A sealing 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.
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