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A butterfly valve comprises a valve shaft placed across a flow passage and a plate-like valve element provided on the valve shaft so as to be rotatable about the valve shaft to regulate a flow rate of fluid in the flow passage. The valve element has a section that gradually decreases in thickness fr

A butterfly valve comprises a valve shaft placed across a flow passage and a plate-like valve element provided on the valve shaft so as to be rotatable about the valve shaft to regulate a flow rate of fluid in the flow passage. The valve element has a section that gradually decreases in thickness from the valve shaft toward an outer edge in a direction nearly perpendicular to the valve shaft. The valve element further includes a plurality of inclined surfaces on each side so that the corresponding inclined surfaces on both sides of the valve element are identical in section in a direction parallel to the valve shaft. The valve element is provided on each side with a plurality of flow straightening ribs each extending in a direction perpendicular to the valve shaft and inclining along each inclined surface.

대표청구항 ▼

What is claimed is: 1. A butterfly valve mountable in a valve body formed with a flow passage, the butterfly valve comprising: a valve shaft placed across the flow passage; and a plate-like valve element provided on the valve shaft so as to be rotatable about the valve shaft to regulate a flow rate

What is claimed is: 1. A butterfly valve mountable in a valve body formed with a flow passage, the butterfly valve comprising: a valve shaft placed across the flow passage; and a plate-like valve element provided on the valve shaft so as to be rotatable about the valve shaft to regulate a flow rate of fluid in the flow passage; wherein the valve element includes a front side and a back side each including at least a flow straightening surface so that a portion of the valve element including the flow straightening surface has a cross section having a thickness gradually decreasing from the valve shaft toward an outer edge in a direction nearly perpendicular to the valve shaft and being uniform in a direction parallel to the valve shaft, wherein the valve element includes a flow straightening rib on each of the front side and the back side and the flow straightening ribs thus provided are symmetric between the front side and the back side. 2. The butterfly valve according to claim 1, wherein the flow straightening surface is an inclined surface, and the valve element includes identical inclined surfaces on an upstream side and a downstream side of the valve shaft. 3. The butterfly valve according to claim 2, the flow straightening rib extending in the direction nearly perpendicular to the valve shaft and inclining downward from the valve shaft toward the outer edge as with the inclined surface. 4. The butterfly valve according to claim 2, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side. 5. The butterfly valve according to claim 3, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side. 6. The butterfly valve according to claim 1, wherein the flow straightening surface is a curved surface, and the valve element includes identical curved surfaces on an upstream side and a downstream side of the valve shaft. 7. The butterfly valve according to claim 6, the flow straightening rib extending in the direction nearly perpendicular to the valve shaft and inclining downward from the valve shaft toward the outer edge as with the curved surface. 8. The butterfly valve according to claim 6, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side. 9. The butterfly valve according to claim 7, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side. 10. The butterfly valve according to claim 1, wherein the flow straightening surface is an inclined surface and a curved surface, and the valve element includes the inclined surface on an upstream side of the valve shaft and the curved surface on a downstream side of the valve shaft. 11. The butterfly valve according to claim 10, the flow straightening rib extending in the direction nearly perpendicular to the valve shaft and inclining downward from the valve shaft toward the outer edge as with the inclined surface and the curved surface. 12. The butterfly valve according to claim 10, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side. 13. The butterfly valve according to claim 11, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side. 14. The butterfly valve according to claim 1, wherein the flow straightening surface is an inclined surface and a curved surface, and the valve element includes the curved surface on an upstream side of the valve shaft and the inclined surface on a downstream side of the valve shaft. 15. The butterfly valve according to claim 14, the flow straightening rib extending in the direction nearly perpendicular to the valve shaft and inclining downward from the valve shaft toward the outer edge as with the inclined surface and the curved surface. 16. The butterfly valve according to claim 14, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side. 17. The butterfly valve according to claim 15, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side. 18. The butterfly valve according to claim 1, the flow straightening rib extending in the direction nearly perpendicular to the valve shaft and inclining downward from the valve shaft toward the outer edge as with the flow straightening surface. 19. The butterfly valve according to claim 1, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side. 20. The butterfly valve according to claim 18, wherein the valve element is provided, on each side thereof, with a groove extending in the direction nearly perpendicular to the valve shaft while traversing the center of each side.