Clock escapement

Gravity escapement

Verified

Gravity arms are alternately raised by the clock train and then released to fall against the pendulum, delivering an impulse of almost constant force regardless of variation in the train's driving torque or friction.

Schematic arrangement

How it is laid out

Outline schematic only, drawn to show the characteristic arrangement of wheel, locking member and oscillator. It is not a dimensioned working drawing and should not be used for setting up or repairing a movement.

Advantages

Impulse is largely independent of train friction and driving-weight variation
Well suited to large, exposed turret-clock movements affected by wind and weather

Drawbacks

Mechanically more complex than a simple deadbeat or recoil escapement

Attribution and period

Nineteenth century; the double three-legged form is associated with Edmund Beckett Denison (Lord Grimthorpe) and was used for the Great Clock at the Palace of Westminster

Horological firsts are frequently contested. Where an invention is attributed to a named maker, that attribution is recorded as such rather than treated as settled fact.

How to recognise it

Two pivoted gravity arms that are lifted by the train and fall onto the pendulum.
A legged escape wheel (the double three-legged form has two sets of three legs with lifting pins).
Encountered almost exclusively in turret and tower clock movements.

Servicing and conservation

Turret clocks are heavy, exposed and often driven by large weights; work on them is a specialist discipline with real physical hazard. The gravity arms and their stops must be set so the pendulum receives a consistent impulse — an adjustment made in situ by a turret-clock specialist.

Work on an antique escapement by a qualified watchmaker or clockmaker. Conservation of original parts is preferred to replacement wherever the object will still run.