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A new fireproof control valve could help prevent dangerous leaks caused by
fires in industrial plants. Most control valves are designed with a fail-safe
mechanism, in which a spring can force a valve actuator shut in the event of a
system failure. But in a fire, the spring can crystallise and the fail-safe
mechanism pack up. So Samson AG of Frankfurt has developed a heat sensitive
cartridge that fits in the spring and consists of two cylinders of slightly
different diameters, placed so one can slide inside the other. The gap between
them is filled with a material that swells on heating, pushing the outer
cylinder against the actuator and triggering the fail-safe mechanism.