Most sprinkler systems are kept closed by which component?

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Fires are detected by a heat-triggered release mechanism, and the fusible link is the component that keeps the sprinkler system closed until that heat is present. This is a small metal strip built into the valve actuation. When it reaches its melting temperature, it fails safely and releases the valve or clapper, allowing water to flow into the piping network and out through the sprinklers. This design provides a simple, reliable automatic response without needing power or complex controls, so water only enters the system when required by heat. Other mechanisms exist in some systems, but fusible links are the standard device used to hold the system closed under normal conditions.