Originally Posted by
wylk
I'll just cut and paste from another thread:
The pressure system, or pressure bars, is a mechanical system that presses the door very firmly into the door frame. This ensures the door can be locked tightly without any gaps that could allow explosives (such as nitroglycerine) to be poured in. It also helps seal the door against fire, smoke, and flooding. It can also mitigate problems from normal wear on the hinges that cause the door to sag, by pulling the door up against its taper and thus lift it upward. And when it comes time to open a tightly pressed-in door, the pressure bars can exert force to help break it free of the door frame.
Pressure systems can generate very great forces, many tons in most cases.
The system usually consists of one, two, three, or four bars across the door that rotate less than one turn. The bars are rotated by a large hand wheel and gears. Each bar has an offset pin that engages an anchor with a curved slot. In some cases the bar has a rotating slot and the pin is in the anchor.
The pressure needs to be evenly applied across the door.
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Your other question, how does that door lock and unlock, is another small story. For a time there were worries that burglars could punch lock spindles through the door and use the hole(s) to somehow unlock the door (which would include messing with the time lock). One approach to avoid this problem is the side-mount control as seen in this thread (with or without the viewer optics which simply gives greater security against visual eavesdropping) which places the locks well away from the time locks. The other approach, as in the door you show, is to use the time lock to cause the door to open itself using a bolt motor (big springs) which requires zero holes in the door or vault. In this case, at closing time, two big springs are compressed and latched, and the time lock is set for the next scheduled opening. When the door is closed one of the springs is tripped and the door locks itself. At opening time the other spring is tripped and the door unlocks itself. The springs and timers are usually doubled (or more) for redundancy in case a spring breaks but that's the basic idea. The bad part about an automatic door is that it will unlock itself even if nobody is there, such as a blizzard that makes travel nearly impossible for the bank manager but not criminals who seize the opportunity. Or riots. One refinement was a time lock that could have time added to it remotely using a telephone circuit. I've always felt that both approaches (side-mount controls, automatic boltwork) were solutions in search of a problem and serve as examples of marketing skills.