I saw this recently and wondered:
Why are there two lock cylinders?
How does this work?
Is this how this thing was originally designed?

...and thought someone on this site might have some insights.
The lock was on a closet in a room and building that are generally accessible by the public, which is owned by a civic institution.


Well, the ones inside a bank's vault need Their key and Your Key to open Your safe deposit box. For instance.

Designed that way.

Requires two keys to operate. Normally applied where two separate people hold one key each and need to both be present when the lock is opened.

Depending on design, could also be used so that a primary key is used at the start of working hours and then a secondary key will operate the lock, but only during working hours (the primary key would be run around the building and used to lock the primary lock at closing time.)

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  • Either both keys are required to unlock, or two different keys can unlock (which would be slightly more secure than the master key designs normally seen where each pin position has two shear lines). Given the proximity, I'm thinking it may be two alternate keys because it's difficult to get both keys in there and turning simultaneously. – BMitch Nov 2 '15 at 4:16

My school used to ude that design... It's a more secure mechanism for master keying; two independent plugs each with their own pin stacks and possibly accepting completely different key blanks.

A gearing mechanism is used to transfer action from the upper plug down to in line with the lower, and the tailpieces of the two plugs are stacked and occupy the same soace tat the single tailpiece of a normal cylinder would. That allows installing this double-keyway cylinder into mortise locks originally designed for a mormal single cylinder, so the only additional cost is for these cylinders.

Good product for its time, Though rarely used except in the most complicated master-keyed sites.

These days most such sites have either gone to high-security interchangable-core, or past those to electronic, as less expensive yo maintain.

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  • So does this mean only ONE of the two keys is needed to open the lock? – WBT Nov 2 '15 at 13:25
  • If iy's the same as the Yale system I'm describing, then yes, a single key -- usually on a restricted blank -- will open the lock. – keshlam Nov 2 '15 at 14:55

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