Gate valve

Abstract

A gate valve assembly having a housing with an inlet and outlet and a gated fluid passage between them. There is a valve seat arrangement and a gate-carrying shaft or stem which operates a plate provi

Description

Field of the Invention The present invention relates to a gate valve, more specifically to a through conduit slab-gate valve. More specifically, the present invention relates to an articulation arrangement that can be incorporated, as a compact design, in gate valves subjected to high pressure environments. Background A typical gate valve comprises a housing in which the valve gate is positioned in a fluid passage between an inlet port and an outlet port and is disposable between an open position, in which a fluid passage is maintained between the inlet port and outlet port, and a shut position, in which the fluid passage is closed. To operate reliably at both lower pressures and higher pressures, which may be in the region of 15,000 psi, a valve gate may be designed to abut against a valve seat located in the housing. The gate arrangement is located, typically, between two valve seats, one upstream and one downstream of the gate arrangement. A contacting face of the valve gate is maintained in sliding contact with the corresponding valve seat throughout the range of movement (from closed to open positions), and the contacting face of the valve gate forms a metal-to-metal seal with the valve seat in the closed position. The present invention seeks to further simplify the assembly to allow more compact valve design. Summary of the Invention In accordance with a first aspect of the invention, there is disclosed a gate valve assembly, comprising a housing providing an inlet, an outlet, a valve seat arrangement and a gated fluid passage between the inlet and the outlet, a gate-carrying shaft, and a plate providing a slab gate in slidable engagement with the at least one valve seat and to be operated via the gate-carrying shaft between an open condition and a shut condition, wherein the plate is mounted at one plate end via a retainer engaging a free end of the gate-carrying shaft, the retainer held in a recess of the plate. It will be understood that a slab gate plate has a generally cuboid, slab form of elongate proportions comprising two opposite flats, its body accommodating a fluid passage aperture and a fluid blocking solid portion. The gate plate has edges surrounding the slab form, defining two opposite ends and two opposite lateral edges of the gate plate. Of two opposite ends, one end provides a portion or region of the plate that is mounted in physical connection with the gate-carrying shaft. In that case, the other (opposite, or distal) end can be considered a portion of the gate plate that is not mounted directly to the gate carrying shaft, and may therefore be considered a free end. The valve seat arrangement comprises one or more - typically two - valve seats located within the fluid passage and comprising an aperture forming part of the fluid passage that is formed when each valve seat aperture is aligned to be in registration with the fluid aperture of the plate in the open condition. The plate further comprises a solid plate portion to cover the one or more valve seat apertures, e.g. to cover the two opposite valve seat apertures, in a shut condition. The solid plate portion is understood to be sufficiently large to cover the valve seat apertures to block fluid flow. The plate is moved between the open and shut conditions by way of operation of the gate-carrying shaft. The connection between the gate plate and the gate-carrying shaft comprises a retainer component engaging a free end of the gate-carrying shaft, such that axial movement of the gate-carrying shaft pulls or pushes, respectively, the retainer and thereby the slab. In accordance with the invention, the retainer is a component held in the slab, e.g. within a recess of the slab, preferably within the perimeter of the slab, such that the outer footprint of the slab is not enlarged, or practically not enlarged, by the retainer. The retainer may have smaller dimensions than the recess. As will be understood, the retainer is sufficiently large to ensure reliable retention of the slab to the gate-carrying shaft, while the somewhat smaller dimensions allow for some ‘slack’ or movement of the slab relative to the retainer, and may therefore also permit movement relative to the gate-carrying shaft. Such an arrangement provides some freedom of movement for the slab to articulate, e.g., in a swivelling, rocking, and / or tilting manner. The arrangement may be such that there is also movement allowed in the axial direction, wherein the axial direction is understood as the direction determined by the extension of the gatecarrying shaft. The arrangement may be such that, compared to movement in the axial extension, more movement is permitted in a (towards the valve seat and away) rocking motion, towards and away from a valve seat, and / or in a swivelling motion, (rotating) about the axial direction, and / or in a tilting motion, laterally parallel to a plane of the valve seats. However, this is not necessarily a requirement of all embodiments. The end of the shaft may engage the retainer directly. For instance, the end of the shaft and the retainer may be mechanically connected to each other. In some embodiments, the plate end comprises an opening for the free end of the shaft, the opening joining the recess. Thereby, the free end of the shaft may be received in or through the plate end, and may extend, beyond a joining region, into the recess, sufficiently far to come into contact with the retainer located in the body of the plate. The joining region may be a region where the opening intersects with the recess. In some embodiments, the gate-carrying shaft comprises a smaller cross-section in at least one dimension than a corresponding cross-section of the opening, to allow floating of the plate relative to the gate-carrying shaft. The cross-section of the gate-carrying shaft may be circular, and the corresponding cross-section of the opening may be obround, providing a larger degree of travel along the longer extension than along the shorter extension of the obround cross-section. For instance, the floating connection may allow the slab gate plate to move, or “float” towards and away from the valve seat, and / or between two valve seats on opposite sides of a slab gate plate. In some embodiments, the recess extends perpendicular to the opening. In some embodiments, the recess extends through the body thickness of the plate. In this manner, the recess may be open to both faces of the plate. In some embodiments, the opening is surrounded by a socket-surrounding structure. The opening may be considered an opening of a socket, the socked providing a passage into the recess. The opening may be surrounded, or framed, at all sides by portions of the gate slab, the surrounding portions of the gate slab providing the socketsurrounding structure. In some embodiments, the retainer extends over the full length of the recess. In this manner, the contact area between retainer and slab, i.e. the inner contact surface of the recess, can be maximised to better distribute stress in contact regions. In some embodiments, the recess has a cross-section that is greater than a corresponding cross-section of the opening. The recess may have an opening wider in the face-to-face direction of the plate and / or in the edge-to-edge direction of the plate, compared to the diameter or cross-section of the opening. In some embodiments, the recess has a diameter of at least half the width of the slab. In this manner, the contact area between retainer and slab, i.e. the inner contact surface of the recess, can be widened to provide a wider distribution of stress areas. In some embodiments, one of the recess and the retainer comprises a rounded surface and the other of the recess and the retainer comprises a surface of different roundness or a flat surface. The rounded surfaces of different roundness, or different curvature, may be contacting surfaces at the interfaces between recess and retainer in the axial direction of the gatecarrying shaft. The rounded surfaces may be provided at the interface in the closing direction and / or at the interface in the opening direction. This enables clearance between the retainer and the recess specifically in the axial direction of the gatecarrying shaft, i.e. in the direction of opening or closing the valve. As will be appreciated, one surface may be flat and the other (inner surface) convexly curved. Alternatively, one surface may be concavely curved and the other (inner surface) flat. As a further variant, one surface may have a larger radius curvature than the other. In such arrangements, the retainer and the recess may have a two-region contact at common tangent regions of the two surfaces. In some embodiments, the retainer and the recess comprise contact regions extending in the face-to-face direction of the plate. The face-to-face direction will be understood as a direction of the fluid passage, or generally parallel to the fluid passage. The contact regions may extend over the full length of the retainer, when inserted in the recess, in the face-to-face direction. In some embodiments, the retainer and the recess comprise contact regions extending laterally of the opening. In some embodiments, the retainer and the recess are shaped such that their contact regions come into abutment laterally of the opening, maintaining a clearance region between the contact regions thereby reducing retainer-on-recess contact between the contact regions. The contact regions may be spaced further than the opening, such that retainer-on-recess contact occurs laterally of the opening. Furthermore, the contours or shapes of the retainer and recess may be such, e.g. by way of different curvatures or other nonparallel geometries, that a clearance region remains when spaced-apart contact regions are in full abutment, the clearance region reducing and practically preventing retainer-on-recess contact between the contact regions. As will be appreciated, in this manner stresses are transferred via contact regions and stress transfer is avoided in the clearance region. In some embodiments, the gate-carrying shaft is disposed in the housing in a manner preventing rotation by more than one full turn. The shaft may comprise a mounting of non-circular cross-section, within a channel or guide structure of corresponding shape, to limit axial rotation of the shaft. For instance, the channel may be provided in the form of a track or ridge, and the shaft may comprise a tracking structure such as a protrusion arrangement or roller arrangement, which may be complementarily shaped to fit astride or within the track or ridge, as the case may be. In some embodiments, the gate-carrying shaft is disposed in the housing in a manner preventing rotation by more than 270 degrees, more than 180 degrees, more than 90 degrees, more than 45 degrees, more than 10 degrees, or practically irrotatably. Some degree of rotation be tolerated, or desired, depending on application scenarios. As will be appreciated, the degree of rotation may be defined by the tolerance of the tracking structure and the corresponding track, e.g. the width of a protrusion or roller relative to the track width. The track may comprise a tapering geometry, or bi-directionally tapering geometry, for instance, to alter the degree of tolerated rotation as the shaft is moved axially. For instance, the track may comprise a narrower waist section in which rotation tolerance is smaller, and / or a wider waist section in which the rotation tolerance is greater, than in remaining sections of the track. In some embodiments, the gate-carrying shaft comprises or is operatively connected with a rotation-limiting structure and wherein the housing comprises a corresponding abutment arrangement for engagement with the rotation-limiting structure. In some embodiments, the retainer is located in the recess in a manner limiting its rotation about an axis of the gate-carrying shaft. The retainer may comprise an elongate structure and the recess may comprise a corresponding, larger elongate extension. The elongate nature may limit axial rotation, with reference to the gate-carrying shaft. As such, there may be at least two rotation-limiting mechanisms, a shaft-rotation limiting mechanism to limit rotation of the gate-carrying shaft relative to the housing and / or its drive means, and a plate-rotation limiting mechanism to limit rotation of the plate relative to the gate-carrying shaft. In some embodiments, the retainer is threadedly engaged with the gate-carrying shaft. In some embodiments, the retainer engages the gate-carrying shaft via at least one of a quarter-turn arrangement, a circlip, a pin joint and a staple pin. In some embodiments, the retainer is of unitary form. In some embodiments, the assembly comprises a single slab gate. In some embodiments, the assembly comprises two slab gates, e.g. in the form of a split gate arrangement. The split gate arrangement may comprise two identical plates. In some embodiments, the assembly comprises two gate-carrying shafts, each having a free end, wherein the plate is mounted such that two plate ends each engage via a respective retainer the free end of a gate-carrying shaft. The invention may be incorporated in a design in which a plate may be actuated by two shafts, e.g. arranged at two opposite ends of the plate (e.g., the “top” and “base” or “left” and “right”), allowing actuation of the gate-carrying shafts to be coordinated to push and pull, i.e. to simultaneously push from one end and pull against the other end, respectively, during operation of the slab gate. The features described herein allow for a more compact form of a gate valve assembly. Description of the Figures Exemplary embodiments of the invention will now be described with reference to the Figures, in which: Figure 1A is a section view of a slab gate valve assembly; Figure 1B is another section view of a portion of the slab gate valve assembly; Figure 2 is an isometric view of a valve stem component; Figure 3 is an isometric view of a valve slab component; Figure 4 is an isometric view of a retainer component; Figure 5 is a partial side view of, and through, a recess of the Figure 3 component; Figure 6 is a side view of the Figure 4 component; Figure 7 is a partial side view of an assembly of the components of Figures 3 and 4; Figure 8 is partial exploded view of the components of Figures 2 to 4; Figure 9 is partial isometric view of an assembly of the components of Figures 2 and 4; Figure 10 is a partial side view of the components of Figures 2 to 4, assembled, and Figure 11 is a cutaway view of an assembly of an embodiment. Description Referring to the accompanying figures, initially referring to Figures 1A and 1B, a gate valve 10 comprises a housing with control and driving means, a gate valve body 12 providing a chamber comprising a fluid passage connecting an inlet 22 and an outlet 24 (see Figure 1B). Between the inlet 22 and the outlet 24, there is provided a valve chamber 18 accommodating a gate valve mechanism 20 operable to open or shut the fluid passage via an actuator 16 acting on a valve stem 30, constituting a gate-carrying shaft, held slidably in relation to the valve gate body 12 and extending to the exterior actuator side of the valve gate body through a valve bonnet 14. The chamber 18 comprises a port 17 providing access into the chamber 18 for assembly and / or maintenance. Port 17 is closed by the valve bonnet 14 comprising a passage for components of the gate valve mechanism 20. When assembled, the valve bonnet 14 is seated on the port 17 of the valve gate body 12 to enclose the valve chamber 18. While a gate valve may be designed with a designated upstream end or downstream end, for the purposes of the present disclosure the fluid passage is symmetric, and the outlet and inlet ends may be reversed. The actuator 16 may be of one of many suitable forms operable to axially move the valve stem 30, e.g. remotely actuatable, and / or biased into a proximal or distal position, and may operate slidably or rotationally to effect an opening or shutting of the valve. The present disclosure uses the example of a gate valve assembly 20 of the valve gate body 12. The actuator 16 comprises, or is operatively connected, with a rotationlimiting arrangement, here in the form of two rollers 16a, 16b providing protrusions to each engage in a corresponding track 15a, 15b, respectively. Each of the tracks 15a, 15b permits axial travel of its roller 16a, 16b, respectively, while limiting the ability of the stem 30 to rotate more than a tolerance provided by the widths of the tracks 15a, 15b. The rotation-limiting arrangement achieves that the valve stem 30 may be actuated, e.g. by a rotational actuator such as a helical drive, to axially move the valve stem 30, while preventing its rotation about its axis. As will be appreciated, other rotation-limiting arrangements may be used, depending on the driving means and / or actuator for the valve stem. For instance, the valve stem may comprise a polygonal cross-section, and / or keying structure, to pass through a corresponding keyhole passage of the housing for at least part of its travel range to ensure the valve stem is limited against rotating while moved between open and shut conditions. A certain amount of rotation may be permitted, depending on tolerances of the rotation-limiting arrangement, e.g. the width of the protrusions (here: rollers) relative to the tracks. The rotation-limiting arrangement may comprise a friction-reducing configuration, here in the form of rollers, to avoid interference with axial movement. The slab gate valve assembly 20 comprises said valve stem 30 whose outer end protrudes through the bonnet 14 to connect to the actuator 16 and whose inner end carries a gate slab 40. The gate slab 40 comprises a fluid aperture 44 and a solid slab body portion 42. The valve stem 30 can be actuated by operation of the valve actuator 16, from outside the valve gate body 12, between an axially proximal position (towards, or further towards the inside of, of the valve gate body 12) and an axially distal position (away from, or further towards the outside of, the valve gate body 12). Actuation of the valve stem 30 allows moving the gate slab 40 into a first, open, position, in which the fluid aperture 44 is in registration with the fluid passage, therefore providing a passage between the inlet 22 and the outlet 24, or into a second, shut, position, in which the fluid aperture 44 is not aligned with the fluid passage and the fluid passage between the inlet 22 and the outlet 24 is blocked by the solid slab body portions 42. Figures 1A and 1B show the gate valve assembly 20 in a shut condition, such that the fluid aperture 44 is out of alignment with the fluid passage between the inlet 22 and the outlet 24, and the solid slab body portion 42 is located to block the fluid passage. In the shut condition, a void portion 18a of the valve chamber 18 provides a space which may be occupied by the solid slab body portion 42 of the gate slab 40 when moved into the open position. Opposite the actuator 16, the valve gate body 12 comprises a closed end 19 (in Figs. 1A and 1B, at the lower end). In some embodiments, the lower end of the valve gate body 12 may comprise an aperture providing access to the valve chamber 18 that may be closed with a separate bonnet component to close the valve gate body 12. The valve seats 26, 28 are, here, floating or biased (sprung) valve seats allowing each valve seat 26, 28 individually to move within a predetermined range to come into, and to maintain, sealing contact abutment with the gate slab 40. Alternatively, the valve seats may be solidly mounted, e.g. screwed in solid, and the gate slab may be of a floating design comprising more leeway to move relative to the valve seats. Solidly mounted, e.g. screwed-in, valve seats may be better suited to a split gate valve design comprising multiple (usually, two) valve slabs, although this is not necessarily a requirement of all embodiments. Figure 2 shows a valve stem 30 of generally cylindrical form, comprising an elongate stem 33, an actuator end 32 and a gate-facing, free stem end 34, the actuator end 32 for connection to an actuation mechanism or drive, the gate-facing end 34 for connection to a gate slab 40. With reference to Figures 8, 9 and 10, the gate-facing end 34 comprises a collar 35, here in the form of a circumferential flange comprising an annular back stop surface facing in the direction of the gate-facing end 34. The gatefacing end 34 comprises a free stem end 36 protruding beyond the collar 35 and comprising, here, a threaded stem portion 38 along part of its axial length. A portion 37 between the threaded stem portion 38 and the collar 35 is unthreaded, although an unthreaded portion this is not necessarily a requirement of all embodiments. Figure 3 shows a gate slab 40 comprising a generally cuboid body 43 comprising a stem-facing end 41, a distal end 45 opposite the stem-facing end 41, a solid body portion 42 near the distal end 45, and a fluid aperture 44 located approximately centrally between the stem-facing end 41 and the distal end 45 and extending between two opposite faces 40a, 40b of the slab 40 to provide a fluid passage. The gate slab 40 has a slab thickness in the face-to-face direction defined by the distance between the opposite faces 40a, 40b that is dimensioned to bridge a gap between valve seats 22, 24. The gate slab has a slab width in the edge-to-edge direction perpendicular to the face-to-face direction that is sufficiently wide to surround the valve seats when in registration with the fluid aperture 44. As mentioned above, the valve seats 22, 24 may be sprung or otherwise biased to accommodate for tolerances while maintaining a tight seat-to-slab engagement. Alternatively, one or both valve seats may be mounted, e.g. screwed, tightly, in the housing, and the gate slab 40 may be of a floating design to allow it to move relative to the fixed seats to maintain a tight seat-to-slab contact. The stem-facing end 41 is provided with a socket 46, here of generally obround or oval dimensions and sufficiently large in diameter to receive the free stem end 36 of the valve stem 30. Referring to Figure 4, the socket 46 has a length dimension 46L in the thickness direction, or face-to-face direction, of the slab 40, and a width dimension 46W perpendicular to the length dimension 46L, in the edge-to-edge direction, wherein the length dimension 46L is greater than the width dimension 46W. As will be appreciated, a stem end 36 of cylindrical cross-section is thereby allowed to float in the in the length dimension 46L more, e.g. in the direction from face 40a to face 40b, or in the direction between the valve seats 22, 24, respectively, than perpendicularly to those directions. While the illustrated embodiment has been found to be practical for manufacturing, the invention is not necessarily limited to the illustrated design. For instance, the socket 46 may have other cross-sectional geometry, e.g. cylindrical (round) or generally polygonal cross-sectional geometry, and the stem end 36 may have a corresponding anisometric geometry that provides a greater floating freedom in the face-to-face direction of the slab 40 than perpendicularly to it. Referring to the stem-facing end 41, the surface of it surrounds the socket 46 and comprises two shoulders 42a, 42b, respectively and two web portions 41, 41b. The two shoulders 42a, 42b extend in the face-to-face direction between the faces 40a, 40b. The web portions 41, 41b provide a bridge connection in the edge-to-edge direction between the shoulders 42a, 42b. The web portions 41a, 41b and the shoulders 42a, 42b are regions of a unitary slab 40 and surround the socket 46 from all sides. Thereby, the stem-facing end 41 provides, or is constituted by, a socketsurrounding structure that is believed to better resist splaying forces that may otherwise act on sides of the slab 40. Between the stem-facing end 41 and the fluid aperture 44, the slab 40 comprises a recess 48, here extending through the thickness of the slab 40 and open to both faces 40a, 40b. The recess 48 extends perpendicularly to the socket 46 and intersects with the socket 46 at a joint 46a. As such, the socket 46 provides an opening joining the recess 48, and as will be set out below, permits the valve stem 30, through the socket 46, to connect to a retainer component held in the recess 48. The recess 48 is of generally oval or ovoid perimeter, comprising an elongate dimension perpendicular to the axis of the socket 46 and wider than the socket 46. Here, the recess 48 is longer than the cross-section of the socket 46 in the face-to-face direction. Furthermore, the recess 48 is wider than the socket 46 in the edge-to-edge direction. In this manner, when the free stem end 36 is inserted into the socket 46 and beyond the joint 46a, it extends into the recess 48 and is surrounded by a free volume of the recess 48. Figure 4 illustrates a nut 50 constituting a retainer component, the nut 50 being of a length corresponding to the face-to-face thickness of the slab 40, comprising a generally oblong cross-section extending uniformly along its length. The nut 50 comprises two first faces 52a, 52b that are top and base faces in the reading orientation of the Figures, and four lateral faces including two flat edges 54a, 54b and two rounded edges 56a, 56b, the rounded edges comprising a contour defined by the obround cross-section. The two flat edges 54a, 54b correspond to the face-to-face direction when the nut 50 is seated in the recess 48, and the rounded edges 56a, 56b correspond to the direction between opposite lateral edges of the gate plate. The nut 50 comprises a threaded bore 58, here extending through the body of the nut 50 and (from top to base of the nut) open to both faces 52a, 52b. As will be appreciated, the threaded bore 58 may be open to one side only and / or may not necessarily be located centrally. The threaded bore 58 matches the threaded stem portion 38. The nut 50 may be shorter, in the face-to-face direction, than the thickness of the slab, to ensure the nut remains within the silhouette of the slab 40 regardless of the floating position of the free stem end 36 along the socket 46. However, a shorter nut geometry is not necessarily a requirement of all embodiments. Figures 5 to 7 show the stem-facing end 41 of the slab 40, and the nut 50, respectively, in lateral view to better illustrate their arrangement in an assembly. The obround silhouette of the nut 50 is dimensioned to fit into the oval silhouette of the recess 48. Due to a concave curvature of the inner faces 49a, 49b of the recess 48, the flat faces 52a, 52b are able to come into contact along two curved contact regions 60a, 60b laterally of the socket 46. The obround silhouette and the concave curvature are examples of surfaces with different roundness and achieve that a clearance region 61a, in the manner of a non-contact void, remains between the contact regions 60a, 60b when the nut 50 is in abutment with the recess 48 at the contact regions 60a, 60b. The contact regions 60a, 60b are laterally of the socket 46, outside the socket 46, such that - in the edge-to-edge direction - the clearance region 61a avoids contact of the nut 50 against the web portions 41a, 41b. The illustrated embodiment shows a clearance region 61 between the contact regions 60a, 60b in the edge-to-edge direction of the plate 40, whereas the contact regions 60a, 60b permit, when aligned in abutment, a contact region in the face-to-face direction along the full length of the nut 50. In a further variant, the nut 50 and the recess 48 may be shaped to provide a three-region contact, or a four-region contact, or multi-region contact of more than four contact regions, e.g. such that the nut abuts the recess surface in the manner of a tripod, four-region contact arrangement, or via a crown arrangement or crenelation arrangement providing multiple clearance regions, laterally of, and / or spaced apart from each other, between contact regions in both the edge-to-edge direction and the face-to-face direction. More generally, the arrangement provides one or more clearance regions between contact regions of the nut against the recess, allowing it to reduce or to avoid contact of the nut 50 with the web portions 41a, 41b and / or to reduce or to avoid contact along the shoulders 42a, 42b. As will be appreciated, in this manner, stress transfer is directed via contact regions where the nut and the recess come into abutment, whereas stresses through direct contact load transfer are avoided in clearance regions. The contact regions may be spaced to sit laterally outward of the opening 46. As will be appreciated, the nut 50 may comprise similar contact regions laterally of, or arranged to surround in a spaced-apart manner, non-contact clearance regions in both the opening-direction nut-to-recess contact faces and the shutting-direction nut-to-recess contact faces. Illustrating this with reference to Figure 7, the same or similar clearance region configuration may be provided on the opposite (in Figure 7, on the underside) side of the nut 50, to provide a clearance region 61b between contact regions 60c, 60d. The nut 50 is threadedly mounted to the free stem end 36 and prevented from rotating about the stem axis by engagement of the rounded edges 56a, 56b with the side walls 47a, 47b, respectively, along curved contact regions 60a, 60b. Referring to Figure 10, the stem end 36, nut 50 and slab 40 are dimensioned such that the collar 35 is typically spaced from the stem-facing end 41, such that a gap 35a remains between the collar 35 and the stem-facing end 41. By maintaining a gap 35a, it can be avoided that the nut 50 is tightened against the inner surface 49a, and thereby permits rocking and / or swivelling of the slab 40 relative to the stem 30, and also a small degree of axial movement of the nut 50 within the recess 48. Furthermore, the absence of a tight engagement facilitates the anisometric floating engagement of the stem end 36 in the socket 46, which permits floating of the slab between, i.e., towards and away from, the valve seats. The axial position of the nut 50 may be adjusted along the threaded stem portion 38. Since the valve stem 30 is part of an arrangement preventing or limiting rotation relative to the housing 12 (see rollers 16a,16b and tracks 15a,15b in Figure 1A), the axial position of the nut 50 along the threaded stem portion 38 remains fixed during operation of the gate valve 10. In practice, the axial position of the nut 50 can be set during assembly of the gate valve 10, for instance using a jig for adjustment, while the valve stem 30 is not (yet) engaged with the rotation-limiting mechanism of the actuator 16. In the present embodiment, the nut 50 is of a symmetric design, permitting 180° rotation along the threaded stem portion 38 for adjustment of its axial position along the threaded stem portion 38. In practice, it was found that a sufficiently fine thread or ultrafine thread, in combination with a nut adjustable in 180° increments along the threaded stem portion 38, provides a sufficient degree of granularity to set a desired axial position of the nut 50 along the stem portion 38. However, it will be appreciated that other arrangements may be used, e.g. a cushion-shaped nut in which the edges 54a, 54b are curved corresponding to the rounded edges 56a, 56b, which would allow the nut to be adjusted in 90° increments. As another example, in some embodiments the rotation-limiting arrangement of the actuator 16 may comprise more stop positions than in the illustrated exemplary embodiment. For instance, the rotation-limiting arrangement may comprise four, six, or eight stop positions to permit fixing the rotational shaft position in 90-degree increments, 60-degree increments or 45-degree increments, or other increments, respectively. Once assembled with a rotation-limiting mechanism, the nut 50 is prevented or limited from rotating about the axis of the valve stem 30 by being seated in the recess 48, the slab 40 is rotation limited by the geometry of the chamber 20, and the valve stem 30 is prevented or limited from rotating relative to the housing 12 or gate valve body by the rotation-limiting arrangement. The arrangement achieves that the nut 50 is axially fixed in position on the valve stem 30, or within a tolerance range determined by the rotation-limiting arrangements, without requiring abutment of the collar 35 against the stem-facing end 41. The arrangement also facilitates the design of a threaded connection, or other connection using a rotational engagement, such as a quarter-turn connection, between nut and valve stem through a socket 46 surrounded by a socket-surrounding structure. The design as illustrated in Figure 10 permits actuation of a slab 40 that is mounted to an end of the stem 30, while permitting some articulation in directions other than the stem axis, in the form of floating, rocking, swivelling and / or tilting, to provide a better slab-on-seat contact. At the same time, the elongate distribution of contact regions in the face-to-face direction is believed to provide a self-steering effect, wherein pushing or pulling the slab 40 axially leads to abutment of all contact regions, such as the contact regions 60a, 60b (in a pulling direction) or the contact regions 60c, 60d (in a pushing direction) and, once fully abutted, the slab 40 is axially aligned with the valve stem 30. The arrangement reduces and in effect avoids the need for an external slab guide structure such as tracks or a cage. Thereby, the overall volume of the gate assembly 20 within the valve chamber 18, and of the valve chamber 18, can be designed more compact than would otherwise be the case. The attachment using a nut 50 inserted within a recess 48 achieves that mechanism of stem-plate connection is entirely, or practically entirely, within the footprint, or external contours, of the slab body 43, depending on the degree of floating permitted by the geometry of the socket 46 and the length of the nut 50 relative to the recess 48. This, in turn, avoids a need to reduce the face-to-face thickness of the slab in connection areas, or, respectively, enables the use of thicker slabs within a given available space. The radii of the curvatures of the rounded edges 56a, 56b and the side walls 47a, 47b, respectively, can be relatively greater, and their contact regions spaced apart further or distributed over a wider area, than the diameter of the valve stem 30, providing more load capacity and better distribution of loads. Furthermore, the curvatures of the rounded edges 56a, 56b and the side walls 47a, 47b can be designed to maintain clearance regions between contact regions when the retainer nut is in abutment. The arrangement is believed to better distribute stresses, over wider contact regions, compared to concentrated stresses that would otherwise be expected in a more focused region at the slab-stem interface. Thereby, the slab 40 is enabled to float while stresses that may otherwise be experienced during axial movement at the nut-stem interface are better distributed that would be the case if the nut 50 had to be tightened to the stem. The provision of a socket-surrounding arrangement, here in the form of the web portions 41a, 41b and the shoulders 42a, 42b at the stem-facing end 41, is believed to further increase the resilience to stresses, while the provision of clearance regions between contact regions reduces stress exposure at or near at least part of the socket-surrounding regions. The valve is suitable for high pressure environments in which seals are provided by metal-on-metal contact, of the slab gate plate against a valve seat. Fluid pressures experienced in the intended use scenarios can result in the valve components experiencing relatively large loads urging parts thereof into surface-to-surface contact engagement. Such surface-to-surface contact engagement can risk damage and require premature maintenance or replacement if loads are applied unevenly. An articulated joint is believed to improve a repeatedly consistent and reliable seating, particularly for metal-on-metal contact between valve gate slab and valve seat surfaces. The restriction in the axial (stem shaft) direction ensures that push and pull forces are transmitted from the gate stem 30 onto the gate slab 40 reliably when the assembly is operated under high pressures with minimum, and practically no dead movement region. Furthermore, by providing an oblong or oval cross-section of the retainer 50, the gate slab 40 is inhibited from swinging in the plate plane more than permitted by set tolerances. The present arrangements allow for a compact design, to fit into small installation envelopes. Furthermore, the present gate valve design uses relatively few (here, three) gate components and a relatively small number of moving components, reducing the maintenance requirements, rendering the design particularly suitable for hard-to-reach areas such as subsea installations. While the embodiments described in the Figures show a design utilising a threaded engagement between stem and retainer, the free stem end and the retainer may be shaped as corresponding quarter-turn arrangement, or other suitable arrangement. In the illustrated embodiment, the free stem end is threaded for engagement in the recess of the retainer nut. In some embodiments, the stem end may comprise a socket to engage an intermediate component, such as a pin or bolt threaded on two ends, one end to engage the retainer and another end to engage the free stem end. In the illustrated designs, the recess comprises oval abutment faces for contact with the flats of the retainer. In other embodiments, the recess may be flat and the retainer surfaces curved. The profile of the retainer and / or the recess may comprise lateral lobes or a generally reniform silhouette, or other suitable geometries to provide clearance regions between contact-regions. The solid body portion 42 of the slab 40 is closer to its distal end 41 than the fluid aperture 44. In some embodiments, the solid body portion (here 42) is located centrally and the fluid aperture (here 44) nearer the distal end (here 43). In that case, it will be appreciated that a fluid conduit is opened by pulling the slab in a direction away from the valve chamber 18, and closed by moving the slab further into the valve chamber 18. The floating stem-socket engagement permits an articulated, tight contacting engagement of the gate slab against the valve seat. Thereby, the gate slab is more likely to remain in practically permanent contact with the valve seat surface, whether it is open, shut, or moved between the open and shut position. A design to maintain metal-to-metal gate-on-seat contact reduces, and practically prevents, the likelihood of particles or debris to be entrapped at interface surfaces, and provides a wiping effect, thereby prolonging the practical service life. In this context, it should be borne in mind that the slab-to-seat contact and seal quality is intended to be maintained under high pressure subsea conditions, as a metal-to-metal surface contact without reliance on other seal materials. The illustrated arrangement is believed to be beneficial for single slab gate valves in combination with adaptable (floating and / or sprung) valve seats, as well as for split gate valves comprising two slabs in combination with tightened valve seats. Slab gate plates used in embodiments of the invention may have a form other than cuboid, e.g. obround, and it will be appreciated that one end of the plate (or, in the case of split gate valves, of each plate) is mounted to the gate-carrying stem and the opposite end of the, or each, plate is a free end. While the illustrative embodiments show a single valve stem 30 connected to one stem-facing end 41 of the slab 40, the distal end 45 being illustrated as a free end, the invention may be embodied in designs using two actuator stems, one valve actuator stem connected at a “first” stem-facing end 41 and another valve actuator stem connected at the distal end 45, providing a “second” stem-facing end. The connections may each use a connector component such as the nut 50, which may be of the same 5 design for both stem connections on the same plate 40, or may be of different design for the two stem connections on the same plate 40. A two-stem actuation design may allow push and pull actions to be coordinated when operating the plate. As will be appreciated, the, or each, plate or gate slab is in that case dimensioned to accommodate two (opposite) sockets and recesses each to retain a nut, as well as a 10 fluid aperture to allow the plate to provide a passage to open the valve, and a solid portion to allow the plate to block a passage to shut the valve. It will be appreciated that the description hereinbefore is exemplary in accordance with embodiments the invention and that a wide range of modifications and alterations may 15 be made thereto without departing from the scope of the invention as defined by the appended claims.

Claims

1. A gate valve assembly comprising a housing providing an inlet, an outlet, a valve seat arrangement and a gated fluid passage between the inlet and the outlet, a gate-carrying shaft, and a plate providing a slab gate in slidable engagement with the at least one valve seat and to be operated via the gate-carrying shaft between an open condition and a shut condition, the plate comprising a fluid passage in its face-to-face direction and an edge-to-edge direction perpendicular to the face-to-face direction, wherein the plate is mounted at one plate end via a retainer engaging a free end of the gate-carrying shaft, the retainer held in a recess of the plate, wherein the plate end comprises an opening for the free end of the gate-carrying shaft, the opening joining the recess, wherein the opening is surrounded from all sides, by two shoulders extending in the face-to-face direction and bridge connections extending in the edge-to-edge direction between the two shoulders, and wherein the retainer and the recess are shaped such that their contact regions come into abutment laterally, in the edge-to-edge direction, of the opening, maintaining a clearance region to avoid contact of the retainer with the bridge connections between the contact regions, when the contact regions are in full abutment.

2. The assembly according to claim 1, wherein the gate-carrying shaft comprises a smaller cross-section in at least one dimension than a corresponding cross-section of the opening, to allow floating of the plate relative to the gate-carrying shaft.

3. The assembly according to claim 1 or 2, wherein the opening comprises a length dimension in the face-to-face direction, and a width dimension in the edge-to-edge direction, wherein the length dimension is greater than the width dimension, thereby allowing the gate-carrying shaft to float in the face-to-face direction more than in the edge-to-edge direction.

4. The assembly according to any one of the preceding claims, wherein a stem the gate-carrying shaft comprises anisometric geometry providing greater floating freedom in the face-to-face direction than perpendicularly to it.

5. The assembly according to any one of claims 2 to 4, wherein the retainer is shorter, in the face-to-face direction, than the plate, whereby the retainer remainswithin the silhouette of the plate regardless of floating position of the gate-carrying shaft in the opening.

6. The assembly according to any one of the preceding claims, wherein the recess extends perpendicular to the opening.

7. The assembly according to any one of the preceding claims, wherein the recess extends through the body thickness of the plate.

8. The assembly according to any one of the preceding claims, wherein the recess has a cross-section that is greater than a corresponding cross-section of the opening.

9. The assembly according to any one of the preceding claims, wherein the recess has a diameter of at least half the width of the slab.

10. The assembly according to any one of the preceding claims, wherein one of the recess and the retainer comprises a rounded surface and the other of the recess and the retainer comprises a surface of different roundness or a flat surface.

11. The assembly according to any one of the preceding claims, wherein the retainer and the recess comprise contact regions extending in the face-to-face direction of the plate.

12. The assembly according to claim 11, wherein the contact regions extend over the full length of the retainer in the face-to-face direction.

13. The assembly according to any one of the preceding claims, wherein the retainer and the recess are shaped to provide a three-region contact at an interface between recess and retainer.

14. The assembly according to any one of the preceding claims, wherein the retainer and the recess are shaped to provide a four-region contact at an interface between recess and retainer.

15. The assembly according to any one of the preceding claims, wherein the gatecarrying shaft is disposed in the housing in a manner preventing rotation by more than one full turn.

16. The assembly according to claim 15, wherein the gate-carrying shaft is disposed in the housing in a manner preventing rotation by more than 270 degrees, more than 180 degrees, more than 90 degrees, more than 45 degrees, more than 10 degrees, or practically irrotatably.

17. The assembly according to claim 15 or 16, wherein the gate-carrying shaft comprises or is operatively connected with a rotation-limiting structure and wherein the housing comprises a corresponding abutment arrangement for engagement with the rotation-limiting structure.

18. The assembly according to any one of the preceding claims, wherein the retainer is located in the recess in a manner limiting its rotation about an axis of the gate-carrying shaft19. The assembly according to any one of the preceding claims, wherein the retainer is threadedly engaged with the gate-carrying shaft.

20. The assembly according to any one of claims 1 to 18, wherein the retainer engages the gate-carrying shaft via at least one of a quarter-turn arrangement, a circlip, a pin joint and a staple pin.

21. The assembly according to any one of the preceding claims, wherein the retainer is of unitary form.

22. The assembly according to any one of the preceding claims, comprising a single slab gate.

23. The assembly according to any one of claims 1 to 21, comprising two slab gates.

24. The assembly according to any one of the preceding claims, comprising two gate-carrying shafts, each having a free end, wherein the plate is mounted such that two plate ends each engage via a respective retainer the free end of a gate-carrying shaft.A

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