GB2054804A

GB2054804A - Anti-vibration valve

Info

Publication number: GB2054804A
Application number: GB8022208A
Authority: GB
Original assignee: Centre Technique des Industries Mecaniques CETIM
Current assignee: Centre Technique des Industries Mecaniques CETIM
Priority date: 1979-07-19
Filing date: 1980-07-07
Publication date: 1981-02-18
Also published as: EP0023172B1; IT1131728B; DE3063113D1; JPS5918588B2; JPS5618167A; EP0023172A1; FR2461864B1; FR2461864A1; CH636420A5; IT8023553A0

Description

SPECIFICATION Anti-vibration valve This invention relates to valves and more particularly to turbine control valves especially steam turbines. There are known turbine control valves, having a valve member with a spherical head which blocks to a greater or lesser degree the passage of fluid to a recovery nozzle. The purpose of this nozzle is to recover to a maximum the kinetic energy of the fluid by transformation to piezometric energy such that the overall output of the installation is not greatly affected by the valve when working with large passage openings. The valve member is arranged within a chamber which is generally fed laterally, and its movements along the output axis of the fluid against a narrowing of the passage forming a seat, are governed by a control system. Rapid and especially supersonic flow, through a valve of the abovementioned type gives rise to mechanical vibrations which are dangerous for the whole of the installation; to flow instabilities which upset the control system; and to abnormal load losses and extensive noise. One has noticed in particular, that on small openings of the valve member and at intermediate openings, a recompression shock wave is produced between the valve member and the seat. The turbulent flow seems to be due to an adhering of jets of fluid to the wall of the valve member, adhering which takes place in a random fashion and which results in vortices being formed in the fluid by the walls. One has also observed an asymmetry of fluid flow around the valve member, the flow can be supersonic in one zone and subsonic in another, resulting in substantial transverse forces on the valve member and in formation of rotary flow. These turbulent flows produce forces not only on the valve member but equally on all the elements arranged downstream and principally on the first stage of the turbine where variations in overall output can appear. The present invention has as its object to overcome the above mentioned disadvantages and thus to improve control valves in general and turbine control valves in particular. This invention has as its object an anti-vibration valve for control of passage of fluid, comprising a valve body defining a passage where the fluid flows into a chamber containing a valve member movable, as desired along the output axis of said fluid against a narrowing of said passage forming a seat for said valve member, in order to control the passage of said fluid;said valve being characterised in that, in all the positions of the valve member between complete closure and full opening, the cross-section of the fluid passage between said valve member and its seat decreases in the direction of flow, said valve member having a surface interruption in the region downstream of the area of contact of said valve member with said seat, and the wall of the valve ) member seat being defined, in axial section, by at least one curve which joins a straight portion in the region downstream of the point of contact of said curve with said valve member, the wall of said seat having a discontinuity, forming a stop, at the level of the point of joining of said curve and said straight portion. The interruption of the surface in the region downstream of the area of contract of the valve member with the seat results in avoidance of large fluid adherence to the wall downstream of the valve member as would occur in the case with a spherical headed valve member. One thus avoids converging diverging nozzle type flow between the valve member and the seat and suppresses all possibility of recompression on the valve member. . Similarly, discontinuity of the seat wall with the formation of a stop improves flow and ensures a free jet. According to the invention, the wall of the valve member seat can be defined in axial section by at least one convex curve to which there is joined a straight portion forming an angle of at least 90[deg] with a perpendicular to the axis of the valve member through the point of joining, said angle being greater than the angle formed by said perpendicular with the tangent to said curve at said point of joining. In accordance with one embodiment of the invention, the wall of the valve member at the area of contact of the seat is defined, in axial section, by at least a first convex curve to which there is joined a second curve in the region downstream of a point of contact of said first curve with the valve member seat, said first and second curves being completely located upstream of the perpendicular to the axis of the valve member through the point of joining of said curves. It is to be noted that within the ambit of this invention the expression "the region downstream of the point of contact" signifies that the distance between point of joining of the curves and point of contact with the seat is very small in relation to the dimensions of the valve member. By way of example, for a valve member having a diameter of about 300mm, the point of joining is about 1 mm from the point of contact. This ensures the provision of a positive stop at the level of the point of joining. According to one embodiment of the invention, the second curve is the generatrix of a spherical axial opening in the valve member. According to another embodiment of the invention the second curve is a straight portion which forms with the perpendicular to the valve member axis through the point of joining of said portion with the first curve, an angle greater than 0. and at least equal to 90[deg], said straight portion being therefore the generatrix of a cylindrical or conical axial opening in the valve member. In accordance with a preferred embodiment, the tangent to the first curve at the point of meeting forms with the perpendicular to the valve member axis through the point of meeting, an equal greater than 0[deg] and less than 90[deg] . In accordance with another embodiment, the wall of the valve member seat also has a surface interruption in the region downstream of the area of contact with the valve member. The invention will be better understood by the reading of the following detailed description and examination of the attached drawings which show by way of non-limitative examples, several embodiments of the invention. Figure 1 shows an axial section of a valve in accordance with the invention. Figure 2 shows to a greater scale, a part of the valve of Figure 1. Figures 3 to 5 show variations of the valve member according to the invention. Figure 6 shows schematically another embodiment of the invention. In Fig. 1 there is shown a control valve for a steam turbine. The valve comprises a valve body 1, a chamber 2, fed laterally by a conduit 3 and a valve chamber 4 which can block to a greater or lesser degree the passage of fluid towards a recovery nozzle 5. The valve member 4 is movable along the output axis A-A' of fluid against a narrowing which forms a seat constituted by an insert 6. In a known manner, the valve illustrated includes an intermediary valve 7 having a valve member 8 smaller than the valve member 4, and which controls flow of fluid in an axial passage 8' in the valve member 4. Initial opening of the valve member 8 reduces the force necessary for opening of the valve member 4. As can be seen from Figure 2 which is an axial section, the wall of the valve member 4 in the area of contact with the seat 6, is defined in the example by a convex curve such as an arc of a circle 9 to which there is joined a straight portion 10 at a point 11 1 located in the region downstream of a point of contact 12 of the arc of the circle 9 with the seat 6. The arc of circle 9 and the straight portion 10 are entirely located upstream of the perpendicular 13 to the axis A-A' through the point of joining 11. The portion 10 forms an angle alpha of 90[deg] with the perpendicular 13 to the axis A-A', whilst the tangent T to the arc of the circle 9 at the point of joining 11 forms with perpendicular 13 an angle beta equal to approximately 45[deg].The valve member 4 thus has at the area of contact with the seat a convex spherical surface having an interruption producing a cylindrical axial opening 13' in said valve member 4. It is to be noticed on the drawings, that the distance between the point of contact 12 and the point of joining 11 has been exaggerated for the sake of clarity. In axial section, the wall of the seat 6 is defined by a convex curve such as an arc of a circle 14 to which there is joined a straight portion 15 at a point 16 located in the region downstream of the point of contact 12' of the arc of the circle 14 with the valve member 4. The arc of the circle 14 is located upstream of perpendicular 17 to the axis A Ȧ' through the point of joining 16 whilst the straight portion 15 is located downstream of the perpendicular 17. The tangent T' to the arc of the circle 14 at the point of joining 16 forms an angle y of approximately 45[deg] with the perpendicular 17, whilst the straight portion 15 forms an angle 8 of 90. with the perpendicular 17. The seat therefore has a toric surface which extends downstream through a cylindrical surface. The angle 8 being greater than the angle y, the wall of the seat 6 has a discontinuity forming a stop at 16. In the embodiment of Figures 1 and 2, the seat 6 of the valve member 4 is followed downstream by a narrowing which forms a neck 18 of a diverging nozzle 19. To obtain an interruption of the surface in the region downstream of the point of contact of the valve member with the seat, it is sufficient that the angle a shown in Figure 2 between the straight portion 10 and the perpendicular 13 through the point of joining 11 is greater than 0[deg], its maximum value preferably being equal to 90[deg]. In Figures 3 to 5, there are shown other embodiments of a valve member according to the invention. These valve members 20, 21 and 22 are for use with direct control valves, that is to say valves not having an intermediate valve and therefore as a result, not having an axial passage for fluid such as the passage 8' of Figure 1. Figure 3 corresponds to the case where the angle a equals 90[deg] and the valve member therefore has a blind cylindrical axial opening 24. Figure 4 corresponds to an angle a greater than 02 and less than 90[deg], the valve member 21 thus having a conical axial opening 25. Figure 5 corresponds to the case where the straight portion 10 shown in Figure 2 is replaced by an arc of the circle 26, the valve member 22 having a spherical axial opening 27. The wall of the seat of the valve member can equally have a surface interruption in the region downstream of the point of contact with said valve member. This surface interruption is obtained by the value of the angle 8 (shown in Figure 2) between the perpendicular 17 and the straight portion 15 being greater than 90[deg]. In Figure 6 there is shown an embodiment in which the interruption 29 of the wall of the seat is defined by an angle 8 equal to 180[deg]. It is to be understood, that the invention is not limited to the embodiments described and shown, numerous modifications being available to the man skilled in the art, in accordance with the desired application and without departing from the spirit of the invention as a result. Thus, in particular, the invention is not limited to supersonic flow in control valves for steam turbines, the invention being applicable to all valves or stop cocks through which there flows a fluid which is compressible or otherwise.

Claims

1. An anti-vibration valve for control of passage of fluid, comprising, a valve body, a passage in said body through which fluid flows into a valve chamber, a valve member in said valve chamber and movable as desired along an output axis of said fluid in order to control the passage of said fluid, a narrowing in said passage forming a seat for said valve member, wherein, in all the positions of said valve member between complete closure and full opening, the cross-section of the fluid passage between said valve member and said seat decreases in the direction of flow, said valve member having a surface interruption in a region downstream of the point of contact of said valve member with said seat, and the walls of the valve member seat being defined in axial section by at least one curve to which there is joined a straight portion in a region downstream of the point of contact of said curve with said valve member, the wall of said seat having a discontinuity forming a stop at the level of the point of joining of said curve with said straight portion.

2. A valve as claimed in claim 1, wherein the wall of the seat of the valve member is defined in axial section by at least one convex curve to which there is joined a straight portion forming an angle of at least 90[deg] with a perpendicular to the axis of the valve member through the point of joining, said angle being greater than the angle formed by said perpendicular with the tangent to said curve at said point of joining.

3. A valve as claimed in either claim 1 or claim 2, wherein the wall of the seat of the valve member has a surface interruption in the region downstream of the area of contact with said valve member.

4. A valve as claimed in any preceding claim, wherein, in axial section, the wall of the valve member, in the area of contact with the seat, is defined by at least a first convex curve to which there is joined a second curve in the region downstream of the point of contact of said first curve with the valve member seat, said first and second curves being entirely located upstream of a perpendicular to the axis of the valve member through the point of joining of said curves.

5. A valve as claimed in claim 4, wherein the tangent to the first curve at the point of meeting with the second curve forms with the perpendicular to the axis of the valve member through said point of joining an angle greater than 0. and less than 90[deg].

6. A valve as claimed in either claim 4 or claim 5, wherein the second curve is the generatrix of an axial spherical opening in said valve member.

7. A valve as claimed in any one of claims 4 to 6, wherein the second curve is a straight portion which forms with the perpendicular to the axis of the valve through the point of joining of said portion with said first curve an angle greater than 0. and less than or equal to 90[deg].

7. A valve as claimed in any one of claims 4 to 6, wherein the second curve is a straight portion which forms with the perpendicular to the axis of the valve through the point of joining of said portion with said first curve an angle greater than 0. and at least equal to 90[deg].

8. A valve as claimed in claim 7, wherein the said straight portion as a generatrix of a conical axial opening in the valve member. 9. A valve as claimed in claim 7, wherein the said straight portion is a generatrix of a cylindrical axis opening in the valve member.

10. An anti-vibration valve for control of passage of fluid substantially as hereinbefore described with reference to the accompanying drawings. New claims or amendments to claims filed on 13/10/80 Superseded claims 7 New or amended claims :-