Pressure Bar Reduction Gearing

wylk · 2015-03-29T18:53:55+00:00

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?

Huw Eastwood

Bingo! Good find wylk. That’s a real box of tricks and would explain the high spin rate and ratio being achieved without worm gearing on a door like the Cleveland Fed. Think I’ve just about got it, but there’s a few immediate parts off the spindle where the numbers are a bit vague. Going to need a really close look at this one 🙁y):

wylk

This might make a fun 3D printer project if the needed details can be figured out!

Huw Eastwood

wylk wrote
This might make a fun 3D printer project if the needed details can be figured out!

Itd be even more fun in origami..🙁party):

[unknown]

wylk

Speaking of Fort Knox, here is a video showing a vault door being opened in 1974. It is stated the hand wheel needs to be turned 14 times. The door opening starts at about 1:30.

https://www.youtube.com/watch?v=JRZc7YEV8rU

The same sequence is https://www.youtube.com/watch?v=z0Cy_3wFEZc at about 14:34.

wylk

Here’s another example of a Mosler door, found on eBay. It’s surprising the bevel gears are not covered. The seller states “Vintage 1940s.”

wylk

Another pressure-system layout, this time a Hall’s door in the Hilton, downtown Milwaukee. Notice the chain of four gears to convey cranking from the bottom to the top bar. This is more commonly done with a rod, and gearing at each end. Was there a cover, or was all of this exposed by design?

I enjoy the “hanging” doors above. There must have been a second floor which was removed to make the area more spacious and open.

Doug MacQueen

Wylk, you’re like a friggin magician pulling this crap off the net. Okay not crap. Actually very interesting and obviously a fairly early Hall vault door. Doubt it had a cover though.

David Hovey

Do you know what the indicator is for? I always assumed it was for the TL.

wylk

I doubt the time lock would have enough strength to move such an indicator. I might suggest it was tied to the pressure system but that picture isn’t clear enough. Some other doors have pointers; it could be a bad day if you slam a door shut and the pins aren’t aligned in the slots; and it’s a nice feature to let you know when you can pull a door open.

Doug MacQueen

I see the pressure bars do not work the same as what we are used to seeing. Instead of rotating, they move in and out. So that indicator is showing the bar position. Never saw that setup before.

wylk

I found the patent for the Hall’s door - http://pdfpiw.uspto.gov/.piw?Docid=00363118&idkey=NONE

[upl-image-preview uuid=ea62ae61-869f-4549-bad3-117d156e8f04 url= alt=363118.jpg thumbnail_url=https://cdn.antique-locks.com/2026-07-22/1784681805-624569-363118-thumb.webp]

David Hovey

A very rare door indeed.

Huw Eastwood

Doug MacQueen wrote
I see the pressure bars do not work the same as what we are used to seeing. Instead of rotating, they move in and out. So that indicator is showing the bar position. Never saw that setup before.

Hats off to Doug, well spotted on those expanding pressure bars.

The whole door has an almost steampunk look from that massive train of spur gears, like something out of a H G Wells novel. Great to see such early and rare examples still intact and original.

[unknown]

wylk

More on the Hall’s door in Milwaukee, I found a couple of nice images today -

I used to wonder if the pressure system originally had a cover, but the idler gears are etched, so apparently not.

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