It turns out this ring piece provides the 'hotel function' found on many hotel room doors (non electric with standard keys). It's a simple yet elegant solution.
From the Sargent 'Cylinders and Components' Catalog here's a description:
Hotel Type Cylinder
• Guest and Master keys will only retract the latch bolt but not project or retract the dead bolt
• Emergency keys retract the latchbolt and deadbolt and can also project the deadbolt
Basically, when you're inside the room and lock the deadbolt all guest keys and maid (master) keys cannot open the door (retract the deadbolt). However, emergency keys will throw/retract the deadbolt as well as open the latch bolt.
The ring piece accomplishes this by limiting the travel of the plug for guest/maid keys so only the latchbolt is engaged. Emergency keys can turn the plug all the way around, thus engaging the deadbolt.
Here's some pictures:
Sargent Mortise Cylinders x2 - Each with own key - KD
Rear of cylinder and tailpiece.
Tailpiece removed - ring piece now visible surrounding plug.
Front view with ring piece in-place. See 5 round pin chambers and 1 square slot in ring piece for 6th pin.
View inside the cylinder from back with plug removed. Ring piece still in-place.
Ring piece
Rear of cylinder - ring piece removed.
Dissassembled. Gotta love the bittings you can find on Sargent
Pins - master pins found on all except chamber 6.
Keys x2 - each KD.
Kind regards,
Sean
Note:
I originally posted this a few months ago but due to a LP101.com database error the post was lost. At that time I received some excellent responses that informed me of the hotel function aspect of the ring piece, however I can't remember from whom to give proper credit. Anyway, thanks to those helpful lp101 members last time around.
