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The Encyclopedia of Horology

Glossary · Mechanism

Duplex escapement

A watch escapement combining a frictional-rest locking action with a single impulse per swing, using two sets of teeth on one escape wheel.

Explanation

The duplex escapement, developed in the late eighteenth century and associated with makers such as Thomas Tyrer and later English watchmaking, uses an escape wheel with two sets of teeth: long locking teeth that rest on a small ruby roller on the balance staff, and short impulse teeth that act on a notch in that roller once per swing. The balance receives impulse in one direction only.

The duplex offered better timekeeping than the cylinder and suited the English preference for robust, high-quality watches; it was widely used in good English pocket watches and in watches made for the Chinese market. Its weaknesses are sensitivity to shock — a jolt can disengage the locking and stop the watch — and the single-direction impulse. It was displaced by the lever as manufacturing made the lever cheaper and more reliable.

Identification cues: the characteristic escape wheel with two tooth levels, the ruby roller with its notch, and typically an English full-plate or three-quarter-plate movement. Record the escapement from the movement; duplex watches are frequently misdescribed as lever watches in trade listings.

Sources & references

  1. de Carle, D., Practical Watch Repairing — technical further reading; exact procedures require calibre documentation
  2. Reymondin et al., The Theory of Horology — construction and terminology further reading

Where sources disagree, the disagreement is stated rather than resolved silently.

Distinctions at a glance

FeatureDuplex escapementComparison
LockingLong teeth rest on a ruby rollerCylinder locks on the cylinder rim
ImpulseOnce per swing, one directionLever impulses in both directions
Typical hostEnglish pocket watches, Chinese-market watchesContinental thin watches favour cylinder
Shock behaviourCan disengage and stop after a joltLever resists this with guard action

What to record

  • Confirm the two-level escape wheel before naming the escapement.
  • Note any stopping after shock as characteristic behaviour, not necessarily a fault.
  • Keep trade-listing descriptions separate from inspected construction.

Do not shake or sharply rotate a duplex watch to restart it; if the locking has disengaged, the watch needs a watchmaker.

In the object catalogue

Catalogued objects whose own source record mentions “Duplex escapement”. The quoted line shows where; it is the seller’s or museum’s wording, not independent verification.