This is how the Cornish Cycle works (click here for diagram).
The condensed water in the condenser chamber is extracted by means of the Air Pump(so called because there is also air in the condenser and the pump extracts this as well). The Air Pump discharges the condensed water into the Hot Well which is the boiler feed reservoir.
The condenser chamber and associated pumps are contained in a tank of water to keep them cool. The water in this tank is continuously pumped out to the canal feeder by the Circulating Pump and replenished by fresh water tapped off of the rising main, thus keeping the tank contents cool and maximising condenser efficiency. Hover over the thumbnail for a picture of Crofton’s No 1 Condenser Tank.
It should be noted that the vacuum produced by these engines provides a significant proportion of their power. Both engines at Crofton run at a vacuum of -
Both of the engines at Crofton employ the Cornish Cycle, so called because it was developed by Cornish engineers for use in their tin mine pumping engines. The Cornish Cycle combines the use of steam pressure to push upon the piston and the vacuum produced when steam is condensed in an enclosed space to pull the piston. James Watt used both steam pressure and vacuum, but the arrangement of Watt valve gear and condenser was not as efficient as that employed by the Cornish engineers and, strictly speaking, engines built to the Watt design were not Cornish Cycle Engines. When originally installed at Crofton, both the 1809 and the 1812 engines employed Watt valve gear but the 1812 engine was converted to the Cornish Cycle by Harvey's of Hayle in 1843 when they replaced the boilers and changed the valve gear to cope with the increased steam pressure. At this time the 1809 engine was also replaced.
The Cornish Steam Cycle