of the second type have a width twice the width of the channels (plus eventual overlap p), and the leading edges of the third type have the width of the channels (plus eventual overlap p). This embodiment has the advantage that two partial closure modes are available, in which a part of the channels is completely closed and the remaining part of the channels is completely open. It is thus possible to propose two optimized modes of partial closure of the control diaphragm.

[0043] The number n can be even higher, but with a higher value of n, the channels shrink quickly, and such systems have an optimal operating mode or modes only with larger steam extractions upstream of the diaphragm.

[0044] Of course, such a control diaphragm with nozzle governing also has its disadvantages - in addition to slightly more complicated to manufacture than the known standard control diaphragm, it is primarily the fact that when fully opened, the narrow leading edges do not fully align with the fixed parts of the blades, and therefore this diaphragm has slightly increased losses compared to a standard diaphragm. However, this disadvantage is significantly outweighed by the advantages of this invention in the area of partial opening, when in machines where such modes are required and are of great importance to the operator, it is possible to achieve an enormous gain in efficiency by using a diaphragm designed according to this invention.

[0045] Figures of drawings

[0046] The invention will be explained in more detail by means of specific examples of embodiments shown in the drawings in which it represents

[0047] Fig. 1 longitudinal section of an axial stage with a control diaphragm,

[0048] Fig. 2 one embodiment of the diaphragm according to the invention for an axial stage, in an unfolded partial section through a cylindrical surface with an axis identical to the axis of the diaphragm, in the fully open position,

[0049] Fig. 3 diaphragm from fig. 2, in an unfolded partial section through a cylindrical surface with an axis identical to the axis of the diaphragm, in the partially open position.

[0050] Fig. 4 diaphragm from Fig. 2, in an unfolded partial section through a cylindrical surface with an axis identical to the axis of the diaphragm, in the fully closed position,

[0051] Fig. 5 another embodiment of the diaphragm according to the invention for the axial stage, in an unfolded partial section of a cylindrical surface with an axis identical to the axis of the diaphragm, in the fully open position,

[0052] Fig. 6 another embodiment of the diaphragm according to the invention for an axial stage, in an unfolded partial section through a cylindrical surface with an axis identical to the axis of the diaphragm, in three different positions, from top to bottom: fully open, partially open and closed, and Fig. 7 longitudinal section of a radial-axial stage with a control diaphragm with a radial blade row.

[0053] Embodiments of the invention

[0054] Fig. 1 shows a partial longitudinal section of an axial stage with a control diaphragm. The blade profiles are made up of two parts: the fixed parts 1, which are firmly connected to the stator, and the leading edges 2. The leading edges are connected by two rings 3, 4 at the hub and at the tip, forming a grid that can rotate with respect to the fixed parts 1.

[0055] A partial section through the cylindrical surface with an axis identical to the axis of the diaphragm according to Fig. 2 to 6 is taken in one selected place of the control diaphragm between the two rings 3, 4 at the hub and at the tip. Although the shape of the blades is usually not constant along their entire length, the profiles on the smaller inner diameter are usually axially and circumferentially smaller than the profiles on the larger outer diameter, in order to compensate for the blades pitch which is proportional to the diameter. However, the dimensions ratios designed according to this invention are preferably applicable to all positions of the cylindrical surface between the two rings 3, 4 on the hub and on the tip.

[0056] Fig. 2 to 4 represent an advantageous embodiment of the control diaphragm according to the present invention with two types of leading edges (n = 2) - part of the leading edges has the same circumferential width as the fixed part 1 and in the fully open position it smoothly aligns with it (wide leading edges 2a), the other part, however, is half the circumferential width and in the fully open position smoothly aligns only with the pressure or trough side of the fixed parts 1 of the blades (narrow leading edges 2b). As can be seen in particular in Fig. 2 and 3, the channels between the leading edges are also of two types - those adjacent to the suction sides of the wider leading edges have the same width as the channels between the fixed sections of the profiles, while those adjacent to the suction sides of the narrower leading edges have a width equal to double width of the channel between the fixed parts of the profiles. In this embodiment, the blade profile of the diaphragm therefore has, in the plane of cutting into the fixed and rotatable part, a thickness slightly greater than 2 / 3 of the pitch. Less than 1 / 3 of the pitch remains for the inter-blade channel. This is best seen by comparing Figures 2 and 4.

[0057] When closing this control diaphragm from a fully open state, first the wide leading edges 2a gradually close the channels adjacent to them. At the moment of their complete closure, the channels adjacent to the narrow leading edges 2b are still fully open, and the flow passing through them is not throttled in any way and therefore works without throttling loss (Fig. 3). At this moment, the narrow leading edges 2b smoothly align with the suction side of the fixed parts 1.

[0058] The control diaphragm is optimized for this flow rate. By choosing the number of leading edges of these two types and grouping them, it is possible to adapt this flow rate to the most likely operating mode of the steam turbine. Only during further closing process will the narrow leading edges 2b begin to close the remaining channels and gradually the diaphragm will be completely closed (Fig. 4).

[0059] Fig. 5 shows another advantageous embodiment, which includes three different types of leading edges (n - 3). At the moment of complete closure of the wide leading edges 2a, the channels adjacent to the remaining types of leading edges 2b and 2c are still fully open. This position represents the first optimal mode of partial closure of the control diaphragm. At the moment of complete closure of the leading edges 2a and 2b, the channels adjacent to the leading edges 2c are still fully open. This position represents the second optimal mode of partial closure of the control diaphragm. By choosing the number of leading edges of these three types and grouping them, it is possible to adapt these two optimal modes to the most probable operating modes of the steam turbine. Only during further closing process will the third leading edges 2c begin to close the remaining channels and gradually the diaphragm will be completely closed.

[0060] This second embodiment thus enables optimization for multiple operating modes. However, the price for this is a relatively (compared to the width of the inter-blade channels) larger circumferential width (of fixed parts) of the blades. Therefore, they have worse properties of the diaphragm in a completely open state, and optimal operating modes are only achieved with larger steam extractions upstream of the diaphragm.

[0061] Fig. 6 shows another advantageous embodiment according to claim 3. In this case, the leading edges of the same type are arranged in groups. There can be one such group or more groups from each type of leading edge on a wheel. The number of leading edges in the group again allows the design of the control diaphragm to be adapted to the customer's requirements for flow rates through the diaphragm in operations important to him. This arrangement is advantageous in operations where there are open channels downstream of one type of leading edges and closed channels downstream of an adjacent type of leading edges. Through the gap between the stator and rotor blades, the spaces downstream of the group with open channels are connected to the space downstream of the closed channels only at the fringes of the open group (or groups). Compared to the alternating arrangement of individual types of leading edges, less steam escapes from the open channels through the above-mentioned gap into the rotating blades downstream of the closed channels, and as a result, there is a smaller loss of kinetic energy and a smaller reduction in the efficiency of the diaphragm associated with it. On the other hand, downstream of the stage with a diaphragm with leading edges arranged in groups, the flow field is much more uneven and it is necessary to leave a larger gap downstream of the diaphragm in front of the downstream stage, so that the steam can flow from the rotor blades downstream of the open channels of the diaphragm into the space downstream of the closed channels of the diaphragm. Greater unevenness of the flow would cause greater losses in the blade rows of the stages downstream of the diaphragm.

[0062] The embodiments shown in drawings 1 to 6 relate to examples for axial stages, where in figures 2 to 6 partial sections of a cylindrical surface with an axis identical to the axis of the diaphragm (and the entire turbine) are shown, unfolded into the surface of the drawing.

[0063] However, it is obvious that the same arrangement of leading edges of different types can be implemented analogously for radial and radial-axial turbine stages. Fig. 7 shows a partial longitudinal section of an example of a radial-axial stage with a control diaphragm with a radial blade grid. Neglecting the curvature of the radial control diaphragm (i.e. as if the rotor had an infinite diameter) even the relevant blade sections would look the same as in Figs. 2 to 6, only (instead of section of a cylindrical surface with an axis identical to the diaphragm axis) it is necessary to consider a plane section perpendicular to the axis of the diaphragm (and the entire turbine).

[0064] Reference signs list

[0065] 1 fixed part (of the blades of the control diaphragm)

[0066] 2 leading edge (of the blades of the control diaphragm)

[0067] 2a leading edge (of the first type, or wide leading edge)

[0068] 2b leading edge (of the second type, or narrow leading edge)

[0069] 2c leading edge (of the third type if applicable)

[0070] 3 ring (connecting the leading edges of the control diaphragm at the tip)

[0071] 4 ring (connecting the leading edges of the control diaphragm at the hub)

Claims

CLAIMS1. A steam turbine control diaphragm, having- a fixed part of the diaphragm formed by fixed parts (1) of the blades arranged with a mutual pitch (t), whereby the channels between the fixed parts (1) of the blades have a width (c) at the inlet, and- a rotatable part of the diaphragm, formed by leading edges (2) of the blades, whereby the rotatable part of the diaphragm is, for the gradual closing of the channels between the fixed parts (1) of the blades, rotatable with respect to the fixed part of the diaphragm, characterized in that the width of the fixed parts (1) of the blades is n times the width (c) of the channels plus eventual overlap (p), where n is a natural number greater than 1, whereby the leading edges (2) of the blades of the rotatable part are of n types:- of first type, having a width (bi) that is the same as the width of the fixed parts (1) of the blades, i.e. bi = n * c + p,- of second type, having a width (n-1) times the width (c) of the channels between the fixed parts (1) of the blades plus eventual overlap (p), i.e. b2 = (n-1) * c + p, and so on, until- of nth type, having a width equal to the width (c) of the channels between the fixed parts (1) of the blades plus eventual overlap (p), i.e. bn— C + p, and are spaced so that- in the fully open state all the leading edges (2) are, with their sides that are backward in the direction of rotation of the rotatable part during closing, in alignment with the edges of the corresponding fixed parts (1) and all the channels are open,- in the state after turning by the width (c) of the channels between the fixed parts (1) of the blades in the direction of rotation of the rotatable part during closing- the leading edges of the first type close the channels adjacent in the direction of rotation and remaining channels are open, and- the leading edges of the second type are, with their sides that are frontal in the direction of rotation, in alignment with the edges of the corresponding fixed parts (1)- in the state after turning by the double width (c) of the channels between the fixed parts (1) of the blades in the direction of rotation of the rotatable part during closing- the leading edges of the first and second type close the channels adjacent in the direction of rotation and remaining channels are open, and- the leading edges of the possible third type are, with their sides that are frontal in the direction of rotation, in alignment with the edges of the corresponding fixed parts (1), and so on, until- in the state after turning by n times the width (c) of the channels between the fixed parts (1) of the blades in the direction of rotation of the rotatable part during closing, all channels are closed.

2. The control diaphragm according to claim 1, characterized in that the leading edges (2) of the blades of the rotatable part are arranged alternately regularly around the entire circumference of the control diaphragm, i.e., the leading edge (2a) of the first type is followed by the leading edge (2b) of the second type, followed by possible leading edge (2c) of the third type, and so on, until the leading edge of the (n-l)th type being followed by the leading edge of the nth type, next to which the leading edge (2a) of the first type follows again, and so on around the entire circumference of the control diaphragm, whereby the number of leading edges of different types is the same.

3. The control diaphragm of claim 1, characterized in that the leading edges (2) of the blades of the rotatable part are arranged in groups according to individual types, i.e. next to a group of several leading edges of one type, there is a group of several leading edges of another type, and so on around the entire circumference of the control diaphragm, whereby the blades of one of each type can be all together in one group, or they can be divided into several groups.

4. The control diaphragm according to any of the preceding claims, characterized in that the overlap (p) is non-zero, i.e. p > 0.

5. The control diaphragm according to claim 4, characterized in that p > 3 mm.

6. The control diaphragm according to any of the preceding claims, characterized in that p < 8 mm, preferably p < 6 mm.

7. The control diaphragm according to any one of claims 1 to 6, characterized in that the leading edges (2) of the blades of the rotatable part are of two types, i.e. n = 2, and thus:- leading edges (2a) of the first type have a width that is the same as the width of the fixed parts (1) of the blades bi - 2 * c + p- leading edges (2b) of the second type have the width (c) of the channels between the fixed parts (1) of the blades plus eventual overlap (p), b2 = c + p.

8. The control diaphragm according to any one of claims 1 to 6, characterized in that the leading edges (2) of the blades of the rotatable part are of three types, i.e. n = 3, and thus:- leading edges (2a) of the first type have a width that is the same as the width of the fixed parts (1) of the blades, bi = 3 * c + p- leading edges (2b) of the second type have a width bz = 2 * c + p- leading edges (2c) of the third type have the width (c) of the channels between the fixed parts (1) of the blades plus eventual overlap (p), bs = c + p.

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