Butterfly valve and a method of producing a butterfly valve

Abstract

This invention relates to butterfly valve comprising a valve housing (2, 3) with a passage (4) for a fluid medium; a valve seat in the form of a seat ring (8) displaceable in a radial direction, relative to the axis of said passage (4), in a slot (7) in said valve housing (2, 3); a throttle (5) arranged so as to be pivotable about an axis of rotation (23) by means of a stem (6) between an open position and a shut-off position, said throttle (5) having a seal face (21) on the periphery (18) which is pressed against said seat ring (8) when said throttle (5) is in said shut-off position; wherein a plurality of round circles (Dn) form said periphery (18) and a largest round circle (De) of said periphery (18), is positioned in a plane (Pe) parallel with and closest to a base plane (P0) including said axis of rotation (23) and having a center point (Ce) defining a center line (22) of the throttle (5) positioned centrally in relation to said largest round circle (De), wherein said planes (P0, Pe) extend perpendicularly in relation to said center line (22), and wherein a center point (Cs) of a smallest round circle (Ds) of said periphery (18) is positioned in a lower plane (Ps) parallel to said planes (P0, Pe) and having a center point (Cs) that in a plane of symmetry (PP) including said center line (22) is positioned along said center line (22) and in perpendicular plane (PS) to said plane of symmetry (PP), including said center line (22) having said center point (Cs) positioned off-set a distance (Xs) from said center line (22) of the throttle (5), wherein said seal face (21) has a curved spherical shape.

Description

[0001] BUTTERFLY VALVE AND A METHOD OF PRODUCING A BUTTERFLY

[0002] VALVE

[0003] FIELD OF THE INVENTION

[0004] This invention relates to a butterfly valve comprising a valve housing with an axial passage for a fluid medium; a valve seat in the form of a seat ring of metal or other material with comparable rigidity, the seat ring being displaceable in the radial direction in a slot in the valve housing, a throttle arranged so as to be pivoted about an axis of rotation by means of a stem between an open position and a shut-off position, a peripheral seal face on the throttle being pressed against the seat ring in said shut-off position.

[0005] BACKGROUND OF THE INVENTION

[0006] A throttle of the above mentioned type is described e.g. in U.S. Patent 4284264. This throttle can cooperate with valve seat rings which may have various designs. By way of example the seat ring may have the design which is shown in the said U.S. patent specification or a design disclosed, e.g. in SE-B-445 382, US 3963213 or GB 2199641. Other designs are conceivable if means are provided to retain the seat ring in the position which the ring has adopted when the throttle has been rotated from the open position to the shut-off position when the valve is being assembled, i.e. at the so called "virgin shut-off movement".

[0007] It is a common feature of these seat rings that they have a curved sealing surface, turned towards the fluid passage. The sealing contact between the two sealing surfaces in the sealing position will therefore occur along a narrow zone and with practically linear contact. In order to obtain simultaneous tightening between the throttle and the seat around the circumference, the known throttle has an ovality in a plane parallel 2 to the side surfaces of the throttle, hereafter referred to as the zero- plane, the major axis being perpendicular to the axis of rotation of the throttle, and thereby also avoiding the throttle touching the seat at an initial phase of the shut-off movement, as well as substantial sliding between the surfaces. For the same purpose the periphery of the throttle has been given a complex double-curved shape, wherein that the lines of intersection between the throttle periphery and a first plane of intersection through the throttle, coinciding with the axis of rotation and perpendicular to plane of symmetry through the throttle, consist of arcs of a circle having its centre substantially on the axis of rotation, while the lines of intersection between the throttle periphery and a second plane of intersection defined by the said symmetry plane through the throttle, perpendicular to the axis of rotation, consist of straight lines, the extensions of which will meet, and the curvature of the sealing face of the throttle successively merges from the first mentioned circle in the said first plane of intersection into indefinitely large circles, that is to say, straight lines in the said plane of symmetry. This known butterfly valve has in comparison with previous designs brought about a considerable technical achievement and is today the dominant butterfly valve in Scandinavia, at least in the paper and pulp industry.

[0008] However, the above-mentioned valve has a few deficiencies. Thus, the geometry of the throttle surface is difficult to manufacture with a mathematically correct shape due to the fact that the shape is difficult to program for computerized production. Some approximations must be made in the computer program which means that a mathematically exact shape will not be achieved. In practice this means that the sealing surface on the throttle periphery will have some humps which counteract simultaneous sealing contact between the seat and the throttle around the whole periphery.

[0009] Therefore, the sealing face on the periphery of the throttle must have a larger breadth than the breadth of the zone of contact in a certain sealing position, so that the plane coinciding with the contact line or contact zone in a certain sealing position may be permitted to form an angle with the zero-plane. Initially this angle is negative, which means that one will achieve the shut-off position slightly before the zero-plane when the throttle is shut off for the first time. Also, in this position absolute tightness shall be achieved without subjecting the stem of the throttle to high torques. A good sealing result can be achieved in these positions if one has a high ratio between, on one hand, the surface pressure between the throttle and the seat and, on the other hand, the torque applied to the stem, at the same time as the throttle has a perfect or nearly mathematically perfect elliptic shape in the plane coinciding with the line or zone of contact in each sealing position.

[0010] These ideal conditions do not exist in the above mentioned, known valve type wherein the lines-of intersection between the plane of symmetry and the periphery of the throttle are defined by straight lines. The straight line in the said section will cause a lower surface pressure / torque ratio than what is desirable, and the shape of the line or zone of contact in the said plane which forms an angle with the zero plane will be more or less distorted, resembling the shape of a longitudinal section through an egg. SUMMARY OF THE INVENTION

[0011] An objective of the present invention is to further improve the above-mentioned known type of butterfly valve, which is achieved by a butterfly valve as defined in claim 1, wherein the seal face has a curved spherical shape.

[0012] The purpose of the invention thus is to provide a valve by which a simultaneous sealing contact is achieved around the periphery at the same time as a high-sealing pressure is obtained at a relatively low torque, as well as providing a valve wherein a sealing good contact between the seat and the throttle in the line or zone of contact is achieved. The latter purpose in its turn means that the geometry of the periphery of the throttle shall be such that it can be easily programmed for computerized production, that is to say that such approximations need not be introduced into the computer program which would cause humps or other deviations from the desired geometric shape during production. More particularly, the latter in its turn means that the sealing face of the throttle in a plane coinciding with any conceivable line or zone of contact within the area of the sealing face of the throttle shall have a nearly perfect desired circular shape.

[0013] Thanks to the invention using an algorithm that calculates diameters of circles at a plurality of levels of the sealing surface in relation to displacement of these there is achieved a so-called curved spherical shape and thereby achieve the possibility of obtaining very good application between throttle and seat with high tightness as a result.

[0014] Hence, by means of the invention there is provided an algorithm that can be used to easily produce a shape in which each level consists of exactly round circles which are displaced in one direction in order to achieve a suitable arrangement between the throttle and the seat. With the above-mentioned roundness of the throttle, a corresponding round / circular seat is allowed to be used, which may be made a material that is in the form of a rigid construction but still achieve very good tightness at a given torque regardless of what level on the periphery of the throttle the seat is placed on.

[0015] Accordingly, the said algorithm may provide for perfect roundness at all levels of the sealing surface of the throttle with a curved spherical shape that allows forgiving "rubbing" when rotating the throttle towards the seat while very good application is obtained by the curved spherical shape at a relatively low torque. The algorithm is preferably used for producing the 3D geometry by means of CAD for CAM preparation and / or CNC programming for machining.

[0016] The algorithm may also allow the possibility of varying the steps of the levels (Znl) and the number of degrees between each calculation per revolution, which entails the possibility of higher cutting speed during machining. The machining and moving speed of the machining machine of cutting tools determines the levels of steps (Znl) and degrees between each calculation per revolution without, for example, too much “facet formation” occurring. Rough machining before fine inserts can, however, allow facet formation to a certain extent and thus a higher cutting speed is allowed with a reduction of machining time and thus cost as a result.

[0017] These and other objectives can be achieved through the provision of the invention as set forth in the appended claims and following description of a number of preferred embodiments.

[0018] BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0019] The invention will be explained, in more detail, with reference to the drawings, in which:

[0020] Fig. 1 is a cross-sectional view of a valve housing with a butterfly valve according to the invention in a closed position,

[0021] Fig. 2 is a view along line A- A in Figure 1,

[0022] Fig. 3 is a plan view of the bottom side of a throttle according to the invention,

[0023] Fig. 4 is a cross-sectional view along the line B-B in Fig. 3,

[0024] Fig. 5 is a cross-sectional view along the line C-C in Fig. 4, and,

[0025] Fig. 6 schematically illustrates in a perspective view the geometry of the sealing surface of the throttle according to the invention,

[0026] DESCRIPTION OF PREFERRED EMBODIMENTS

[0027] With reference first to Figs. 1 and 2 there are shown cross-sectional views of valve housing, 2, 3 comprising a main part 2 and a cover ring 3. A passage through the valve has been designated 4. A throttle 5 can be rotated, from a sealing position as shown in Fig 1, to an open position and vice versa. This is achieved by means of a stem 6. The throttle 5 includes an attachment part 50 with a bore for fixed (preferably releasably) attachment to the stem 6. The stem 6 is journalled in the main part 2 of the valve housing 2, 3. For rotation of the stem 6 around its central axis 23, there are provided actuating means (known per se) which are not shown in the drawings.

[0028] A seat ring 8 is provided in an annular slot 7 in the valve housing 1 between the main part 2 and the cover ring 3. The seat ring 8 normally consists of stainless, acid resistant steel, but may also be made in other metals / materials, e.g. a rigid composite or plastic material. At the inner end of the seat ring 8, which is directed toward the throttle 5, there is arranged a rounded surface 80, which constitutes the sealing surface of the valve seat against which the throttle 5. A pair of annular members may extend radially, symmetrically outward, which preferably are pressed resiliently, by spring action, in the axial direction against the walls of the slot 7, to ensure the desired combination of radial rigidity, axial flexibility and sealing ability.

[0029] The slot 7 is so deep that the ring 8 may be displaced radially, i.e. the diameter of the slot 7 is essentially greater than the maximal outer diameter of the seat ring 8. The position of the seat ring 8 may thus adapt to the throttle 5 when the throttle 5 valve is rotated. The flanges at the same time preferably are so stiff or rigid, in other words, their spring action is so great, that it ensures that the seat ring 8 will retain its axial position.

[0030] The periphery of the throttle 5 has been designated 18. A circumferential middle line on the periphery 18 has been designated 19. A plane coinciding with this middle line 19 defines a zero-plane, which has been designated 20. In the ideal case, the middle line 19 is the line of contact between the throttle 5 and the seat ring 8 when brought to sealing contact. It should, however, be understood that the contact between the throttle and the seat ring does not occur along a line in the mathematical sense, but along a narrow zone. It should also be understood that the line or zone of contact may rarely occurs along the exact middle line 19 and zero-plane 20 because of the influence of manufacturing tolerances, wear, varying temperatures and deformations caused by such variations, etc. For these reasons one may make use of a larger area of the periphery 18 of the throttle, which may be referred to as the sealing face 21 of the throttle 5. The breadth of this sealing face 21 may vary from case to case. In many applications a practical rule for the breadth of the sealing face 21 may be 1 / 3-2 / 3 of the breadth of the peripherylS of the throttle 5. A-reason why the periphery 18 of the throttle is somewhat broader than the sealing face 21 is that the outer surfaces of the periphery on both sides of the sealing face 21 constitute a safety zone against a "super rotation,' of the throttle, that is a rotation of the throttle beyond the seat when closing the valve, which, if it occurred, may cause the valve to be inoperable. The shape of the periphery 18 of the throttle 5 according to the invention now will be explained more closely with reference to Figs. 3-6.

[0031] As shown in Figs. 3 and 4 there exist a center line 22 of the throttle 5, which centre line is positioned centrally in relation to an upper plane Pe (which may coincide with the upper surface 51) including the upper round circle (see De and Dn in Fig. 4 and 5, respectively) of the periphery surface 18. Perpendicularly to that plane 51 there exist a plane PS that includes the cross-sectional plane B-B shown in fig. 3 and accordingly therefore also the centre line 22. Hence, in this plane PS the diameters DO, DS, etc of the peripheral surface 18 of the throttle 5 will be coaxially positioned in relation to the centre line 22, see Fig. 4, i.e. along this plane PS all circles with have their centers Cs, Cn, Ce positioned along the center line. The radius HO from a crossing point CP between the central axis 23 and the center line 22, will therefore be the same on both sides of the plane PS. However, in a perpendicular plane PP including centre line 22, see Figs 5 and 6, the round circles DO, DS, etc. of the peripheral surface 18 will not be coaxially positioned in relation to the centre line 22, but having the center Cs, Cn, Ce displaced a certain distance Xn, Xs from the center line 22 at certain levels Zn, Zs. This perpendicular plane PP presents a plane of mirror symmetry.

[0032] As has been mentioned in the introductory part of this specification, the invention is intended to provide a valve with a high ratio between the pressure exserted by the throttle 5 upon the seat 8 and the torque applied to the stem 6, by means of a constant radius circular shape, Ds to De, in each plane of such a circle parallel with a base plane P0, of the line or zone of contact in each position of contact on the sealing face 21 of the throttle 5; a simultaneous sealing contact around the periphery; and a possibility to transfer the geometry to a computer program for computerized production of the periphery of the throttle, which objectives can be achieved through the new design of the geometry of the throttle.

[0033] DO, see Figs. 4, 5 and 6, is a theoretically intended target diameter of the sealing surface 21 at a level ZO for seat abutment of the throttle 5 in a closed position of the valve, wherein ZO is measured from a base plane PO, including the axis 23 of the stem 6, parallel with the plane of the DO circle. DO has in the true sense no limitation on dimension, but can preferably be limited to a range of diameters from 50 mm up to 3000 mm.

[0034] Brief description of the calculation procedure. • First there is defined a target circle diameter DO of the throttle periphery 18, which target circle diameter DO is positioned somewhere between the smallest diameter Ds and the largest diameter De of the periphery 18, preferably adjacent a middle plane PO of the throttle periphery 18, see Fig. 4

[0035] • Then there is defined a distance ZO between the center line 23 of the stem 6 / shaft hole 53 and the plane PO of target circle DO.

[0036] • Then HO is calculated using ZO and DO and the below formula:

[0037] • Thereafter a start level Zs, see Fig. 4, is determined for the smallest diameter Ds by using ZO and Za and the below formula, wherein Za is a predetermined distance chosen in dependence of how large the breadth, Za+Zb, of the body forming the periphery 18 shall be :

[0038] • Then the start diameter Ds is determined by using HO and Zs and the below formula:

[0039] • Thereafter the offset Xs from the center line 22 along the plane PP for the smallest circle Ds is determined by HO, Zs, DO and a constant Cf, by use of the below formula, wherein Cf usually is between 1 and 2, but can be both smaller and larger.

[0040] Now the starting circle Ds is determined and may be produced, e.g. by milling, turning, forging, etc.

[0041] The shape of the following surface of the periphery 18 may preferably be in the form of small steps, AZ, or by a continuously adapted shape by use of the below formula:

[0042] Wherein Zn = Zs - AZ

[0043] Hence, the dimension Dn, the position Zn may be determined by the offset Zn of the next round circle, whereby the use of small steps AZ will provide for a smoothly curved periphery 18.

[0044] When shaping the periphery 18 by machining, it may be an advantage to use the feed rate, e.g. distance / rev to calculate AZ, e.g. mm / revolution and then use a feed rate distance / rev that is relatively low, at least along the sealing face 21.

[0045] The embodiment above describes only one illustrate examples of reducing the basic principle of the invention to practice. It is realized that variations utilizing the basic principle of the invention are conceivable.

Claims

CLAIMS1. A butterfly valve comprising a valve housing (2, 3) with a passage (4) for a fluid medium; a valve seat in the form of a seat ring (8) displaceable in a radial direction, relative to the axis of said passage (4), in a slot (7) in said valve housing (2, 3); a throttle (5) arranged so as to be pivotable about an axis of rotation (23) by means of a stem (6) between an open position and a shut-off position, said throttle (5) having a seal face (21) on the periphery (18) which is pressed against said seat ring (8) when said throttle (5) is in said shut-off position; wherein a plurality of round circles (Dn) form said periphery (18) and a largest round circle (De) of said periphery (18), is positioned in a plane (Pe) parallel with and closest to a base plane (PO) including said axis of rotation (23) and having a center point (Ce) defining a center line (22) of the throttle (5) positioned centrally in relation to said largest round circle (De), wherein said planes (PO, Pe) extend perpendicularly in relation to said center line (22), and wherein a center point (Cs) of a smallest round circle (Ds) of said periphery (18) is positioned in a lower plane (Ps) parallel to said planes (PO, Pe) and having a center point (Cs) that in a plane of symmetry (PP) including said center line (22) is positioned along said center line (22) and in perpendicular plane (PS) to said plane of symmetry (PP), including said center line (22) having said center point (Cs) positioned off-set a distance (Xs) from said center line (22) of the throttle (5), characterized in that said seal face (21) has a curved spherical shape.

2. A butterfly valve according to claim 1, wherein said periphery (18) is shaped to be curved spherically by use of an algorithm defining:wherein Zn = Zs - AZ and Zs= Z0 + Za , wherein ZO is a a distance between the center line (23) of the stem shaft center (53) and the plane PO of a target circle (DO) which is positioned somewhere between the smallest diameter (Ds) and the largest diameter (De) of the periphery (18), and wherein (Za) is a the distance of the breadth (Za+Zb) of the body forming the periphery (18).

3. A butterfly valve according to claim 1 or 2, wherein all said round circles (Ds-De) in the region of said seal face (21) have a constant radius.

4. A butterfly valve according to claim 3, wherein all said round circles (Ds-De) in the region of said periphery (18) have a constant radius.

5. A butterfly valve according to claim 1, 2, 3 or 4, wherein at least 30%, preferably at least 50%, more preferred at least 60%, of said periphery (18) including the seal face (21) has a surface roughness in the range of Ra 0,05-6,3 μm, preferably 0,2 - 1,6 μm, more preferred less than 0,5.

6. A butterfly valve according to any of claims 1-5 , wherein said seat ring (8) has an inner sealing face (80) having a constant radius.

7. A butterfly valve according to claim 6, wherein said seat ring (8) is made in a polymer material having a hardness in the range of about 50 Shore D to 90 Shore D, preferably 60 Shore D to 85 Shore D.

8. A butterfly valve according to claim 6, wherein said seat ring (8) is made in a hard material, preferably metal, having a hardness from about 180 HB to 300 HB or from 30 to 55 Rockwell C, preferably in the range of 210 to 300 HB or 30 to 45 Rockwell C.

9. A butterfly valve according to any one of claims 1 to 6, wherein said center point (Cs) is positioned off-set a distance (Xs) in said perpendicular plane (PS) from said center line (22) of the throttle (5) within a range defined by the formula:wherein Cf is between 0,5 to 50, wherein preferably said seat ring (8) is made in a polymer material having a hardness in the range of about 50 Shore D to 90 Shore D, preferably 60 Shore D to 85 Shore D, and wherein Cf is between 0,5 to 1.

10. A butterfly valve according to claim 6, wherein said seat ring (8) is made in a hard material, preferably metal, having a hardness from about 180 HB to 300 HB or from 30 to 55 Rockwell C, preferably in the range of 210 to 300 HB or 30 to 45 Rockwell C and wherein Cf is between 1 to 3.

11. A method of producing a butterfly valve, comprising the steps of: a) attaching a throttle body into a machine for machining of a periphery (18) to include a seat surface (21) of a throttle (5), b) defining a target circle diameter (DO) of the throttle periphery (18) and deciding the position of a middle plane (Po) of said target circle diameter (DO) somewhere between a preset smallest round circle (Ds) and a preset largest round circle (De) of the periphery (18), preferably adjacent said middle plane (Po) of the throttle periphery (18), c) defining a distance (Z0) between a base plane (P0) including a center line (23) of a stem shaft hole (53) and the parallel middle plane (Po) of said target circle (DO), d) calculating a distance (HO) by using the formula,e) determining a predetermined distance (Za) deciding the breadth, Za+Zb, of the body forming said periphery (18), f) determining a start level (Zs) for said smallest round circle (Ds) by using ZO + Za, g) determining a start circle diameter (Ds) by using the formula,h) determining an offset (Xs) for a center point (Cs) of said smallest round circle (Ds) from a predetermined center line (22) of the throttle (5) along the intersection between a perpendicular plane (PS) perpendicular to the plane of symmetry (PP), by use of the below formula, wherein Cf is chosen to be in the range 0,5 to 50,i) Starting machining and using the below formula, wherein Zn = Zs - AZand using small steps (AZ) to provide for a smoothly curved spherical periphery (18).

12. Method according to claim 11, wherein the feed rate distance / rev of the machine is used to calculate said small steps (AZ).

13. Method according to claim 12, wherein said feed rate is in range of 0,02 mm / rev to 0,6 mm / rev, preferably 0,06 mm / rev to 0,4 mm / rev, most preferred less than 0,3 mm / rev.

14. Method according to any of claims 11-13, wherein said seat ring (8) is made in a polymer material having a hardness in the range of about 50 Shore D to 90 Shore D, preferably 60 Shore D to 85 Shore D, and wherein Cf is between 0,5 to 1.

15. Method according to any of claims 11-13, said seat ring (8) is made in a hard material, preferably metal, having a hardness from about 180 HB to 300 HB or from 30 to 55 Rockwell C, preferably in the range of 210 to 300 HB or 30 to 45 Rockwell C and wherein Cf is between 1 to 3.

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