Asealing device was developed that acts as a high-temperature shutoff valve for pipes and ducts. The device is an annular ring that can be slipped over the outside of the pipe (or built into a flanged spool piece). The cavity inside the device is filled with a gas, liquid, or even a solid. When exposed to an elevated temperature, the material in the cavity expands, providing sufficient inward force to collapse the thinner process pipe wall, stopping flow within the pipe.
The ring can be installed above the stem of a gate valve. In this case, the ring has a thinner lower wall and a thicker upper wall. When heated, the expanding lower wall of the ring will force the stem downward to push the gate into the pipe. To use as a seal, the ring can be inserted inside a pipe, with the thinner wall in contact with the inner wall of the pipe. High temperature will cause the thinner wall to expand outward, providing a tight seal against the pipe. The expanding ring wall will accommodate irregularities in the pipe wall.
The choice of material for constructing the ring depends on specific process parameters, such as corrosivity, activation temperature, and elevated-temperature mechanical properties of the valve or process system. The cavity may be filled with a gas such as nitrogen, with a volatile non-corrosive liquid, or with a volatile solid.