I recently came across some terminology in the Godfather novel and do not understand the exact meaning behind the word. The appropriate quote from the novel is:
...The first person he called was Luca Brasi. There was no answer. Then he called the safety-valve caporegime in Brooklyn, a man of unquestioned loyalty to the Don. This man's name was Tessio.
I understand that caporegime within the Italian-American mafia is a rank within the family. I also understand what a safety valve is within other contexts (e.g. within pressure systems to release pressure to avoid a disaster). I have never heard the terminology referring to a person, however.
From context clues elsewhere in the novel, I think it might refer to someone who is used in emergencies. This also ties in with the pressure-system usage. It also seems to be used to describe other caporegimes in different scenarios, as opposed to just a one off. This made me think it's potentially an actual term/rank.
I would like to confirm the difference between a safety-valve caporegime and a regular caporegime. I'd also like to understand if this terminology is used for other people/contexts, as I've never heard it used in this way before. I'd also be interested if this is a real rank/use within the Italian-American mafia, though I understand that may be out of scope for English.SE.