FR2824365A1 - Sealing system for coolant pump used in nuclear power plant, has back-up sealing arrangement shaped to close its seal gap, when pump shaft is not rotating - Google Patents

Abstract

A primary sealing arrangement forms a seal gap that reduces the pressure of fluid entering with high pressure irrespective of the rotation of a shaft (34) in the pump. A back-up sealing arrangement in flow communication with the high pressure end of the primary seal arrangement is shaped such that its seal gap is closed, when the shaft is not rotating to prevent any fluid leakage across the gap.

Description

Sealing system for closed high pressure systems containing a

  The present invention relates generally to sealing systems for sealing between a closing shaft in a closed high pressure system and a housing, and more particularly relates to sealing joints. shafts used in extremely high pressure systems, for example

  example in a main heat pump used in a nuclear power plant.

  In pressurized water nuclear power plants, a coolant is used to transport heat from the reactor core to steam generators for steam production. The steam is then used to drive a turbo-generator and generate electricity. The primary cooling circuit of a reactor comprises a plurality of separate cooling loops, each connected to the heart of the reactor and containing a steam generator and a primary reactor pump. Normally, circuits of this type operate at pressures greater than 6900 kPa; in a pressurized water nuclear power plant, the pressure

  in the operating circuit clearly exceeds 6900 kPa.

  Typically, a primary reactor pump is in the form of a single-stage vertical centrifugal pump, designed to move large volumes of coolant at elevated temperatures and pressures, such as 290 C and up to 17,225 kPa. Essentially, the pump includes a hydraulic seal for the intermediate shaft located between a hydraulic wheel located below and a motor located above. The hydraulic system located below includes a wheel mounted at the lower end of a pump shaft which can operate in a pump housing to pump a coolant around the respective loop. The motor located above includes a motor coupled to the rear

pump and entering it.

  Above the hydraulic system there is an internal thermal barrier and external cooling coils which serve to cool the liquid in the circuit which passes through them. Above the thermal barrier can be an additional pure liquid injected into the housing which is at a lower temperature and therefore isolated from the circuit temperature by the thermal barrier and the cooling coils. Two-part bearings are also provided for the motor and pump arbors, as well as suitable thrust bearings for the latter,

  none being part of the present invention.

  According to the prior art, the intermediate or shaft seal comprises a plurality of vertically separated tandem seals, more particularly a primary seal located at the lower end of the shaft in the immediate vicinity and above pump housing; above the latter is the secondary (emergency) sealing device; and above the latter is an upper or tertiary sealing device. The seals are arranged concentrically at and near the upper end of the pump shaft and in a housing disposed above the pump impeller. Their overall function consists in mechanically retaining the high positive pressure coolant in the reactor cooling circuit in order to prevent leaks along the pump shaft towards the reactor containment

  during normal and abnormal operating conditions.

  The primary primary seal is the primary means of sealing the pump. Typically, it is a hydrostatic seal with a film of running water, with controlled leakage, with radial taper, the main elements of which are a movable annular ring which rotates with the pump shaft and a ring. non-rotating sealing ring sealingly mounted on the housing of the sealing device located at the bottom. The initial design of such a primary seal is described in U.S. Patent 3,347,552 to E. Frisch and has been subsequently modified in detail, for example by U.S. Patent 3,522,948 to A. N. MacCrum. Primary seal (or # 1) causes a pressure drop of approximately 15,500

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  kPa at 205-345 kPa, cooling water passing over the joint. It allows a detit of 3.8 to 11.4 liters per minute. The liquid coolant which escapes through the joint n 1, which is then normally at a very reduced pressure, goes up along the shaft extending upwards and penetrates in the housing of the joint until reaching a region of the median or emergency sealing device. This latter sealing device (or seal No. 2), according to the prior art, was a seal of the type with rubbing surfaces. Its main constituent elements were a rotating mobile crown having an upwardly facing sealing surface and a non-rotating ring, axially mounted, arranged above the mobile crown. In normal operation, this ring and this lO crown constitute a seal with rubbing surfaces. However, in the unlikely event of a detail in seal no.1, the distribution of pressure on the ring and crown of seal no.2 causes them to behave like springs and to flex around their centers of gravity respective, the ring bending counterclockwise and the movable ring of the joint bending clockwise, so as to create the converging space of a hydrostatic seal of the film type d 'running water. According to the prior art (cf. U.S. Patent 4,961,678, column 2), as a seal of the running water film type, seal # 2 undergoes all of the high pressure of the cTrcuit during this incident. However, during normal operation, a large part of the leaks from the seal are diverted to a leak circuit. The remainder of the coolant passes through joint no 2, leaking at a low flow rate of approximately 7.5 liters per hour, the pressure in joint no 2 being approximately 205 kPa at the (inlet) end at highest pressure, which pressure is reduced to 20.5 48 kPa by the gasket n 2 at the (outlet) end at lower pressure. Even lower pressure cooling water escaping through seal # 2 continues to rise along the shaft and passes through a region of the tertiary seal

higher (n 3).

  According to the prior art, the upper or tertiary sealing device (or seal No. 3) consisted of a seal of the type with rubbing surfaces, its main elements also being a rotating mobile ring and a non-rotating ring, with axial mobility. The major part of the leaks escaping from the joint n 2 is evacuated by the joint n 3 via the leak circuit of the joint n 2. The joint n 3 of the type with friction surfaces appeared in two possible forms: either it has a double dam seal with two concentric sealing faces, or it has a single dam. The normal minimal leaks from seal # 3 are intended to pass through a leakage circuit # 3 until it ends up in the confinement atmosphere, a situation that reactor system designers would like if

possible avoid.

  In many nuclear power plants, a material that removes neutrons is dissolved in the reactor cooling water. It is normally boric acid enriched in isotope B, which serves as a neutron suppressor. The quantity of boric acid which can be retained in the coolant in the circuit of a reactor depends on the pressure and the temperature. Thus, when the pressure drops in a part of the circuit of a reactor, as occurs in the seals n 1, n 2 and n 3, the quantity of boric acid dissolved in the coolant frequently risks n ' not be fully retained in the coolant; thus, boric acid may precipitate in the space of the seal to the point of hindering the proper closing of the seal. To prevent this phenomenon, the additional liquid injected into the joint region is intentionally free of boron; as the contact area between the circuit liquid and this additional liquid is extremely small, only a minimal amount of boron

  dissolved in the circuit liquid will mix with the pure liquid added.

  Although failure of the No. 1 seal is very unlikely to occur, failure is envisaged for the purpose of safety studies by operators of nuclear power plants. It is therefore important that back-up systems are provided for this unlikely event. Likewise, it is unlikely that joint # 2 could fail on its own or at the same time as joint # 1; however, this case also constitutes a postulated safety event and joint # 3 is designed to deal with a failure of only joint # 2. In the case where both seal # 1 and # 2 fail, either at the same time or one after the other, while the power station is still under pressure, the No. 3 seal will have to bear the entire pressure of the circuit. As will be seen, an objective of the present invention consists in providing an emergency sealing device which can withstand the entire pressure of the circuit in the very unlikely event that the seals n 1 and n 2 fail at the same time , this event can

  however, be considered by some regulatory bodies.

  Another important requirement placed on reactor cooling circuits is that the sealing systems operate for long periods between replacements of the fuel from the reactor core and do not cause the plant to shut down. However, during the replacement of a reactor fuel, the maintenance of the seals constitutes a critical path element. It must be carried out very quickly so that the downtime for joint maintenance does not exceed the time necessary for the rest of the maintenance and for refueling the core.

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  reactor. Thus, a reduction in the maintenance or replacement time for the primary and emergency seals in order to ensure that the maintenance of the seals does not lengthen the critical path for the maintenance of a plant is an important objective for all the

sealing systems.

  Another important requirement imposed on the sealing system is to limit as much as possible, or even completely prevent leaks of primary coolant through the seal in the reactor containment, in the unlikely event of a failure of the seal. With the systems according to the prior art, this is achieved by means of a leakage circuit adjacent to the emergency sealing device; however, a device to ensure that a seal will not fail regardless of whether the pump shaft turns or does not rotate at the time of the alleged failure of seal # 1 or # 2, separately or simultaneously, is an important objective of the

present invention.

  Another objective is to provide, as an emergency seal (n 3) for normal operation at low pressure, a seal

  Rayleigh-type hydrodynamics upstream of joint # 2, the primary backup joint.

  A Rayleigh type # 3 seal, normally pushed to a closed position when the shaft is fixed, is desirable for the sealing system. Furthermore, with a low pressure upstream of the No. 3 seal in a main heat transfer pump where the pump artery is normally in the vertical position, associated with a possible accumulation of gas in the sealing interval and in the presence of circuits. leaks between seals n 2 and n 3, the liquid level may be below the entry of a Rayleigh type n 3 seal space, or a gas pocket may be present at this entrance. In this case, the Rayleigh type seal may run dry and therefore wear out quickly. The present invention aims to achieve a Rayleigh type seal in which the dry operation thereof in

  normal operating conditions is severely limited.

  Concrete experiences with seals n 1 and n 2 were examined in US Pat. No. 5,071,315 to Bice et al, in which the use of simple O-rings (with inserts fitted with Teflon) on the secondary sealing face of each of the seals n 2 and n 3 may cause problems, especially if the O-ring comes out of the groove which retains it and gets stuck between the sealing ring and the adjacent fixed part of the housing. In the case where the axial movement of bringing the sealing ring closer and further away from its movable ring surface can be prevented, and a sealing ring risks remaining "hung" so that

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  The joint space does not close the normal axial height. In this case, the expected pressure drop in the seal space may not occur, and the circuit pressure, or a large part of it, may be applied to the high pressure side of the next seal by upstream. The present invention also aims to reduce such risks. The objectives of the present invention mentioned above are achieved globally and individually in the pre-delivery embodiment thanks to the proposal of a new improved sealing device for the main heat transfer pumps of a nuclear reactor system. As in the prior art, the primary seal may comprise a hydrostatic sealing ring with a film of running water, of the type with conical faces, which causes a pressure exceeding 6900 kPa to drop to around 205-345 kPa (it being understood that all the pressures cited in the

  present description are pressures above atmospheric pressure and are

  therefore manometric pressures). The primary sealing ring can approach and praise, within certain limits, a surface of a rotating mobile crown of a primary seal. The primary seal ring also has a secondary seal which uses the combination of a fixed ring seal housing with a generally R-shaped cross section precisely received in the seal ring, and an interposed seal such as a normal O-ring (with or without attached Teflon elements cooperating therewith) disposed on the sealing ring and in contact with the housing lining. Thus, the only step of flow of fluid from between the primary sealing ring and the pressure housing in which it is located is located along the space between the radial sealing face of the movable crown. primary seal and the additional seal face present on the hydrostatic annular seal ring with axial mobility. It should be noted that in a central

  nuclear, the circuit pressure in normal operation is around 17,225 kPa.

  The invention provides a plurality of emergency seals in series for the passage of a fluid with the seal n 1 and which will be referred to here as seals n 2, n 3 and n 4, all of which perform an emergency function for the seal n 1 According to the invention, the seal No. 2 constitutes an annular sealing ring of the type with sealing face, mounted to approach and move away axially from a sealing surface present on a sealing ring. arranged radially. According to the invention, the seal No. 2 is a hydrodynamic seal and comprises a plurality of grooves or pockets of the Rayleigh type formed in the surface of the crown rather than in the surface of the ring, the

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  Rayleigh type pockets being formed in an insert which is preferably made of silicon nitride, which insert is mounted on the metal sealing ring. Preferably, the sealing ring is made of metal and also comprises an insert which is normally separated from the sealing surface of the crown by a sealing space containing a fluid, and which is produced in a desirable manner. using a composition containing carbon or a carbide. The joint 2 has a secondary sealing device which uses an annular lining associated with a modified L-shaped profile constituting a part of the housing; however, the secondary seal for seal # 2 is an arrangement of piston rings rather than an O-ring arrangement, which provides a seal between the seal ring and the housing gasket. The hydrodynamic seal No. 2 has the effect that a sealing space is only created when the shaft rotates; otherwise, when the tree is stopped,

  The space of joint No. 2 is brought to be completely closed.

  In addition, according to the present invention, the shaft is advantageously provided with one or more removable cartridge sleeves mounted thereon facing the seals 2, 3 and 4 so as to be hermetically fixed thereto. and held in a fixed position. The cartridge sleeve (s) can be removed from the shaft by lifting them from their upper end. The movable sealing rings for seals n 2 and n 3 are fixedly mounted on the outer surface of the sleeve (s), so that removing the sleeve (s) involves removing the entire seal 2, 3, or 4 as well as adjacent housing parts by a single lifting movement, or possibly two lifting; moreover, the whole of this device can be quickly replaced by new (or reconditioned) sub-assemblies pre-assembled,

  which reduces the time of the maintenance intervention in.

  Downstream of the joint 2 is a joint 3, mounted vertically above the joint 2 and comprising a sealing ring mounted on the aforementioned cartridge sleeve. The sleeve 3 also includes an annular sealing ring mounted to cooperate with a fixed annular packing housing of the L-shaped profile and has a sealing face opposite a radial sealing face present on the sealing ring. . The radial sealing face of the sealing ring approaches and deviates axially, with the sealing ring, relative to the sealing face of the sealing ring, forming a space of variable axial dimension tightness. In the present invention, the seal No. 3 constitutes a hydrodynamic seal of the Rayleigh type in which the pockets of the Rayleigh type are formed in the sealing ring and the sealing ring comprises an element.

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  reported in carbon or a combination of carbon and graphite, mounted in the metal sealing ring. The No. 3 hydrodynamic seal is also designed to be normally closed to prevent leakage along the sealing space when the shaft is stationary. In normal operation, when the shaft rotates, the seal 3 serves to lower the pressure from 205-345 kPa downstream of the seal 2 to obtain a pressure of approximately 6.9 to 20.5 kPa. Although it is normal for the pump system to leak downstream of seal # 2 under seal # 3, it may be (1) that the fluid level upstream of seal # 3 is located below the 'sealing space, or (2) that gas pockets are formed at the entrance to the sealing space, so that the seal No. 3 is caused to run dry. In order to avoid this situation, the Rayleigh type bags present in the gasket no. 3 are formed in the sealing ring with pumping passages which extend vertically downwards from the lower surface of each of the bags. Rayl ei gh of the sealing crown, crossing the crown with a slight inclination towards the central axis of the tree. The passages will allow the liquid located at a level below the bottom of the Rayleigh type bags of the sealing ring to be sent into the pockets, by pumping, but above the lower end of the pumping passages, thereby ensuring that the No. 3 seal operates with liquid in the pockets. In addition, a gas evacuation orifice can be formed in the sealing ring n 3 in the immediate vicinity of the entrance to the sealing space in order to prevent the formation of gas pockets. The No. 2 seal ring also has a

  gas exhaust port formed thereon, at the same location as on the No. 3 gasket.

  The present invention also provides a new emergency seal called here seal # 4, located vertically above seal # 3, which serves as an emergency seal and stop capable of preventing leakage of liquid (or even mist) from inside to outside of the pump housing regardless of the pressure in seals 1 to 4 and regardless of the rotation of the pump arDre. To this end, the No. 4 seal is in the form of a segmented annular seal whose primary sealing surface cooperates with a surface which extends vertically on the pump arDre. In the present example, the sealing surface on the pump shaft is formed on a cartridge sleeve sealingly mounted on the pump shaft in order to prevent leakage therebetween. During normal operation, the seal No. 4, of the segmented type, may consist of a seal with friction surfaces on which there is a hydrodynamic means serving to create a negative hydrodynamic height in a sealing surface of the segments of the ring. tightness, in the case where a liquid reaches the joint n 4 at a pressure higher than normal or with a complete pressure of the system in this one. For example, a seal of the type described in U.S. Patent 4,082,296, issued to Philip C. Stein is very useful in this case. It should be noted that, in the unlikely event of failure of seals 1 and 2, total system pressure may appear in seal 3, designed to be fully closed when the arDre is stationary . If the gear rotates at the time of the envisaged failure, the total system pressure may affect joint 3 and not be able to be completely reduced by joint 3 even if a certain drop in pressure is obtained, and thus a significant part of the pressure of the entire system would reach and pass through the seal no. 4. If a very high pressure from the system appears in the No. 4 seal, it will be used to push the sealing rings into contact with the sealing surface of the shaft sleeve and the sealing surface of the adjacent housing, regardless of whether whether the shaft rotates or does not rotate, and will thereby prevent (for a long period of time during which the reactor will be stopped) leaks from escaping from inside the

pump housing.

  The invention and many of the advantages attached to it will become apparent

  easily more clearly in reference to the detailed description below, made in

  consideration of the appended drawings, in which: FIG. 1A is a schematic representation of a cooling loop of a conventional cooling circuit for a nuclear reactor, comprising a steam generator and a primary reactor pump mounted in series with the heart of the reactor in a closed coolant circulation circuit; Fig. 1B is a perspective view of a motor-pump unit used with the reactor circuit of FIG. 1A and of which parts are deleted and shown in section for clarity of understanding of the operation of the present invention; FIGS. 2A, 2B, 2C and 2D, placed end to end, form an enlarged sectional view of the sealing part of the motor-pump unit of FIG. lB, representing the shaft and the primary and emergency sealing systems for the pump; Fig. 3 is a plan view, partially in section, of a segment of the sealing surface of the movable crown of the seal No. 3, taken along lines 3-3 of FIG. 2B; Fig. 4 is a view, similar to FIG. 3, of the joint 2 representing the sealing surface of the added element of the movable crown of the joint 2, taken along lines 4-4 of FIG. 2C;

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  Fig. S is a top plan view of the segments forming the # 4 joint; Fig. 6 is a plan view showing the vertical interior surface of part of the sealing segments of the seal no. 4 of FIG. S. taken along lines S 6-6 thereof; Fig. 7 is a plan view from above of the housing and the pump shaft of FIG. l B. taken along lines 7-7 of FIG. 1B; and Fig. 8 is a sectional view showing the piston ring seal

  for joint 2 in Figures 2B and 2C.

  Now considering the drawings, and in particular FIG. 1A, there is a schematic representation of a loop among several cooling loops 10 of a conventional cooling circuit for a nuclear reactor of the pressurized water type. The cooling loop 10 includes a steam generator 12 and a reactor coolant pump 14, mounted in series with a nuclear reactor core 16 in a closed coolant circulation circuit. The steam generator 12 comprises primary tubes 18 communicating with inlet and outlet chambers 20 and 22 of the generator. The inlet chamber 20 of the steam generator 12 provides flow communication with the outlet of the core 16 of the reactor in order to receive from it a heated coolant which follows the flow path 24 of the closed flow circuit. The outlet chamber 22 of the steam generator 12 provides flow communication with an inlet suction side of the reactor coolant pump 14 on the flow path 26 of the closed flow circuit. The outlet pressure side of the reactor coolant pump 14 provides flow communication with the inlet of the reactor core 16 to provide that

  ci a cold coolant along the flow path 28 of the closed flow circuit.

  In short, the reactor coolant pump 14 pumps the coolant under high pressure along the course of the closed flow circuit. In particular, the hot coolant leaving the core 16 of the reactor is led to the inlet chamber 20 of the steam generator 12 and to the primary tubes 18 communicating with it. While in the primary tubes 18, the hot coolant circulates by exchanging heat with cold edible water supplied to the steam generator 12 via conventional means (not shown). The drinking water is changed and partially turns into steam used to drive a turbo alternator (not shown). The coolant, whose temperature has been lowered by

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  the heat exchange, is then returned to the circuit of the reactor core 16 by

  via the heat transfer pump 14 The reactor coolant pump 14 must be able to circulate from

  large volumes of reactor coolants at high temperatures and pressures throughout the closed circulation circuit. Although the temperature of the coolant passing from the steam generator 12 to the pump 14 after the heat exchange has been lowered substantially below the temperature of the coolant flowing to the steam generator 12 from the reactor core 16 before the exchange of heat, its temperature remains relatively high, usually about 260 C. The pressure of

  l O coolant produced by the pump is usually about 15,500 kPa.

  As can be seen in FIGS. 1B, 2 and 7, the pump 14 of the reactor coolant generally comprises a housing or housing 30 for the pump which terminates in one end of an annular sealing housing 32 in several parts. The pump 14 also comprises a pump shaft 34 extending centrally in the housing 30; it is mounted in a sealed and rotatable manner inside the housing 32 of seals. The lower part of the pump shaft 34 is connected to a impeller 31 (FIG. 1B), while an upper part of this is connected, by means of a coupling device 58 described below. , to an electric motor 29 of the high-power induction type. When the motor 29 is running, the shaft 34 and its wheel 31 inside the pump housing 30 cooperate to circulate the coolant which passes through the pump housing 30 at pressures between ambient pressure and approximately 17,225 kPa . With the pump housing 30 forms a main pump flange 38 on which is mounted the lower annular segment 33 of the housing 32 of seals. Annular segments 35 and 37 for housing the seals, mounted in tandem, are fixed to each other by bolts and are fixed to a segment 33 to complete the housing 32 with seals, the upper end of the housing 32 having a closure cover 39 with an annular structure in two parts. The upper end of the pump shaft 34 extends through the seal housing 32 and the cover.

closure 39.

  On the pump flange 38 is also mounted a motor support 40, generally annular, with which the lower and upper flanges 42 and 44 form a body. The lower flange 42 has a plurality of openings formed through it and aligned with openings in the pump flange 38 through which threaded bolts 46 extend. Thus, the motor support 40 is fixed to the pump flange 38 by threaded bolts 46 passing through openings in the support flange 42

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  engine and through openings such as the openings 41 (Fig. 2D) on the segment 33 of the seal housing. The bolts 46 have threaded upper ends to which are fixed nuts 48 used to securely mount the motor support 40 on the pump flange 38, while simultaneously fixing in place the lower segment 33 of the housing 32 of seals. In addition, the lower end of the motor 29 rests on the upper flange 44 of the motor support 40, to which it can also be fixed by bolts (not shown). The motor support 40 has a large lateral opening 51 which occupies between 90 and 180 of the circumference of the motor support and which discovers for maintenance purposes, as will be described, the pump shaft 34, l motor shaft 52 lO, coupling 58, closing cover 39 and upper segments

  37, 35 and 33 of the housing 32 of seals relative to the outside of the motor-pump unit.

  More particularly, the motor 29 comprises a motor shaft 52 located above and in alignment with the pump shaft 34. The motor shaft 52 ends with a flange 54, and the pump shaft 34 ends at its upper end with a complementary flange 56 which, if necessary, can be removable. If the flange 56 is removable, it is desirable that it has a multi-sided or grooved opening which precisely receives an upper end, with grooves

  complementary, of the shaft 34 so that the flange 56 and the shaft 34 rotate together.

  The flanges 54 and 56 are spaced from one another, and a removable coupling 58 of shafts, with flanges, is interposed between the flanges 54 and 56. The removable coupling 58 of shafts comprises a pair of flanges of dimensions complementary to those of the flanges 54 and 56 and is placed so as to be disposed exactly between these latter flanges and to be fixed thereto by suitable means such as bolts 60 with heads passing through aligned openings in the flanges. In this way, the maintenance of the motor pump group can be carried out by removing the bolts 60 with head, by removing the coupling 58 from arres and by removing, if necessary, the flange 56 from the pump arDre. As explained below, the vertical distance between the motor flange 54 and the upper end of the pump shaft 34 is increased to a maximum to allow the removal of some of the sealing elements in the form of sub-assemblies, which allows them to be repaired and / or replaced quickly. Access to the bolts 60 and to the coupling 58 of arches is made through the opening 50 formed in the engine support 40. Obviously, a removable cover (not shown) can, if desired, be placed on the opening 50

of the motor support 40.

  To further facilitate rapid access to the pump seals and to the seal housing segments 33, 35 and 37, the seal housing 32 has a

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  closure cover 39 in two parts, consisting of two substantially identical complementary halves 39A and 39B, which also serve to support the seal No. 4 and

  are tightly fixed by bolts 64 to the segment 37 of the seal housing.

  As will be seen in FIG. 7, the cover 39 placed on the seal housing is divided vertically into 66; at the division level, each half 39A and 39B of the cover 39 has a pair of flanges 68 which extend radially. These flanges 68 of each half 39A and 39B of the cover 39 complement each other and therefore allow the removal of part of the cover 39, revealing the upper seal (n 4) and the interior of the housing 32 of joints. The two halves 39A and 39B of the cover 39 are kept aligned with one another by conical alignment pins 69 and are tightly sealed to each other by bolts 70, shown by transparency in Fig. 7. The axial surfaces of the two halves 39A and 39B of the closure cover 39 overlap flat so that, once assembled, no leakage escapes from the cover 39 thanks to its two-part structure. The sealing system described here is designed to be accessible and removable

  to facilitate the maintenance of the motor pump skucture described above.

  In order for the pump shaft 34 to rotate freely inside the seal housing 32 while maintaining the pressure limit of 17,225 kPa between the interior and the exterior of the seal housing, sealing devices 72 , 74, 76 and 78 in tandem, respectively comprising a primary lower device (n 1) a secondary device (n 2), a tertiary device (n 3) and a stop device (n 4) are placed as illustrated in the Fig. 2 above the pump wheel 31 and inside the pump housing 30 and the seal housing 32. The primary lower sealing device 72 (n 1), which provides most of the pressure sealing (about 15,550 kPa), is advantageously of the contactless hydrostatic type, as illustrated in the aforementioned Frisch and MacCrum patents. According to the invention, the seals no 2 and no 3 are of the hydrodynamic type, normally closed, and the seal no 4 is a segmented seal with minimal or even zero leaks during normal operation, and which can serve as a stop seal in an emergency to prevent leaks outside the pump housing in the event of separate or simultaneous malfunction of seals no 1, no 2 and 3. As shown in figures 2A and 2B, the sealing device lower hydrostatic primary 72 (the seal n 1) of the pump 14 generally comprises a lower annular movable crown 80 mounted on the pump shaft 34 to rotate with it, and an annular sealing ring upper 82 rise from

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  fixedly in the housing 32 of seals. The lower ring 80 has a front plate or upper annular insert 83, of wear-resistant material such as silicon nitride, supported by an annular hydrostatic clamping element 80 on the surface of the ring 80 facing upwards. The crown 80 is keyed onto the pump shaft 34 by an anti-rotation device such as a spindle (not shown) extending, for example, into a shoulder 96. The upper annular sealing ring 82 has a front plate or upper annular insert 86, also made of wear-resistant material such as silicon nitride, supported by an annular hydrostatic clamping element 88 on the annular sealing ring 82. The sealing ring 82 is itself keyed onto a seal ring support 104 by an anti-rotation means such as a pin (not shown) extending from the support 104 into an opening in the top of the seal ring 82 aDm to prevent any movement of rotation of the upper sealing ring 82 relative to the housing 32 of seals while still allowing an axial movement of approaching and moving away from the sealing ring eity 82 along the pump shaft 34 with respect to the sealing ring 80 and its insert 83. The mutually opposite surfaces 92 and 94 of the respective front plates 86 and 83 of the ring and the ring form the seal space 93 for seal n 1. They are pushed towards each other due to the pressure of the coolant exerted on the pump shaft 34. However, normally, the surfaces 92 and 94 along the joint space 93 do not rub against each other, since the two surfaces 92 and 93 have a low taper (at their high pressure edges respectively), which keeps them apart from each other, thus allowing the lower ring 80 and its insert 83 to rotate under running water film conditions relative to the upper seal ring 82 and its added element 86,

  both when the rear turns and when it is stationary.

  It will also be noted that the sealing ring 80 of the seal n 1 is mounted on a shoulder 96 formed on the shaft 34, the shoulder 96 being oriented upwards and situated towards the outside of the rest of the upper part of the tree. In addition, one of a number of removable annular shaft seals 98, precisely mounted, is arranged to rest on a shoulder 100 located above the shoulder 96 on the shaft and mounted so as to be subject to fixed way to the shaft 34 and, of course, to be able to rotate with the latter. The seal housing 32 comprises a vertical annular inner element 102 for supporting the seal, mounted in the seal housing 32, the lower part of the latter facing the ring.

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  82 of seal No. 1 and having an L-shaped annular support 104 attached to a surface thereof facing downwards, the vertically oriented part 106 of L-shaped support 104 having the same extension as an upper part of the sealing ring 82. The sealing ring 82 comprises a U-shaped secondary seal 108 in which is engaged an O-ring 109 situated in a recess machined in the face, facing inward, of the part upper of the sealing ring 82, and which receives the O-ring 109 to prevent leaks between the sealing ring 82 and the seal support 104, sanf by the seal space 93. Examples of U-108 seals and O-rings

  109 appear in the Bice et al. supra.

  To ensure the passage of coolant along the joint 1 only through the joint space 93, several O-rings are arranged in complementary recesses to prevent the passage of leaking fluids for example, an O-ring in the recess 110 s extends towards the rear 34 under the shoulder 96 to ensure a seal between the shaft 34 and the sealing ring 80. In addition, two O-rings in two recesses 112 prevent leaks between the outer surface of the ring d seal 80 and the clamping ring 84, while an O-ring in a recess 114 seals the surface between the insert 83 of the

  sealing ring and sealing ring 80.

  An additional seal 115 consisting of an O-ring and a recess is formed on the lower surface of the sealing ring 82 which comes into contact with its insert 86. Likewise, the clamping ring 88, which tightens the insert Sealing ring 86 against sealing ring 82 n 1, has a pair of seals formed by recesses and O-rings 116 to prevent leaks between the tightening ring 88 and sealing ring 82 n 1. In addition, the L-shaped seal support 104 is fixed to the seal support element 102 by a sealing means interposed between them and represented in the form of an O-ring and a recess 118, which prevents leaks between these parts of the housing. In addition, the seal support element 102 is mounted in a sealed manner in the seal housing 32 so as to prevent any leakage between these parts using a combination 120 of an O-ring and a recess. , both of annular shape. These latter sealing devices all serve to prevent leakage except through the gasket space 93 of the seal n 1. It will be seen that the sealing ring 82 is retained in the support element 102 of the seal and the support 104 seal so that the ring

  sealing 82 has the same extension as a portion of each of these latter parts.

  More particularly, the segment 106, oriented downwards, of the sealing support 104

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  retains the vertical surface, oriented inwards, of the sealing ring 82, while the surface 122, oriented outwards, of the sealing ring 82 is placed so as to have the same extension as a flange 124, extending downward, present on the seal support member 102, so that the sealing ring 82 is loosely installed in the flange 124. The lifting movement of the ring sealing 82 is stopped by the surfaces 126 and 128, oriented downwards, present respectively on the support element 102 of the seal and on the support 104. The flange 124, extending downward, of the support element 102 of seal has an annular recess 130, oriented inward, which has the same extension as a portion of the sealing ring 82, and lO the latter comprises a ring 132, extending outward, tight between the sealing ring 82 and the clamping ring 88, which extends end up into the recess 130 of the support element 102 for the seal. As the ring 132 is placed above the shoulder at the lower end of the recess 130, when the seal support element 102 is lifted outwards from the seal housing 32, it takes with it the sealing ring 82 of the seal n 1 due to the position of the ring 132 in contact with the shoulder at the lower end of the recess 130. As will be seen below, the removal of the element joint support 102 by a lifting movement will drive with it the sealing ring 82 n 1, including the insert 86

  sealing ring, for maintenance and replacement.

  An intermediate removable shaft sleeve 134, located in the seal housing 32 and mounted on the shaft 34, is vertically aligned with and rests over a lower shaft sleeve 98. A combination 136 of an O-ring and a recess is formed between the sleeve 134 and the shaft 34 to prevent leakage from the interior of the seal housing 32 on a path between the sleeve 134 and the shaft 34. The intermediate sleeve 134 has, vertically, the same extension as the device

  seal 74 n 2 of the sealing system for the motor-pump 14.

  The sealing ring 138 for the joint 2 is mounted on the intermediate shaft sleeve 134, in the immediate vicinity of the lower edge thereof, and is fixedly mounted so that it can rotate with it. The crown extends radially towards the outside of the sleeve 134 and comprises at its upper end an insert element 140 of the crown which forms the horizontal sealing surface, facing upwards, of the crown 138. A lug (not shown) extends upwards from the crown 138 into an opening of the sealing element 140 of the sealing crown to ensure that the insert rotates with the shaft 34. The insert 140 of the sealing crown is fixed to the sealing ring 138 by an annular tightening ring 139. An annular groove 141 is formed in the surface, facing upwards, of the sealing ring 138 and receives an O-ring which comes into contact with the 'insert 140 of the sealing ring to prevent leakage therebetween. A second O-ring 143 is placed between the clamping ring 139 and the insert 140 of the crown in the immediate vicinity of the outer edge of the insert. The O-ring 143 serves as a means of elastic contact between the crown insert 140 and the clamping ring 139. The sealing crown 138 is immobilized on the shaft sleeve 134 by a lock nut 142 which is screwed to the lower end of the shaft sleeve 134 of fa, con to extend outside of that lO ci and is immobilized by a metal locking cup 144. The underside of the sealing ring 138 rests on the top of the lock nut 142 and the locking cup 144. A pair of alignment fingers (only one being shown), force fitted into the bore of the crown 138, engage in slots machined in the sleeve 134 of the shaft to prevent mutual rotation, ensuring that the crown 138 rotates with the arDre 34. The upward movement of the sealing crown 138 along the shaft sleeve 134 is prevented by a sleeve

spacing 148.

  The gasket 74 n 2 also comprises an annular sealing ring, movable within certain limits between the upper surface of the insert 140 of the crown of the gasket n 2 and a fixed element 154 of the seal housing. The sealing ring 150 has an annular flange 152, oriented downwards, disposed radially outside the axial external surface of the sealing ring 138 and of the crown insert 140. The annular segment 35 for housing the seals, which rests on the annular segment 33 for the housing of the seals and extends upwards of the said segment, contains the seal device No. 2. It has the same extension towards the outside as the ring. seal 150 of the joint n 2 and extends above this ring towards the shaft 34. The segment 35 for housing the seals also comprises the inner annular element L-shaped housing 154, oriented downwards, which is fixed to the internal surface, oriented downwards, of the underside of the housing segment 35, and comprises an annular branch 162, oriented green at the bottom, interposed between the shaft 34 and the internal peripheral surface 156 of the ring d seal 150. The base 158 of the L-shaped element 154 is fixed by threaded bolts 160 to the housing segment 35 of the seal no 2, and the annular branch 162, oriented downwards, has the same extension as a large part of the inner peripheral surface 156 of the sealing ring 150. A piston ring seal 164 is interposed between the sealing ring 150 and the branch

18 2824365

  162 of housing element 154. The seal 164 is shown in detail in FIG. 8 and

will be described below.

  The sealing ring 150 has an attached sealing element 166, desirably made of carbon-based material and graphite, located in a recess 168, oriented downwards, on the lower surface of the sealing ring 150, towards the inside of the flange 152, so that the insert element 166 of the sealing ring is placed above and in alignment with the insert element 140 of the crown. The seal ring insert 166 is fixed to the seal ring by suitable means, for example by a tight fit between the relatively strong metal seal ring 150 and an expansion insert relatively low, carbon-graphite. In the event that an accumulation of pressure occurs between the sealing ring 150 and the insert 166, an annular groove 167 on the outer periphery of the insert 166 is provided, as well as a plurality of spaced orifices, for example 169, extending radially inward from the groove 167 to the low pressure inner edge of the insert 166

sealing ring.

  According to the present invention, the sealing device 74 n 2 is designed in such a way that the sealing ring 150 and the sealing ring 138 form a hydrodynamic seal, a seal space 170 extending between the sealing ring. sealing 150 and sealing ring 138. The sealing ring is designed so that a high pressure, present in the region between the housing segment 35 of the seal 2 and the sealing ring 150, biases the sealing ring 150 towards the sealing ring 138 so that, when the shaft 34 does not rotate, the added element 166 of the sealing ring 150 comes against the added element 140 of the crown sealing to close the space 170 of the joint. This can be seen by comparing the surface of the sealing ring 150 exposed to the high pressure urging the sealing ring down, with the surface of the sealing ring 150 exposed to the high pressure. urging the sealing ring upwards. The effective force acting on the sealing ring is such that it keeps the space closed when the shaft 34 is stationary. The insert element 140 of the sealing ring, according to the invention, is made of a relatively hard, wear-resistant material, such as silicon nitride, and comprises in its upper surface a plurality of shallow pockets 172, of Rayleigh type, precision machined (Fig. 4), connected to the outer peripheral surface of the insert 140 by a plurality of feed grooves 174, extending radially to connect the pockets 172 to the high pressure fluid on the outer periphery of the insert

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  crown. As is known in the art, pockets of the Rayleigh type are relatively shallow pockets which create an axial force (upwards) therein due to the shear rate gradient of the fluid, gaseous or liquid,

pushed towards the pockets.

  The pockets 172 are shallower than the feed grooves 174, so that the liquid which enters the seal space 170 enters the feed grooves 174 and then into the pockets 172. The forces created in the Rayleigh pockets are used to push the sealing ring 150 and its attached element 166 so that they rise away from the upper surface of the sealing ring 138 to create a gap or a film of small dimensions but nevertheless positive between the sealing ring 50 and the sealing ring 138. It should be emphasized that the pockets 174 and 172 with precise machining of the added element of the sealing ring are, according to the present invention, machined from a relatively material resistant to erosion, harder than the material forming the seal ring insert 166, which risks being in frictional contact against the insert 140 of the crown nchéité. The insert element 166 of the sealing ring, made of a relatively softer material such as carbon-graphite, will wear out more quickly than the insert element 140 of the sealing crown. Thus, any wear caused by friction of the insert 166 against the insert 140 will affect the insert 166 of the sealing ring, the machining of which is less complex and the replacement of which is therefore less costly. In addition, it will be observed that a groove 178 is machined in the insert element 166 of the sealing ring so as to be above a portion of the feed groove 174 located radially inward of the inner edge 176 (Fig. 4) of the pocket and to be above a portion of the upper surface of the sealing ring 140 radially towards the inside of the edge 176 of the Rayleigh pocket 172. Thanks to this construction, it will be observed that the added element 166 of the sealing ring actually forms the sealing threshold 180 for the seal No. 2. Thus, any wear of the sealing threshold following a friction contact will affect the element. insert 166 of the sealing ring rather than the insert 140 of the sealing ring. In order to ensure proper operation of the Rayleigh type No. 2 seal, it is important for the present application that the Rayleigh 172 bags contain a liquid rather than a gas or vapor. To prevent the formation of a gas pocket between the sealing ring 150 and the sealing ring 138, which would prevent the passage of liquid in the seal space 170, a plurality of passages 183 are provided,

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  spaced in the circumferential direction, which extend through the sealing ring, from the seal space 170 to the high pressure region above the

sealing ring 150.

  When the shaft is stationary, the sealing ring 150 is in the closed position, the sealing threshold 180 being in contact with the upper surface of

  the crown insert 140, which prevents any leakage through the seal space 170.

  Leakage by other paths, for example between the surface 156 of the sealing ring and the vertical branch 162 of the annular L-shaped element 154 for housing is prevented by the seal 164. Similarly, any leakage path other than the seal space 170 is prevented by the use of a series of O-rings and grooves in the correct position, extending between adjacent parts, as shown in FIG. 2. For example, the aforementioned assembly 141 comprising an O-ring and a groove is disposed between the insert element 140 of the sealing ring and the sealing ring 138. In addition, a plurality of holes 182 in L (exposed to low pressure) are machined in the sealing ring 138, equidistant from each other around the upper surface of the sealing ring 138, between the inner end of the sealing threshold 180 and the outer surface of the sleeve positioning 148. Furthermore, holes (not shown) exposed to high pressure can be machined in the sealing ring 138 between a surface of the ring 138 exposed to high pressure and the internal surface thereof located at immediate vicinity of the shaft sleeve 134. It should be emphasized that the low pressure holes 182 and the high pressure holes produce a recovery moment during operation for the joint device 2, which limits the roll movement of the crown 138 and of the insert 140 - for example, a rolling movement around their center of gravity. When the shaft 34 rotates and the circuit is under pressure, the high-pressure fluid which exits through the seal n 1 arrives on the outer periphery of the sealing ring 150 n 2 and part of the liquid passes through the space 170 of gasket to be found in the pockets of Rayleigh 172 via the feed grooves 174, in which an upwardly directed force is created by the shear speed gradient in the pockets of Rayleigh 172, which separates the ring d sealing of the sealing ring 138 to form a small but positive gap in order to allow

  weak but positive leaks through the seal device 174 n 2.

  To prevent leaks through joint 2, except through the seal space 170, the secondary seal 164, placed between the branch 162 of the seal housing and the sealing ring 150 prevents leaks between them but allows a axial movement of

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  approximation and distance of the sealing ring 150 relative to the sealing ring 138. The seal 164 is located at the upper end of the axial surface

  inside 156 of the sealing ring 150 and is shown in more detail in FIG. 8.

  As we have noticed, an O-ring such as that used on seal 1 has the possibility of remaining suspended and possibly preventing a complete sealing action of a seal 72, 74 or 76, since it prevents the axial movement of approaching or moving the sealing ring away from it relative to the sealing ring. Thus, U-joints such as the joint 108 which may at some point have higher frictional forces than are desirable may present a problem. The sealing device for seal # 2 of this embodiment is a piston ring seal and is received in a recess 186 facing inward and upward, formed in the sealing ring 150 to 1 'upper end of the inner surface 156 thereof. The upwardly facing surface 188 of the recess 186 is precision machined to serve as a secondary sealing surface for a two-part piston segment 190. The piston ring 190 is constructed like a conventional piston ring and is advantageously made of composite material of the carbon-graphite type, divided by an overlapping interlocking system to allow radial movement of the segment inwards and

  outside, but in such a way that there is practically no leakage through the division.

  The piston ring 190 has an inner surface 192 of precision machined bore in contact with the outer surface, located opposite, of the branch 162, which surface has also been machined with precision to ensure adequate sealing. A garter spring 194 is placed in a complementary recess formed on the surface of the piston segment 190 opposite the surface 192 of the bore to push the piston segment into contact with the surface, located opposite, of the branch 162 of housing. The piston ring 190 is fixed in the recess 186 by a spring leaf 196 which is in contact with the surface, facing upwards, of the piston segment 190 and by a corrugated lock washer 198 in contact with the blade. spring 196. The wavy lock washer 198 is then kept in compression by a split elastic ring 202 which is fitted into a peripheral groove formed at the upper end of the cutout 186. The surface 189 forming the lower face of the piston ring at contact of the surface forming the machined face 188 of the recess is also machined with precision and has a peripheral groove 204 (except that the groove

  device 204 is not continuous at the division of the piston segment 190).

  A plurality of radially extending spaced passages 206, represented by

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  transparency, extend from the groove 204 to the outer surface of the piston ring to allow pressure relief. The surface 192 of the bore of the piston ring has a peripheral groove 200 which stops on either side of the division of the piston ring 190. The pressure in the groove 200 is released by multiple axial grooves 201. This makes it possible to limit the stresses exerted on the bore and therefore to limit friction by sliding. Thus, the piston ring segment 190 comprises a bore sealing threshold 203 situated between the groove 200 and the surface 189 of the lower face, and the surface 189 of the lower face of the piston ring segment 190 comprises a sealing threshold 205 of face between the groove 204 thereof and the intersection of the surface 189 of the lower face with the bore surface 192. It is known in the art that a carbon-graphite piston ring seal experiences less friction stress than an O-ring; thus, the probability that the piston ring seal device 164 greatly hinders the axial movement of the sealing ring 150 towards and away from the sealing ring 138

  is greatly limited in comparison to the risk of such a problem due to an O-ring.

  Above the joint device 74 n 2 is the joint device 76 n 3 which, in the present example of the invention, is also a hydrodynamic joint of the Rayleigh type. The seal device No. 3 comprises a sealing ring 208 and a sealing ring 210 mounted in the housing segment 37 above the ring 208 and capable of approaching and moving away axially relative to the shaft 34 from the upper surface of the crown. The sealing ring 208 has an annular shape and precisely receives the shaft sleeve 134 at its center. The sleeve 134 has a shoulder 212 formed therein and oriented downwards, which shoulder comes into contact with the upper end of the crown 208 and limits the elevation movement of the latter. A pair of spaced alignment pins such as lug 214 extends between the crown 208 and the sleeve 134 to prevent the crown 208 from rotating relative to the sleeve 134. A sealing device 216, facing the outer and consisting of an annular groove and an O-ring, is formed on the outer surface of the sleeve 134, the O-ring thereof being in contact with the axial inner surface of the crown 208 of the seal No. 3 to prevent leakage between them .. The lower end of the crown 208 is in contact with the upper surface of the spacer sleeve 148. It can thus be seen that the crown 208 of the seal n 3, the spacer sleeve 148 and the crown 138 of the seal n 2 are all held in place on the sleeve 134 by the lock nut 142 and the

locking cup 144.

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  As can be seen more clearly in FIG. 3, the horizontal upper surface 217 of the crown 208 of the joint 3 is precision machined and comprises a plurality of relatively shallow Rayleigh pockets 218, oriented upwards, aligned in the circumferential direction, formed therein, s 'extending over the entire periphery of the surface 217 and respectively connected, at the level of the front edge of each pocket, to a relatively deep supply groove 220, with radial orientation. Pump passages 222 are formed in the base of each of the feed grooves 220, extending downward and inward through the crown 208 at an acute angle with respect to the shaft 34 to open into an interior region 224 of the housing, which is on the highest pressure side of the gasket 76 n 3. As the passages 222 extend outward and vertically, from top to bottom, they serve to pump liquid from the region 224 of the housing to the supply grooves 220 and, from these, to each of the Rayleigh pockets 218. Thus, the supply grooves 220 and the pumping passages 222 serve to ensure that the Rayleigh pockets are supplied with liquid when the shaft 34 rotates. This creates the shear rate gradient forces that act on the sealing ring 210 allowing the seal 3 to function even if the level of the liquid in the region 224 of the housing does not reach the

  level of the upper surface 217 on the crown 208 of the joint no 3.

  The joint system 76 n 3 is placed, in the joint housing 32, in an annular zone of the housing above joint No. 2, this region being formed by the annular segment 37, generally in L, of the housing, fixed by sealingly above and into the annular housing segment 35 by a pair of bolts 226 spaced apart in the circumferential direction. A tight seal is created between the housing segments 35 and 37, so as to prevent leaks, by a combination 228 of a recess and an O-ring in contact with vertical surfaces, located opposite, of the segments 35 and 37 of the housing. A similar seal is created between the segments 35 and 33 of the housing by a combination 229 of a recess and an O-ring. Finally, these seal housing segments 35 and 37 are fixed to each other, and these segments are also fixed to the seal housing 33 using eight large bolts.

63 (Figures 2A, 2B and 7).

  The upper end of the housing segment 37 extends inwardly toward the arDre 34 and is located above the sealing ring 210 of the seal 3. An annular portion 230, in L, of the housing is mounted on the lower interior surface of the housing segment 37 and has a branch 232 oriented

24 2824365

  downwards, located between the upper inner surface of the sealing ring 210 and the upper end of the sleeve 134. The part 230 of the housing and its branch 232 play the same role for the joint 3 as the part 158 of the housing and its branch 162

  for joint No. 2, and that the portion 104 of the housing and its branch 106 for joint No. 1.

  The outer surface of the leg 232 is machined with precision, and the vertical inner surface of the ring 210, located opposite the outer surface of the leg 232, has a seal 234 which, in the present example, consists of a seal O-ring (or by a combination of a U-ring and an O-ring) placed in an annular groove, oriented inwards, formed in the sealing ring 210 and filling the space between the branch 232 and the sealing ring 210. Although the O-ring of the seal 234 comes in sealing manner in contact with the external surface of the branch 232, it nevertheless allows a movement of approximation and axial separation of the sealing ring 210 along of the branch 232 relative to the movable crown 208 of the seal, at the same time preventing the passage of fluid through the seal 234. The sealing ring 210 n 3 has an annular flange 236 extending downward, located radially outwards from the axial surface of the seal ring 208. The sealing ring 210 comprises an annular sealing element 238, advantageously made of carbon-graphite composite material, located in a recess pointing downwards on the lower surface of the sealing ring 210 and towards the inside of the rim 236, so that the seal insert 238 is located, covering, over the Rayleigh pockets 238 of the upper surface 217 of the seal crown 208. The seal insert 238 is fixed to the ring 210 of seal # 3 by suitable means, for example by tight fitting between the relatively more expandable metal seal ring 210 and the relatively less expandable insert 238 , in carbon-graphite. An annular groove, together with a plurality of spaced orifices similar to the groove 167 and the orifices 169 of the seal 2, are made in the sealing insert 238 to relieve the pressure between the sealing insert 238 and the sealing ring 210. Thus, the sealing ring 210 and its attached element 238 form a sealing space 240 between the attached element 238 of the sealing ring and the upper surface 217 of the sealing ring. 208. As the sealing ring 210 has the flange 236 facing downwards near the sealing space 240, the sealing ring 210 and the reLord 236 risk creating a gas pocket in the edge area. outside the sealing gap 240. Such a gas pocket is prevented by the presence of spaced orifices 242 passing through the upper end of the rim 236,1'extrême

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  the interior of the orifices 242 being exposed to the sealing gap 240 and the outer end of the orifices 242 opening into the region of the housing on the high pressure side of the sealing ring 210, that is to say the region of the housing between the outer surface of the sealing ring 210 and the inner surface of the housing segment 37. The orifices 242 play the same role as the orifices 183 of the seal No. 2. The seal device 76 No. 3 is formed so that the seal ring 210 and the seal crown 208, together with the Rayleigh pockets 218, form a normally closed hydrodynamic type seal for seal 3. To this end, the downward facing surface of the insert 238 of seal 10 3 has an annular groove 244 formed therein, located partially above the inner edge of the Rayleigh pockets 218 closer to the shaft 34 and partially above the surface 217 of the crown, so that the segment of the joint element 238 of seal disposed towards the inside of the groove 244 serves as a watertight threshold 245 for seal No. 3. However, it is important that the outer edge of groove 244 ends inside the supply grooves 220 and that the rest of the surface, facing the bottom, of insert 238 of seal, located outside the groove 244, ie a segment in contact with the part of the surface 17 of the sealing ring 208 situated outside the Rayleigh pockets 218. In this way, the Rayleigh pockets have a surface of the joint insert 238 on which the upwardly directed force can be exerted, created by a Rayleigh pocket, when the shaft rotates, in order to create a sealing space or a film of small dimensions but positive

along space 240.

  As indicated above, the seal device 76 is of the hydrodynamic type so that, when the shaft 34 is stationary, the sealing threshold 245 comes into contact with the upper surface 17 of the crown 208 to produce a closed seal. Indeed, the high pressure which acts downwards on the sealing ring 210 acts on a larger surface due to the orientation of the force downwards than on the

  surface of the sealing ring 210 subjected to an upwardly directed force.

  However, when the shaft rotates, the liquid is pushed into the Rayleigh pockets 218 of joint # 3 through the pumping passages 222 and, thanks to the shear rate gradient and the upward force, it is pushed onto the sealing ring 210 as opposed to the effective downward force to create the gap or small film

  dimensions but positive between the sealing ring 208 and the sealing ring 210.

  In the prior art, the use of a seal No. 1, a seal No. 2 and a seal No. 3 constituted all of the sealing means used for

26 2824365

  applications to reactor coolant pumps. However, in the present embodiment of the invention, a relief or stop seal No. 4 is provided, functioning in a conventional manner as a seal during normal operation and as a stop seal in emergency conditions, whether the shaft turns or does not turn. According to the invention, it is important that the seal No. 4 is a segmented seal with low wear cooperating with an axial part of the rotary shaft and that it is designed so that, in the case where an extremely high pressure appears in the seal # 4, the seal continues to function either as a friction seal, if the shaft turns, or as a stop seal if

the tree is motionless.

  The gasket 78 n 4 of the present embodiment is placed in the two halves 39A and 39B of the closure cover 39. The two halves 39A and 39B are attached to each other by alignment fingers 69 s' extending between the corresponding flanges 68 thereof, then are machined in one piece so that a horizontal surface 266, facing downward, of the two halves 39A and 39B become a continuous sealing surface for the seal 78 n 4. The two-part closure cover 39 is fixed to the top of the joint housing segment 37 by bolts 64 with heads which are locked by appropriate bolt locking means. The radial position of the closure cover 39 relative to the top of the joint housing segment 37 is fixed by complementary shoulders at 250, formed on the upper surface of the housing segment 37, in order to form a slight recess in the surface of this one facing up. An O-ring 252 is disposed in a recess in the latter surface to provide a seal between the closure cover 39 and the housing segment 37. The ring 256 of the joint no. 4 shown in detail in FIGS. 5 and 6 is illustrated in the present example as having six assembled segments 256A. These segments 256A have a primary sealing surface on their inner peripheral surface or bore surface 257 and a secondary sealing surface on the surfaces 266, facing upwards, of each segment 256A of the sealing ring 256. An annular seal-receiving recess 254 is formed in the closure cover 39 (when the halves thereof are assembled with one another) and is oriented downwards on the inner periphery of the closure cover 39. A particularly cooperative combination is obtained if the segmented seal device 78 n 4 is a seal of the hydrostatic charge type, described in the aforementioned US Pat. No. 4,082,296 issued to Philip C. Stein. Thus, in the present embodiment, a segmented seal with hydrostatic charge will be described as a preferred means. We will find

  further details in the aforementioned Stein patent.

27 2824365

  Each annular segment 256 of seal with hydrostatic charge comprises, in the present example, two pockets 258, spaces in the circumferential direction, in the surface 257 of connected bore, at the rear edges of the pockets 258, at the high pressure edge of the surface 257 of bore by respective transverse grooves 265 which, when they receive a fluid, create forces which move each segment 256A of sealing ring towards the internal rotary element such as the shaft 34, reducing the 'joint gap between them. This inward movement results from the fact that the fluid received in the pockets 258 is returned by pumping

  in the highest pressure part of the housing, from which it came.

  The segments 256A of the hydrostatic charge seal 78 in FIGS. 2, 5 and 6 of this document are mounted in the closure cover 39 so that a high pressure (HP) appears to the right of the bore surface 257 (FIG. 6) and that a low pressure (LP) appears to the left of the bore surface 257. The pumping action of the hydrostatic charge bags 258 causes the fluid to come out of the bags 258

  to send it back. in the direction of arrow 260, in the high pressure region of the seal.

  A sealing threshold 262, formed on the (upper) side at low pressure of the bore surface 257 between the pockets 258 and the edge of the bore surface 257, serves as a friction face, normally almost wear-free, between the rings 256 of the sealing ring and the shaft in rotation almost in the absence of a pressure difference in the seal. However, if an enormous pressure, for example a pressure of 17225 kPa generated by a reactor, were to appear in the segments 256A of the hydrostatic joint 78 n 4, the total pressure would be exerted on the outer periphery of each of the segments of the seal, bringing the surface 257 of the bore of the seal segments into contact with the rotating shaft 34 (or the sleeve placed thereon) to ensure friction between the sealing threshold 262 and the member rotation, and simultaneously increasing the contact force of the sealing threshold 255 formoe on the upper surface 264 of the segments 256A and the sealing surface 266, facing downwards, of the closure cover 39. Under these conditions, wear and tear much stronger the sealing threshold 262 would occur. The outer periphery of each of the joint segments 256A has holes 269 (shown by transparency in FIG. 5) intended to receive compression springs (not shown) extending from the radial surface of the recess 254 for receiving seal up to the receiving holes 269

  springs formed in the axial outer surface of the seal segments 256A.

  As shown in Fig. 5, three coil springs extend into three holes 269 in each joint segment 256A to exert a positive clastic force

28 2824365

  towards the rear 34 on the segment 256A of the annular ring and the surface 257 of bore. The secondary seal between the surface 264 of the seal segments 256A and the downward-facing surface 266 of the housing in the recess 254 of the closure cover 39 may include a circumferential decompression recess 261 formed approximately midway in the surface 264 256A seal segments and

  connected to the high pressure side of the seal by radial cutouts 263 (Fig. 5).

  Now considering FIG. 2A, it can be seen that an upper shaft sleeve 268 is mounted on the arDre 34 and rests on the intermediate shaft sleeve 134; its length is relatively short in comparison with the length of the sleeve 134. It is placed opposite the segments 256A of joint No. 4 to react with these. The outer surface of the sleeve 268 is precisely machined to form a sealing surface intended to cooperate with the sealing threshold 262. The rotation of the upper sleeve 268 relative to the arDre 34 is prevented by the presence of at least two keys 270 extending downward from the lower edge of the sleeve 268 to complementary openings in the intermediate sleeve 134. The upward movement of the sleeve 268 is prevented by a fixing sleeve 280 and a fixing nut 282 which immobilizes the sleeve 280 relative to the artery 34 by conventional means (not shown). The secondary seal formed between the surfaces 264 of the seal segments 256A and the downwardly facing surface 266 of the recess has a precision machined surface, of flat shape, to serve as a sealing surface. The sealing ring segments 256A are coupled with each other by a socket assembly 284 and 286, more particularly described in the

Stein patent cited above.

  As shown in Fig. 2A, each half 39A and 39B of the closure cover comprises a semi-circular plate 288 of spring support fixed to the latter by bolts such as the bolt 290, the plate 288 having the same extension as the lower radial surface of the half, respectively 39A and 39B. The movement of each of the segments 256A inwards is stopped by a tab 289 extending upwards from the spring support plate 288 into a radial slot 291 located on the lower surface of each segment 256A, extending from the bore surface 257 thereof and terminating approximately mid-distance in the segment, in a radial direction. Each radial slot 291 is placed on its segment 256A between the two pockets 258 of hydrostatic charge thereof so that the slot 291 does not interfere with the pockets 258. A single tab 289 and a single slot are used

291 for each 256A segment.

29 2824365

  Helical springs (not shown) are mounted on each plate 288 and extend upwards therefrom to be received in axial openings 267 (Fig. 5) of segments 256A to bring the sealing threshold 255 to the contact of the sealing surface 266 in order to provide a seal therebetween. In the present example, three coil springs are used with each joint segment 256A, so that each semicircular plate 288 for spring support carries nine of these coil springs. Thus, the joint device 75 n 4 is assembled to form two independent sub-assemblies each comprising a half 39A (or 39B) of the closure cover, three segments 256A of annular ring, a support plate 288 of springs comprising three tabs 282 , nine coil springs for axially biasing the sealing ring segments 256A and nine compression springs for biasing the seal segments 256A radially towards

  the interior towards the shaft sleeve 268.

  The normal operation of the sealing system is such that high pressure is present on the exterior surface of the seal No. 1, its value reaching a maximum of 17,225 kPa. The seal nl is a hydrostatic seal of the flm type with running water, already described, and reduces the pressure from 17,225 kPa to about 205-345 kPa in the seal space 93 on the internal side at low pressure of the ring. seal 82. This pressure is applied to the outer surface of the seal ring 150 of the seal 74 n 2. When the shaft 34 rotates, the high pressure prevailing outside the seal ring 150 n 2 (approximately 345 kPa) penetrates into the Rayleigh pockets of the insert 140 of the crown of the joint 2, creating a thin but positive sealing film in the space 170 of the joint 2, and reducing pressure in space 170 allows a decrease of 345 kPa up to around 20.5-41 kPa. This last pressure is then applied to the low pressure side of the ring 150 of the seal No. 2, and the liquid at this pressure penetrates into the region 224 of the housing, where it is exposed to the outer surface, or at the highest pressure, of the ring 210 of the seal n 3. When the shaft turns, this pressure is reduced to approximately 6.9-13.8 kPa by the seal n 3 and its Rayleigh pockets, this pressure extending to the outer periphery of the 78 n 4 seal device, where it is completely absorbed by the 78 n 4 seal. Thus, during normal operation, there is not even a leak mist which

  the exterior of the seal housing 32.

  Although this is not described as part of the present invention, it will be seen from FIG. 1B that several fluid passages are formed

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  in the seal housing 32, for example the passage A on the low pressure side of the seal n 1 for the possible evacuation of liquid; passage B for the low pressure side of the seal n 2 for the possible evacuation of liquid; and two passages C respectively

  for the evacuation of liquid and the possible injection of liquid upstream of the joint n 3.

  These passages will not be described further since they do not play a role in the

  operation of the sealing system according to the present invention.

  In the case where the motor-pump unit according to the present invention is not running and the shaft 34 is stationary, the hydrostatic seal 72 n 1 continues to reduce the pressure in the circuit by passing it from 17,225 kPa from high pressure side at around 345 kPa on the low pressure side thereof. However, the seal No. 2, which is of the hydrodynamic type, is caused to close by the downstream pressure exerted on the ring 150 of the seal No. 2, which brings the sealing threshold 180 into contact with the upper surface of the crown insert to completely stop any flow of liquid in seal no. 2. Obviously, the secondary seal 164 of the piston ring simultaneously prevents any passage of liquid. Since there is no pressure in the No. 3 joint, or at most a minimal pressure drop therein, the No. 3 and No. 4 joints will also be substantially closed. In the unlikely event that seal # 1 malfunctions, all of the pressure may pass through until seal # 2 is reached. Even if the latter is designed for normal operation with pressure of about 345 to 620 kPa in this one, it receives the totality of the pressure and it is brought to close if the shaft is stationary, or else it reduces this pressure as a joint of the Rayleigh type normally does in the case o the shaft 34 rotates. Likewise, if the arDre 34 is stationary, the seal n 3 is put in the closed position and the seal n 4 is in the closed position due to the elastic forces acting on the segments of the sealing ring. Any pressure not reduced by seal # 2 will be reduced by the Rayleigh seal function of seal # 3, and any pressure not reduced by seal # 3 will be absorbed by seal # 4, which will pump the liquid back at high pressure. in the high-pressure housing, in accordance

  the principle of a segment seal with hydrostatic charge.

  However, if seal # 2 and seal # 1 are simultaneously detectable when the shaft turns, all of the circuit pressure will be in seal # 3, and this seal, although it is normally designed to reducing a low pressure will reduce a large part of the total circuit pressure. Seal # 4, in which a much greater pressure reduction will occur due to the fact that only Seal # 3 reduces the system pressure upstream of it, will continue to

31 2824365

  act as a hydrostatic seal, pumping liquid back to the high pressure area. Even if the reduced pressure in this one is close to the total pressure of the circuit, the segments of the joint n 4 will move so that its sealing threshold comes to rub strongly against the upper sleeve 268 disposed on the shaft 34 and that 'It substantially contains the voltage for sufficient time to allow the shutdown and depressurization of the entire circuit for repair and / or replacement thereof. If the seals n 1 and n 2 fail simultaneously while the shaft is not rotating, the hydrodynamic seal n 3 will be subjected to the entire pressure and the tightness threshold 245 of the seal n 3 will come into contact with the upper surface 17 of the crown 208 of the joint 3 to close the joint 3 and withstand all of the pressure. If joint # 3 also experiences problems, and if all of the pressure passes through it without significantly decreasing while the shaft is stationary, all of the pressure will be in joint # 4, bringing the secondary sealing surfaces 264 and 266 coming to establish a sealed contact due to the pressure of the circuit. The sealing threshold 262 present on the seal segments 256A must be in contact with the external surface of the shaft sleeve 268 to absorb all of the pressure of the circuit substantially without

* no leaks.

  According to the present invention, the seal devices n 2, n 3 and n 4 are designed to be deposited in the form of sub-assemblies for their maintenance, repair and / or replacement, in a manner in which the engine 29 does not have to be removed from the pump 14. More particularly, in the case where a scheduled maintenance or an unscheduled maintenance is desired, and if the reactor system is stopped and

  cooled, it is possible to access the seals through the opening 50 of the engine support 40.

  In particular, when the bolts 60 are removed, the removable coupling device 58 of ArDres can be removed through the opening 50 to make the upper end of the shaft 34 accessible. If the sleeves 280, 268 and 134 d 'arDre have a sufficient diameter to receive the lower flange 56 in the openings of the sleeves, it is not necessary to remove the lower flange 56 from the upper end of the pump shaft 34. However, if the flange 56 cannot be received in the openings of the aforementioned shaft sleeves, then the flange 56 must be removed. The distance between the flange 54 and the flange 56 (that is to say the length of the coupling device 58) is set to a maximum to allow the passage of the various shaft sleeves and the various parts of the housing between the free ends of the motor shaft 52 and the shaft 34 of

32 2824365

  pump. However, when a new, longer shaft seal system is installed on existing motor pump units, it is too costly to lift the engine block further above the pump and replace or enlarge the engine support 40 and the coupling device 58. Thus, for existing motor pump groups, it may be necessary to use an additional shaft sleeve such as the upper sleeve 268. Thus, for certain motor pumps, the longest member that can pass laterally between the motor shaft 52 and its flange 154 and the top of the pump shaft 34 may be the intermediate shaft sleeve 134; for this reason, an upper sleeve 268 may be necessary to improve existing motor pump groups with the seal No. 4 according to the present invention. If not needed, the intermediate sleeve 134 can be extended to extend fully

  up to the fixing sleeve 284 instead of being extended by a separate sleeve 268.

  In this example, all parts of the housing which are removed are shorter than the intermediate shaft sleeve 134 and can be removed without lifting the

motor 29.

  To remove the gasket n 4, first remove the fixing nut 282 and the fixing sleeve 280. Then, remove the sleeve 268. Then, the bolts 64 which fix the closing cover 39 on the segment 37 are removed, and the 78 n 4 seal device can then be lifted in one piece upwards over the upper end of the pump shaft 34, then laterally between the upper end of the shaft 34 of the pump and the lower end flange 54 of the motor to be released through the opening 50 of the support 40 of the motor. It is also possible to remove the closing cover 39, comprising the sealing device 78 n 4, at the same time as the sleeve 268 (after having removed the fixing elements constituted by the nut 282, the sleeve 280 and the bolts 264 ). Then the seals # 2 and 3 can be removed in one lifting operation, and the seal ring # 1 can be removed when

  a separate lifting operation, as described below.

  If it is only desirable to examine the 78 n 4 seal system or to replace the 256 A segments of the 4 n seal, this can be done, according to the present invention, without detaching or removing the coupling 58 from the shafts. It suffices to remove the head bolts 64, the conical alignment pins 69 and the lateral bolts 70 from the flanges 68 of the closure cover 39 to separate the two halves 39A and 39B of the cover. Then, the closure cover 39 can be lifted slightly above the additional shoulders 250, and one of the subsets of the seal no. 4, contained in one of the halves of the closure cover, for example 39A, can then be

33 2824365

  separated from the sub-assembly of joint No. 4 contained in the other half 39B. All of the components of seal # 4, including the seal segments 256A, can be removed as two subassemblies without removing the coupling device 58

  artres, the sleeve 268 or the nut 282 and the fixing sleeve 280.

  However, for normal maintenance, the seal device 78 n 4 can be removed either by separating the two halves of the closure cover 39, as described above, before or after removing the sleeve 268, or at the same time as removing it. of the upper sleeve 268 of the closure cover without separating the halves 39A and 39B. The preferred embodiment of the present invention consists in first removing the sleeve 268 and then in separating the two sub-assemblies contained in the

  closure cover 39, thereby removing each subassembly separately.

  During normal maintenance, examination and / or replacement of seals concerns seals 2 and 3. After seal 4 has been removed, seals 2 and 3

  are removed in one piece by a single lifting operation, as follows.

  First of all, the bolts 63 which connect the housing segments 35 and 37 to the housing segment 33 are unscrewed and removed through the opening 50 of the motor support. A suitable lifting tool is then placed on the shaft sleeve 134 to lift the sleeve 134 over the upper end of the pump shaft 34, carrying with it, in one piece, the lock nut. 142 and the locking cup 144, the seal device 76 no 3, the housing segment 35 of the no 2, the housing segment 37 and the seal device 74 no 2. If desired, the support element 102 of seal n 1, which is then accessible from above the lower segment 33 of housing, can be lifted in one piece by entraining with it the sealing ring 82 n 1 by interaction between the outer ring 132 located on it ci and the shoulder located in the bottom of the recess 130 of the joint support element 102. The examination of the seals no 2 and no 3 and, if desired, of the sealing ring 82 no 1, can be carried out at this time, or alternatively spare sub-assemblies can be introduced into the housing 32 of seals, so that the examination of the different seals can be carried out later and the pump can be put back into service more quickly. Seal ring # 1 and seal systems # 2, 3, and 4 (or seal # 4 only) can be reassembled and the seal housing can be closed by reversing the order of operations. I1 is understood that the diameter of the arDre 34 for motor pump groups for reactors can be of the order of 178 to 203 mm. It is also understood that the motor-pump unit according to the present invention, which includes a new

34 2824365

  improved sealing system described above, makes it possible to ensure, practically in all circumstances, that a safe system of sealing without leakage exists for the group, the repair and the replacement of the joints being able to be carried out by stopping the system for a minimum of time. In addition, many aspects of the elements of the present invention are interrelated but can also be used separately; together, they contribute by their coordinated action to create a system and a combination of parts with stable functioning. Although the elements constituting the present invention can be used separately or together without praising the framework and the spirit thereof, it is understood that the specific embodiment will be interpreted as broadly as possible. prior art and not in

a limiting sense.

2824365

Claims (18)

  1. Sealing system for a pump (14) having a fixed housing (30, 32) containing a liquid under high pressure and having an inlet section (26) subjected to high pressure and an outlet section (37) exposed to a lower pressure and a shaft (34) in said housing (32) with an axis of rotation, for a closed circuit (10) intended to contain a liquid operating at high pressures higher than 6900 kPa, said system of sealing comprising a primary sealing device (72) for reducing the pressure and an emergency sealing device (74 or 76) for reducing the pressure, arranged in series in the direction of flow of the fluid from said inlet (26 ) up to said outlet from said housing, each sealing device (72 and 74 or 76) sealingly supporting said shaft (34) relative to said housing (32), said primary (72) and emergency sealing devices (74 or 76) each comprising a neck radial ring (80 and 138 or 208) of a seal which can rotate with said shaft (34), having an annular sealing face (94, of 140 or 217) extending radially on said crown, a sealing ring (82 and 150 or 210) with axial mobility surrounding said arUre (34), and a sealing face (92 and 180 or 245) on said ring facing said sealing face (94 of 140 or 217) of crown, of respectively, a secondary seal (109 and 164 or 234) sealingly supporting said sealing ring (82 and 150 or 210) relative to said housing (32) except in a space (93 and 170 or 240) of formed seal between said ring sealing face (92 and 180 or 245) and said crown sealing face (94, 140 or 217), said primary sealing device (72) being disposed between said shaft (34) and said housing (32) so that the higher pressure liquid passes from said housing inlet (26) to the first end é of its seal gap (93) exposed to the highest pressure and in said seal gap (93) to the other end thereof where the pressure has normally been reduced to a lower pressure, and said emergency sealing device (74 or 76) being placed between said shaft (34) and said housing (32) so that said other end of the space (93) for sealing the primary sealing device (72) allows fluid communication with the end at the highest pressure of the seal space (170 or 240) of said emergency seal (74 or 76); characterized in that said primary sealing device (72) is of the hydrostatic type, so that the fluid pressure is reduced in its joint space (93) regardless of whether said shaft (34) rotates or does not rotate, and in this 36 2824365   that said emergency sealing device (74 or 76) is of the hydrodynamic type, in which the pressure in its seal space (270 or 240) is reduced to achieve a controlled reduction in the pressure made between said shaft (34) and said housing (32) only when said arDre (34) rotates, and in that said emergency sealing device (74 or 76) is designed so that its seal space (170 or 240) is closed when said shaft (34) does not rotate, to prevent any leakage into space (170 or   240) seal thereof, unless said shaft (34) rotates.   2. Sealing system according to claim 1, characterized in that said secondary seal (109, 164 or 234) of said primary sealing device (72) and / or of said emergency sealing device (74 or 76) is a piston ring spring (164) in two parts, urged to establish leaktight contact with both the sealing ring (82, 150 or 210) of said primary and / or emergency sealing device (72,   74 or 76) and said housing (in 106, 162 or 232).   3. Sealing system according to claim 2, characterized in that said sealing device (72, 74 or 76) is said emergency sealing device (74 or 76).   4. Sealing system according to claim 2, characterized in that   said sealing device (72, 74 or 76) is said primary sealing device (72).   5. A sealing system according to claim 1, characterized in that said emergency hydrodynamic sealing device (74 or 76) comprises Rayleigh pockets (172 or 218) in its space (270 or 240) of joint, in that the Rayleigh pockets (172 or 218) are formed in the seal crown (139 or 208), and that a sealing threshold (180) or (245) for the emergency sealing device ( 74 or 76) is formed on one face of the sealing ring (150 or 210) forming the space (170 or 240) of seal.   6. A sealing system according to claim 5, characterized in that said Rayleigh pockets (172) are located in the joint space (170) on an annular horizontal surface (on 140) of said joint crown (138). and in that said seal space (170) has a first end located in a region of higher pressure than in the region of the housing located at the other end of said seal space, said seal ring (138) emergency relief having spaced pressure relief passages which open into the region of said housing adjacent to said other end of said emergency seal space (170) and having additional pressure relief passages spaced in the sealing ring (166) (167, 169 ) stubbing in the region of said housing adjacent to said other end of said space 37 2824365   (170) of emergency seal, in that said passages present in said seal ring (183) and said passages present in said crown (139) of seal cooperate to prevent rotation of said crown (138) of emergency seal and said emergency sealing ring (150) thereof relative to the center of gravity, thereby keeping said horizontal annular surfaces in a horizontal position   forming said seal space (170) when a pressure difference prevails therein.   7. Sealing device according to claim 1, characterized in that the emergency sealing device (74) comprises an insert (140) located in the ring (138) of joint along the space (170) seal thereof, in that Rayleigh pockets (172) are formed on said insert (140) and are exposed to the seal space (170), and in that said insert (140) is relatively harder material than the material (166) forming the seal space (170) on the ring sealing (150).   8. Sealing device according to claim 7, characterized in that lS said emergency sealing device (74) comprises an insert (166) formed in the sealing ring (150), which insert (166) has a surface exposed to part of the seal space (170), and in that said insert (166) is made of relatively softer material than the material forming the insert seal crown.   9. A sealing device according to claim 8, characterized in that the added element (140) of the emergency seal ring is made of silicon nitride, in that the added element (166) of the sealing ring relief is of carbon-graphite type, and in that the sealing threshold is formed on the added element (166) of the sealing ring.   10. Sealing device according to claim 1, characterized in that the emergency sealing device (74) comprises a plurality of Rayleigh pockets (218) spaced in the circumferential direction in the space (240) of joint, in that the Rayleigh pockets (218) are formed so as to be oriented upwards and are located in the seal ring (208), and in that a pumping groove (222) extends from each pocket Rayleigh (218), down through the crown (208) and also inward towards the shaft (34) to provide liquid   feeding the Rayleigh bags (218).   11. Sealing device according to claim 1, characterized in that a second emergency sealing device (76) is provided, and in that the second emergency sealing device (76) is a hydrodynamic seal 38 2824365   normally closed which forms a normally closed seal space (240) in fluid communication with the low pressure side of the seal space (170) of the   emergency sealing device (74).   12. Sealing device according to claim 1, in which said shaft (34) comprises a removable sleeve (134) mounted thereon to rotate with it, and in that said emergency sealing device is mounted on said muff   (134) and can be removed from said housing (32) when removing said sleeve (134).   13. A sealing device according to claim 11, characterized in that said second emergency sealing device (76) comprises a plurality of Rayleigh pockets (218) spaced apart in the circumferential direction in the joint space (240) , in that said Rayleigh pockets (218) are oriented upwards and are located in the crown (208) of the seal of said emergency sealing device (76), and in that a plurality of pumping grooves ( 222) extend from each Rayleigh pocket (218) through the seal crown (208), both downward and inward towards the shaft (34) and opening into a region (224) from   housing located upstream of the last joint space (240) mentioned.   14. Device according to claim 1, characterized in that a stop joint (78) with rubbing surfaces is arranged downstream of said emergency sealing device (74 and / or 76) and in fluid communication with the joint space (170 and / or 240) thereof, said stop joint (78) having a segmented joint (256) in which a bore surface (257) of each segment (256A) surrounds said shaft ( 34) and comprises pumping grooves (258) in said surface (257) of bore of each of said segments (256A) to return by pumping in said housing (32), to said emergency sealing device (74 or 76 ), the liquid leaving said grooves (258), 2S each of said segments (256A) of sealing ring being pushed into grooves (269) in contact with said shaft (34) and each of said segments (256A) of sealing ring comprising a secondary sealing surface (2 64) pushes in contact with a complementary sealing surface ( 266) present on said housing (39), and in that the surfaces of said sealing ring segments (256A) facing the bore surface (257) of these and facing the sealing surface secondary (264) are exposed to a higher pressure so that, in the event of malfunctions of the primary sealing device (72) and / or the emergency sealing devices (74 or 76) during which the high pressure is not significantly reduced, this high pressure is exerted on said last mentioned surfaces of said 39 2824365   sealing ring segments (256A), which urges the bore surface of said sealing ring segments (256A) to come in sealing contact with said shaft (34) and said secondary sealing surface (264) said segments (256A) coming into contact with said complementary sealing surface (266) present on said housing (39). 15. A sealing device according to claim 1, in which said stop joint (78) consists of two semicircular subassemblies (39A) joined to each other at the level of surfaces (66) s extending axially opposite one another and comprising keys (69) connecting said subassemblies (39A, 256A and 288) to align them in the axial direction and fixing devices (70) for fixing   the sub-assemblies (39A, 256A and 288) to each other.   16. A sealing system according to claim 1, characterized in that said sealing ring (150 or 210) has an annular portion (152 or 236) extending downward, located outward and extending downwards to be placed above a part of the external surface of said ring (138 or 206) of seal at the high pressure end of said space (170 or 240) of seal of said emergency sealing device (74 or 76), and said sealing ring (150 or 210) having at least one opening (183 or 242) extending through said sealing ring (150 or 210) from the entry side of said space (170 or 240) of seal to a high pressure region of said housing (30, 32) to prevent the accumulation of pressurized gas at the entrance of said seal space (170 or 240) in the immediate vicinity of said portion annular (152 or 236), which would otherwise prevent the liquid from entering said space (170 or 240) seal.   17. Sealing system for fixed housing (30, 32, 39) containing a liquid under high pressure, having an inlet section (26) exposed to high pressure, an outlet section (adjacent to 37, 39) exposed at a lower pressure, and a rotary shaft (34) in said housing (30, 32, 39) with an axis of rotation, for a closed circuit (10) containing a liquid operating at high pressures greater than 6900 kPa, said sealing system comprising a primary pressure reducing sealing device (72) and an emergency pressure reducing sealing device (78), arranged in series in the direction of flow of the fluid from said inlet (26) up to said outlet from said housing (30, 32, 39), each sealing device (72, 78) sealingly supporting said shaft (34) relative to said housing (30, 32, 39), said sealing device primary seal (72) comprising a ring (80) of extending joint radially, rotatable with said shaft (34), comprising a 2824365   annular sealing face (94) of crown which extends radially, a sealing ring (82) with axial mobility surrounding said shaft (34) and a sealing face (92) of ring on that here, facing said crown sealing face (94), said sealing ring (82) having a secondary seal (109) mounted in a sealed manner to support said sealing ring (82) relative to said housing (32, 102, 106) except in the joint space (93) formed between said ring sealing face (92) and said crown sealing face (94), said primary sealing device (72) being disposed between said shaft (34) and said housing (32) so that the liquid at the highest pressure passes from the inlet (26) of the housing to a first end of said seal space (93) which is exposed to higher pressure and in said seal space (93) to the other end thereof where the pressure has normal has been reduced to a lower level, and said emergency seal (78) being disposed between said shaft (34) and said housing (32) so that the other end of said seal space of the seal primary (72) is in fluid communication with the highest pressure end of the seal space (at 265) of said emergency sealing device (78), said sealing system being characterized in that said emergency seal (78) has a segmented hydrodynamic seal (Fig. 5) having a surface (257) of bore of each segment (256A) which surrounds said shaft (34) and having in said surface (257) of bore of each of said segments (256A) pumping grooves (258, 265 ) which return in said housing (30, 32, 39), towards said primary sealing device (72), the liquid leaving (260) of said grooves (258, 265), each of said segments (256A) of sealing ring being pushed (in the openings 269) in contact with said shaft (34) and each of said segments (256A) of sealing ring having a secondary sealing surface (264) pushed in contact with a complementary sealing surface (266 ) present on said housing (39), and in that the surfaces of said sealing ring segments (256A) facing the bore surface (257) thereof and facing the secondary sealing surface (266) are exposed to a higher pressure, so that, in the event of a malfunction of the primary seal e (72) in which the high pressure of the circuit is not significantly reduced by said primary sealing device (72), this high pressure is exerted on said last cited surfaces of said segments (256A) of sealing ring, which pushes the surface (at 262) of bore of said segments (256A) of sealing ring in a sealed manner in contact with said shaft (34) and said secondary sealing surface (264) of said segments (256A) in a sealed manner in contact with said sealing surface   complementary (266) present on said housing (39).   18. Sealing system according to claim 17, characterized in that, in said outlet section (37) of said housing (30, 32, 39), said shaft (34) passes S through an opening thereof, in that said housing (30, 32) comprises a closure cover (39) of annular shape, with axial division forming two halves (39A, 39B) mounted on said outlet section (37) thereof, said shaft (34 ) passing therethrough and being precisely received in the opening of said closure cover (39), fasteners (64) sealingly sealing said closure cover (39) to said outlet section (37 ) of the housing and of the additional fixing devices (70) fixing the two halves (39A, 39B) of said closure cover (39) to each other, alignment fingers (69) coupled to the two halves (39A , 39B) of said closure cover (39) and aligning them axially with respect to each other, said cover d The closure (39) forming an annular recess (254) of housing which surrounds said arDre (34) and is exposed inside said housing (Fig. 2A), said segments (256A) of sealing ring being located in said recess (254) for housing said closure cover (39), said complementary sealing surface (266) present on said housing (39) being a surface annular (266) inside said recess (254) which surrounds said shaft, each i. said halves (39A, 3: 9B) of said closure cover (39) having a half ring (288) located opposite and spaced apart from said complementary surface (266), said ring segments (256A) sealing being placed in said recess (254) between said complementary surface (266) and said half ring (288), and a lug (289) and a slot (391) cooperating on said half ring (288) and each of said segments (256A) seal to stop the movement of said segments (256A) towards said shaft (34), whereby said halves (39A, 39B) can be removed separately from said housing (30, 32, 37) at the division ( in 66) between them in order to