The Museum of Power
Langford

The engine has three cylinders, with bores of 20 inches (508 mm) diameter (high pressure), 35 inches (889 mm) diameter (intermediate pressure) and 56 inches (1422 mm) diameter (low pressure). The stroke is 42 inches (1067 mm). Each piston rod is 5 inches (127 mm) diameter. The steam cylinders are double acting and are fitted with drop valves for both steam and exhaust. The cut off point of the inlet valves on all cylinders is controlled by trip gear with large springs and dampers. The inlet valves on the high pressure cylinder are controlled by the governor, which maintains the engine at approximately 32 revolutions per minute. All other inlet valves are adjusted manually to suit. The exhaust valves are operated by a simple lever arrangement. All valves are driven from eccentrics and a shaft and gearbox system from the crankshaft.

Steam was supplied to the high pressure cylinder at 210 p.s.i. (14.3 bar) direct from the boilers. As the engine is of the triple expansion type, the same steam is used in each cylinder in turn. However, when the steam is exhausted from the high pressure cylinder its pressure has dropped and therefore the intermediate cylinder has to be of increased diameter so that the same power can be exerted on the intermediate crankpin. The same situation applies to the intermediate cylinder exhaust and a further increase in diameter of the low pressure cylinder is required.

Before exhaust steam is passed to the next cylinder it is piped into the reheater, (or heat exchanger), which is constructed in two parts, where it passes through tubes which are surrounded by steam at full boiler temperature and pressure, which in turn raises the temperature and pressure of the ‘exhaust’ steam before it goes into the next cylinder. The final exhaust steam is piped down to the condenser below floor level, and the resultant condensate is pumped back to the boiler house for reuse as boiler feed water. All steam cylinders are steam jacketed to reduce heat loss and condensation and thus improve efficiency. The cylinders, steam pipes and reheater were lagged with asbestos, which was removed in January 1997. The flywheel is 14 feet (4267 mm) diameter and weighs 18 tons (18.29 tonnes).