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?

[Doug MacQueen]

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

[Doug MacQueen]

Here are few examples of the Diebold.

[Doug MacQueen]

Actually the idea is not so far fetched. Accessing any manufacturing and service info is the problem and in my opinion should be in hand if possible, prior to any investigation. This info unfortunately is not held by the bank. So it remains at a standstill until I can solve that problem.

[VaultDoors]

Here are few examples of the Diebold.

Here's a picture showing what appears to be individual horizontal pressure bars on a 4 point system:



Perhaps the vertical pressure bars are separate too?

[Huw Eastwood]

I'd forgotten about the channels on the emergency doors. Good point that, shows how tight that gap is even where the crane is a fair way off the door on large diameter pivots.

[wylk]

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:



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:



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?

[wylk]

Another video of a round door closing is at https://www.youtube.com/watch?v=v3hk_r9CJa8 in which the hand wheel executes about 12 revolutions. Assuming the pressure bars turn 90 degrees or so that turns out to be a 48:1 overall ratio.



I wonder if there is a rough correlation between the weight of a door and the ratio of the gearbox. It would make sense that the heaviest doors might need the greatest pressure to seat them. Of course a larger hand wheel gets you part way there. It also fits observations that light doors need fewer revolutions and that the lightest ones just use a lever.

[Huw Eastwood]

If a door is swinging perfectly into into its frame and is balanced on roller bearings as perfectly as all the manufacturers tell us, I would have thought that the gearing and pressure system would be designed and governed by they effective pressure they designed the door to have on it.

In terms of opening and closing, a 25 ton door shouldn't need that much more force to open or close than a 10 ton door if it's all working properly. Likewise, the Cleveland Fed being 2 or 3 times the weight of many of the big doors is seen being pulled open and pushed shut by 2 guys- probably possible by 1, just a case of getting that initial dead weight moving and some momentum behind it.

We've all seen the makers claims of a door weighing 20 or 30 tons which can be pushed closed by a persons finger- it does figure as roller bearings are amazing, you only have to look at extreme examples like open-cast mining shovels, walking draglines and turbines etc to see the sort of immense loads they can take- loads which make even the Cleveland Fed door seem like a toy.

The door in the video is unusual for a big one in that the pressure bars are behind the crane hinge found more typically on the lighter doors. On most of the big 30-40 ton doors they are more commonly positioned outside the crane like on the Cleveland Fed. If you think about it this drastically alters their positioning in the housing drum or gearbox. On the Cleveland Fed and One King West the pressure bars are close to the front, leaving a lot more room towards the back. This is also common on the big doors with 3 point bar systems. The one in the video is the other way around, pressure bars at the back behind the hinge means all the gearbox space is at the front. No wiser but a bit more food for thought..

[VaultDoors]

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."