1820s Beam Engine 'Princess'
Originally potters’ mills were powered by water and very occasionally by wind. Although these mills gave a good service to the industry production was stopped in times of drought and light wind. In addition it was very difficult to control the speed of the mill which gave an inconsistent product and affected the quality and loss rate of the manufactured pottery. The introduction of the steam engine to the pottery industry in the 1770 improved productivity and quality. “Princess” is a double acting condensing rotative beam engine to the design of James Watt. She was purchased second hand and installed when the mill was built in 1856/7. She is thought to have been manufactured by Bateman and Sherratt of Salford, Manchester in the 1820s who were rivals and competitors of the famous Boulton and Watt company in Birmingham.
How 'Princess' Operates
Steam enters the single large vertical cylinder through a main steam valve and is directed to one end of the cylinder via valves operated by a rocking shaft beneath the floor which is, in turn, operated by an eccentric from the flywheel axle. The quantity of steam is controlled by the ‘governor’ which keeps the speed consistent. Exhaust steam is converted to water in a condenser located beneath the floor and cooled by water from the canal. This creates a vacuum in the condenser which is opened to the other side of the cylinder thus the pressure difference between steam pressure on one side and vacuum on the other moves the piston. The valves change over and the process is repeated on the other side of the piston. The two gauges on the wall show the strength of the vacuum and the steam pressure. For the engine to be double acting (pull and push) the beam must have a solid connection to the piston rod which emerges from the cylinder head through a ‘metallic’ gland packing. The piston rod must travel in a vertical straight line but the end of the overhead beam, which transmits the power, transcribes an arc as it rocks. This would try to pull the rod backwards and forwards which it cannot be allowed to do. James Watt overcame this problem with his great invention – parallel motion; a trapezoidal connection. At the other end of the beam is the sweep rod which connects via a crank to the axle which carries a flywheel of 20 feet (6.1 metres) in diameter and 10 tons (10.16 tonnes) in weight. The flywheel’s momentum carries the engine over top dead centre and bottom dead centre when the piston is at the end of its stroke and not providing power. The axle extends through the wall into the gear room.