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  1. #1
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    Default Pressure Bar Reduction Gearing

    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:

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

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    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?

  2. #2
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    Don't forget the mechanical advantage starts with the lever arm of the pilot wheel. I will dig through my pictures as I think I have some that show the mechanism. Some early doors, such as Diebold, have the worm gear exposed. Doug

  3. #3
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    Here are few examples of the Diebold.
    Attached Thumbnails Attached Thumbnails 014_14.JPG   031_31.JPG   032_32.JPG   DSCN2752.jpg  

  4. #4
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    Doug, thanks for the images. It's nice to see the gearing exposed.

    Two hallmarks of a worm drive include the 90-degree angle between the worm and the gear, and the offset between the two axes. Here is another example:

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    Notice that the wheel's axis is offset to the left of the vertical pressure bars which strongly suggests a worm drive is inside the case. Bevel gears are the most likely candidate for transmitting the power to the horizontal bars.

    In contrast, let's look at one of our favorites at One King West, Toronto:

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    Here the gearbox is huge plus the wheel's shaft and the pressure-bar shaft intersect which is not possible with a simple worm drive. There is probably more going on inside the case, but what?

  5. #5
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    American Architect and Architecture from 1927, volume 132 states, "This mechanism is termed a 'Pressure System' and consists of a series of worm and bevel gears, cams and eccentrics operated by a hand wheel."

  6. #6
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    Although I don't remember how they were set up, a central spur gear on the handwheel shaft could operate other spur gears which are attached to separate worm gear shafts. Obviously on the 3 way pressure system there are 3 bars, so likely on the King West there are 2 separate bars not one continuous bar. A 3 way would have 3 spur/ worm gears surrounding the central spur. The worm gear shafts would be offset from the bars themselves. This may not be the method but a possible way to do it. Doug

  7. #7
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    It's a real interesting topic this one- it's the Cleveland Fed door that's had me baffled, the fact they spin that massive capstan handle for what seems ages- and fast as well, you see the guy putting his hand against it (bad idea?) as a friction brake.

    All that shouts worm gearing to me, as I can't see how spur or planetary gearing would have enough difference on the ratios to allow that many revolutions and that much speed. The problem with worm gearing though, is the offsetting that wylk mentioned. Not easy to cram all of those types into the housing drum since the offsetting takes up a lot of space and bearing in mind the actual bearings and supports would need to be massive. I can't remember what the One King West door is like- I'm assuming it's lack of capstan handles on the hand wheel possibly means it's turned slower and for less revolutions?

    On the One King West door, one thing that will determine if the 2 pressure bars are separate is they will rotate in opposite ways. If it's a single bar straight through the housing driven by a single crown and pinion gear then it'll turn it one way. If the pressure bars are individual and each is driven by its own gear on opposing sides of the drive gear, then the left bar will rotate in the opposite direction to the right. Not an easy thing to determine from even the clearest of videos though, I think you'd need to be there and try it! My guess is crown and pinion bevel gearing on the One King West door, but the Cleveland Fed I'd love to know. Doug, what's your chances of pulling the front cover off the drive housing lol

  8. #8
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    When the One King West vault door is open the pressure plug (on the combo viewer) is at the bottom of the vertical slot and the pressure hinge pin (on the hinge side of the door) is at the bottom of the hinge bracket; notice the hinge pin extends below the bracket.

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    I assume when the door is closed (and compressed) the pressure plug and pressure hinge pin move up and the hinge pin would extend above the bracket.

    I am not sure if the pressure system has one or two bars but the pressure plug and pressure hinge pin appear to move in the same direction when compressed/decompressed.

  9. #9
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    Here's a pic of the One King West pressure hinge pin raised. The pressure wheel must have been spun after the door was open.

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  10. #10
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    I watched that Cleve Fed video again and it does appear the number of revolutions is considerably more than on any of the smaller doors I have closed. That video I am guessing is from around the 1950's, so the door is not very old at that point and still in top condition. The fact he can get it spinning that fast would indicate everything is working very smoothly, and there is considerable gear reduction. With no door dragging on the jamb, the amount of required the move the door is shown by the two men moving the the door into position. What would that be? Several hundred pounds but not the several thousand pounds which the pressure system is more than capable of achieving.

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