AU771488B2

AU771488B2 - Butterfly valve

Info

Publication number: AU771488B2
Application number: AU52784/02A
Authority: AU
Inventors: Masaharu Fukuchi
Original assignee: Okumura Engineering Corp; Okumura Engineering Corp OKM
Current assignee: Okumura Engineering Corp OKM
Priority date: 2001-07-04
Filing date: 2002-07-04
Publication date: 2004-03-25
Anticipated expiration: 2022-07-04
Also published as: KR20030004009A; CN1393650A; MY128868A; HK1051063A1; TW496934B; CN1309977C; AU5278402A; JP2003014139A

Description

P/00/011 28/5/91 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: BUTTERFLY VALVE The following statement is a full description of this invention, including the best method of performing it known to us BUTTERFLY VALVE BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a butterfly valve wherein a valve disc provided in a valve casing is rotated about a valve axis in order to open and close a valve and control a fluid flow flowing through the butterfly valve.

Prior Art: In a general butterfly valve, a valve disc of a substantially disc-like shape provided in a valve casing is rotated about a valve axis, which passes through in the diametral direction of the valve disc, in order to open and close a valve and control a fluid flow flowing through the butterfly valve. At an inner circumferential surface of the valve casing is provided with a seat ring made of a rubber elastic body. When the valve is closed, the valve disc is rotated about the valve axis in the direction of the closed position at which a disc surface is positioned perpendicular to the direction of fluid-flow and a circumferential edge portion of the disc makes a pressurized contact with the seat ring to create a seal between the inner circumferential surface of the valve casing and the valve disc.

One conventional seat ring is shown in Fig. 8. Said seat ring 101 has an outside face opened radially outwardly and is of a ring-like shape having a substantially U-shaped cross section. Said concave outside face is closely fitted to a projection provided on the inner circumferential face of the valve casing to fix the seat ring to the valve casing. Further, the inner periphery of the seat ring is provided with a circular projection 102 continuously protruding radially inwardly in the circumferential. direction. The circular projection 102 makes a pressurized contact with the outer periphery of the valve disc 103 to create a seal between the seat ring 101 and the valve disc 103.

In a general seat ring of such a type that said seat ring is forced to be pressed by the outer periphery of a valve disc to a radially outward direction of the flow passage, the outer periphery of the valve disc slides on the surface of the seat ring with pressing the seat ring to a radially outward direction of the flow passage until the seat ring is deformed to a prescribed amount, and a frictional force induced thereby increases a rotary torque required to close the valve.

In the case of a seat ring 101 shown in Fig. 8, however, the circular projection 102 provided on the inner periphery thereof is pressed towards a closing direction by the outer periphery of the valve disc 103, so that a frictional force for closing a valve can be minimized and a rotary torque required to close a valve becomes lower.

Namely, as shown in Fig.8, the valve disc 103 in the opened position is rotated about the valve axis 104 towards a closing direction and contacts the circular projection 102 in the contact position Then the valve disc 103 is further rotated towards a closing direction to reach the closed position When shifting from the contact position to the closed position the outer periphery of the valve disc 103 slides on the surface of the circular projection 102.

However, since the outer periphery of the valve disc presses little the seat ring to a radially outward direction of the flow passage, a frictional force for closing a valve is minimized.

In the closed position there is induced a counterforce, at the bulged portion with the height H of the circular projection 102 deformed towards a closing direction, to force back the outer periphery of the valve disc 103 towards an opening direction. The effect of seal is attained when the counterforce overcomes a fluid pressure.

The counterforce becomes larger in proportion to the thrust deformation amount induced at the time when the valve disc shifts from the contact position to the closed position In order to maintain substantially the same thrust deformation amount in the circumferential direction of the circular projection 102, the circular projection 102 has the same cross section in the circumferential direction thereof. When viewing the circular projection 102 from the direction of the valve axis 104, the contacting portion 105 and the longitudinal axis 106 of the circular projection 102 make two parallel straight lines. And the contacting portion 105 is substantially parallel also to the outer periphery of the valve disc 103 in the closed position and the space therebetween equals to the thrust deformation amount When observed from the view point of the valve axis 104, however, the outer periphery of the valve disc makes a straight line which pass through the valve axis, and the straight line of the outer periphery of the valve disc rotates about the valve axis. Since the straight line of the outer periphery of the valve disc and the straight line of the contacting portion do not overlap each other, when a valve is closed, the outer periphery of the valve disc does not contact the circular projection at the same instant. The contact timing of the outer periphery of the valve disc depends on the distance from the valve axis.

Namely, the movement of the outer periphery of the valve disc, when the valve disc is rotated about the valve axis, is proportional to the distance from the valve axis in the direction perpendicular to the valve axis. The rotary angle of the valve disc at the time when the movement of the outer periphery of the valve disc becomes equal to the thrust deformation amount is larger in the vicinity of the valve axis than in the central portion between the valve axes. As a result, when the central portion between the valve axes is in the contact position the vicinity of the valve axes is made a pressurized contact in some degree with the circular projection.

Although the circular projection is made a pressurized contact in some degree with the vicinity of the valve axes, a seal can not be achieved until the outer periphery of the valve disc is brought into contact with the central portion of 0 the circular projection. In view of this, the pressurized contact of the outer 0 periphery of the valve disc with the vicinity of the valve axes until the outer 20 periphery of the valve disc is brought into contact with the central portion of the circular projection does not contribute to a seal performance, thus resulting in an e unnecessary increase of rotary torque for closing a valve.

In addition, the contact of the outer periphery of the valve disc with the circular projection in the vicinity of the valve axes occurs when the valve disc is 25 rotated towards a closing direction for limiting the fluid flow. Thus the deterioration S. of the seat ring is accelerated in the vicinity of the valve axes.

SUMMARY OF THE INVENTION An object of the present invention is to provide a seat ring for a butterfly valve wherein a periphery of a valve disc is entirely and substantially at the same instant brought into contact with a contacting portion. of a circular projection provided between a pair of bosses.

The present invention provides a seat ring for a butterfly valve provided at an inner circumferential surface of a valve casing so as to create a seal between the inner circumferential surface of a valve casing and a valve disc when closing a valve, including a pair of opposite valve stem holes for inserting valve stems positioned radially outwardly of a flow passage and a circular projection continuously protruding inwardly in the circumferential direction between a pair of bosses formed around said each valve stem hole and contacting with a periphery of the valve disc for closing the valve, a contacting portion of said circular projection with which the periphery of the valve disc contacts being formed at a portion apart from the bosses to be curved swelling towards the periphery of the valve disc in the direction of the flow passage so that the entire periphery of the valve disc contacts with the contacting portion substantially at the same instant.

In contrast with the case of a circular projection having the uniform cross section in the circumferential direction, in case the contacting portion is formed, at a portion apart from the bosses in the circumferential direction, to be curved swelling towards an opening direction, the periphery of the valve disc can be entirely and substantially at the same instant contacted with the contacting portion of the circular projection. Namely, in case where a circular projection has the uniform cross section in the circumferential direction and the contacting portion is formed parallel to the axis of the circular projection, a periphery of a valve disc shifting towards a closing direction first contacts with a circular projection in the vicinity of bosses and thereafter contacts with a portion apart from the bosses, but by swelling a portion apart from the bosses, the periphery of the valve disc can contact with the contacting portion of the circular projection entirely and substantially at the same instant in the circumferential direction thereof.

Besides, in case a cross section of a portion of the circular projection to be deformed and bulged towards a closing direction by contacting with the periphery of the valve disc for closing the valve is made substantially uniform in the circumferential direction, the portion where a thrust deformation amount towards a closing direction is small increases the height of contact with the periphery of the valve disc, and as a result, a sealing efficiency of substantially the same in the circumferential direction can be achieved.

In other words, by swelling the contacting portion apart from the bosses of the circular projection towards an opening direction, the thrust deformation 4a amount of the circular projection towards a closing direction, from the contacting position to the closed position, becomes larger at the central portion apart from the bosses than in the vicinity of the bosses. Although the counterforce per unit area pushing back the valve disc towards an opening direction at the time when the circular projection contacts closely with the i e• periphery of the valve disc is small in the vicinity of bosses and becomes larger at the central portion, the increase of the contact height makes the sealing efficiency substantially uniform in the circumferential direction.

Furthermore, in the seat ring having a tapered face formed at the opening side of the circular projection closely contacting with the periphery of the valve disc for closing the valve, in case said tapered face is formed so as to vary the slant in the circumferential direction in such a manner that the slant is steep in the vicinity of the bosses and gentle in the portion apart from the bosses, the cross section of the portion to be deformed and bulged towards a closing direction by contacting with the periphery of the valve disc for closing the valve can be made substantially uniform in the circumferential direction.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: Fig. 1 is a front view of a butterfly valve illustrating one embodiment according to the present invention; Fig. 2 a sectional view taken along the line A-A of Fig. 1; Fig. 3 a sectional view of a seat ring taken along the valve axis; Fig. 4 a sectional view of a seat ring taken along perpendicular to the valve axis; Fig. 5 is a partially sectional view illustrating the periphery of the valve disc closely contacting with the circular projection; Fig. 6 is a view explaining the conditions of close contact in the vicinity of bosses and at a central portion between the bosses; Fig. 7 is a view explaining the relation between a counterforce induced at a contact portion and a fluid pressure; and Fig. 8 is a sectional view of a seat ring of a prior art butterfly valve.

DETAILED DESCRIPTION OF THE EMBODIMENTS Preferred embodiments of the present invention will be explained in detail below with reference to the accompanying drawings.

A butterfly valve according to the present invention is disposed at a joint portion between two pipes through which a fluid flows, and adapted to open and close the flow passage and besides to control the fluid flow rate. Said butterfly valve comprises an annular valve casing 1 tightly sandwiched between said two pipes in the axial direction (flow passage direction), a valve disc 2 substantially of a disc-like shape disposed inside the valve casing 1, valve stems 3a and 3b rotatably supporting the valve disc 2 around a valve axis 3 (an axis passing through the center of the valve casing 1 and perpendicular to the flow passage), and a seat ring 4 provided at an inner periphery of a valve casing 1 to make a seal between the inner periphery of a valve casing 1 and the valve disc 2.

The valve casing 1 is made of, for example, steel and comprises a tubular casing body 5 tightly sandwiched between two pipes in the flow passage direction and a circular protrusion 7 having a flange 6, said protrusion 7 being formed continuously in the inner circumferential surface of the tubular casing body 5. A circular groove is formed in the central portion of the inner circumferential surface of said protrusion 7 and a slippage prevention means 19 of the seat ring 4 is fitted therein so as to prevent a deviation of the seat ring 4 in the flow passage direction.

Stem holders 8a, 8b are provided at the valve casing 1 radially outwardly in the direction of the valve axis 3 and stem holes are formed through the stem holders and the protrusion 7 to support the valve stems 3a, 3b rotatably therein.

Provided at and projected from the stem holder 8a is a stem cover 9 made of, for example, steel through which the valve stem 3a inserted. At the upper end portion of the stem cover 9, an outer peripheral flange 10 is fixed, and a split come-off prevention means 11 made of, for example, synthetic resin is secured to said outer peripheral flange 10 by means of screws 12 so as to prevent the valve stem 3a from slipping out.

Positioning plates 13 are provided at both sides of the stem holder 8a in the circumferential direction of the casing body 5. Said positioning plates 13 have bolt holes 14 through which pipe connecting bolts are inserted to position and set the valve casing 1 accurately between two pipes.

On the radially outer surface of the stem holder 8b, a cover plate 15 made of, for example, steel is secured with an interposition of a thin plate 16 made of rubber elastic body by means of screws 17 in order to prevent the valve stem 3b from coming off and to prevent the fluid leakage through the stem hole.

The valve disc 2 is of substantially a disc-like shape formed of, for example, steel and has a diameter smaller than an inner diameter of the annular protrusion 7 of the valve casing 1. The valve disc 2 is disposed inside the valve casing 1 by arranging its diametrical direction in conformity with the valve axis 3.

By rotating said valve disc 2 about the valve axis 3, when its plate face is made parallel to the direction of fluid flowing, the flow passage is opened, and when the plate face is made perpendicular to the direction of fluid flowing, the flow passage is closed. By arranging the rotation angle of the plate face, the fluid flow rate can be controlled.

Provided at opposite positions in the direction of the valve axis 3 of the valve disc 2 are stem fitting portions 18a, 18b in which end portions of the valve stems 3a, 3b are closely fitted respectively to support the valve disc 2 inside the valve casing 1. A fitting hole of the stem fitting portion 18a is substantially of square in a cross section while a fitting hole of the stem fitting portion 18b is substantially of circular.

The valve stem 3a is made of, for example, steel and is of bar-like shape having a circular cross section and inserted in the stem holder 8a and the stem cover 9. The upper end of the valve stem 3a extending outwardly of the stem cover 9 is formed substantially in a square shape in cross section for engagement with a operating handle not illustrated to rotate the valve stem 3a about the valve axis 3.

The lower end of the valve stem 3a extending to the inside of the valve casing 1 is formed substantially in a square shape in cross section for engagement with the fitting hole of the stem fitting portion 18a and the valve disc 2 can be rotated about the valve axis 3 when the valve stem 3a is rotated about the valve axis by the handle.

A circular cross sectional portion of the valve stem 3a positioned near the upper end of the stem cover 9 is provided with a circumferential groove in which the inner periphery of the split come-off prevention means 11 is fitted and the valve stem 3 is prevented from slipping out by securing the split come-off prevention means 11 to the outer peripheral flange The valve stem 3b is made of, for example, steel and is of bar-like shape having a circular cross section and inserted in the stem holder 8b. The upper end of the valve stem 3b extends to the inside of the valve casing 1 so as to be fitted in the circular fitting hole of the stem fitting portion 18b, thereby supporting the valve disc 2 rotatably about the valve axis 3. The axially outer end of the valve stem 3b is prevented from axially outward movement by the cover plate secured with an interposition of the thin plate 16 to the radially outer surface of the stem holder 8b.

The seat ring 4 is formed of rubber elastic body and has an outside face opened radially outwardly and is of a ring-like shape having substantially a Ushaped cross section. The outer side of the seat ring is bent inwardly to embrace the flange 6 of the protrusion 7 and attached to the inner circumferential surface of the valve casing 1. The outer diameter of the seat ring 4 is large enough to be fitted in the casing body 5 and the inner diameter is larger than the diameter of the valve disc 2.

In the central portion of the outside face of the seat ring 4, the slippage prevention means 19 is formed so as to project continuously in the circumferential direction and fitted into a circular groove formed on the projection 7 of the valve casing 7, thereby preventing the seat ring 4 from deviating towards the direction of the flow passage due to opening and closing a valve.

Provided at opposite positions of the seat ring 4 radially outward of the flow passage in the direction of the valve axis 3 are a pair of valve stem holes through which the valve stems 3a, 3b are inserted. In the inner circumferential surface of the valve stem holes 20 and approximately at a center portion in the direction of the valve axis 3, valve stem sealing portions 21 are formed continuously protruding in the circumferential direction to seal a leakage through the valve stem holes 20 along the valve stems 3a, 3b. A ring-shaped reinforcing member 22 is embedded around the valve stem holes A pair of bosses 23 are formed protruding inwardly around the valve stem holes 20 to make a seal with the portion of the valve disc 2 positioned near the valve axis 3. Said bosses 23 are consisted of a sliding surface 24 substantially in a circular shape on which the radially outward portion of the stem fitting portions 18a, 18b of the valve disc 2 slides and a tapered portion 25 positioned between said sliding surface 24 and the inner surface of the seat ring 4. In order that the slide surface 24and the radially outward portion of the stem fitting portions 18a, 18b of the valve disc 2 may be closely contacted with each other, the slide surface 24 is formed of a concave spherical surface and the radially outward portion of the stem fitting portions 18a, 18b is formed of convex spherical surface and besides they are formed substantially in the same size.

Between a pair of bosses 23, there is provided a circular projection 26 continuously protruding inwardly in the circumferential direction. This circular projection 26 is formed substantially in a trapezoidal shape in cross section, and is consisted of a radially inward top portion 27, a contact face 28 closely contacting with the valve disc 2 in the closed position, and a protective face 29 positioned on the opposite side to the contact face 28 in the flow direction.

The top portion 27 is formed parallel to the flow passage having a constant height from the inner circumferential surface of the seat ring 4 in the circumferential direction and constitutes a part of a cylinder face having a constant width in the direction of the flow passage. The inner diameter of a cylinder defined by said top portion 27 is smaller than that of the valve disc 2 so that the periphery of the valve disc 2 may have a close contact with the circular projection 26. This top portion 27 is formed with an given width at the opposite side of the contact face 28 across an axis of the circular projection passing the valve axis 3 so that the whole circular projection 26 may be prevented from being deformed easily when contacting with the periphery of the valve disc 2.

The contact face 28 is formed as an inclined face slanting from the top portion 27 towards the inner surface of the seat ring 4 and closely contacted with the periphery of the valve disc 2. Further the contact face 28 is formed as a radially inwardly convex face which becomes parallel to the flow passage in the vicinity of the top portion 27 and is formed with the slant varying in the -circumferential direction in such a manner that the slant is steep in the vicinity of the bosses 23, 23 and gentle in the central portion between the bosses 23, 23.

Due to the variation of slant, the end portion of the contact face 28 crossing with the inner face of the seat ring 4 forms a curved line swelling towards the axial direction of the flow passage at the central portion between the bosses 23, 23. When observed from the valve axis 3, the end portion of the contact face 28 forms a straight line inclined towards the axial direction of the flow passage at the central portion between the bosses 23a.

The protective face 29 is a constantly inclined face slanting from the top portion 27 towards the inner surface of the seat ring 4 at the opposite side of the contact face 28 in the direction of the flow passage, and protect the circular projection 26 not so as to be deformed in its entirety when the contact face 28 is closely contacted with the periphery of the valve disc 2.

Now, how to make a seal between the circular projection 26 of the seat ring 4 and the valve disc 2 will be explained with reference to the appended drawings Fig. 5, Fig. 6 and Fig. 7.

When the valve disc 2 in the opened position rotates about the valve axis 3 towards a closing direction and shifts to the contact position the peripheral edge 30 of the valve disc 2 is brought into a close contact with the contact face 28. At this time, an angle between the plate face of the valve disc 2 and a plane perpendicular to the direction of the flow passage is small. A height from the inner surface of the seat ring 4 to the peripheral edge 30 of the valve disc 2 is approximately equal to the difference (R1-R2) between a radius (R1) of the inner circumferential surface of the seat ring 4 and a radius (R2) of the valve disc 2. Namely, the portion of the contact face 28 corresponding to said given height is a contacting portion 31.

The contacting portion 31 is formed so as to be curved swelling towards the axial direction of the flow passage at the central portion between the bosses 23, 23, since the slant of the pressurized contact face 28 varies gradually. As a result, the entire peripheral edge 30 of the valve disc 2 is brought into contact approximately at the same time with the contacting portion 31 of the contact face 28. Namely, when observed in the direction of the valve axis 3, the contacting portion 31 forms a straight line passing through the valve axis 3 and inclined towards the axial direction of the flow passage at the central portion between the bosses 23, 23, and said straight line overlaps with a straight line formed by the peripheral edge 30 of the valve disc 2, so that the entire peripheral edge 30 of the valve disc 2 is brought into contact with the contacting portion 31 approximately at the same time.

When the valve disc 2 rotates to shift from the contact position to the closed position the straight line formed by the periphery of the valve disc 2 becomes substantially parallel to the axis of the circular projection 26 viewing from the side of the valve axis 3, and the circular projection 26 is brought into contact with the periphery of the valve disc 2 by the thrust deformation amount A part of the circular projection 26 pressed in the direction of the flow passage acts as pushing back the valve disc 2 in the opposite direction of the flow passage and closely contacts with the periphery of the valve disc 2 with the contact height to accomplish a seal effect.

In the closed position a fluid at an upstream side tends to penetrate into a close-contact portion formed between the circular projection 26 and the periphery of the valve disc 2 and to open the close-contact portion to flow out towards a downstream side. The fluid pressure is reduced gradually along the close-contact face due to frictional resistance. At the position where the fluid pressure becomes lower than the counterforce per unit area of the circular projection 26 pushing back the valve body 2, penetration of fluid is prohibited and a seal can be achieved.

Namely, the sealing efficiency is enhanced by increasing the contact height to reduce the fluid pressure or increasing the counterforce per unit area of the circular projection so as to increase the fluid pressure by which the penetration of fluid is not induced.

The counterforce per unit area of the circular projection 26 pushing back the valve disc 2 is increased in proportion to the thrust deformation amount So, by making the thrust deformation amount and the contact height (H) larger to increase the cross section of the pushed out portion of the circular projection, the sealing efficiency can be enhanced. The cross section of the pushed out portion of the circular projection 26 is generally calculated by an equation x H/2) using the thrust deformation amount and the contact height The thrust deformation amount becomes larger in conformity with the swell of the contacting portion 31 towards an axial direction of the flow passage, and the contact height becomes larger in conformity with the slant of the contact face 28. The contact face 28 of the circular projection 26 is arranged to have a steep slant in the vicinity of the bosses 23, 23 by gradually varying the slant and the contacting portion 31 at the central portion between the bosses 23, 23 is swelling towards an axial direction of the flow passage. As a result, at the position where the thrust deformation amount is large, the contact height is small, while at the position where the thrust deformation amount is small, the contact height is large. Accordingly, the cross section is substantially equal in the circumferential direction, thereby achieving a sealing efficiency substantially equal in the circumferential direction.

The circular projection 26 pressed by the valve disc 2 is deformed to rise at the side of the valve disc 2 and closely contacts with the periphery of the valve disc 2. Although there yields a slight gap between the circular projection and a peripheral portion of the valve disc 2 positioned outwardly of the peripheral edge 30 in the axial direction of the flow passage as the circular projection is pulled in the opposite axial direction of the flow passage due to frictional force caused by the valve disc 2, the sealing effect is attained by the close contact of the periphery of the valve disc 2 with the circular projection 26.

As the contacting portion 31 of the circular projection 26 is swelling towards the axial direction of the flow passage at the central portion between the bosses 23, 23, and the periphery of the valve disc 2 contacts with the contacting portion 31 approximately at the same time when closing a valve, a torque required for contacting the entire periphery of the valve disc 2 with the circular projection 26 becomes small.

In addition, as the circular projection 26 is arranged to have a steep slant in the vicinity of the bosses 23, 23 and a gentle slant at the central portion between the bosses 23, 23 by gradually varying the slant of the contact face 28 and the contacting portion 31 is swelling in the axial flow direction at the position where the slant of the contact face 28 is gentle, the pushed out portion of the circular projection 26 pressed with the valve disc 2 when closing a valve has approximately the uniform circumferential cross section determined by the thrust deformation amount and the contact height and thereby the sealing efficiency substantially equal in the circumferential direction.

It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. For example, the top portion 27 of the circular projection 26 may be arranged not only to have a constant width, but also to be swelling towards the periphery of the valve disc in the direction of the flow passage at the central portion between the bosses 23, 23. In this case, without varying the slant of the contact face 28, the periphery of the valve disc 2 can be brought into contact with the circular projection 26 substantially at the same time. Besides, it also may be arranged not only that the top portion 27 of the circular projection 26 is constant in its height from the inner circumferential surface of the seat ring 4, but also that said height is varied in such a manner that the cross section of the pushed out portion of the circular projection 26 pressed by the periphery of the valve disc 2 when closing a valve, is substantially equal in the circumferential direction. In this case, without varying the slant of the contact face 28, the sealing efficiency in the circumferential direction becomes substantially equal.

According to the present invention, as apparent from the above description, the circular projection of the seat ring can be brought into contact with the periphery of the valve disc substantially at the same time since the contacting portion of the circular projection is swelling towards the axial direction of the flow passage. As a result, there occurs no contact before the contact of the periphery of the valve disc with the circular projection is completed. Thus, useless torque not contributing to a sealing can be avoided. Also, when controlling the fluid flow rate by rotating the valve disc about the valve axis, the periphery of the valve disc around the valve axis is not brought into contact with the circular projection, so that the durability of the circular projection can be improved..

In addition, by varying the slant of the contact face gradually, the contact height at the portion where the thrust deformation amount is small becomes large, and as a result, the cross section of the pushed out portion of the circular projection pressed by the periphery of the valve disc 2 at the time when closing a valve, is substantially equal in the circumferential direction, so that the sealing efficiency is substantially equal in the circumferential direction and useless contact can be avoided.

Claims

1. A seat ring for a butterfly valve provided at an inner circumferential surface of a valve casing so as to create a seal between the inner circumferential surface of a valve casing and a valve disc when closing a valve, including a pair of opposite valve stem holes for inserting valve stems positioned radially outwardly of a flow passage and a circular projection continuously protruding inwardly in the circumferential direction between a pair of bosses formed around said each valve stem hole and contacting with a periphery of the valve disc for closing the valve, a contacting portion of said circular projection with which the periphery of the valve disc contacts being formed at a portion apart from the bosses to be curved swelling towards the periphery of the valve disc in the direction of the flow passage so that the entire periphery of the valve disc contacts with the contacting portion substantially at the same instant.

2. A seat ring as claimed in Claim 1, wherein the cross section of the pushed Vo0% O *0 out portion of the circular projection pressed by the periphery of the valve disc for V. closing a valve is substantially uniform in the circumferential direction. 0e

3. A seat ring as claimed in Claim 1 or Claim 2, wherein the circular projection has an inclined face to which the periphery of the valve disc closely contacts for closing a valve, said inclined face being formed with a slant varying in the o circumferential direction in such a manner that the slant is steep in the vicinity of the bosses and gentle at the central portion between the bosses. 01 4. A butterfly valve provided with a seat ring as claimed in any one of Claims S 1,2, or 3. A seat ring substantially as hereinbefore described with reference to any one of Figures 1 to 8.

6. A butterfly valve substantially as hereinbefore described with reference to any one of Figures 1 to 8. DATED this 2 nd day of Febraury 2004 OKUMURA ENGINEERING COR WATERMARK PATENT TRADE MARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA