Title: Operating mechanism and an assembly

The invention relates to an operating mechanism for operating a lift and turn valve. The invention also relates to an assembly provided with a lift and turn valve.

A lift and turn valve as such is known from practice. The known valve is utilized for, for instance, sealing off fluid pipes, for instance gas and/or oil pipes.

It is known to operate this valve manually. To this end, the valve body is first pulled up from its seat and is then turned through an angle of 90°. Manual operation of the valve is disadvantageous in view of the required labour, especially if the valve is to be used in a difficultly accessible location, for instance under water or the like. In addition, the valve body can undergo a relatively high load during use, which may hinder manual operation.

In addition, an operating mechanism is known for automatically operating the valve while utilizing a multiple rotating movement (i.e. with a large number of rotations of 360°), see for instance US 4,436,280. This known actuator contains, in particular, a power actuator, which, by means of screw thread, engages a shaft to be linearly moved. This known mechanism is relatively sizeable, complex, and contains relatively many parts. This renders this known mechanism expensive and susceptible to malfunction. Heretofore, it has appeared difficult to provide a reliable, durable and compact operating mechanism for a lift and turn valve.

The present invention contemplates obviating the above-mentioned problems. The invention contemplates in particular providing a reliable and relatively powerful automatic operation of a lift and turn valve. To this end, according to the invention, the valve operating mechanism comprises:

- a housing;

- an operating element connectable to a valve body of the valve;

It is additionally advantageous when the cooperation between the transmission parts is such that movement of the third transmission part over a third distance following the second distance leads to a second translation of the operating element, which second translation has an opposite direction relative to said first translation.

Preferably, a valve body can be lifted, turned and replaced by having the second transmission body carry out only one movement, in particular only one turning movement (in one direction of rotation relative to the housing), without translation of this body relative to the housing. Preferably, a valve body can be lifted, turned and replaced by having the third transmission body carry out only one movement, in particular only one translation movement in one direction, without rotation of this body relative to the housing.

According to a preferred embodiment, the first and second engaging means each comprise respective groove/cam-assemblies. It is preferred that the grooves of the second engaging means extend only in helical paths having a particular (first) pitch. It is preferred that the grooves of the first engaging means each comprise helical path parts having a smaller, second pitch than the first pitch mentioned. In view of efficient manufacture, an advantageous, compact and robust mechanism has a second transmission part which is provided with: either the grooves of both the first and second engaging means, or the cams of the engaging means.

The invention further provides an assembly provided with a lift and turn valve, which valve comprises a valve body for sealing a passage in a sealed position, and releasing it in a releasing position, wherein the assembly is provided with an operating mechanism according to the invention for bringing the valve body from the sealing position into the releasing position and vice versa. In this manner, the above-mentioned advantages can be obtained in such an assembly.

Further elaborations of the invention are described in the subclaims. Presently, the invention will be clarified on the basis of a non-limitative exemplary embodiment and the drawing. In the drawing:

Fig. 1 shows a cutaway, perspective side view of an exemplary embodiment of the invention;

Fig. 2 shows a view as Fig. 1 of the exemplary embodiment, from a different angle;

Fig. 3 shows a perspective side view of a third transmission part of the exemplary embodiment; Fig. 4 shows a perspective side view of a first transmission part of the exemplary embodiment;

Fig. 5 schematically shows a cutaway part of the exemplary embodiment, in spread-out representation, with an initial situation;

Fig. 5 shows a similar drawing as Fig. 5, after a first partial translation of the third transmission part for translating the first transmission part;

Fig. 7A shows a similar drawing as Fig. 5, after a second partial translation of the third transmission part and just before the start of the rotation of the first transmission part; Fig. 7B shows a detail Q of Fig. 7A;

Fig. 8 shows a similar drawing as Fig. 5, after a third partial translation of the third transmission part and at the start of the rotation of the first transmission part;

Fig. 9 shows a similar drawing as Fig. 5, after a fourth partial translation of the third transmission part and during rotation of the first transmission part;

Fig. 10 shows a similar drawing as Fig. 5, after a fifth partial translation of the third transmission part upon termination of rotation of the first transmission part;

Fig. 11 shows a similar drawing as Fig. 5, after a sixth partial translation of the third transmission part with a second translation of the first transmission part;

Fig. 12 shows a similar drawing as Fig. 5, upon termination of the translation movement of the third transmission part;

Fig. 13 schematically shows an assembly provided with a valve and an operating mechanism; and

Fig. 14 shows a longitudinal cross-section of the exemplary embodiment. Identical or corresponding features are indicated in this specification with identical or corresponding reference numerals.

Figs. 1 — 12, 14 show an operating mechanism M for operating a lift and turn valve (in particular a plug shutoff). An assembly provided with such a valve with such an operating mechanism M is represented in Fig. 13. The valve is provided with a valve body L which serves for, for instance, sealing a fluid channel C in a first position, and for allowing a passage in a second position. Such a valve is known as such from the prior art, and can be designed in different manners. The valve body (for instance valve plug) L can for instance have a substantially cylindrical, spherical, conical, frusto-conical, tapering and/or other form. The valve body L may be provided with a passage H. In Fig. 13, the first position of the valve body L is represented, wherein the valve body rests in a seat and blocks the channel C substantially fluid-tightly. The valve body L can be lifted from this first position, from the seat (in a lifting direction indicated with an arrow Z), is then rotatable through an angle of approximately 90° and can then be reseated into the seat, to the second position. In the second position, the passage H runs parallel to the channel C for allowing the passage of fluid. For the purpose of moving the valve body L, this body L is coupled with the operating mechanism M, via, for instance, a coaxial shaft K. The operating mechanism M (provided with the valve) can be mounted, by means of coupling means, for instance by means of

one or more suitable flanges 1 (only one shown) on the wall T surrounding the channel. This wall T is provided with, for instance, the valve seat mentioned, as shown in Pig. 13.

Figs. 1 — 2 show an exemplary embodiment of the mechanism M in an assembled condition, represented in an exploded manner. Figs. 5 - 12 schematically show the operation of the mechanism (see below). Fig. 14 shows a longitudinal section of a further elaboration of the mechanism M, provided with a linear actuator and spring means.

The present valve operating mechanism M is provided with a housing 1, 2, 8 and an operating element 9 connectable to said valve body L of the valve. The operating element 9 is preferably detachably couplable to a valve body L, for instance to a shaft K of the valve body L, or can engage the valve body L directly. The operating element 9 can for instance be provided with suitable coupling means and/or engaging means 9a for engaging, for instance in a detachable manner, the lift and turn valve to be operated, and preferably via a coupling secured against rotation. Such coupling means and/or engaging means 9a can be designed in different manners and comprise, for instance, a snap connection, clamping coupling, coupling provided with screw thread, cam-groove coupling and/or blocking means, or the like. Preferably, the housing 1, 2, 8 of the mechanism M is stationary after mounting, in particular relative to the channel wall of a channel C to be sealed off. The housing can for instance comprise a flange 1, for instance an annular flange 1, designed to be fixedly mounted on a wall of a fluid channel. Preferably, the housing is designed for at least partly covering the internal parts of the mechanism, i.e. screening them off from a surrounding. The present housing is provided to this end with a first housing part 2, in particular a cylindrical part 2 which is coaxial relative to the flange 1. The first housing part 2 is mounted on the flange 1, preferably detachably via, for instance, bolt means 41, or, alternatively, undetachably. With the exemplary embodiment, a coaxial distancing means 42 is provided between the flange 1

and the first housing part 2. The first housing part 2 can also be manufactured from one piece with the flange 1. The present stationary housing further contains a second housing part 8, which is held in the flange 1, for instance between the distancing means 42 and the flange 1, and is preferably coaxial with the first housing part 2. After mounting, the flange 1 and the first and second housing part 2, 8 are secured against rotation relative to each other.

Preferably, the mechanism M is provided with a first transmission part 11, translatable relative to the housing 1, 2, 8 over a particular distance, in particular translatable in axial direction relative to a centerline of this part 11, which direction is parallel to the lifting direction Z (in this case an axial direction). The first transmission part 11 is furthermore rotatable relative to the housing 1, 2, 8 (with the rotation axis parallel to the lifting direction Z). Rotation of the first transmission part 11 can take place after this part (from an initial position, see Fig. 5 or Fig. 12) is axially translated over a particular distance. Preferably, the first transmission part 11 is rotatable through an angle of at most approximately 90°. In particular, this part 11 is, successively, translatable, rotatable, and in particular translatable again, relative to the housing.

The transmission part 11 is coupled with the operating element 9 for the purpose of the desired valve operation. As follows from Fig. 4, the first transmission part 11 and the operating element 9 are preferably manufactured from one piece, at least form the same part. A translation distance of the first transmission part 11 suffices, after mounting, to first, unseat from an associated valve seat a valve body L coupled thereto, and to then turn it. The mechanism M is further provided with a second transmission part 12 which is only rotatable (about the rotation axis mentioned) relative to the stationary housing 1, 2, 8. For instance, the housing 1, 2, 8 and the second transmission part 12 can cooperate with each other to prevent axial translation of the second transmission part 12 relative to the housing. The housing may be designed for confining the second transmission part 12 in a

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form locking manner (for instance between concentric blocking edges) such that the housing allows only rotation of this part 12 and prevents translation. The housing and/or the second transmission part can further be provided with, for instance, one or more bearings 43, for accompanying such rotation. In the present, compact design, the second transmission part 12 comprises a preferably substantially cylindrical, hollow body, for instance a cylindrical bush. The second transmission part 12 can extend along, and in particular enclose, parts of the first 11 as well as of the third transmission part 13 (see Figs. 1 - 2). Preferably, the first transmission part 11 extends from the second transmission part 12 into a first direction (in particular along the flange 1) to be coupled with a valve body L via the operating element 9. To this end, the second part 12 is of open design on a first side (a side facing downwards in Fig. 1). In the example, the third transmission part 13 extends from the second transmission part 12 into a second direction opposite the first direction, from the second part 12. To this end, the second part 12 is of open design at a second side (a top side in Fig. 1). Preferably, the first 11 and third transmission part 13 are each provided with central axial parts 11a, 13a, extending opposite each other, at least aligned with each other.

The second transmission part 12 can further be designed to surround with relatively little clearance and guide in axial direction Z at least a cylindrical part 11a (in this case a central axial part 11a mentioned) of the first transmission part 11. In a similar manner, the second transmission part 12 can be designed to surround with relatively little clearance and guide in axial direction Z at least a cylindrical part 13b (i.e. a central axial part 13b) of the third transmission part 13.

The present operating mechanism M contains a third transmission part 13 movable relative to the stationary housing. Preferably, the third transmission part is only translatable relative to the housing 1, 2, 8, in particular parallel to said lifting direction Z, such as in the exemplary embodiment.

Preferably, after mounting, a linear drive is provided, preferably a hydraulic or pneumatic drive, for linear movement of the third transmission part 13. Such a drive can be designed in different manners, and for instance form part of the mechanism M (see Pig. 14). The first, second and third transmission part 11, 12, 13 are preferably arranged coaxially relative to each other, with the respective virtual axis parallel to the lifting direction Z mentioned (see the Figures).

The first and second transmission part 11, 12 can advantageously cooperate with each other via first engaging means 5, 34 (which can also be called guide means or cooperating means). The second and third transmission part 12, 13 can cooperate via second engaging means 6a, 33 (which can also be called guide means or cooperating means). This cooperation is in particular such that a first movement of the third transmission 13 part over a first distance leads to only a first translation of the operating element 9 (see Figs. 5 - 7), and that a second movement of the third transmission part over a following, second distance leads to a first turning movement of the operating element 9 (see Figs. 8 - 10).

According to a further elaboration, the cooperation between the (three) transmission parts 11, 12, 13 is such that movement of the third transmission part 13 over a third distance following the second distance leads to a second translation of the operating element 9, which second translation has an opposite direction relative to the first translation (see Figs. 10 — 12).

In the exemplary embodiment, the cooperation between the transmission parts 11, 12, 13 is such that the second translation of the third transmission part 13 over the second distance leads to only a rotation of the second transmission part 9, preferably also through an angle of approximately 90°.

Thus, the cooperation between the transmission parts 11, 12, 13 is in particular such that the movement of the third transmission part 13 leads only to rotation of the second transmission part 2. The cooperation between the

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transmission parts 11, 12, 13 is furthermore such that the rotation of the second transmission part 12 leads to, successively, translation and a turning movement of the first transmission part 11. Here, the housing in particular forms a guide or movement limiting element, to prevent translation of the second transmission part 12, and to prevent rotation of the third transmission part 13 (see above).

As follows from the Figures, first guide means 7, 32 are provided, via which the housing 2 and the first transmission part 11 cooperate for guiding the first transmission part 11 relative to the housing 2 between successive positions of this transmission part 9, preferably such that the first turning movement of the operating element 9 is limited to a rotation of approximately 90°.

In the exemplary embodiment, these first guide means comprise cam/groove assemblies 7, 32, of which the grooves 32 are designed for guiding the cams 7 along respective lift-turn paths, for the purpose of the translation and rotation of the valve body. To this end, the grooves 32 are each provided with axially extending end parts 32a, 32c for the purpose of translation movements of the first transmission part 11, and a tangential groove part 32 extending between these end parts for the purpose of the turning movement of the first transmission part 11. In this case, the stationary housing (in particular the second housing part 8) is provided with the grooves 32 of the first guide means.

The cams 7 (in this case only two) of the first guide means extend in radial (transversal) direction from the first transmission part 11, in opposite directions, and are each provided with an angular circumference (in particular a square or rectangular contour) which can be held with relatively little clearance between opposite guiding sides of a respective guide groove 32. In particular, each of these cams 7 has two side faces 7a extending substantially radially, to be guided in axial (lifting) direction along the end parts 32a, 32b of a groove 32, and two substantially tangentially extending side faces 7b, to be

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guided in the turning direction through the tangential groove part 32b (see Figs. 2, 5 - 12).

The housing and the third transmission part 13 can cooperate via second guide means 6b, 31 to prevent rotation of the third transmission part 13 relative to the housing. In this case, the second guide means (only two) comprise aligned cams 6b of the third part 13, which cams 6b are guidable through respective axially extending slots 31 of the housing 2. In particular, each of these guide cams 6b is a bearing roller which is rotatably coupled with the third transmission part 13 (in particular rotatable about a rotation axis which proceeds at right angles relative to the lifting direction Z).

As follows from the Figures, the above-mentioned first and second engaging means each comprise (in this case each time two) respective groove/cam assemblies 33, 6a; 34, 5. In particular, the (two) cams 5 of the first engaging means extend in radial (transversal) direction from an end part 11a of the first transmission part 11, preferably in opposite directions. As follows from Fig. 4, these cams 5 can for instance extend at a particular axial distance from the cams 7 of the first guide means, axiaEy opposite these cams 7, for the purpose of a stable operation.

The cams 5, 6a mentioned of the first and second engaging means can each comprise a bearing roller 5, 6, which bearing roller 5, 6a is rotatably coupled with the respective transmission part 11, 13 (in particular rotatably about a rotation axis which runs at right angles relative to the lifting direction Z).

In the exemplary embodiment, the (two) cams 6a of the second engaging means also extend in radial (transversal) direction from an end part 13b of the third transmission part 13. Preferably, these cams 6a of the second engaging means and the cams 6b of the second guide means are aligned with each other (see Fig. 3). To this end, these cams 6a, 6b can be integrated with each other.

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In this case, the grooves 33 of the second engaging means are arranged in the second transmission part 12, and extend only in helical paths with a first pitch. In the exemplary embodiment, the pitch of each of these helical paths is constant, this is however not necessary. The grooves 34 of the first engaging means can each comprise symmetrical, substantially helical path parts 34a, 34b which each have a smaller, second pitch than the first pitch mentioned. Preferably, these path parts 34a, 34b each have a pitch with the same pitch size (but with opposite hand, as in the Figures). In particular, the grooves 34 of the first engaging means are each provided with a first groove part 34a and a second groove part 34b (see Figs. 1, 6 - 8), wherein a helical direction of the second groove part 34b has the same direction as the helical direction of the grooves of the first engaging means, and the helical direction of the first groove part 34a is opposite to the helical direction of the grooves of the first engaging means. In particular, the grooves 34 of the first engaging means are each provided with a central, tangential return part 34c (see Figs. 1, 7A, 8) for receiving a respective cam 5 during the second movement of the third transmission part. The return part 34c is located at a position away from the valve operating element 9, at least at an axially greater distance from the operating element 9 than end (i.e. tangential) faces of the grooves 34. The grooves of the first engaging means can each make at most a quarter rotation (at least include an angle of rotation of approximately 90° between the tangential groove ends) about the virtual rotation axis. The grooves 33 of the second engaging means can each make at least half a complete rotation (at least include an angle of rotation of at least 180° between the respective groove ends) about a virtual rotation axis of the mechanism. In the exemplary embodiment, each engaging groove 33 makes a part of a rotation, about the rotation axis, in the range of 180° - 270°.

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The second transmission part 12 can further be provided with: either the grooves 34, 33 of both the first and the second engaging means, as is the case in this exemplary embodiment, or, alternatively, with the cams of those engaging means. The mechanism M can further be provided with suitable lubricants, for instance gel or an oil, for lubricating the movements of the different parts 11, 12.

The operation of the mechanism M is schematically represented in Figs. 5 - 12. These Figures each show a part of the mechanism, in a side view spread out from a circumferential plane to a 2-dimensional plane. In these

Figures 5 - 12, "horizontal movements" (Le. movements in de Figures from the left to the right and vice versa) correspond, in practice, with rotational movements of respective parts of the mechanism M. Vertical movements in these figures 5 — 12 correspond with axial movements of the parts of the exemplary embodiment M.

Fig. 5 shows an initial situation, wherein the operating mechanism 9 is in a first position, for holding a valve body in a respective valve seat (for instance in a sealing position, or, conversely, the releasing position). Here, guide cams 7 of the first transmission part 11 are located in the first guide groove part 32a of the housing, and roller cams 5 of the first transmission part 11 are located in ends of the second groove parts 34b of the second transmission part 12. The roller guide cams 6 of the linearly movable transmission part are in ends (lowest in the Figure) of the helical path slots 33 of the second transmission part 12. The third transmission part 13 is in a first (lowest in the Figure) initial position.

From the position represented in Fig. 5, the third transmission part 13 can be moved linearly, continuously, relative to the housing 2, in a direction Z away from the flange 1. Through the cooperation of the cam parts 6a of this third part 13 with the helical slots 33 of the second transmission part 12, the second transmission part 12 will rotate continuously

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relative to the housing. This rotation is indicated in the Figures with arrows R. As a result of this continuous rotation, the operating element 9 is first linearly lifted, then turned through an angle of approximately °90, and then linearly moved back. Fig. 6 shows the position of parts 11, 12, 13 of the mechanism after a first translation movement of the third transmission part 13, wherein first transmission part 11 is translated over a particular distance (in axial direction). Translation of the first transmission part leads to rotation R of the second transmission part 12, so that each roller cam 5 of the first transmission part 11 is urged from the initial position towards the central return part 34c of the respective guide groove 34. This leads to axial displacement of the first transmission part 11, whereby each angular cam 7 of this first transmission part cooperates with the end part 32a of the guide groove 32 of the housing 2 for blocking rotation of the first part 11. As the pitch of the grooves 33 of the second engaging means is greater than the pitch of the guide groove parts 34b which cooperate with the first transmission part 11, a relatively low translation force for moving the third part 13 can be converted into a relatively high lifting power for translating the first transmission part 11 (and valve body). Figs. 7A and 8A show a following situation during the valve operation, after a second translation operation of the third transmission part 13 and just before the start of the rotation of the first transmission part 11. As shown in detail in Fig. 7B, here, the angular cam 7 of the first part 11 is located precisely in the tangential part 32b of the respective guide groove 32 (such that a bottom side (or corner) of this cam 7 extends opposite a (top) side of this groove part 32b) .The roller cam 5 of the first transmission part is located in a first position (on the right side in the drawing) before the central (tangentially extending) return part 34c of the respective guide groove 34 (at least a groove 34 of the second transmission part 12 turning under the influence of the third transmission part 13). Each return part 34c of

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each guide groove 34 of the second transmission part can be provided at an underside with an additional inclination or convex guide part 34d in order to stimulate or effect setting the angular cam 7 in the tangential part 32b of the groove 32. Fig. 8 shows a following position, after a third partial translation of the third transmission part 13 and at the start of rotation of the first transmission part 11. In this case, the roller cam 5 of the first transmission part is in a second position (left side in the drawing) in the central (tangentially extending) return part 34c of the respective guide groove 34. In this position, the roller cam 5 rests against a top side of the return part 34c of the groove 34, and is located at an entrance to the first groove part 34a which has a pitch opposite to that of the second groove part 34b. Further movement of the roller cam 5, into the first groove part 34, would lead to a downwards movement of the first transmission part 11, this is however prevented in that each angular cam 7 already contacts a top side of the tangential groove part 32b of the housing (see Fig. 7B). As a result of this blocking, the angular cam 7 moves through the tangential groove part 32b, in the direction of the other end part 32c of the respective groove, which is represented in Figs. 9 and 10. Figs. 9 and 10 show the rotation (with arrow S) of the operating part 9 and the first transmission part 11, resulting from the following fourth and fifth translation and turning movements Z, R of the third and second transmission part 13, 12. Here, the first part 11 rotates along with (at least in the same direction as) the second transmission part 13. The rotation S of the part 11 takes place under the influence of the rotation R of the second transmission part 12, via cooperation of the respective engaging means 5, 34 (with the cams 5 in the return parts 34c of the grooves 34). The rotation of the first transmission part 11 proceeds in particular through an angle of approximately 90° for bringing the valve body for instance from the sealing position to the releasing position (or vice versa). There, the axial movement of

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the first transmission part 11 is blocked in that the cams 7 of this part 11 are guided through the tangential slot parts 32b of the stationary housing. As shown in Figs. 10 and 11, a second translation of the first transmission part 11 is obtained with further axial translation of the third transmission part 13. Here, further turning of the first part 11 and operating part 9 is blocked through cooperation of the angular cams 7 with the respective grooves 32 of the housing 2. The second axial end parts 32c are now available for the cams 7 for moving against the lifting direction Z, so that the first transmission part 11 with operating part 9 can move back in its axial direction, towards the position shown in Fig. 12 (for reseating a valve body coupled with the mechanism M into a valve seat). This return movement is indicated in Figs. 11 -12 with arrows TI. As follows from the Figures, this return movement TI furthermore takes place under the influence of the rotation of the second transmission part 12, via cooperation of the respective engaging means 5, 34, wherein the cams 5 are guided through the groove parts 34a of the grooves 34.

Fig. 12 shows an end situation of the operating mechanism M, upon termination of the translation movement of the third transmission part 13. In this position, the guide cams 7 of the first transmission part 11 rest on the bottoms of the second guide groove parts 32c of the housing; the roller cams 5 of the first transmission part 11 are in ends of the first groove parts 34a of the second transmission part 12. The roller guide cams 6 of the linearly movable transmission part are now in the uppermost ends of the helical path slots 33 of the second transmission part 12, and the third transmission part 13 is in an end position moved in a lifting direction Z.

The above-described steps (see Figs. 5 — 11) can then be carried out in reverse order for lifting, turning in opposite direction and moving back the operating element 9.

In this manner, a particularly reliable, compact and relatively powerful operation of the lift and turn valve is enabled. The exemplary

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embodiment can be built up from relatively few parts, while use of for instance sprocket transmissions and the like can be avoided. In the exemplary embodiment, relatively little torque is required with respect to axial forces for lifting and turning the first transmission part 11. As a result, for instance only a relatively small tangential contact surface between the angular cams 7 and guide grooves 32 (see Fig. 7B) needs to be available for initiating turning of the first transmission part 11.

Preferably, the exemplary embodiment M is provided with spring means (for instance a spiral spring, tension spring, elastic resilient means, resilient material or the like), which spring means are designed for applying a spring force for cooperation with the lifting movement of the first transmission part 11 (in the lifting direction Z). Such spring means can be designed for applying, for instance, a spring force for cooperation with the first movement of the third transmission part 13. The spring means can furthermore counteract a reverse return movement (in direction Z') of the transmission part 11.

In this manner, an unseating force provided by the mechanism M for lifting a valve body L from a seat can be greater than a reseating force provided by the mechanism M, which reseats the valve body L back into the seat, so that blocking of the valve can be prevented. To this end, such spring means can engage, on the one side, for instance, the first transmission part 11 and, on the other side, the housing, and/or form an integral part of the transmission part 11 or the housing.

Fig. 14 shows a further elaboration of the exemplary embodiment, provided with an actuator comprising a piston/cylinder assembly 150, 151. The piston 150 is translatable relative to the cylinder 151 (by hydraulically or pneumatically regulating the pressure in the cylinder 151 and preferably also under the influence of spring force of a spring 152), for linearly translating the third transmission part 13 coupled to the piston 150. The cylinder comprises an entrance 155 for feeding a pressure building medium, for instance, a fluid, gas, air or oil, to the cylinder inner space for regulating the pressure in the

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cylinder. A spring 152 (in particular a spiral spring) is provided, designed for applying a spring force in order to cooperate with a particular movement of the piston 150. To this end, the spring 13 engages, on the one side, the piston 150 and, on the other side, another suitable part of the mechanism. The spring 13 may be biased when the piston is in the initial position of Fig. 14 (while the third transmission part 13 is in the initial position according to Fig. 5). The spring 152 can for instance act to apply a force for moving the piston 150 over a desired distance through the cylinder (for instance a spring force that acts for pushing the piston in the direction of an opposite cylinder wall 151a). It is self-evident that the invention is not limited to the described exemplary embodiment. Various modifications are possible within the framework of the invention as set forth in the following claims.

For instance, the engaging means can be designed in different manners. In an alternative embodiment, a second transmission part may be provided with a helically toothed outside surface and a helically toothed inside surface for cooperating with helically toothed surfaces of the first and third transmission part.

According to an alternative, the first engaging means can for instance comprise helical engaging means, with a first helical direction, wherein the second engaging means comprise helical engaging means of which a second helical direction is opposite to said first helical direction.

The mechanism can further be provided in different manners with blocking means for preventing rotation of particular transmission parts (for instance the first transmission part), during particular operating conditions. The static housing mentioned can furthermore be designed in different manners, which will be clear to the skilled person, and consist of one or more parts.