| 摘要 |
To lock the head of a latchbolt in extended, or locked position therein to prevent opening of a door in case of fire the latch bolt head is provided with a spring driven locking pin reciprocatably mounted in a transverse direction. In the extended locked position of the latch bolt head the locking pin is in alignment with but withdrawn clear of a hole in the latch bolt case. At the inside end of the locking pin is a groove and a fusible pin normally engages the groove holding the locking pin in withdrawn position. This permits normal latch bolt action. When the fusible pin melts because of heat from a fire the locking pin is released and driven by spring action into the hole in the latch bolt case to physically bar withdrawal of the latch bolt, and consequent opening of the door.
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