1. Field of the Invention
The present invention relates to a valve device suitably used for general valves, such as a globe valve, a gate valve and a butterfly valve, incorporated in pipelines laid in factories, plants and the like.
2. Description of the Prior Art
Factories or plants have a large number of pipelines allowing fluids having very high internal pressures to flow therethrough unlike general air-conditioning equipment. A valve device for controlling a flow passage allowing a fluid having such a very high internal pressure to flow therethrough must be rendered air-tight enough to prevent the fluid from leaking to the exterior of the valve device.
FIG. 12 is a view showing a prior art valve device disclosed, for example in Japanese Utility Model Publication No. Hei 1-24465. In the figure, reference numeral 1 denotes an upper lid; 1a is a packing box constituting an upper half of the upper lid 1; 2 is a valve stem vertically movably inserted in the packing box 1a; 6 is a gland packing interposed between the packing box 1a and the valve stem 2; 7 is a packing flange disposed on the upper surface of the gland packing 6; and 11 is a coil spring disposed under the gland packing 6 in the packing box 1a in such a manner as to be held between coil spring seats 12a and 12b.
The operation of the above valve device will be described below.
In the structure of such a coil spring type, the gland packing 6 is pressed to the packing flange 7 by means of the repulsive force of the coil spring 11, to thereby keep the neighborhood of the valve stem airtight.
FIG. 13 is a view showing another prior art valve device disclosed in the above document, Japanese Utility Model Publication No. Hei 1-24465. In the figure, reference numeral 13 denotes a tap bolt screwed in the upper lid 1 via a through-hole formed in the packing flange 7; and 14 is a conical disc spring interposed between the packing flange 7 and the head of the tap bolt 13. It should be noted that the same or similar parts as or to those shown in FIG. 12 are denoted by the same reference numerals and the explanation thereof is omitted.
The operation of the above valve device will be described below.
In the structure of such a conical disc spring type, the conical disc springs 14 and the packing flange 7 are fastened by means of the tap bolts 13, so that the gland packing 6 is pressed by the packing flange 7 to thereby keep the neighborhood of the valve stem airtight.
The prior art valve devices having the above configurations have problems. That is to say, the prior art coil spring type valve device entails the problem that a fluid having a high internal pressure leaks to the exterior of the valve device because the repulsive force of the coil spring 11 to the gland packing 6 is small and thereby the force of the gland packing 6, applied to press the packing flange 7, is insufficient.
Meanwhile, the prior art valve device of the conical disc type entails the problem that it is difficult to keep up with a secular change in pressing force of the gland packing 6 itself because the repulsive force of the conical disc spring 14 to the packing flange 7 is sufficiently large but the displacement of the conical disc spring 14 in the pressing direction is small.
The conical disc type, in which the packing flange 7 is disposed under the tap bolts 13 via the springs, also entails the problem that it is difficult to fasten the packing flange 7 because as the tap bolts 13 are screwed, there tends to be two fulcrums with the result that the packing flange 7 tends to be tilted.
In the prior art valve devices having the above structures, since all of the tap bolts 13 must be removed to add a new spring to increase the spring force after assembly of the gland packing, there arises a problem that it takes a lot of labor to add such a new spring.
In the prior art valve devices having the above structures, since a large-sized coil spring or a large number of conical disc springs must be provided to prevent leakage of a fluid, it is difficult to reduce the weight of the valve device and thereby the pipeline must bear an increased load, with a result that there arises a problem that it is difficult to keep the air-tightness of the pipeline for a long period of time.