What is a characteristic of a properly functioning fusible plug?

A properly functioning fusible plug is designed to melt at a specified temperature, which is a critical feature for its operation. This melting point is set to ensure that if the boiler overheats, the fusible plug will fail and allow steam or boiling water to escape, thereby reducing pressure and preventing more severe explosions or damage. The material used in a fusible plug is engineered to respond accurately under specific thermal conditions, making this characteristic vital for safety.

The other characteristics described do not apply to a functioning fusible plug. For instance, rusting over time would indicate corrosion and potential failure rather than a sign of proper functionality. Constant adjustments are not typically required for a fusible plug, as it is designed to operate reliably without the need for frequent modifications. Additionally, while it is advisable to replace any safety component when necessary, frequently replacing a fusible plug is not a standard requirement if it is functioning correctly and within its operational limits.