System and method for controlling the sealing of the upstream purge cavity of a turbomachine

Abstract

The invention relates to a system (10) for controlling the sealing of the upstream purge cavity of a turbomachine (1) which comprises a low-pressure turbine (90) comprising a plurality of discs (91) and an internal ring (99) secured to the discs (91), the discs (91) and the internal ring (99) delimiting the upstream purge cavity (80), each of the discs (91) being assembled to the adjacent disc (91) by an inter-disc connection (50) located in the upstream purge cavity (80). The system (10) comprises a vacuum pump (11), a flow measurement device (12) and a side wall (13), and is capable of being assembled on the turbomachine (1) so as to seal a portion (81) of said upstream purge cavity (80) which is delimited upstream by the side wall (13) and which contains at least one of the inter-disc connections (50), and the flow measurement device (12) is capable of measuring the leakage flow rate from the portion (81). Figure 2

Description

Title of the invention: System and method for controlling the sealing of the upstream purge cavity of a turbomachine

[0001] The present invention relates to a turbomachine 1, as illustrated in [Fig. 5]. A turbomachine 1 with longitudinal axis X (axis of rotation) comprises a nacelle 2 with a fan 3 comprising blades which forms an opening for the admission of a determined flow of air towards the engine. The turbomachine 1 comprises, downstream of the fan, a compressor 4 which serves to compress the air (generally this compressor 4 comprises, upstream, a low-pressure compressor 4a and downstream, a high-pressure compressor 4b). The air thus compressed is admitted into the combustion chamber 5 and mixed with fuel before being burned therein. The hot combustion gases resulting from this combustion are then expanded in the different turbine stages by passing into a turbine vein V. A first expansion is made in a high-pressure turbine 6 which is located immediately downstream of the combustion chamber 5 and which receives the gases at the highest temperature.The gases are expanded again by being guided through a low-pressure turbine 90 located downstream of the high-pressure turbine 6. The high-pressure turbine 6 comprises at least one stage E and the low-pressure turbine 90 comprises several stages E, these stages E being located in the turbine duct V. Each stage E consists of a row RF of fixed turbine blades, also called a nozzle, followed by a row RM of mobile turbine blades spaced circumferentially around the longitudinal axis X. The turbomachine 1 also comprises a rotor 7 whose axis of rotation is the longitudinal axis X. The mobile turbine blades of the high-pressure turbine 6 and the low-pressure turbine 90 are integral with the rotor 7. Thus, the rotation of these mobile turbine blades rotates the rotor 7 which in turn rotates the low-pressure compressor 4a, the high-pressure compressor 4b and the blades of the fan 3.The rotation of the blades of the fan 3 contributes, with the high-speed ejection of the gases leaving the combustion chamber 5, to the propulsion of the turbomachine 1.

[0002] [Fig. 6] is an enlarged view of region R of [Fig. 5] which includes a portion of the low pressure turbine 90 and the high pressure turbine 6. Each row RF of fixed turbine blades deflects the gas flow exiting the combustion chamber 5 toward the movable turbine blades RM at a suitable angle and speed to rotate these movable turbine blades. Thus, for the low pressure turbine 90, each row RM of turbine blades 92 is mounted on a turbine disk 91. Each turbine disk 91 includes a rim 93 which carries the blades 92 and which is extended radially inwardly by a web 94 (which is a ring which extends in a plane perpendicular to the longitudinal axis X) whose radially internal end is a bore 941. The rim 93 extends obliquely towards the longitudinal axis X and upstream by an upstream ferrule 95m whose radially internal end is an upstream (radial) flange 96m. The rim 93 extends obliquely towards the longitudinal axis X and downstream by a downstream ferrule 95v whose radially internal end is a downstream (radial) flange 96v. All these discs 91 are assembled together two by two in a rigid manner by inter-disc connections 50 such that each inter-disc connection 50 connects a downstream flange 96m of a first disc 91 to the upstream flange 96m of the disc 91 adjacent downstream to this first disc 91. The inter-disc connection 50 is a mechanical connection which is made up of a plurality of bolts and nuts which tighten the upstream flanges 96m and the downstream flanges 96v by passing through holes in these flanges (96m, 96v).The rim 93, the web 94, the upstream shell 95m and the upstream flange 96m, and the downstream shell 95v and the downstream flange 96v are visible in [Fig.7] which is a perspective and sectional view of a portion of a single disc 91. The holes in the upstream flange 96m (respectively in the downstream flange 96v) receive the inter-disc connections 50. These holes are located on radial protrusions (each protrusion is pierced with a hole) on the radially inner edge of the upstream flange 96m (respectively of the downstream flange 96v). Any two of these adjacent radial protrusions of the upstream flange 96m (respectively of the downstream flange 96v) are separated by an upstream festoon 97m (respectively a downstream festoon 97v). Each upstream festoon 97m (respectively downstream festoon 97v) is a radial notch such that the radially internal edge of the upstream flange 96m (respectively of the downstream flange 96v) is crenellated.

[0003] A movable sealing ring 70 comprises an annular radial flange 71 which extends radially inward (i.e. towards the longitudinal axis X) and which is sandwiched between an upstream flange 96m and a downstream flange 96v at this inter-disc connection 50. For example, when the inter-disc connection 50 is a mechanical connection, the radial flange 71 is pierced with holes through which the bolts pass. This movable ring 70 is visible in [Fig.6]. A portion of this movable ring 70 alone is also shown in [Fig.8], in perspective and in section. The holes in the radial flange 71 receive the inter-disc connections 50. These holes are located on radial protrusions (each protrusion is pierced with a hole) on the radially inner edge of the radial flange 71. Any two of these adjacent radial protrusions are separated by a scallop 72.Each scallop 72 is a radial notch such that the radially inner edge of the radial flange 71 is crenellated. Each of these scallops 72 has in its middle a crescent 73 which is a depression on the surface of the radial flange 71. This crescent 73 extends radially on either side of the downstream flange 96v when the movable sealing ring 70 is assembled with the discs 91 such that the crescent 73 forms a radial passage between the upstream purge cavity 80. (defined below) and turbine vein V.

[0004] One of the discs 91 of the low-pressure turbine 90 located in the downstream region of the low-pressure turbine 90 extends radially towards the longitudinal axis X by a downstream wall 98 which is fixed to an internal ring 99 of longitudinal axis X. This internal ring 99 is itself in sealed connection with a lip 62 which extends a fixed wall 61 of the high-pressure turbine 6. The discs 91, the downstream wall 98, the internal ring 99, the fixed wall 61 and the lip 62 delimit an upstream purge cavity 80, as illustrated in [Fig.5]. More precisely, it is the upstream shells 95m and downstream shells 95v which delimit the upstream purge cavity 80, such that the fabrics 94 extend into the upstream purge cavity 80. The upstream purge cavity 80 is thus bordered radially externally by the upstream shells 95m and the downstream shells 95v and is surrounded by the turbine vein V.

[0005] The disks 91 of the low-pressure turbine 90 are subjected to high temperatures due to the gases leaving the combustion chamber 5 which circulate in the turbine flow path V. In order to improve their service life, these disks 91 are cooled with colder air (approximately 400 to 500°C). This air is taken from the high-pressure compressor 4b and is brought into the upstream purge cavity 80. This air, called “purge air”, is then injected into the turbine flow path V by passing radially between the high-pressure turbine 6 and the low-pressure turbine 90 (arrow F in [Fig. 6]). The purge air also passes at the level of the lunules 73 from the upstream purge cavity 80 to the upstream shrouds 95m and to the rims 93 in order to contribute to the cooling of the disks 91.

[0006] The purge air flow rate (called "purge flow rate") must be sufficient to prevent the gases circulating in the turbine vein V from entering the upstream purge cavity 80 and heating the fabrics 94 of the turbine disks 91, which could cause the disks 91 to rupture. However, if the contact (plating) between the upstream flange 96m, the downstream flange 96v and the radial flange 71 is not sufficient, leaks occur at this location which reduce the purge flow rate. These contact defects are mainly due to geometric defects in the parts (flatness, parallelism) and to very significant axial clamping between the movable ring 70 and the disk 91 which deforms the parts.

[0007] To ensure that the flanges (96m, 96v, 71) are correctly plated, the opening at the bottom of the scallop (97m, 97v, 73) is currently systematically checked during assembly using so-called "spangle shim" checks. This check consists of passing a 0.02 mm spangle shim between the upstream scallops 97m (respectively downstream scallop 97v) and the scallops 73 of the radial flange.

[0008] Thus, a system is known for controlling the sealing of the upstream purge cavity of a turbomachine which comprises a low-pressure turbine comprising a plurality of discs and moving blades mounted on these discs and an integral internal ring of these discs, these discs and the internal ring delimiting this upstream purge cavity, each of the discs being assembled to the adjacent disc by an inter-disc connection located in the upstream purge cavity.

[0009] The control described above is time-consuming because it must be done manually, and tedious and expensive, which is undesirable. Description of the invention

[0010] The present invention aims to remedy these drawbacks.

[0011] The invention aims to propose a leak control system which makes it possible to control the purge flow rate more quickly, therefore at lower cost, and more easily.

[0012] This aim is achieved by virtue of the fact that the leak control system comprises a vacuum pump, a flow rate measuring device and a side wall and in that the system is capable of being assembled on the turbomachine so as to seal a portion of the upstream purge cavity which is delimited upstream by the side wall and which contains at least one of the inter-disc connections and the flow rate measuring device is capable of measuring the leak rate from the portion of the upstream purge cavity.

[0013] Thanks to these arrangements, it is possible to avoid having to carry out the tedious manual inspection of all the inter-disc connections. The leak-tightness inspection system according to the invention makes it possible to check the leak-tightness of the upstream purge cavity of the turbomachine in a single, faster operation.

[0014] For example, the sidewall includes an outer connecting member that establishes a sealed connection between the sidewall and a first of the discs, and includes an inner connecting member that establishes a sealed connection between the sidewall and the inner ring.

[0015] Thus, the assembly of the sealing control system in the upstream purge cavity is facilitated.

[0016] For example, the external connecting element establishes a sealed connection between the side wall and the bore of a first of the discs.

[0017] For example, the outer connecting element is housed in a groove formed by the first of the discs and the side wall, and the inner connecting element is housed in a groove formed by the inner ring and the side wall.

[0018] For example, the external connecting element comprises a first external O-ring of C-shaped cross-section and a second external O-ring of circular cross-section which is housed in the first external O-ring, and the internal connecting element comprises a first internal O-ring of C-shaped cross-section and a second internal O-ring of circular cross-section which is housed in the first internal O-ring.

[0019] Thus, the sealing of the portion of the upstream purge cavity is improved.

[0020] For example, the inter-disc connections are mechanical connections with bolts and nuts.

[0021] For example, the portion includes all inter-disc connections of the upstream purge cavity.

[0022] Thus, the system is able to control leaks throughout the upstream purge cavity.

[0023] The invention also relates to a method for checking the sealing of the upstream purge cavity of a turbomachine which comprises a low-pressure turbine comprising a plurality of discs and moving blades mounted on these discs and an internal ring secured to these discs, these discs and the internal ring delimiting this upstream purge cavity, each of the discs being assembled to the adjacent disc by an inter-disc connection located in the upstream purge cavity.

[0024] According to the invention, the method comprises the following steps: (a) an upstream purge cavity leak control system is provided which includes a vacuum pump, a flow measuring device and a sidewall; (b) the system is assembled on the turbomachine such that the system seals a portion of the upstream purge cavity which is delimited upstream by said side wall and which contains at least one of the inter-disc connections; (c) measuring the leakage flow rate from said portion of the upstream purge cavity using the flow rate measuring device.

[0025] For example, the side wall comprises an external connecting element and an internal connecting element and in step (b) the external connecting element is sealed to a first of the discs and the internal connecting element is sealed to the internal ring such that the system encloses a portion of the upstream purge cavity which contains the inter-disc connections located downstream of the first disc.

[0026] For example, the method further comprises the following steps: (d) comparing the leak flow rate measured in step (c) with a previously chosen leak threshold flow rate; (e) if the leakage flow rate measured in step (c) is greater than the threshold flow rate, then the inter-disc connections are tightened and step (d) is carried out again.

[0027] The invention will be better understood and its advantages will appear better, on reading the detailed description which follows, of embodiments shown as non-limiting examples. The description refers to the appended drawings in which:

[0028] [Fig-1] [Fig.l] is a longitudinal sectional view of a turbomachine equipped with a system for controlling the sealing of the upstream purge cavity of this turbomachine.

[0029] [Fig.2] [Fig.2] is an enlarged view of region S of [Fig.l] illustrating a system for controlling the sealing of the upstream purge cavity.

[0030] [Fig.3] [Fig.3] is a schematic view of an internal connecting element of a system for controlling the sealing of the upstream purge cavity

[0031] [Fig.4] [Fig.4] is a schematic view of an external connecting element of an upstream purge cavity sealing control system

[0032] [Fig.5] [Fig.5], already described, is a longitudinal sectional view of a turbomachine.

[0033] [Fig.6] [Fig.6], already described, is an enlarged view of region R of [Fig.5].

[0034] [Fig.7] [Fig.7], already described, is a perspective and radial sectional view of a part of a high pressure turbine disk of the turbomachine of [Fig.5].

[0035] [Fig.8] [Fig.8], already described, is a perspective and radial sectional view of a part of a movable sealing ring of the turbomachine of [Fig.5]. Detailed description of the invention

[0036] Consider a turbomachine 1 with a longitudinal axis X (axis of rotation) as illustrated in [Fig.l]. In the description below, the terms "internal" and "interior" designate an element oriented towards the longitudinal axis X or arranged closer to this axis. The terms "external" and "exterior" designate an element oriented in the opposite direction from the longitudinal axis X or arranged further from this axis. The turbomachine 1 comprises a nacelle 2 with a fan 3 comprising blades which forms an opening for the admission of a determined flow of air towards the engine. The turbomachine 1 comprises, downstream of the fan, a compressor 4 which comprises, upstream, a low-pressure compressor 4a and downstream, a high-pressure compressor 4b, and comprises a combustion chamber 5. The air compressed by the compressor 4 is admitted into the combustion chamber 5 and mixed with fuel before being burned therein.The hot combustion gases from this combustion are then expanded by passing into a turbine vein V. This turbine comprises a high-pressure turbine 6 which is located immediately downstream of the combustion chamber 5 then a low-pressure turbine 90 located downstream of the high-pressure turbine 6. The high-pressure turbine 6 comprises at least one stage E and the low-pressure turbine 90 comprises several stages E, these stages E being located in the turbine vein V. Each stage E consists of a row RF of fixed turbine blades, also called a nozzle, followed by a row RM of movable turbine blades spaced circumferentially all around the longitudinal axis X. The turbomachine 1 also comprises a rotor 7 whose axis of rotation is the longitudinal axis X. The movable turbine blades of the high-pressure turbine 6 and of the low-pressure turbine 90 are integral with the rotor 7.Thus, the rotation of these moving turbine blades turns the rotor 7 which in turn drives the low pressure compressor 4a, the high pressure compressor 4b and the blades of the fan 3 into rotation.

[0037] [Fig.2] is an enlarged view of region S of [Fig.l] which includes a portion of the low pressure turbine 90 and the high pressure turbine 6. Each RF row of blades of fixed turbine blades deflects the gas flow exiting the combustion chamber 5 towards the movable turbine blades RM at an appropriate angle and an appropriate speed in order to rotate these movable turbine blades. Thus, for the low-pressure turbine 90, each row RM of turbine blades 92 is mounted on a turbine disc 91. Each turbine disc 91 comprises a rim 93 which carries the blades 92 and which extends radially inwards by a web 94 (which is a ring which extends in a plane perpendicular to the longitudinal axis X) whose radially inner end is a bore 941. The rim 93 extends obliquely towards the longitudinal axis X and upstream by an upstream shroud 95m whose radially inner end is an upstream (radial) flange 96m. The rim 93 extends obliquely towards the longitudinal axis X and downstream by a downstream ferrule 95v whose radially internal end is a downstream (radial) flange 96v.All these discs 91 are assembled together two by two in a rigid manner by inter-disc connections 60 such that each inter-disc connection 60 connects a downstream flange 96m of a first disc 91 to the upstream flange 96m of the disc 91 adjacent downstream to this first disc 91. For example, the inter-disc connection 50 is a mechanical connection which is made up of a plurality of bolts and nuts which tighten the upstream flanges 96m and the downstream flanges 96v by passing through holes in these flanges (96m, 96v). The rim 93, the canvas 94, the upstream ferrule 95m and the upstream flange 96m, and the downstream ferrule 95v and the downstream flange 96v are identical to those already described with reference to [Fig.7].

[0038] A movable sealing ring 70 comprises an annular radial flange 71 which extends radially inward (i.e. towards the longitudinal axis X) and which is sandwiched between an upstream flange 96m and a downstream flange 96v at this inter-disc connection 50. For example, when the inter-disc connection 50 is a mechanical connection, the radial flange 71 is pierced with holes through which the bolts pass. This movable ring 70 is visible in [Fig. 2]. This movable ring 70 is identical to the movable ring 70 already described with reference to [Fig. 8].

[0039] One of the discs 91 of the low-pressure turbine 90 located in the downstream region of the low-pressure turbine 90 extends radially towards the longitudinal axis X by a downstream wall 98 which is fixed to an internal ring 99 of longitudinal axis X. This internal ring 99 is itself in sealed connection with a lip 62 which extends a fixed wall 61 of the high-pressure turbine 6. The discs 91, the downstream wall 98, the internal ring 99, the fixed wall 61 and the lip 62 delimit an upstream purge cavity 80, as illustrated in [Fig.2]. More precisely, it is the upstream shells 95m and downstream shells 95v which delimit the upstream purge cavity 80, such that the fabrics 94 extend into the upstream purge cavity 80. The upstream purge cavity 80 is thus bordered radially externally by the upstream shells 95m and the downstream shells 95v and is surrounded by the turbine vein V.

[0040] This turbomachine 1 is capable of receiving a leak control system 10 according to the invention. This leak control system 10 is shown schematically in [Fig.2]. This leak control system 10 is capable of being mounted on the turbomachine 1 and comprises a vacuum pump 11, a flow measurement device 12 and a side wall 13. The leak control system 10 is assembled in the upstream purge cavity 80 so as to seal a portion 81 of the upstream purge cavity 80 which is delimited upstream by the side wall 13. The side wall 13 is annular. The portion 81 of the upstream purge cavity 80 is delimited downstream and radially internally by the downstream wall 98, the internal ring 99 and possibly the side wall 13. The portion 81 of the upstream purge cavity 80 is delimited radially externally by the upstream ferrules 95m and the downstream ferrules 95v.

[0041] The portion 81 of the upstream purge cavity 80 contains at least one of the inter-disc connections 50 of the upstream purge cavity 80. By extension, by “an inter-disc connection 50” is meant here all of the inter-disc connections for a disc 91 of a given stage E, that is to say between the disc 91 of this given stage E and the disc 91 of the adjacent stage E, over the entire circumference of this given stage E. For example, the portion 81 contains all of the inter-disc connections 50 of the upstream purge cavity 80.

[0042] The flow rate measuring device 12 is capable of measuring the leak rate from the portion 81. If the measured leak rate is greater than a threshold rate which is set in advance, then it is known that leaks are occurring at one or more of the inter-disc connections 50. These inter-disc connections 50 can then be tightened. Advantageously, a traditional measuring tool such as glitter shims will be used to determine which of the inter-disc connections 50 is the source of the leak. Conversely, in the case where the measured leak rate is less than the threshold rate, then it is known that it is not necessary to tighten the inter-disc connections. Indeed, the value of the threshold rate has been chosen precisely for this purpose. For example, when the portion 81 comprises three inter-disc links 50 (i.e. the inter-disc links 50 between discs 91 on four stages E), the threshold flow rate has a value of 1 g / s (1 gram / second).

[0043] The portion 81 of the upstream purge cavity 80 is sealed upstream by the side wall 13. For this, the side wall 13 is fixed to elements of the low-pressure turbine 90. In one embodiment, the side wall 13 comprises an external connecting element 20 which establishes a sealed connection between the side wall 13 and a first of the discs 91a, and comprises an internal connecting element 30 which establishes a sealed connection between the side wall 13 and the internal ring 99. By "a first of the discs 91a" is meant a disc 91a which is part of the discs 91. Obviously, the first disc 91a is positioned such that there is at least one inter-disc connection 50 in the portion 81 so that the system for controlling the leaktightness of the upstream purge cavity 80 is capable of controlling the leak rate on at least this inter-disc connection 50. For example, the first disc 91a is the most upstream disc of all the discs 91 of the portion 81 so that the leaktightness control system 10 is capable of controlling the leaktightness of all the inter-disc connections 50 of the upstream purge cavity 80.

[0044] For example, the external connecting element 20 establishes a sealed connection between the side wall 13 and the bore 941a of the first disc 91a. This solution is practical since the side wall 13 bears on the bore 941a.

[0045] For example, the external connecting element 20 is housed in a groove formed by the first of the discs 91a and the side wall 13. For example, one of the sides and the bottom of the groove is formed by the external connecting element 20, the other side of the groove is formed by the first of the discs 91a.

[0046] For example, the internal connecting element 30 is housed in a groove formed by the internal ring 99 and the side wall 13. For example, one of the sides and the bottom of the groove is formed by the internal connecting element 30, the other side of the groove is formed by the internal ring 99.

[0047] For example, the external connecting element 20 comprises a first external O-ring 21 of C-shaped section and a second external O-ring 22 of circular section which is housed in the first external O-ring 21. [Fig. 4] illustrates the external connecting element 20 which establishes a sealed connection between the side wall 13 and the bore 941a of the first disc 91a.

[0048] For example, the internal connecting element 30 comprises a first internal O-ring 31 of C-shaped section and a second internal O-ring 32 of circular section which is housed in the first internal O-ring 31. [Fig. 3] illustrates this configuration and shows the internal connecting element 30 which establishes a sealed connection between the side wall 13 and the internal ring 99.

[0049] The invention also relates to a method for checking the sealing of the upstream purge cavity 80 of a turbomachine 1 which comprises a low pressure turbine 90 comprising a plurality of discs 91 and moving blades 92 mounted on these discs 91 and an internal ring secured to these discs 91, as detailed above.

[0050] A system 10 for controlling the tightness of the upstream purge cavity 80 is provided, which comprises a vacuum pump 11, a flow measurement device 12 and a side wall 13 (step (a)).

[0051] This system 10 is then assembled on the turbomachine 1 in such a way that the system seals a portion 81 of the upstream purge cavity 80 which is delimited upstream by the side wall 13 and which contains at least one of the inter-disc connections 50, as detailed above (step (b)).

[0052] Using this flow rate measuring device 12, the leakage flow rate is measured from the portion of the upstream purge cavity (step (c)).

[0053] For example, the method further comprises the following steps: (d) The leakage flow rate measured in step (c) is compared to a previously chosen leakage threshold flow rate. (e) If the leakage flow rate measured in step (c) is greater than the threshold flow rate, then the inter-disc connections 50 are tightened and then step (d) is carried out again. On the contrary, if the leakage flow rate measured in step (c) is lower than the threshold flow rate, then it is not necessary to tighten the inter-disc connections 50.

Claims

Claims

1. System (10) for controlling the sealing of the upstream purge cavity of a turbomachine (1) which comprises a low pressure turbine (90) comprising a plurality of discs (91) and moving blades (92) mounted on these discs (91) and an internal ring (99) integral with said discs (91), said discs (91) and said internal ring (99) delimiting said upstream purge cavity (80), each of said discs (91) being assembled to said adjacent disc (91) by an interdisc connection (50) located in said upstream purge cavity (80), said system (10) being characterized in that it comprises a vacuum pump (11),a flow measurement device (12) and a side wall (13) and in that said system (10) is capable of being assembled on said turbomachine (1) so as to seal a portion (81) of said upstream purge cavity (80) which is delimited upstream by said side wall (13) and which contains at least one of said inter-disc connections (50) and said flow measurement device (12) is capable of measuring the leakage flow rate from said portion (81) of the upstream purge cavity (80).,

2. A leak control system (10) according to claim 1 such that said side wall (13) comprises an outer connecting element (20) which establishes a leaktight connection between said side wall (13) and a first of said discs (91a), and comprises an inner connecting element (30) which establishes a leaktight connection between said side wall (13) and said inner ring (99).

3. A leak control system (10) according to claim 2 such that said external connecting element (20) establishes a leaktight connection between said side wall (13) and the bore (941a) of said first of said discs (91a).

4. A leak control system (10) according to claim 2 or 3 such that said outer connecting element (20) is housed in a groove formed by said first of said discs (91a) and said side wall (13), and said inner connecting element (30) is housed in a groove formed by said inner ring (99) and said side wall (13).

5. A leak control system (10) according to claim 4 such that said external connecting element (20) comprises a first external O-ring (21) of C-shaped section and a second external O-ring (22) of circular section which is housed in said first external O-ring (21), and said internal connecting element (30) comprises a first internal O-ring (31) of C-shaped section and a second internal O-ring (32) of circular section which is housed in said first internal O-ring (31).

6. Method for controlling the tightness of the upstream purge cavity (80) of a turbomachine (1) which comprises a turbine (90) comprising a plurality of discs (91) and moving blades (92) mounted on these discs (91) and an inner ring (99) integral with said discs (91), said discs (91) and said inner ring (99) delimiting an upstream purge cavity (80), each of said discs (91) being assembled to said adjacent disc (91) by an inter-disc connection (50) located in said upstream purge cavity (80), said method being characterized in that it comprises the following steps: (a) a system (10) for controlling the tightness of said upstream purge cavity (80) is provided which comprises a vacuum pump (11), a flow measurement device (12) and a side wall (13);(b) assembling said system (10) on said turbomachine (1) such that said system (10) seals a portion (81) of said upstream purge cavity (80) which is delimited upstream by said side wall (13) and which contains at least one of said inter-disc connections (50); (c) measuring the leakage flow rate from said portion (81) of the upstream purge cavity (80) using said flow rate measuring device (12).;

7. A method according to claim 6 such that said portion (81) comprises all the interdisc connections (50) of said upstream purge cavity (80).

8. Method according to claim 6 or 7 such that said side wall (13) comprises an external connecting element (20) and an internal connecting element (30) and such that in step (b) said external connecting element (20) is tightly assembled on a first of said discs (91a) and said internal connecting element (30) is tightly assembled on said internal ring (99) such that said system (10) encloses a part (81) of said upstream purge cavity (80) which contains the inter-disc connections (50) located downstream of said first disc (91a).

9. Method according to any one of claims 6 to 8 such that it further comprises the following steps: (d) comparing said leak rate measured in step (c) with a previously chosen leak threshold rate; (e) if said leak rate measured in step (c) is greater than said threshold rate, then said inter-disc connections (50) are tightened and then again step (d).

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