The invention relates to a valve actuator for a ball or s flap valve comprising a valve housing having a flow channel in which there is rotatably mounted a valve body which is rotatable between a closed and an open position by means of the actuator.

Valves of the above-mentioned type are used in many different fields within the industry. One field is the offshore 0 industry wherein such valves, especially ball valves, are used as closing valves at the upper end of risers where these are introduced into underwater buoys for the transfer of hydrocarbons (oil and gas) to a tanker or production vessel. Such buoys, which suitably may be introduced in a submerged receiving space in the s topical vessel, is constructed so that the vessel when required may turn about the buoy, under the influence of wind and weather. In order to allow such a turning, a swivel unit, i.e. a rotating connector which i.a. provides for the transfer of hydrocarbons from the risers to a pipe system on the vessel, is arranged at o the top of the buoy.

Recently, there have been developed special multi- course swivel units which are intended for connection to a corresponding number of risers which have been pulled up into the buoy. In this connection it has appeared that one of the 5 bottlenecks is to have disposed the desired number of risers in the buoy, because of the space demand of the above-mentioned valves with associated actuators. These must be placed internally in the upper part of the buoy, and a separate valve with actuator is required for each riser. In a buoy of the so-called STL or STP 0 type (see for example the Norwegian laying-open prints 175 419 and 176 129) the diameter in the upper part of the buoy normally is about 2,7 meters. With the traditional and known ball valve actuators there will not be sufficient space for placing for example eighteen valves with associated actuators, which is a 5 desired number in practice.

On this background it is an object of the invention to provide a new and simple valve actuator which simultaneously is not very space demanding.

The above-mentioned object is achieved with a valve

actuator of the introductorily stated type which, according to the invention, is characterized in that it comprises an inner and an outer sleeve which are coaxially arranged and surround the flow channel, the sleeves defining an intermediate annulus which is arranged to be pressurized with a pressure medium for relative axial movement of the sleeves, at least one of the sleeves being operatively connected to the valve body for rotation thereof by hydraulic pressurization of the annulus.

The invention will be further described below in connection with an exemplary embodiment with reference to the drawing, wherein

Fig. 1 shows an axial sectional view of the left half of a ball valve having an actuator according to the invention; and Fig. 2 shows a side view of the valve actuator itself, as viewed in the direction of the arrow A in Fig. 1.

The axial sectional view in Fig. 1 shows the left half of a ball valve comprising a valve housing 1 having a through¬ flow channel or a pipe course 2 in which there is rotatably mounted a valve body 3 in the form of a valve ball having a through opening 4. The valve is shown in open position, wherein the opening 4 is aligned with the pipe course 2, and can be closed by 90° rotation of the valve ball 3 by means of the actuator, as further described below. As mentioned, the sectional view in Fig. 1 shows only the left half of the valve structure. Advantageously, the valve and its actuator may be designed so that the two halves are equal, i.e. so that the complete axial section will be symmetric about the centre line CL in Fig. 1. However, this does not need to be the case, especially in the case of the elements for operative interconnection of the actuator and the valve body 3.

The ball valve itself is of a known type and comprises commonly known seals 5, 6 for sealing between the valve ball 3 and adjacent ends of a pair of valve housing members 7, 8 which define the channel or pipe course 2. The valve ball 3 is rotatably mounted in the valve housing 1 (about the axis X-X shown in Fig. 1) by means of a spindle or stem 9 which projects from and is fastened to the ball, the stem being rotatably mounted on a journal or neck 10 which is carried through an

opening in the outer part 11 of the valve housing. The neck 10 is kept in place by means of a disc 12 which is fastened to the outer valve housing part 11.

A corresponding spindle or stem with a corresponding bearing means is arranged at the diametrically opposite side of the valve ball 3.

As appears from Figs. 1 and 2, the actuator comprises an inner and an outer sleeve-like member (in the following referred to as sleeves) 13 and 14, respectively, which are coaxially arranged and surround the pipe course 2. The sleeves define an intermediate annular space or annulus ( "piston space" ) 15 which is arranged to be, preferably, pressurized with a hydraulic liquid for relative axial movement of the sleeves. As an alternative, pneumatic operation is conceivable. The annulus is sealed against the outside by means of O-ring seals 16 and 17 disposed in grooves in the mutually abutting sleeve walls. The hydraulic liquid, or generally the pressure medium used, is supplied to or drained from the annulus 15 by means of a non- illustrated supply means. The sleeves 13 and 14 are operatively connected to the valve ball 3 for rotation thereof by hydraulic pressurization of the annulus 15. For this purpose the two sleeves in the illu¬ strated embodiment are provided with cooperating, axially extending toothed rack portions 18 and 19 arranged on lower end portions of the sleeves and meshing with opposite sides of the stem 9 of the valve ball, the stem being formed as a gear spindle with adapted teeth. As appears from Fig. 2, the arrangement entails that the stem 9, and therewith the valve ball, is rotated with opposite axial movement of the sleeves 13 and 14. in the illustrated embodiment, each sleeve 13, 14 is provided with a pair of toothed rack portions 18 or 19 (only one of each portion is shown) which are in engagement with a respective one of a pair of gear spindles 9 projecting outwards at diametrically opposite sides of the valve ball. This is a preferred embodiment, since it leads to a simple construction and safe operation, with rotationally locked sleeves causing rotation of the valve ball with opposite axial movement of the sleeves, at the same time as the forces from the sleeves are distributed on two spindles at separate sides of the valve ball.

As an alternative one could conceive of an embodiment wherein only one sleeve is operatively connected to the valve body by means of a toothed rack portion meshing with a coopera¬ ting gear spindle. Such an embodiment would, however, require extra measures for rotational locking of the sleeves, and in order to keep the other sleeve axially fixed for achieving the necessary force transmission.

As shown, a number of mechanical prestressing or biasing springs 20 are disposed between opposite abutment surfaces 21, 22 arranged at respective upper ends of the sleeves

13 and 14. These springs have the task to move the sleeves 13 and

14 back to an initial position with pressure relief of the annulus 15 after pressurization thereof.

When the valve ball 3 is to be rotated, the annulus 15 is pressurized and the sleeves 13, 14 pressed axially apart a distance corresponding to a 90° rotation of the ball (open position in Fig. 1). This takes places against the force from the spring or springs 20 placed between the sleeves. When the valve ball is to be rotated in the opposite direction, this takes place in that the annulus is depressurized and the spring or springs presses/press the sleeves together a corresponding distance, i.e. in the illustrated embodiment to the closed position of the valve.

In the illustrated embodiment the two inner members 7, 8 and the outer member 11 of the valve housing 1 form a closed annular space or annulus 23 in which the coaxial sleeves 13, 14 are placed. Thus, the actuator is protected against influence from the ambient surrounding. This is operationally advantageous, and with the illustrated actuator structure this may be achieved without any substantial radial extension of the valve.

In the embodiment according to Fig. 1 a sleeve 24 is sealingly inserted into the pipe course 2 at the upper end of the valve housing member 7. In a practical application, this sleeve may form a connection with an associated pipe course in a plate (not shown) at the top of an STL/STP buoy, for connection to a multi-course swivel unit, as mentioned in the introduction. The lower member 8 of the valve housing then will be adapted for connection to a hanger means for suspension of the upper ends of the topical risers which have been pulled up into the buoy.