Sealing principle of globe valve: Part 3

3. Spherical seal: Making the valve disc spherical and the valve seat conical, the ball of the disc can rotate freely in the hole of the stem. Therefore, the disc can be adjusted by a certain range of rotation on the valve seat. Since the contact between the two sealing surfaces is almost a line, that is - the line seal, the sealing stress is high and it is easy to seal. And because the disc sphere can use cemented carbide or ceramic materials, the hardness can reach 40 ~ 60HRC, and can withstand high temperatures. Therefore, it can be used as a high temperature globe valve. The disadvantage is that the linear contact of the sealing surface is easily damaged by erosion. Therefore, the valve seat should be selected with a material that is resistant to erosion. Spherically sealed globe valves can be used for gases or liquids with tiny solid particles in the medium.

The sealing principle is that when the medium flows in from under the valve disc, the sealing force applied must be equal to or slightly greater than the sum of the specific pressure generated on the sealing surface and the upward force of the medium. When the medium flows in from above the disc, the sealing force applied must be equal to or slightly greater than the difference between the specific pressure generated on the sealing surface and the force applied downward by the medium.

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