Pressure Bar Reduction Gearing

[wylk]

Pressure bars (pressure systems) are used on older vault doors and safe doors to pull the door into the frame (vestibule), ensuring a tight fit that in some cases was water-tight when new. I think it's safe to say that bevel gears were often used to distribute the power from the hand wheel assembly to the ends of the bars, such as in these images:



On some doors, no gearing at all was used and the bar was powered directly by hand:



But on the bigger doors there was some sort of reduction gearing to amplify the force available. There is a video for example of the monster door at the Cleveland Federal Reserve being opened (see https://www.youtube.com/watch?v=5IqpCFTDo_M at around 2:20), and I think it was a program on the Discovery channel about the Fort Knox depository that included footage of the door being opened. In these cases the hand wheel goes through at least a dozen rotations while the pressure bars themselves operate perhaps 90 degrees. So there is some kind of reduction gearing at work.

I thought I'd seen something long ago that suggested this was done using a worm gear arrangement (http://en.wikipedia.org/wiki/Worm_gear) but I can't find anything about this aspect. I suppose planetary gears might also work (http://en.wikipedia.org/wiki/Planetary_gear) or helical gearing (http://en.wikipedia.org/wiki/Helical_gear#Helical).

Does anybody have information on this aspect? Patents, drawings, imagery, recollections?