Sealed Transmission Device Using Metal Bellows, Suitable for Quarterturn Valves

1. Field of the invention

The invention concerns a bellows type sealed transmission device suitable for controling a high-security valve which is operated by a quarter-turn rotation or less. The invention is directed to simplifying the structure of this type of device and to improving the working conditions of the bellows in order to increase its reliability and durability.

2. Description of the prior art

There is a known metal bellows type sealed control device designed to be associated with a valve mechanism, the bellows isolating the mechanism from the external environment. A device of this kind has been developed for the requirements of the nuclear industry, for controling a valve that may be in contact with a toxic and radioactive fluid. This device comprises a control shaft and a receiver shaft isolated from each other. The bellows is disposed to surround the receiver shaft completely and it is welded in a sealed way by its axial ends to a fixed part of the casing of the device, on the one hand, and to a mobile transfer member coupled both to the receiver shaft and to the control shaft, on the other hand. For the bellows to be durable in exercizing its function, it is essential that it is not subjected to any torsion force. This is why the transfer member, which is generally flat, is constrained to move in such a way as to perform a so-called "circular-translation" movement. This movement may be obtained positively by an appropriate kinematic system or in a "resultant" way by virtue of various mechanical prohibition means. The former is preferable but generally requires complicated and costly mechanisms. Devices of this kind are described, for example, in British Patent No. 826 513 and in Patent of Addition No. 78 358 to French Patent No. 1 248 634 which corresponds to U.S. Pat. No. 3,082,632 issued to Vulliez on Mar. 26, 1963. This Patent of Addition describes an embodiment which is particularly suited to controling a quarter-turn valve.

Until now the complexity of known systems has limited their application to specific fields, in particular the nuclear industry. A first objective of the invention is to simplify this type of control device using a metal bellows in order to diversify its application into other sectors of the chemicals industry. The invention is particularly directed to the operation of a quarter-turn valve by means of a bellows type sealed transmission device in which the aforementioned "circular-translation" movement is generated positively by an appropriate kinematic system of simple design.

The basic idea of the invention, from which the structural simplification results, consists in physically offsetting the control shaft and the receiver shaft by placing the axes of these two shafts at the ends of one side of a deformable parallelogram type articulaion system including said transfer member.

The present invention consists in a sealed rotary transmission device comprising a control shaft, a receiver shaft parallel to and spaced from said control shaft, a bellows surrounding said receiver shaft, a casing to which one end of said bellows is fixed in a sealed way, a transfer member constrained to move parallel to a plane perpendicular to said receiver shaft and to which the other end of said bellows is fixed in a sealed way, and a respective crank on each of said control and receiver shafts eccentric to the axis thereof by the same distance, coupled to said transfer member and spaced by the same distance as said shafts, to enable circular translation of said transfer member.

Another objective of the invention is to optimize the trajectory of the end of the bellows attached to the transfer member, to reduce the offset to which the bellows is subjected during its actuation travel and consequently to reduce fatigue stresses on this fragile member. With this in view, the invention is also concerned with a device as defined hereinabove in which the center of the perimeter where the bellows joins the transfer member is offset relative to the axis of said receiver shaft in a direction tending to reduce said offset. These arrangements, whereby the bellows is less stressed and its strength under pressure is improved, lead to a very rugged construction of the parts subjected to the torque to be transmitted, which can be very high in certain industrial applications of this type cf quarter-turn valve.

The invention will be better understood and other advantages of the invention will emerge more clearly from the following description of a sealed transmission device in accordance with the invention, given by way of example only with reference to the appended drawings.

FIG. 1 is a view in elevation of a bellows type control device in accordance with the invention, shown in cross-section on the line I--I in FIG. 2.

FIG. 2 is a cross-section on the line II--II in FIG. 1.

FIG. 3 is a simplified schematic view of the device from FIG. 1 shown in cross-section in the plane which bisects the trajectory of the crank on the receiver shaft and explains one characteristic of the invention.

FIG. 4 is another simplified schematic view as seen in the direction of the arrow IV in FIG. 3.

Referring to the drawings, the sealed transmission device comprises a casing 11 consisting of a substantially cylindrical tubular body 12 with annular flanges at its axial ends and surmounted by a member forming a cover 13 in which a control shaft 14 is rotatably mounted. The body 12 is assembled by one of its flanges to another flange 18 of a structural member 19 enclosing a mechanism actuated by a receiver shaft 20 of the transmission device. The body 12 is assembled to the flange 18 by bolts 21 with an annular gasket 16 between them. The mechanism actuated by the shaft 20 is not shown. It may be a valve mechanism, for example. The receiver shaft 20 is guided in the bore 22 of a bush 23 attached to the structural member 19; in this example this bush is forged in one piece with said structural member. A metal bellows 26 surrounds the bush 23 and consequently the receiver shaft 20. One end of the bellows is fixed in a sealed way, in this example by welding, to a fixed part of the casing consisting in this example of a ring 28 projecting inwardly from the wall of the tubular body 12, in the vicinity of the end of the latter which is assembled to the structural member 19. The other end of the bellows is assembled in a sealed way (welded) to another ring 30 projecting from the wall of a transfer member 32 constrained to move inside the casing 11, parallel to a plane perpendicular to the axis O.sub.1 of the receiver shaft 20. This transfer member 32 is disk-shaped overall and its radially outermost part is engaged between two parallel annular guide surfaces 38, 40 belonging respectively to the body 12 and to said cover 13. This transfer member is provided with pegs 42 through which it is in sliding contact with the two annular surfaces 38, 40.

According to an important characteristic of the invention, the control shaft 14 and the receiver shaft 20 are parallel, being spaced from each other by a distance d (as measured between their axes) and situated one to each side of the transfer member 32, each shaft comprising a respective crank 14a, 20a eccentric by a common pre-determined distance x from its own axis. The two cranks 14a, 20a are coupled to the transfer member, being spaced by the same distance d as the shafts themselves. This defines a deformable parallelogram articulation structure including said transfer member and adapted to allow circular translation of the transfer member and consequently of the end of the bellows 26 that is attached to it.

The control shaft 14 is rotatably mounted in an appropriate housing of said member forming the cover 13, with a ball bearing 44 and a needle roller bearing 45 spaced coaxially from each other placed between them. The crank 14a associated with this shaft is in the form of a journal inserted into a hole 48 formed in the transfer member externally of the bellows. A needle roller bearing 49 is disposed between the lateral surface of this hole and that of the journal. The crank 20a associated with the receiver shaft is also in the form of a journal inserted in a blind hole 50 formed in the transfer member 32 and opening into the center of the latter, inside the bellows 26. At this stage in the description it is seen quite clearly that any trace of toxic fluid that might flow between the shaft 20 and the bore 22 cannot escape from the space delimited by the bellows 26 and the transfer member 32.

FIGS. 3 and 4 explain another important characteristic of the invention. In these figures only the receiver shaft 20 and its crank 20a have been represented, together with the bellows 26 and the transfer member 32. Also, these figures show the crank 20a at the center of the actuation travel of the device, that is to say when the axis O.sub.2 of the journal constituting this crank is in the plane AB bisecting its own trajectory inscribed within the right angle CO.sub.l D in FIG. 4. This trajectory is represented by the circular arc EF. In accordance with the invention, the center O.sub.3 of the perimeter where the bellows joins onto the transfer member 32 (that is to say, in concrete terms, the center of the ring 30) is offset from the axis O.sub.1 of the receiver shaft in a direction adapted to reduce the offset of the bellows during the displacement of the transfer member. The offset of the center O.sub.3 is such that it is substantially in the bisecting plane AB and between the two parallel axes O.sub.1 and O.sub.2 of the shaft 20 and its crank 20a when said shaft is at the middle of its trajectory. In an embodiment that is currently preferred, this offset is chosen so that the projection of the center O.sub.3 on the axis O.sub.1 of the receiver shaft when the crank is at the middle of its trajectory is substantially equal to the value of the dip f of the arc EF. Under these conditions, when it moves in circular translation, the center O.sub.3 moves to O'.sub.3 in a plane perpendicular to the bisecting plane AB when the crank arrives at the end E of its trajectory. The position of the ring 30 at the end of its travel is shown in dashed line in FIG. 4 and the distance O.sub.1 O'.sub.3 represents the aforementioned offset. To give a numerical example, this offset is then 0.707 x whereas it would be 0.765 x if the center O.sub.3 were on the axis O.sub.1 of the shaft 20, as shown in the aforementioned Patent of Addition No. 78 358 of 27 June 1960 to French Patent No. 1 248 634.