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"Cold enough to freeze the balls off a brass monkey"

Posted by Li Yar on June 07, 2004

In Reply to: "Cold enough to freeze the balls off a brass monkey" posted by Alastair on June 07, 2004

: I believe this originates from Steam Trains. The 'Brass Monkey' is the steam safety valve - consisting of 2 brass balls attached to levers. The balls spin round - if they spin fast enough, it opens the steam valve.

well done - we were missing those brass monkeys.

the device used to regulate pressure in that way in steam technology is called 'a governor'. it relies on centripetal force and angular rotation to prevent the easy opening of a valve. when pressure is higher, the rotation causes the weights to spin on the horizontal which raises a sleeve which otherwise closes the valve.
I doubt that even in cold weather the weights would fall off. I recall that there were ways of fixing them on to the shafts that would not easily have come undone simply as a result of contraction of metals.