The present invention relates to a seat ring for a butterfly valve suitable for use in pipe lines for a chemical factory, water supply and sewage, agriculture, fishery and the like; more specifically, it relates to a seat ring with insert for a butterfly valve that improves valve seat sealing performance, valve stem sealing performance, and flange surface sealing performance.
A conventional seat ring with insert for a butterfly valve, as shown in FIG. 9, is configured such that an annular insert 101 comprising a single step 103 having a different outer diameter size and a seat ring 104 formed of rubber and embedded so that the outer peripheral surface thereof forms a single surface with the outer peripheral surface of the insert 101, are fitted in a valve body 110 having on the inner surface thereof a step 111 that engages with the step 103 of the insert 101, so that a valve shaft hole center 108 of the seat ring 104 and valve shaft hole center 112 of the valve body 110 are coaxial in the tube stem direction. In this case, the seat ring 104 protrudes from both ends of the valve body 110.
Because when the butterfly valve in which the seat ring 104 is fitted onto a pipe, the step 103 of the insert 101 and the step 111 of the valve body 110 are in direct contact with each other, a load acting as shear stress on the valve shaft 113 is reduced, and operating torque of the valve shaft 113 is reduced, thereby improving valve stem sealing performance. Further, because lateral portions 105, 106 of the seat ring 104 are compressed to a suitable degree, a suitable flange surface sealing effect between the seat ring lateral surface and piping flange surface can be achieved.
Further, in a conventional method for manufacturing a seat ring with insert for a butterfly valve, as shown in FIG. 10, the step 103 formed on the outer peripheral surface of the insert 101 is engaged with a step 118 formed in advance on the inner diameter portion of an outer die 117; thereafter, in a state where the valve shaft hole 102 is supported by a valve stem pin, and the insert 101 is fixed on the inner surface of the outer die 117, rubber is inserted and molded. The effect thereof is that when a seat ring with insert is molded, without need for a complicated mechanism, positioning in the tube stem direction only of the insert 101 is easily accomplishing using the step 103 as a reference. For example, see Japanese Patent 2972566 (Pages 1-6, FIGS. 1 and 4).
However, the above prior art has the following problems.
(1) As shown in FIG. 11, when a conventional butterfly valve in which a seat ring is fitted is connected to piping flanges 115, 116, or when a conventional butterfly valve is subject to fluid pressure in a fully closed state after connection, only the seat ring 104 is subject to a force causing displacement and deformation in the downstream side direction from a valve body 114 that has been subject to a tightening force for fixing the piping flanges 115, 116 or fluid pressure. While displacement in the tube stem direction of the seat ring 104 can be inhibited by the direct contact between the step 103 of the insert 101 and the step 111 on the inner surface side of the valve body 110, deformation of the seat part 109 along the entire inner periphery of the seat ring cannot be inhibited, resulting in deformation of the portion of the seat ring 104 in press contact with the valve body 114, and thus lowering valve seat sealing performance.
(2) When a conventional butterfly valve in which a seat ring is fitted is connected to the piping flanges 115, 116, it is not the case that the lateral portions 105, 106 of the seat part 109 of the seat ring 104 are compressed uniformly along the entire periphery in the horizontal direction only, but because they deform irregularly in the flow channel inward radial direction or outward radial direction (direction of the arrows of FIG. 11), the compression rate becomes uneven, and flange surface sealing performance is lowered.
(3) When the seat ring 104 is to be fitted on the valve body 110, positioning in the peripheral direction is difficult, so that when the valve shaft 113 is inserted, there is peeling off of the valve shaft hole portions of the seat ring 104 and insert 101, damaging the valve stem sealing 107 of the seat ring 104, and lowering valve stem sealing performance. Further, uncertain positioning in the peripheral direction causes an increase in operating torque.
(4) In the manufacture of a seat ring 104, when the insert 101 is set inside the outer die 117, positioning of the insert 101 in the peripheral direction is difficult; therefore, if the valve stem pin is inserted in a state where the insert 101 is displaced, the valve shaft hole 102 of the insert 101 will become deformed, causing an increase in operating torque and degraded valve stem sealing performance.