Abstract: A valve plug (22, 22a, 22b) is biased inwardly by a spring (78, 78a, 78b) to close an opening (6, 6a, 6b) in a tank. A stem (32, 32a, 32b) extends axially inwardly from the plug (22, 22a, 22b). The stem (32, 32a, 32b) has an inner portion (36, 36a, 36b) which is mechanically interlocked with an outer portion (52, 52a, 52b) to directly transmit axial forces created by the spring (78, 78a, 78b). Fusible material (66, 66a, 66b) holds the stem portions (36, 36a, 36b, 52, 52a, 52b) in an interlocking position but carries only relatively small loads. The plug (22, 22a, 22b) and stem (32, 32a, 32b) move against the force of the spring (78, 78a, 78b) to relieve pressure. At elevated temperatures, the fusible material (66, 66a, 66b) melts to allow the stem portions (36, 36a, 36b, 52, 52a, 52b) to separate and the plug (22, 22a, 22b) and outer stem portion (52, 52a, 52b) to move away from the opening (6, 6a, 6b).

Abstract: A valve plug (22, 22a, 22b) is biased inwardly by a spring (78, 78a, 78b) to close an opening (6, 6a, 6b) in a tank. A stem (32, 32a, 32b) extends axially inwardly from the plug (22, 22a, 22b). The stem (32, 32a, 32b) has an inner portion (36, 36a, 36b) which is mechanically interlocked with an outer portion (52, 52a, 52b) to directly transmit axial forces created by the spring (78, 78a, 78b). Fusible material (66, 66a, 66b) holds the stem portions (36, 36a, 36b, 52, 52a, 52b) in an interlocking position but carries only relatively small loads. The plug (22, 22a, 22b) and stem (32, 32a, 32b) move against the force of the spring (78, 78a, 78b) to relieve pressure. At elevated temperatures, the fusible material (66, 66a, 66b) melts to allow the stem portions (36, 36a, 36b, 52, 52a, 52b) to separate and the plug (22, 22a, 22b) and outer stem portion (52, 52a, 52b) to move away from the opening (6, 6a, 6b).