Probably refers to one or both of the nearby foundries. The first, established in 1783, is marked as 'New Foundry' on James Williamson's 1791 map of Belfast. The second is the Mountpottinger Foundry, established in 1868 (IHTA xvii, map 5). Vulcan is the Roman deity of fire, volcanoes and metalworking, depicted as a smith.
The minutes of the Town Improvement Committee 28 December 1881 indicate the naming of three new streets off Mountpottinger road Vulcan, Sheriff and Chemical streets.