Detainer levers
Detainer Levers (Lever locks)
Detainer levers (detainers) are a type of lever lock component design.
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The term 'movable detainer' is used in British Standard BS3621 to mean any movable member in a lock which keeps the lock locked until correctly set by the key. In this page, 'detainer' means the end-gated levers used in the Chubb detainer locks. 'Detainer' was Chubb's word for these components in the patent for these locks.
Principles of operation
This lock mechanism derives ultimately from Strutt's lock of 1818. One end of a bell-crank rests in a locking notch in the bolt tail, (or in other locks, against an abutment on the bolt tail), and can only be lifted when its other end probe can enter the notches (or 'gates') in all of the end-gated levers. The probe only enters the gates briefly, and does not remain in them, unlike the bolt-stump of most lever locks. Strutt's original lock is still on the gate of Cromford Mill in Derbyshire, and the original gate has now been moved inside to protect it from the weather. This principle has since been used by many other locks. These include a Fichet lock of early-19C, the push-key pancake padlocks, some early-20C Kromer locks, the Chubb Detainer range, Union Butter's System lock, and the Ingersoll M6 lock.
Most levers in common use have a H shaped gate completely contained within the lever pocket. Thus it is impossible to see the position of the gates from outside without penetration of the outer shell or at least the door.
"Detainer" levers however have a cut notch on the front edge. Operation is such that the key lifts the lever to the correct height for a mechanism to test the detainer positions, then resets. This requires a marked increase in complexity so is only found in higher end locks such as the successful high security Chubb 110 series.
(Note that on some newer UK domestic lever locks, the end of the lever is open for the bolt to slide though. They have only half of the H inside the lever, (in effect removing the outer boundary of the locking pocket) and look somewhat like a detainer, but they are not true detainers as they are not tested but directly interact with the stump. The reason for this change is due to the increase of the locking bolt length requirement in BS3621:2003 and manufacturers needed to increase the bolt travel without changing the key size.)
The detainer allows mechanical advantage to amplify the variations of the key in the 110 series, and this allows for 9 cuts to the key, symmetric about the middle 5th cut, interacting with the 5 detainers, to have 9 different lifts with no MACS restrictions. Further, because the mechanism checks the detainer for a notch at the correct height, it is possible to have a detainer with, for example, a notch at the 3rd cut lift height and the 6th cut height which will still prevent a key with a 4th or 5th cut from working, unlike a common lever lock.
