Patent ID: 6889534

Claim:
A locking device, comprising: a shell defined by a chamber, at least one bore hole extending into said chamber, and a tumbler slidably seated in said bore hole; and a cylinder inserted into the chamber of said shell, said cylinder further comprising, a core defined by a keyslot for accepting either one of a control key and a user key, said core also being defined by a radial bore hole corresponding to the bore hole in said shell, and a peripheral recess; a multi-piece sleeve journalled within the recess of said core and defining a first shear line against said core and a second shear line against said shell, and a corresponding core tumbler slidably seated in the bore hole of said core and contacting the shell tumbler at a contact point; whereby normal key operation includes insertion of said user key into the core to align said contact point with said first shear line to allow rotation of the core and opening of the locking device, but insertion of the control key in a first position aligns said contact point with said second shear line, and rotation of said control key to a second position initiates a blocking function which prevents said normal key operation.