page_title: Cornish engine
section_title: Cornish cycle
hierarchical_section_title: Cornish engine / Cornish cycle
caption_attribution_description: The Cornish pumping engine 1877
context_page_description: A Cornish engine is a type of steam engine developed in Cornwall, England, mainly for pumping water from a mine. It is a form of beam engine that uses steam at a higher pressure than the earlier engines designed by James Watt. The engines were also used for powering man engines to assist the underground miners' journeys to and from their working levels, for winching materials into and out of the mine, and for powering on-site ore stamping machinery.
context_section_description: The Cornish cycle operates as follows.
  Starting from a condition during operation with the piston at the top of the cylinder, the cylinder below the piston full of steam from the previous stroke, the boiler at normal working pressure, and the condenser at normal working vacuum,
  The pressurized steam inlet valve and low-pressure steam exhaust valves are opened. Pressurized steam from the boiler enters the top part of the cylinder above the piston, pushing it down, and the steam below the piston is drawn into the condenser, creating a vacuum below the piston. The pressure difference between the steam at boiler pressure above the piston and the vacuum below it drives the piston down.
  Part way down the stroke, the pressurized steam inlet valve is closed. The steam above the piston then expands through the rest of the stroke, while the low-pressure steam on the other side (bottom) of the piston continues to be drawn into the condenser, thereby maintaining the partial vacuum in that part of the cylinder.
  At the bottom of the stroke, the exhaust valve to the condenser is closed and the equilibrium valve is opened. The weight of the pump gear draws the piston up, and as the piston comes up, steam is transferred through the equilibrium pipe from above the piston to the bottom of the cylinder below the piston.
  When the piston reaches the top of the cylinder, the cycle is ready to repeat.
  The next stroke may occur immediately, or it may be delayed by a timing device such as a cataract. If it was not necessary for the engine to work at its maximum rate, reducing the rate of operation saved fuel.
  The engine is single-acting, and the steam piston is pulled up by the weight of the pump piston and rodding. Steam may be supplied at a pressure of up to 50 pounds per square inch (340 kPa).
  Real photos showing the components of the schematic design (East Pool mine Tailer's shaft Harvey's Engine):
caption: Section, circa 1877
exif: {}