FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a valve according to the introductory portion of claim 1. Such a valve is known from US 3 654 950.

Axial flow valves have been adopted throughout the hydrocarbon industry in critical, high integrity and severe service applications. They are best suited to applications where minimal downstream turbulence, low fixed pressure drop, rapid closure, accuracy of control and reliability are important. Axial flow valves can be fully pressure balanced, meaning that the only significant forces resisting valve operation are seal and mechanical friction between the gear system components.

In fields of use such as oil and gas production, process industries, transport, distribution and storage of fluids, valves are used for precise control of pressure, flow or temperature, for instance as a choke (Joule Thompson) valve or as a surge relief valve. Flow of fluids of a wide range may need to be controlled, such as oil products from crude oil to refined products, high gas-oil multiphase fluids, natural gas (which may contain contaminants such as sand).

In view of pressures at which such valves need to operate (pressure classes: 150# ~ 2500#) and operating temperatures from as low as about - 195°C to more than 500 °C, the valves need to be of a very robust construction with a high thermal stress resistance of structural parts, actuating

mechanisms and seals. Also, because of the use in large scale process installations, minimal maintenance and in particular costly downtime should be as brief and infrequent as possible.

Most axial flow valves incorporate linear actuation in order to position the obturator. The most widely adopted linear mechanism available to the market makes use of a 45°, 1: 1 sliding rack to convert actuator linear motion to linear motion of the obturator sheath in order to open and close the valve. Examples of such valves are disclosed in US 4 327 757, W02007/048942, W02008/098702 and WO2015/049525.

As with many sliding gear mechanisms, there are high frictional forces encountered when moving under load. These forces result in a low efficiency rating, thereby increasing the actuation forces required to operate the valve reliably.

There are further inherent weaknesses with this type of mechanism. With enough cycling under load, it will fail due to galling and eventual seizure, particularly in conditions where there is limited or no lubrication. The friction and wear of the gear teeth and sliding bearing areas will result in degradation of these surfaces, eventually abrading away hardened surface treatments.

WO2017/055856 discloses a valve in which linear displacement of a toothed rack actuator perpendicular to an axial direction, in which the flow control obturator sheath is movable, is converted into axial displacement of a toothed rack connected to the flow control sheath by means of a pinion engaging both toothed racks. In such a valve, a galling failure mode is much less hkely to cause the gear train to seize and, as a rolling motion gear system, it has low frictional losses, reducing the actuation forces necessary to operate the valve. Nevertheless, also such an actuating system is sensitive to good lubrication and wear resistance of the teeth is a problem causing failures of the valve, while also strength of the teeth is often a problem.

W02007/048942 discloses a valve in which linear displacement of an actuator perpendicular to an axial direction, in which the flow control obturator sheath is movable, is converted into axial displacement of a plunger connected to the flow control sheath by means of a crank wheel, a connecting rod between the actuator and the crank wheel and a connecting rod between the crank wheel and the plunger. Such an actuating system occupies a relatively large amount of space, is complicated, costly and the relatively small hinged linkages are not robust. W02007/048942, W02009/143028 and WO2015/049525 disclose axial flow valves in which axial movement of the obturator sheath is driven by rotation of an actuator shaft about a centre line perpendicular to the axial direction. A pinion mounted to the actuator shaft engages a toothed rack oriented in the axial direction. Also in such valves, the actuating system is sensitive to good lubrication and wear resistance of the teeth is a problem causing failures of the valve, while also strength of the teeth is often a problem.

Also US 3 654 950 and DE10 2016 101 664 disclose axial flow valves in which axial movement of the obturator sheath is driven by rotation of an actuator shaft about a centre line perpendicular to the axial direction. In these valves, a toggle mechanism including an actuator shaft and a toggle arm coupled to a plunger either via dogs engaging recesses in the plunger or, respectively, via a connecting rod between an end of the toggle arm and the plunger. In such actuating systems, the relatively small hinged hnkages or dogs are not robust and the envelope of movement of the connecting rod requires a relatively large free space inside the valve.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an axial flow control valve that is extremely simple and robust yet easy to operate and allows accurate flow control and a compact construction without compromising low flow resistance. According to the invention, this object is achieved by providing a valve according to claim 1.

Because the mutually contiguous first and second surface portions of the actuating surface of the toggle member at mutually different distances from the pivot axis of the toggle member have mutually different radii of curvature about axes of curvature parallel to the pivot axis, axial displacement of the obturator sheath per unit of angular rotation of the toggle member can be adapted to suit both precision of control requirements and requirements regarding maximum forces for actuating movement of the obturator sheath. Furthermore, the valve can be arranged for pivoting of the toggle member over a larger angular range without increasing variation in the amount of displacement of the obturator sheath per unit of angular rotation of the toggle member, so that a smaller toggle member can be used. In turn, this allows the bulb to be smaller, so that a compact construction can be provided at a given flow resistance.

In a particular embodiment, the motion transfer mechanism of the valve is particularly compact, because the toggle member is in the form of an elongated crank arm pivotable about the pivot axis, the at least one actuating surface is located on the crank arm such that in longitudinal direction of the crank arm, the at least one actuating surface is located spaced from the pivot axis only, the at least one engagement surface is arranged to move along a path in the axial direction, contours of the path being defined by boundaries of the at least one engagement surface, and, in the direction perpendicular to the axial direction and to the pivot axis, the pivot axis is located spaced form the path. This allows the toggle member to be particularly small, while

nevertheless the obturator sheath can be moved over a substantial stroke length between the closed an the open position. Also the construction is robust and easy to assemble, because a shaft to which the toggle member is mounted can extend aside of the operating member coupled to the obturator sheath, without requiring a slot or large cut-out in said operating member.

Further particular elaborations and embodiments of the invention are set forth in the dependent claims.

Further features, effects and details of the invention appear from the detailed description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional perspective view of an example of a valve according to the invention;

Fig. 2 is a cross-sectional top view of the valve shown in Fig. 1 in a maximally open condition; and

Fig. 3 is a cross-sectional top view of the valve shown in Figs. 1 and 2 in a maximally closed condition.

DETAILED DESCRIPTION

In the drawings, a valve 1 for controlling a flow of fluid through tubing attached to flanges 3, 4 of a valve housing 5 is shown. A flow channel 5 extends through the housing 2 from a first end 6 in an axial direction 8 to a second end 7. The flow channel 5 has a first flow channel section 9 extending into the valve 1 from the first end 6 and a second flow channel section 10 extending into the valve 1 from the second end 7. The valve 1 can be mounted for flow through the valve 1 from the first end 6 to the second end 7 and/or from the second end 7 to the first end 6.

A bulb 11 is suspended in the second flow channel section 10 via a bridge 12 (see Fig. 1) connecting the bulb 11 to the housing 2. The second flow channel section 10 extends along the bulb 11 radially outside of the bulb 11 over the full circumference of the bulb 11, except where the bridge 12 is located. Instead of the single bridge 12, two or more bridges may be provided. Depending on requirements and functions of the bridges, the bridges may be of mutually equal or different shapes and/or dimensions. The first flow channel section 9 extending axially from the first end 6 towards the bulb 11.

An obturator sheath 12 is suspended for guided axial movement between an open position (Fig. 2) and a closed position (Fig. 3). In this example, the obturator sheath 12 is guided in the first flow channel section 9 and, via an operating member 13 extending axially in the bulb 11 and connected to the obturator sheath 12, the obturator sheath 12 is guided relative to a guide opening 14 in the bulb 11.

In the closed position, the obturator sheath 12 closes off flow passages 15 (not all designated by a reference number) between the first flow channel section 9 radially inside the flow passages 15 and the second flow channel section radially outward of the flow passages 15, substantially (i.e. apart from some leakage if allowable in the application at hand) blocking flow from the first flow channel section 9 to the second flow channel section 10 and vice versa.

In this example, the flow passages 15 are formed by a pattern of openings in a cylinder liner 16 of which an inner surface 17 is about flush with an inner wall surface of the first end 6 of the flow path 5. However other embodiments are also possible, for instance having a single flow passage, for instance formed by an end of the second flow channel section at a path of the guided movement of the obturator sheath and/or without a cylinder liner.

The obturator sheath 12 in the open position at least partially leaves open the flow passages 15 between the first flow channel section 9 and the second flow channel section 10, allowing flow from the first flow channel section 9 to the second flow channel section 10 and vice versa. Depending on the application, the obturator sheath 12 in the fully open position and/or the openings 15 may to some extent restrict flow through the flow channel 5 of the valve 1.

The operating member 13 has engagement surfaces 18, 19 facing in opposite axial directions 8. A toggle member 20 is pivotably mounted to the bulb 11 so as to be pivotable about a pivot axis 21 between a closing position (Fig. 3) causing the obturator sheath 12 to be in the closed position and an opening position (Fig. 2) causing the obturator sheath 12 to be in the open position. The toggle member 20 has actuating surfaces 22, 23, each in contact with a respective one of the engagement surfaces 18, 19 in a position in a plane spaced from the pivot axis 21 in a direction 25 perpendicular to the axial direction 8 and to the pivot axis 21. In this example, the plane 24 extends through a central axis 24 of the flow channel 5 and the bulb 11, but this plane may also be located further away from or closer to the pivot axis 21. Also, the plane in which the actuating surfaces contact the engagement surfaces may be essentially stationary, as in the present example, or move towards and away from the pivot axis as the toggle member is pivoted.

Furthermore, in this example two pairs of actuating and engagement surfaces 22, 18 and 23, 19 are provided. It is however also possible to provide a single pair of actuating an engagement surfaces in mutual contact for urging the operating member and the obturator sheath in one axial direction only, while movement in the opposite axial direction may for instance be driven by a spring or by a fluid pressure such as pressure of a liquid of which the flow is controlled.

The actuating surfaces have first and second surface portions 22a, 23a; 22b, 23b at mutually different distances from the pivot axis 21 and contiguous to each other. These first and second surface portions 22a, 23a; 22b, 23b have mutually different radii of curvature about axes of curvature parallel to the pivot axis 21.

As can be seen from Figs. 2 and 3, if the toggle member 20 is in the opening position (Fig. 2), the first surface portion 22a of the actuating surface 22 is in contact with the engagement surface 18, while as the toggle member 20 has pivoted to the closed position (Fig. 3) the actuating surface 22 has sled along the engagement surface so that the second surface portion 22b then contacts the engagement surface 18. Since the first surface portion 22a of the actuating surface 22, where the actuating surface 22 touches the engagement surface 18 when the toggle member 20 is in the opening position, has a smaller (average) radius of curvature than the (average) radius of curvature of the second surface portion 22b, where the actuating surface 22 touches the engagement surface 18 when the toggle member 20 is in the closing position, when the toggle member 20 pivots from the opening position to the closing position, at least initially, the displacement of the sheath 16 per unit of rotation of the toggle member 20 about the pivot axis is less than for a toggle member having one radius of curvature between the radii of curvature of the first and second surface portions 22a and 22b. Then, after the toggle member 20 has pivoted to an orientation about perpendicular to the axis 24 of the valve 1, the second surface portion 22b of the actuating surface 22 contacts the engagement surface 18. Because of the larger curvature of the second surface portion 22b, at least ultimately, the displacement of the sheath 16 per unit of rotation of the toggle member 20 about the pivot axis 21 is larger than for a toggle member having one radius of curvature between the radii of curvature of the first and second surface portions 22a and 22b.

Thus, the radii of curvature of the actuating surface portions 22a and 22b are dimensioned such that the ratio between an angular rotation of the toggle member 20 and axial displacement of the obturator sheath 12 is at least more constant than if the actuating surface has a single radius of curvature about axes of curvature parallel to the pivot axis.

In the present example, the toggle member 20 is in the form of an elongated crank arm pivotable about the pivot axis 21. The actuating surfaces 22, 23 are located on the crank arm such that in longitudinal direction of the crank arm, the at least actuating surface 22, 23 are located spaced from the pivot axis 21 only. The at engagement surfaces 18, 19 are arranged to move along a path in the axial direction, contours of the path being defined by boundaries of the engagement surfaces 18, 19, In the direction 25

perpendicular to the axial direction and to the pivot axis 21, the pivot axis 21 is located spaced form the path. This allows the toggle member 20 to be particularly small, while nevertheless the obturator sheath 12 can be moved over a substantial stroke length between the closed an the open position. Thus the construction for operating the valve 2 can be of a particularly compact construction so that the bulb 11 can be of a compact design requiring little deviation in the flow path through the valve. Also the construction is robust and easy to assemble, because a shaft to which the toggle member 20 is mounted can extend aside of the operating member 13 coupled to the obturator sheath 12, without requiring a slot or large cut-out in the operating member 13.

For achieving a constant ratio between the angular rotation of the toggle member 20 and the axial displacement of the obturator sheath 12, it is advantageous if, as in the present example, the first surface portion 22a, which is closer to the pivot axis 21 than the second surface portion 22b has a smaller radius of curvature about an axis of curvature parallel to the pivot axis 21 than the second surface portion 22b. Where the actuating surface 22 passes from the first surface portion 22a to the second surface portions 22b, the orientation of the actuating surface 22 does not change abruptly, so that a smooth transition of movement of the obturator sheath 12 is obtained when the second surface portion 22b contacts the engagement surface 18 after the first surface portion 22a has passed along the engagement surface 18 and vice versa.

Depending on requirements, the radii of curvature of consecutive surface portions can be adapted to provide increased precision of control, reduced maximum forces for actuating movement of the obturator sheath or quick movement of the obturator sheath in a particular range. Furthermore, the valve 1 can be arranged for pivoting of the toggle member 20 over a larger angular range without increasing variation in the amount of displacement of the obturator sheath 12 per unit of angular rotation of the toggle member 20, so that a small toggle member 20 can be used. In turn, this allows the bulb 11 to be small, so that a more compact construction can be provided at a given flow resistance.

For a particularly uniform constant ratio between the angular rotation of the toggle member 20 and the axial displacement of the obturator sheath 12, it is advantageous if, as in the present example, the radii of curvature of a sequence of the actuating surface portions that contact the engagement surface 18 increase continuously with increasing distance from the pivot axis 21.

In the present example, the actuating surface 22 is shaped as an involute of a circle of which the centre is intersected by the pivot axis 21 (i.e. each point on the actuating surface curve is perpendicular to a tangent of the circle on a side of the actuating surface 22 opposite of the direction in which the actuating surface 22 is facing). Thus, a fully constant ratio between the angular rotation of the toggle member 20 and the axial displacement of the obturator sheath 12 is achieved,

The circle of which actuating surface 22 is shaped as an involute curve has a radius equal to the distance from the pivot axis 21 to the path of contact between the actuating surface 22 and the engagement surface 18, which path extends along the central axis 24 of the flow channel 5 and the bulb 11 and the engagement surface 18 is oriented perpendicular to this central axis 24.

Accordingly, the actuating surface 22 and the engagement surface 18, always contact along the central axis 24 of the flow channel 5 and the bulb 11 and are oriented perpendicular to the direction of movability 8 of the obturator sheath 12 at the point of contact. Thus, transverse reaction forces are minimized. Because the actuating surface 22 touches the engagement surface 18 in a fixed central contact position on the engagement surface 18 as the toggle member 20 is pivoted, it is avoided that a tilting moment is exerted onto the obturator sheath 12, so that friction and wear are limited.

Because the fixed contact position on the engagement surface 18 is intersected by the central axis 24 of the obturator sheath 12, exertion of a tilting moment onto the obturator sheath 12 is also reduced in absolute sense.

The toggle member 20 has actuating surfaces 22, 23 on mutually opposite sides, which actuating surfaces 22, 23 each contact an associated one of mutually opposite engagement surfaces 18, 19 facing each other. Thus, movement of the obturator sheath 12 in opening and closing directions is directly controlled by the pivoting position of the toggle member 20. In each operative position of the toggle member 20 a section of the crank arm extends from the pivot axis 21 towards the actuating surfaces 22, 23 in an area outside of a space between the opposite engagement surfaces 18, 19. This allows the opposite actuating surfaces 22, 23 to be relatively close together and the toggle member 20 to be small in directions perpendicular to its

longitudinal direction, which also allows the engagement surfaces 18, 19 to be close together. This further contributes to a compact design of the motion transfer mechanism of the valve.

The actuating surfaces 22, 23 on mutually opposite sides of the toggle member 20 are shaped such that positions in which the actuating surfaces 22, 23 contact the engagement surfaces 18 and, respectively, 19 remain at a constant distance in the axial direction 8 if the toggle member 20 is pivoted in an operating range in which the actuating surfaces 22, 23 remain in contact with the engagement surfaces 18 and, respectively, 19. Thus, the position in opening and closing directions 8 of the obturator sheath 12 is controlled accurately by the pivoting position of the toggle member 20, without leaving a significant amount of play in opening and closing directions 8. Also the opposite actuating surface is preferably shaped as an involute curve.

In the present example, also the curvature of the actuating surface 23 facing in opening direction is shaped as an involute curve of a circle of which a centre is intersected by the pivot axis 21 (i.e. each point on the actuating surface curve is perpendicular to a tangent of the circle on a side of the actuating surface 23 opposite of the direction in which the actuating surface 23 is facing). Thus, a fully constant ratio between the angular rotation of the toggle member 20 and the axial displacement of the obturator sheath 12 is also achieved in opening direction,

Also the circle of which actuating surface 22 is shaped as an involute curve has a radius equal to the distance from the pivot axis 21 to the path of contact between the actuating surface 23 and the engagement surface 19, so that also, the actuating surface 23 and the engagement surface 19, always contact in positions along the central axis 24 of the flow channel 5 and the bulb 11 and are oriented perpendicular to the direction of movability 8 of the obturator sheath 12 at the point of contact.

Since actuating surfaces 22, 23 are opposite involutes of the same circle, positions in which the actuating surfaces 22, 23 contact the engagement surfaces 18 and, respectively, 19 remain at a constant distance in the axial direction 8 if the toggle member 20 is pivoted in an operating range in which the actuating surfaces 22, 23 remain in contact with the engagement surfaces 18 and, respectively, 19.

For a rigid and strong yet compact construction, it is moreover advantageous that the actuating surfaces 22, 23 are on sides of a body of the toggle member 20 extending from the pivot axis 21 and more in particular that the toggle member 20 is integrally formed.

The operating member 13 further has at least chamfer surfaces 26, 27 contiguous with the engagement surfaces 18, 19. This allows the pivot axis 21 to be particularly close to the axis 24 of the obturator sheath 12 and the operating member 13 and allows the toggle member 20 to be pivoted over a large angular range. This in turn allows a compact construction of the bulb 11.

For an efficient construction, the engagement surfaces 18, 19 are flat and oriented perpendicular to the central axis of the obturator sheath 12.