Types of escapements

GRAHAM ESCAPEMENT

1. Definition and classification

The Graham escapement is a dead-beat pallets (lever) escapement, without recoil, developed for pendulums. It belongs to the family of constant-contact escapements, in which the balance — or here the pendulum — remains constantly in contact with a part of the escapement. Unlike recoil escapements, where the eccentric resting surfaces force the escape wheel to move backward during part of the oscillation, the resting surfaces of the Graham escapement are concentric to the center of the pallets: the wheel never recoils.

2. History

The escapement is named after George Graham (1673-1751), a famous English horologist (watchmaker), a student and later husband of the niece of Thomas Tompion, and a member of the Royal Society of London. He developed this dead-beat pallets (lever) escapement for pendulums in 1715. He is also credited with the mercury pendulum (1719) and the refinement of the cylinder escapement (1728), originally designed by Thomas Tompion in 1695.

3. Description

The escape wheel and the pallets (lever) body are made of brass or steel. The pallets, whose position is adjustable, are made of hardened and polished steel, or ruby / jewel.

4. Operation

The resting surfaces of the pallets, concentric to the center of the pallets (lever), allow the wheel to remain motionless during the resting phase, without any recoil whatsoever. This absence of recoil fundamentally distinguishes the Graham escapement from the recoil escapements that preceded it, such as the verge escapement (crown wheel escapement).

5. Advantages

Simple in construction, the Graham escapement gives very good results. It is considered the classic recoil-free pallets (lever) escapement for pendulums.

6. Not to be confused with: Graham’s mercury pendulum

George Graham also invented, in 1719, a separate device also bearing his name: the mercury pendulum. This is a thermal compensation system — a hollow cylinder containing mercury suspended from a steel rod, where the rise in mercury level compensates for the elongation of the rod under the effect of heat. This device has no functional relationship with the Graham escapement, other than sharing the same inventor.

7. See also

For the complete classification of escapements, see Types of escapements.