Abstract:
The invention relates to a blowout valve assembly (blowout preventer (BOP)) comprising a connecting channel, which can be closed by at least one closing device, whereby the closing device can be transversally displaced with regard to the connecting channel by means of a drive device. The aim of the invention is to further improve a blowout valve assembly of this type in order to enable this assembly to be precisely and easily actuated by remote control and while, at the same time, reliably preventing an unintentional opening of the closing device. To this end, the drive device comprises at least two electric motors, which can be operated individually or in a synchronized manner, and comprises a transmission device having at least one irreversible transmission unit. In order to displace the closing device, said transmission unit is drive-connected to both electric motors.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a blowout valve assembly, i.e. a so-called blowout preventer (BOP), with a connecting channel which can be closed by at least one closing device, whereby the closing device can be transversally displaced with regard to the connecting channel by means of a drive device. 
   Such a blowout valve assembly is used both with terrestrial and maritime mineral oil or natural gas drilling wells. The blowout valve assembly is used to prevent an uncontrolled blowout of the mineral oil or natural gas which is conveyed under high pressure along the pipe lines. To achieve this, the blowout valve assembly comprises at least one closing device. A connecting channel of the blowout valve assembly is arranged in the pipe line, whereby the conveyed mineral oil or natural gas also passes through this connecting channel. The closing device can be transversally displaced with regard to the connecting channel and is displaced if necessary by a drive device so far in the direction of the connecting channel that it is closed and an uncontrolled blowout of mineral oil or natural gas is prevented. 
   With the blowout valve assembly known in practice the drive device operates hydraulically. Consequently, the blowout valve assembly must have available an appropriate pipe system for the supply of the hydraulic fluid, and appropriate hydraulic devices for operating this blowout valve assembly, more of these arrangements or also more devices for mineral oil and natural gas supply must be arranged outside of the blowout valve assembly. The drive device is therefore quite complicated. 
   A further disadvantage in this connection is that whereas a large force can be applied by a hydraulic drive device, it cannot be controlled precisely. It can therefore arise that the closing device either does not shut off sufficiently tightly or shuts off too tightly so that it can hardly be opened again. In addition, a slow and partial opening of the closing device is not always possible with a hydraulic drive device. 
   BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS 
   The object of the invention is therefore to improve a blowout valve assembly of the type mentioned in the beginning such that it can be actuated remotely in an exact and simple manner and at the same time unintentional opening of the closing device is reliably prevented. This object is solved in relation to the characteristics of the generic terms of claim  1  in that the blowout valve assembly comprises at least two electric motors, which can be operated individually or in a synchronized manner and comprises a transmission device having at least one irreversible transmission unit, which is drive-connected to both electric motors to displace the closing device. 
   Through the electrical actuation of the blowout valve assembly appropriately complex pipe systems for a hydraulic fluid (external pipes supplying these pipes), a hydraulic fluid source and similar equipment can be replaced by an electrical drive device. The said drive device is connected in a simple manner via electrical feeder cables and can especially be controlled from a remote position. The electrical motors can be operated singly and redundantly or also synchronously and simultaneously. Due to the irreversible transmission unit of the transmission device the blowout valve assembly is, for example, reliably prevented from unintentionally opening when the electric motors are switched off. The irreversible property is only cancelled after the application of a suitable release element by the electric motor or motors and the blowout valve assembly can be displaced for partial or full opening of the connecting channel. 
   In order to obtain electric motors which can be exactly controlled and, with regard to torque and speed, monitored, the said motors can be formed as servomotors, especially as direct current servomotors. Such motors exhibit high reliability and high efficiency. 
   In order to be able to control and monitor the electric motors also separately, each electric motor can be electrically connected to a separate control device. 
   The irreversible transmission unit can be formed in various ways. One example is a planetary gear or similar. To render the transmission unit simple and reliable, it can be a worm gear comprising at least a worm and worm wheel, whereby the worm wheel is associated with the closing device and the worm is associated with the electric motors. Such a worm gear is inherently irreversible, whereby the irreversible property can also be realized in both displacement directions of the transmission. 
   In order to be able to directly drive the worm from the electric motors, the worm can be arranged on a worm shaft which is drive-connected to both electric motors. 
   One possible arrangement of the electric motors can be seen in that the said motors are arranged behind one another at one end of the worm on the worm shaft. A further possible arrangement can be seen in that the electric motors are drive-connected to the opposite ends of the worm shaft. 
   In the simplest case and without the use of additional motor shafts, which would have to be connected to the worm shaft, each end of the worm shaft can be rotationally rigidly connected to one of the electric motors as its motor shaft. 
   In order to enable a still higher gear ratio and to enable the transfer of a still higher torque or a larger force to the closing device by the electric motors, the transmission device can comprise at least one screw drive comprising at least a screw drive nut and a rotating spindle, whereby the worm wheel is rotationally rigidly connected to the screw drive nut or the rotating spindle. 
   One example of such a screw drive is a ball screw drive. Here, the screw drive nut is formed as a ball nut and the rotating spindle as a recirculating ball screw spindle. 
   In order to obtain a screw drive with a high load-bearing capacity, long service life, highest reliability and for adverse ambient conditions, the screw drive can be a roll screw drive. 
   In order to increase the load-bearing capacity of the screw drive and to construct the said drive very ruggedly, the roll screw drive can be a planetary roll screw drive. 
   With the blowout valve assembly known from practice the closing device comprises at least one closing element in the form of a closing wedge or closing jaw. According to the invention, the construction can be simplified in that the rotating spindle of the screw drive is connected to the closing element of the closing device. 
   In order to be able to design the blowout valve assembly still more compact and to be able to dispense with any intermediate parts between the rotating spindle and the closing element, the rotating spindle can be formed as part of the closing device and can exhibit the closing element at its end facing the connecting channel. Here, the rotating spindle and the closing element can be connected together in a manner which facilitates their release. 
   With one embodiment of a blowout valve assembly the closing element is supported in a suitable device housing transverse to the connecting channel and connected with the rotating spindle. In order to be able to displace the rotating spindle in a simple manner together with the closing element in the direction of the connecting channel, the screw drive nut can be supported in the device housing so that it can rotate, but cannot be moved axially. A rotational movement is transferred to the screw drive nut via the worm drive and converted into a linear movement by the said worm drive in combination with the rotating spindle due to the fixed axial position of the screw drive nut in the device housing. 
   In order to be able to use commercially available screw drives and corresponding screw drive nuts, appropriate adaptations relative to the device housing can be achieved, especially in that the screw drive nut is arranged rotationally rigidly in a bearing sleeve which can be rotated in the device housing, but which is supported so that it cannot be moved axially. The bearing sleeve is primarily used as adapter for arranging the screw drive nut in the device housing, whereby the connection between the bearing sleeve and screw drive nut can, for example, occur by shrinking on or also by the releasable attachment of the screw drive nut within the bearing sleeve. The internal dimensions of the bearing sleeve can be varied to accommodate different screw drive nuts, whereas the appropriate external dimensions of the bearing sleeve are always ready-made for the corresponding device housing. 
   In order to transfer the driving force transferred from the electric motors through the worm gear as directly as possible to the screw drive nut, the worm wheel can be connected rotationally rigidly to the screw drive nut and/or the bearing sleeve. Consequently, there is especially the possibility of arranging the worm gear very close to the screw drive. Of course, there is also the possibility of providing or connecting the screw drive nut and/or bearing sleeve with external teeth which engage corresponding external teeth on the worm wheel. With regard to the worm wheel it should be noted that the worm wheel can be, for example, a globoid worm wheel or a spur wheel and correspondingly the worm can be a cylindrical worm or a globoid worm. 
   A simple method of rotationally supporting the bearing sleeve with screw drive nut and simultaneously for the axial fixation of both of them can be seen when the bearing sleeve is rotationally supported using at least one axial bearing in the device housing. The axial bearing can be a roller bearing and especially a spherical roller bearing. The latter can also accept appropriately high axial forces as well as high radial forces. 
   In order to arrange the electric motors independently of the device housing and to simplify access to the said motors, the electric motors can be arranged on both sides with respect to the device housing and especially in motor housings which can be flange-connected to the said device housing. 
   In order to be able to accommodate the worm shaft in the device housing and in the close vicinity of the screw drive, the worm shaft can be rotationally supported in a transverse hole running approximately tangentially to the longitudinal hole of the device housing, the said longitudinal hole accommodating the rotating spindle and screw drive nut. The appropriate motor housings for accommodating the electric motors can be connected to the side of this transverse hole. 
   In order to enable secure closing of the connecting channel, especially at the high pressures in mineral oil production, which may be up to many hundreds of bar, two closing elements which can move towards one another can be supported in the device housing and at least one screw drive, one worm gear and two electrical motors can be assigned to each closing element. Through appropriate synchronization of the movement, both closing elements can be moved towards one another simultaneously and synchronously for closing the connecting channel. Correspondingly, it is possible to move the closing elements back using the electric drive devices slowly and partially or completely from their closed position for opening the connecting channel. 
   In order to be able to apply a still higher force for closing the blowout valve assembly, each closing element can be connected, especially in a releasable manner, to an advance shaft which is connected at its end section, which points away from the closing element, to a transverse beam arranged transversally to its longitudinal axis, the said transverse beam being connected on both sides to the advance shaft with a left and a right screw drive. Consequently, the transverse beam can be moved simultaneously by two screw drives. The movements of the two screw drives can occur through connections to a worm gear and two electric motors associated with it. 
   However, in order to substantially increase the force acting through the screw drives, a worm gear and two electric motors can be assigned to each of the left and the right screw drives. 
   With a blowout valve assembly with two closing elements which can move towards one another four screw drives, four worm drives and a total of eight electric motors can be used in this case. However, to simplify the construction the worm wheel, for example, assigned to the left screw drive can be arranged approximately centrally between two rotating spindles and rotationally rigidly connected to them, whereby the thread pitch on the rotating spindles is opposing and a screw drive nut is arranged on each rotating spindle, the said screw drive nut being connected appropriately to the relevant transverse beam of the closing elements which can move towards one another. In this manner, only two worm gears each with two electric motors are needed for the left and right screw drives of the two closing elements. Here, in each case one worm gear is used for the actuation of two left or correspondingly two right screw drives. 
   The linear movement produced via the screw drives is transferred via the transverse beams to the two closing elements which can be moved towards one another. In the previously described embodiment the worm wheel is rotationally rigidly connected to the rotating spindles, so that correspondingly the screw drive nut executes the linear movement. To prevent the screw drive nut in this relationship from rotating, the screw drive nut can be rotationally rigidly guided along the rotating spindle in a transmission housing in the longitudinal direction of the rotating spindle. 
   In order to translate the linear movement of the screw drive nut along the rotating spindle in a simple manner to an appropriate linear movement of the transverse beams, the screw drive nut can be held in an essentially tube-shaped retaining sleeve, which comprises at least one sliding section which can be rotationally rigidly displaced along the transmission housing. The tube-shaped retaining sleeve can be attached to a transverse beam at its free end. The rotationally rigid support of the screw drive nut does not occur in this connection through a direct action between the screw drive nut and the transmission housing, but instead via the rotationally rigid guidance of the sliding section of the retaining sleeve. 
   In this connection, the construction can furthermore be simplified in that, where applicable, the sliding section is formed at the end of the retaining sleeve facing the rotating spindle and the screw drive nut is rotationally rigidly held in it. In this way retaining sleeves with the least possible length can be used. 
   The rotationally rigid mounting can consequently be realized in a simple manner if the sliding section is essentially quadrilateral appropriate to a cross-section of a guide hole in the transmission housing. One possibility for such a quadrilateral cross-section is, for example, a quadratic or rectangular shape. 
   In order to prevent the sliding section from jamming inside the guide hole and to also reduce the friction when the sliding section slides along the guide hole, sliding plates can be especially arranged on all four outer sides of the sliding section. The said sliding plates slide along corresponding inner sides of the guide hole and thereby reduce the friction during the displacement of the retaining sleeve along the transmission housing. 
   A retaining sleeve of sufficient strength can be especially obtained if the retaining sleeve exhibits an essentially circular shaped cross-section except on its sliding section and protrudes from one end of the transmission housing and is there attached especially in a releasable manner to the transverse beam at its free end. 
   A simple method of attaching the retaining sleeve and the transverse beam can be seen in that the end of the retaining sleeve and transverse beam are screwed together. 
   In order to be able to accommodate the electric motors in a simple way with the side arrangement of the said motors to the device housing and to render them separately accessible, the electric motors can be arranged especially in pairs in a motor housing extending transversely and essentially tangentially to the transmission housing. 
   In order that the worm wheel can be rotationally rigidly connected in a simple manner to the two assigned rotating spindles, the worm wheel can be rotationally rigidly arranged on a connecting rotational sleeve and, on its two ends, ends of the rotating spindle can be attached with opposing screw pitch. The connecting rotational sleeve also permits worm wheels of larger diameters so that the gear ratio can be further increased. In addition the connecting rotational sleeves permit a simple attachment of the rotating spindle in that, for example, it is screwed into them with its ends facing the connecting rotational sleeve. 
   With one embodiment of the blowout valve assembly according to the invention in which the electric motors are employed simultaneously, an appropriate synchronization of the movements of the motors is necessary. An essentially mechanically based synchronization is extremely difficult for reasons of production, because deviations in the construction of the motors, worm shaft, worm, worm wheel, screw drives, etc. can hardly be avoided. According to the invention, the synchronization of the electric motors therefore occurs by software, especially via their control devices. 
   A simple method of synchronization using software can be seen in that one electric motor is wired as the master and the other electric motors as slaves or also all electric motors are wired as masters. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, advantageous embodiments of the invention are explained in more detail based on the figures in the enclosed drawing. 
     The following are shown: 
       FIG. 1  shows a perspective plan view as an exploded view of a blowout valve assembly according to a first embodiment; 
       FIG. 2  shows a side view of a drive device in a cut-away view with transmission for the blowout valve assembly according to  FIG. 1 ; 
       FIG. 3  shows a side view according to  FIG. 2  with additional device housing and retaining sleeves; 
       FIG. 4  shows a cross-section through the device housing according to  FIG. 3 ; 
       FIG. 5  shows a cross-section through a second embodiment of a blowout valve S assembly, and 
       FIG. 6  shows a cross-section along the line VI—VI in  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a perspective plan view from diagonally above onto an exploded view of an embodiment of a blowout valve assembly  1 . This comprises a device housing  36  centrally along a longitudinal axis  29  in which a connecting channel  3  is formed. When the blowout valve assembly  1  is inserted into a pipe line, for example in mineral oil production, the said channel forms part of the pipe line through which the supplied mineral oil flows. 
   A closing hole  90 , in which two closing elements  34 ,  43 , which can be moved towards one another, are supported as part of a closing device  2 , extends transverse to the connecting channel  3  in the device housing  36 . The closing elements  34 ,  43  are formed by closing jaws which engage one another in the region of the connecting channel  3  and close it off completely. 
   The closing elements  34 ,  43  are releasably connected to the advance shafts  44 ,  45  on their rear sides which are positioned opposite the connecting channel  3 . On one end of the advance shafts facing the corresponding closing element, there is a connection adapter  79  arranged, via which the advance shaft and closing element are attached together. The advance shafts also extend in the direction of the longitudinal axis  29  through the housing cover  74 ,  75  and terminate outside of approximately V-shaped arms  76 ,  77 . The said arms are attached to the housing covers  74 ,  75  by the ends of their V-legs. The housing covers  74 ,  75  can be attached to the device housing  36  via threaded studs  78  and suitable nuts which are not shown. 
   Within the end arms  76 ,  77  a yoke  67  as cross-beam  48 ,  49  protrudes from the advance shafts  44 ,  45  transverse to the longitudinal axis  29 . This yoke exhibits holes in both of its outer positioned ends into which the ends  63 ,  64 ,  65 ,  66  of retaining sleeves  54 , where applicable, can be partially inserted and attached by threaded studs. 
   The retaining sleeves  54  extend parallel to the longitudinal axis  29  and exhibit a sliding section  55 ,  56 , enlarged in diameter, opposite their ends  63  to  66 . A screw drive nut  25  to  28  is held rotationally rigidly in this sliding section  55 ,  56 , which is preferably quadrilateral in cross-section. The appropriate screw drive nuts  25  to  28  form a part of the screw drives  21  to  24 . A rotating spindle  30  to  33  is rotationally supported in each of the screw drive nuts  25  to  28 . 
   With the embodiment illustrated in  FIG. 1  the relevant rotating spindles  30  to  33  extend from the screw drive nuts  25  to  28  to worm wheels  15 ,  16 . These worm wheels are rotationally rigidly connected to both rotating spindles  30 ,  31  respectively  32 ,  33  which are each adjacent in the direction of the longitudinal axis  29 . 
   The worm wheels  15 ,  16  each form part of worm gears  11 ,  12  forming transmission units  8 . The other part of the worm gear is formed by an appropriate worm  13 ,  14 , which engages an appropriately toothed corresponding worm wheel  15 ,  16  via appropriate outer teeth. The worms  13 ,  14  are arranged on appropriate worm shafts  17 ,  18 . These are connected with their shaft ends  19 ,  20 , see also the other figures, to electric motors, especially direct current servomotors. One electric motor drives each corresponding shaft end of one of the worm shafts. 
   In one embodiment of the invention each of the electric motors can be connected to control devices  9 ,  10  positioned remote with respect to the blowout valve assembly using appropriate electrical connecting lines  91 . In one embodiment of the invention each electric motor is provided with its own control device. 
   The appropriate threads of the rotating spindles  30 ,  31 , respectively  32 ,  33 , exhibit correspondingly opposing pitches so that with the transmission device  7  positioned to the right of the device housing  36  in  FIG. 1  the screw drive nut  25  moves in the opposite direction along the longitudinal axis  29  as the screw drive nut  26  when the associated worm wheel  15  rotates. This applies analogously to the transmission device  7  illustrated in  FIG. 1  to the left of the device housing  36 . 
   It should be noted that of course appropriate control devices for the supply of each of the electric motors are also provided for the electric motors  5  and  6  in the transmission device  7  illustrated to the left. 
   In  FIG. 2  a side view of a longitudinal section through a left or right transmission device  7  is illustrated partially according to  FIG. 1 . In this figure as in all other figures the same parts are given the same reference symbols and are partially explained in more detail only in connection with a figure. 
   In  FIG. 2  the transmission device  7  is accommodated in a transmission housing  52  which also extends parallel to the longitudinal axis  29  according to  FIG. 1 . In the transmission housing  52  the rotating spindles  30 ,  31  are arranged with the corresponding screw drive nuts  25 ,  26  positioned on them. For clarity the screw drive nut  25  is not illustrated in  FIG. 2  in conjunction with the rotating spindle  30 . 
   The screw drive nut  26  is rotationally rigidly held in the sliding section  56  of the retaining sleeve  54 . The sliding section  56  exhibits, for example, a quadrilateral and especially square cross-section which can be displaced along an appropriately square cross-section of the transmission housing  52 . Sliding plates  60  are arranged between the sliding section  56  and the transmission housing  52  on the corresponding outer sides  59  of the sliding section  56  to reduce the friction. 
   The sliding section  56  is arranged on an end  73  of the retaining sleeve  54  facing the worm gear  11  as transmission unit  8 . The said retaining sleeve  54  exhibits a tube section  86  with an essentially circular-shaped cross-section which extends from the sliding section  56  to the free end of the transmission housing  52  where it is brought out. The corresponding end  64  of the tube section  86 , see also  FIG. 1 , can be attached in the yoke  67  in the appropriate hole. 
   At this point it must be noted that all other screw drives and worm drives for the embodiment according to  FIG. 1  are constructed analogously to the versions according to  FIGS. 2 to 4 . 
   In  FIG. 2  the screw drive nut  26  is displaced so far in the direction of the worm drive  11  along the rotating spindle  31  that the retaining sleeve  54  connected to it is drawn as far as possible into the transmission housing  52 . 
   Transverse to the transmission housing  52  a motor housing  68  extends in which the electrical motors  5 ,  6  are arranged, between which the worm gear  11  extends. The worm gear  11  exhibits the worm  13  arranged on the worm shaft  17 , the said worm engaging with its outer teeth the corresponding outer teeth on the worm wheel  15 . The corresponding teeth on the worm and worn wheel can be formed such that the worm is a globoid or cylindrical worm or correspondingly the worm wheel is a spur wheel or a globoid wheel. The worm wheel  15  is positioned rotationally rigidly on a connecting rotational sleeve  70  which extends in the longitudinal direction of the rotating spindles  30 ,  31  and corresponding ends of the rotating spindles  30 ,  31  are rotationally rigidly mounted in both its ends  71 ,  72 . Appropriate bearings  80 ,  81  are arranged in the transmission housings  52  at the transition to the corresponding motor housing  68  or  69 , see also  FIG. 4 , for the rotational support of the connecting sleeve  70 . 
   The worm shaft  17  is arranged with each of its shaft ends  19 ,  20  in one of the electric motors  5 ,  6  where they are rotationally rigidly attached at their free ends  82 ,  83  with appropriate nuts  84 ,  85 . 
   It is pointed out once again that the rotating spindles  30 ,  31  are formed with opposite running screw pitches  50 ,  51 , so that the corresponding screw drive nuts  25 ,  26  move in opposite directions along the rotating spindles  30 ,  31  when the worm wheel  15  rotates. 
   With regard to the screw drives it is pointed out that these can be ball screw drives or roll screw drives. According to the invention, with the illustrated embodiments roll screw drives and especially planetary roll screw drives are used. 
   In  FIG. 3  a side view analogous to  FIG. 2  is illustrated, especially with the device housing  36  and the housing covers  74 ,  75  mounted on it with appropriate end arms  76 ,  77 . 
   According to  FIG. 3  the two screw drive nuts  26 ,  25  are displaced as far as possible in the-direction of the yoke  67 , respectively the transverse beams  48 ,  49  within the transmission housing  52 . Correspondingly, the tube sections  86  of the retaining sleeves  54  are almost completely pushed out of the transmission housing  52 . The tube sections  86  are attached to the transverse beams  48 ,  49  by the threaded studs  87 , see also  FIG. 1 . In  FIG. 3  it can especially be seen that the screw drive nuts  25 ,  26  are held in the corresponding sliding sections  55 ,  56  by screwing on a mounting ring  92  in the sliding sections  55 ,  56  and are arranged there rotationally rigidly. 
   The transmission housings  52  are closed at their ends positioned remotely from the worm gear  11  by closing caps  93  by screwing to the corresponding ends  61 ,  62 , whereby within these ends appropriate bearings are also arranged for displacing the retaining sleeves  54 . 
   The advance shafts  44 ,  45  protrude with their end sections  46 ,  47  outwards beyond the corresponding end arms  76 ,  77 , see also  FIG. 1 , and, as with the rest of the advance shafts  44 ,  45  they are arranged offset parallel to the rotating spindles  30  to  33 . 
   In  FIG. 4  a section transverse to the illustration according to  FIGS. 2 and 3  is shown, whereby the section is positioned on the side of the left transmission device  7 , see  FIG. 1 , through the motor housing and on the right side of the device housing  36  in the direction of the longitudinal axis  29  offset to the motor housing by the corresponding sliding section  56 . 
   In  FIG. 4  it can be seen especially that the transmission housing  52  and corresponding motor housing  68 ,  69  are flange-connected at the side to the device housing  36 . The corresponding motor housings  68 ,  69  are fitted here sideward offset to the outside on the transmission housings  52 . The motor housing and transmission housing can also be formed out of one piece. 
   The worm shaft  18  extends tangentially to the worm wheel  16  and is held rotationally rigidly at both ends in the corresponding electric motors  5  and  6 , so that both motors can drive the worm shaft  18  simultaneously and synchronously. 
   In the region of the sliding section  56  it can be seen from the figures that the said sliding section exhibits an essentially quadratic cross-section arid is guided in a similarly quadratically formed transmission housing  52  in its longitudinal direction. Sliding plates  60  for reducing the friction are arranged between the sliding section  56  or its outer sides and the transmission housing  52 . 
   In  FIG. 5  a Section  4  through the device housing  36  is illustrated, see also  FIG. 1 , for a second embodiment of a blowout valve assembly  1  according to the invention. 
   This embodiment differs from the previously described embodiment especially in that the screw drive acts directly on the advance shaft and is arranged in the device housing  36 . Accordingly, the worm gear is arranged transverse to the longitudinal axis  29 , see  FIG. 1 , of the device housing  36 , whereby the worm shaft  17  with worm  13  is appropriately supported rotationally in a transverse hole  42  of the device housing, the said hole extending approximately tangentially to the longitudinal hole  41  or closing hole  90 , see  FIG. 1 . The associated worm wheel  15  is rotationally rigidly connected to the corresponding screw drive nut  25  of the associated screw drive  21 . The worm wheel  15 , screw drive nut  25  and rotating spindle  30  are arranged concentrically to the corresponding advance shaft  44  or  45 , whereby the advance shafts  44 ,  45  can be formed in this connection also directly by the corresponding rotating spindles. Consequently, the corresponding closing element  34 ,  43  can be directly attached releasably to the free end of the corresponding rotating spindle via the connection adapter  79  illustrated in  FIG. 1 . 
   The worm shaft  17  is brought out at the side from the transverse hole  42  out of the device housing  36  where it is connected to the electric motors  5 ,  6 . These motors are arranged in appropriate motor housings  39 ,  40 . Within the transverse hole the worm shaft  17  is supported rotationally using appropriate bearings  88 . 
   In  FIG. 6  a section along the line VI—VI from  FIG. 5  is shown. It should be noted that both advance shafts  44 ,  45  according to  FIG. 1  with the second embodiment according to  FIGS. 5 and 6  are driven directly by a suitable screw drive with associated worm gear, whereby at least the screw drives are arranged within the device housing  36 . 
   According to  FIG. 6  the screw drive nut  25  is arranged rotationally rigid within a bearing sleeve  37 . The screw drive nut comprises a circumferential flange  94  which protrudes radially outwards and which is adjacent to a shoulder of the bearing sleeve  37  which protrudes radially inwards and is attached to it by threaded studs or similar. With the radially inwards-protruding shoulder of the bearing sleeve  37  the worm wheel  15  is attached by screwing on the side opposite the circumferential flange  94 . 
   The rotating spindle  30  is passed through the worm wheel  15  and the screw drive nut  25  and is supported in these rotationally. The rotating spindle  30  can in this connection be connected rotationally rigidly at its end facing the corresponding advance shaft  44 ,  45  to the said shaft or it can exhibit a connection adapter  79  itself at this free end, see  FIG. 1 . 
   The bearing sleeve  37  can be rotated within the device housing  36  using an appropriate axial bearing  38 , but is supported without being able to be axially displaced. A threaded ring is screwed onto the bearing sleeve  37  at one end in the axial direction to fix the said bearing sleeve.