Component record · Escapement
Duplex Escapement
Partially verifiedA frictional-rest escapement using an escape wheel with two sets of teeth — long locking teeth and short impulse teeth — acting on a single roller carried on the balance staff.
What it does
Locks the train on the long teeth for most of the balance's vibration and delivers impulse only once per full oscillation via the short teeth, giving a distinctive 'tick, silence, tick' rhythm.
How it works
A notch cut into the locking roller allows one long escape-wheel tooth to pass, unlocking the wheel, once per balance vibration; the wheel then rotates until a short impulse tooth strikes an impulse pallet (often a small ruby pin) mounted on the roller, giving the balance its push before the next long tooth drops onto the roller's edge and re-locks the train.
Because impulse is given only every other vibration (once per full oscillation rather than twice), a duplex escapement is unusually intolerant of the balance stopping mid-cycle: a shock that halts the balance at the wrong point can leave the watch stopped rather than self-restarting, a recognised practical weakness of the design.
Like the cylinder, the duplex is a frictional-rest rather than fully detached escapement, though its locking geometry differs substantially from the cylinder's hollow-drum arrangement.
Evolution
Enjoyed a period of popularity, particularly in English and American watchmaking, for its good performance relative to the cylinder, before being displaced by the more robust and more easily restarted lever escapement through the nineteenth century.
Known variations
- English duplex construction
- American duplex watches produced by nineteenth-century manufacturers before wide lever adoption
Identification for collectors
- Escape wheel shows two distinct tooth forms — long locking teeth and separate short impulse teeth — visible on close inspection
- Balance staff roller has a single notch rather than the cylinder's cutaway drum or the lever's impulse-jewel-and-fork arrangement
Common failure modes
- Failure to self-restart if the balance is stopped by a shock at an unfavourable point in its cycle
- Wear to the roller notch and impulse pin affecting reliability of unlocking and impulse
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- Britten, F. J., Old Clocks and Watches and Their Makers
- Attribution of the duplex escapement's originators varies between sources and is treated with caution here.
Where sources disagree, the disagreement is stated rather than resolved silently.