Shaft seal packing and shaft seal structure for valve
A shaft seal packing exhibits high sealability at the time of initial assembly and also exhibits, even after the packing is retightened, excellent sealability by an increased seal surface pressure obtained through an effect of pressing and by self-sealability obtained through an effect of fluid pressure. A shaft seal structure for a valve includes a body for a valve, a valve shaft, a valve disc disposed within the body so as to be rotatable or capable of ascending and descending, a valve shaft seal chamber having the valve shaft axially attached thereto, a shaft seal packing that is attached to the shaft seal chamber and comprises annular packing bodies stacked and substantially V-shaped in cross section, with stacked layer faces on the inner-diameter side of the packing bodies brought into tight contact with one another and stacked layer faces on the outer-diameter side of the packing bodies formed with prescribed gaps between the adjacent stacked layer faces. In the shaft seal structure for a valve, a tightening load on the packing bodies and fluid pressure are converted to a force in the diametrical direction owing to inclined angles of stacked layer faces on the inner-diameter side to attain a seal by a surface contact between the inner peripheral surface on the inner-diameter side and the outer peripheral surface of the valve shaft on a sliding side, and a lip part on the outer-diameter side is pushed and spread owing to the gaps to attain a seal by a line contact with the shaft seal chamber on a fixed side.
1. A shaft seal packing comprising:
annular packing bodies stacked and substantially V-shaped in cross section, with stacked layer faces on an inner-diameter side of the packing bodies brought into tight contact with one another and stacked layer faces on an outer-diameter side of the packing bodies formed with prescribed gaps between adjacent stacked layer faces,
wherein a valley-side apex of each of the packing bodies is deviated from a mountain-side apex of thereof in an outer-diameter direction to make the mountain-side and valley-side apexes eccentric.
2. A shaft seal packing according to claim 1 , wherein upper and lower stacked layer faces on the outer-diameter side of the packing bodies have different tapered angles to form the gaps.
3. A shaft seal packing according to claim 1 , wherein a mountain-side angle is a tapered angle of an upper stacked layer face on the outer-diameter side of each of the packing bodies, and is in a range of 42.5° to 50°, a valley-side angle is a tapered angle of a lower stacked layer face on the outer-diameter side thereof, and is in a range of 40° to 47.5°, and a relation of the mountain-side angle>the valley-side angle is satisfied.
4. A shaft seal packing according to claim 1 , further comprising a top adapter and a bottom adapter stacked on top and bottom sides of the stacked packing bodies, respectively, to constitute a shaft seal packing and wherein a valley side of the top adapter and a mountain side of the bottom adapter have same angles as the packing bodies.
5. A valve shaft structure for a valve, comprising:
a body for a valve, a valve shaft, a valve disc disposed within the body so as to be rotatable or capable of ascending and descending, a valve shaft seal chamber having the valve shaft axially attached thereto, a shaft seal packing that is attached to the shaft seal chamber and comprises annular packing bodies stacked and substantially V-shaped in cross section, with stacked layer faces on an inner-diameter side of the packing bodies brought into tight contact with one another and stacked layer faces on an outer-diameter side of the packing bodies formed with prescribed gaps between adjacent stacked layer faces,
wherein a valley-side apex of each of the packing bodies is deviated from a mountain-side apex of thereof in an outer-diameter direction to make the mountain-side and valley-side apexes eccentric.
6. A shaft seal structure for a valve according to claim 5 , wherein a tightening load on the packing bodies and fluid pressure are converted to a force in a diametrical direction owing to inclined angles of stacked layer faces on the inner-diameter side to attain a seal by a surface contact between an inner peripheral surface on an inner-diameter side and an outer peripheral surface of the valve shaft on a sliding side, and a lip part on an outer-diameter side is pushed and spread owing to the gaps to attain a seal by a line contact with the shaft seal chamber on a fixed side.
7. A shaft seal structure for a valve according to claim 5 , wherein the valve is a ball valve that has a through hole and is rotatable via the valve shaft, and the valve shaft packing is attached to the valve shaft seal chamber having the valve shaft attached thereto by tightening load given via a gland washer.
8. A shaft seal structure for a valve according to claim 7 wherein the gland washer is a conical disc spring washer and, with the washer, a surface pressure between an outer-diameter side of the shaft seal packing and the shaft seal chamber is capable of being heightened.
9. A shaft seal structure for a valve according to claim 7 , wherein the gland washer is attached to the shaft seal so as to prevent the shaft seal packing from being rotated following rotation of the valve shaft.
10. A shaft seal structure for a valve according to claim 8 , wherein the gland washer is attached to the shaft seal so as to prevent the shaft seal packing from being rotated following rotation of the valve shaft.
11. A shaft seal packing according to claim 2 , wherein a mountain-side angle is a tapered angle of an upper stacked layer face on the outer-diameter side of each of the packing bodies, and is in a range of 42.5° to 50°, a valley-side angle is a tapered angle of a lower stacked layer face on the outer-diameter side thereof, and is in a range of 40° to 47.5°, and a relation of the mountain-side angle>the valley-side angle is satisfied.
12. A shaft seal packing according to claim 2 , further comprising a top adapter and a bottom adapter stacked on top and bottom sides of the stacked packing bodies, respectively, to constitute a shaft seal packing and wherein a valley side of the top adapter and a mountain side of the bottom adapter have same angles as the packing bodies.