Escapements may be classified as:

(1) Frictional rest, in which the balance is constantly in contact with a part of the escapement - e.g. (a) recoil escapements in which the locking faces are eccentric, causing a recoil of the escape wheel. (b) dead-beat escapements, with concentric locking faces, which give no recoil.

(2) Detached escapement, in which the balance is detached from the escapement except at the time of locking and receiving impulse. The verge escapement is an example of 1(a). The cylinder is an example of 1(b) and the lever an example of 2. A single beat escapement gives a single impulse for each double swing of the balance. The duplex and the chronometer detent escapement are examples. A constant-force escapement employs an intermediate spring, a 'remontoire', wound periodically by the train, which spring impulses the balance.


ESCAPE WHEEL. The last wheel in the going train, which permits 'escape' of the motive power, giving impulse to the balance. It is alternately locked and released.