Old Bess was a pioneer in improving engine fuel economy, being the first engine to use steam 'expansively'. The cylinder's steam supply was shut off partway through the engine's stroke and allowed to expand for the remainder.

The experiment was unsuccessful. With expansive working, the engine's movement became too violent, and the engine earned the nickname 'Beelzebub'. It was converted back to its former way of working and remained in use until 1848, earning the kinder nickname 'Old Bess'.