SHUT DOWN VALVE FOR USE IN A SUBWATER POSITION

Abstract: Device for sealing a gap between two co-axial cylindrical surfaces which are displaceable in relation to each other, particularly a sealing device intended for sealing a gap between a trunk piston (17) and a trunk piston shaped valve seat (25). The invention is distinguished in that: the trunk piston (17) comprises a radially outwardly facing conical surface (18) with a diameter decreasing towards the outer end of the trunk piston (17); a sealing ring (20), made of metal, is displaceably arranged above the conical surface (18), of the trunk piston; the valve seat (25) comprises a radially inwardly facing conical surface (27) with a diameter increasing towards the valve outer end of the valve seat (25), and where the sealing ring (20) is pressed between the conical surface of the sleeve (17) and the valve (25) conical surfaces (18, 27) into sealing engagement, when the trunk piston (17) is inserted into the valve seat (25).

Description: Shut down valve for use in a subwater position. TECHNICAL FIELD The present invention relates to a sealing device for a gap between two co-axial, cylindrical surfaces which are displace- able in relation to each other. BACKGROUND ART For valves which are installed in pipelines at great sea depths, certain requirements are necessary for maintenance purposes. It must be possible to replace the internal parts of the valve when the valve housing rests on the sea-bed. It must be possible to carry out this operation without pipelines being filled with water and without it being necessary to reduce the pressure or the flow in the pipeline. In the Norwegian patent publication no. 841360 an apparatus is disclosed which satisfies these requirements, in that a dis- placeable trunk piston is arranged which permits the valve housing and valve mechanism to be separated from the actual pipeline conduit. The problem with this construction has been to achieve a tight sealing system on the leading end of the trunk piston. In this connection, it must be taken into account that the sealing system is intended to be placed in a particularly corrosive environment which will consist of a mixture of oil, gas, water and sand particles. In order to replace packers it will be necessary to shut down the pipe¬ line, which leads to large economic losses. It is therefore a requirement that the trunk piston and it's seals shall have as long an intended life-time as the pipeline itself. Most of the sealing arrangements available today for this purpose are based on elastomers. These do not satisfy the requirements for tightness and reliability during fluctuating high levels of pressure combined with a long life-time in a sandy, corrosive environment. There is then, an urgent demand for a new type of sealing con¬ struction which meets these requirements. This is achieved with a sealing construction as described in the succeeding patent claims. BRIEF DESCRIPTION OF DRAWINGS The invention will be more closely described in the following with reference to the accompanying drawings where: Figure 1 shows a section of an already known valve which will comprise a typical area of application for the new sealing device. Figure 2 shows a detailed section of respectively, the leading edge of a displaceable trunk piston and a receiving valve seat. Figure 3 shows a section corresponding to figure 2, but with the trunk piston displaced forward. Figure 4 shows a section corresponding to figure 2 , but with the trunk piston displaced to the very front. MODES FOR CARRYING OUT THE INVENTION In figure 1 a clack valve 10 is shown, of the type disclosed in the Norwegian patent application no. 841360. The valve includes a valve housing consisting of a cylinder 11 and a radially situated valve chamber 12 in the shown embodiment formed by the upwardly directed, transverse connecting tube 13 r which is provided with a removable cover 14. The valve moreover includes a clack valve body 15 which is moveable from an active closed position to an inactive position with the clack placed in the valve chamber 12 as shown in the upper half of figure 1. The rear part of the cylinder 11 has a smaller diameter than the frontal part of the cylinder. The rear area, together with •? a co-axial inner pipe-piece 16, forms a steering for a trunk piston 17 which is displaceable in the cylinder 11 of the 5 valve housing, from a position where the valve is open and where the trunk piston 17 extends to the limit of the valve housing's radial valve chamber 12, thus dividing this from the valve's flow- conduit (lower part of figure 1) , and a position where the 10 valve is closed, and where the trunk piston 17 is withdrawn from the area of the radial valve chamber 12. The front end of the trunk piston 17 is shown in detail in figure 2 (position A in figure 1) . As it will be apparent from 15 the figure, the outer part of the trunk piston 17 is staged in two steps 18, 19 towards the outer end. The outer step 19 with the smallest diameter, is provided with screw-threads in a preferred embodiment. The inner step 18 is conical with a diameter decreasing towards the outer end of the trunk piston 20 17. A sealing ring 20 with an internal conical form, is placed above the inner step 18. A lock nut 21 is screwed on to the outer step 19 and bears against the sealing ring 20. The lock nut 21 and the sealing ring 20 are preferably both provided with a surface for engagement with each other. 25 The sealing ring 20 is made of a suitable metal material and has a capacity for radial extension which far exceeds the diameter of the trunk piston 17. In a preferred embodiment, the sealing ring's radially extending surface can be divided 30 into respectively, an inner surface 22a which is mainly paral¬ lel to the outer side of the trunk piston 17, and an outer surface 22b with a diameter which decreases towards the outer end of the trunk piston. The sealing ring 20 is moreover pro¬ vided with an external impact surface 23 extending mainly 35 vertically in relation to the centrally extending axis of the trunk piston 17. A valve seat 25 (position B in figure 1) for the trunk piston 17 is arranged on the connecting tube 13 of the valve housing 12, and comprises an inner baffte surface 26, a conical sea¬ ling surface 27 and outermost, a conical entrance surface 28. The inner baffte surface is preferably directed perpendicular¬ ly on the central axis 24 of the trunk piston 17. The conical sealing surface 27 has a slightly increasing diameter towards the outer edge of valve seat and transforms into the conical entrance surface 28 which has a somewhat greater angle in relation to the central axis 24 of the trunk piston. The figures 3 and 4 show in detail the mode of operation of the sealing device (corresponding to position C in figure 1) . When the trunk piston 17 is pushed forward into a position where the valve is open, the sealing ring 20 is guided into the conically formed valve seat 25 until the sealing ring bears against the baffte surface 26 of the valve seat (figure 3) . When the trunk piston is forced further in, the sealing ring will be compressed between the conical surfaces 18, 27 of the trunk piston 17, and the valve seat 25. There will thus be achieved an prestressed metal to metal seal on these sealing surfaces as figure 4 illustrates. By regulating the pressure on the actuator of the trunk pis¬ ton, a pre-stressed sealing with a desired force can be accom¬ plished. By choosing a suitable angle on the conical surface of the sealing surface the desired degree of self-locking action can be achieved. The sealing devises are developed for and described above, with a particular type of valve in mind. However it is obvious that the sealing device can be used in a range of other areas where it is necessary to seal a gap between two co-axial cylindrical surfaces which are displaceable in relation to each other.

Claims: CLAIMS 1. Devise for sealing a gap between two co-axial cylindrical surfaces which are displaceable in relation to each other, in particular a sealing device intended for sealing a gap between a trunk piston (17) and a trunk piston shaped valve seat (25) , c h a r a c t e r i z e d in that - the trunk piston (17) comprises a radially extending conical surface (18) with a diameter decreasing towards the outer end of the trunk piston (17) , - a sealing ring (20) , produced of metal, is displaceably arranged above the conical surface (18) , of the trunk piston - the valve seat (25) comprises a radially inwardly facing conical surface (27) with a diameter increasing towards the outer end of the valve seat (25) , and where, as the trunk piston (17) is inserted into the valve seat (25) , the sealing ring (20) is pressed between the conical surfaces (18, 27) of trunk piston's (17) and the valve seat (25) into sealing engagement. 2. Device according to claim 1, c h a r a c t e r i z e d in that a gradation (19) comprising threads for a retain¬ ing nut (21) , is arranged on the trunk piston's outer portion of the trunk piston outside the conically formed surface (18) . 3. Devise according to claim 2, c h a r a c t e r i z e d in that the diameter of the gradation (19) is smaller than the smallest diameter of the conically formed part (18) . 4. Device according to claim 1, c h a r a c t e r i z e d in that the radially, inwardly-facing surface of the sea¬ ling ring (20) is conically formed, and placed with dia¬ meter decreasing in the direction of the end portion of the trunk piston and externally it comprises two surfaces (22 a, 22 b) where one of the surfaces (22 a) is mainly parallel to the central axis (24) of the trunk piston, and a foremost outer surface with a diameter decreasing to¬ wards the outer end of the sleeve. 5. Device according to claims 1 and 3 c h a r a c t e r i z e d in that the sealing ring (20) comprises a frontal baffte surface (23) . 6. Device according to claim 1, c h a r a c t e r i z e d in that the conical surface (27) of the valve seat (25) has a diameter which increases towards the outer end of the valve seat and in the outermost portion transforms into a conical entrance surface (28) with a greater pitch angle. 7. Device according to claim 1, c h a r a c t e r i z e d in that the innermost portion of the valve seat (25) is terminated by an baffte surface (26) perpendicular to the central axis (24) of the trunk piston.

Inventors: HORVEI KNUT, HORVEI, KNUT
Applicants: NORSKE STATS OLJESELSKAP, DEN NORSKE STATS OLJESELSKAP A.S
Application year: 1987
Main classification: F16K43
IPC codes: E21B34, F16K3, F16K43