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In a steam engine, cutoff is the point in the piston stroke at which the inlet valve is closed. On a steam locomotive, the cutoff is controlled by the reversing gear.. The point at which the inlet valve closes and stops the entry of steam into the cylinder from the boiler plays a crucial role in the control of a steam engine.
With larger engines, the linkages involved in controlling cutoff and direction grew progressively heavier and there was a need for power assistance in adjusting them. Steam (later, compressed air) powered reversing gears were developed in the late 19th and early 20th centuries.
Steam engines are fitted with regulators (throttles in US parlance) to vary the restriction on steam flow, but controlling the power via the cutoff setting is generally preferable since it makes for more efficient use of boiler steam. A further benefit may be obtained by admitting the steam to the cylinder slightly before front or back dead centre.
Frederick Ellsworth Sickels (September 20, 1819; [1] Gloucester County, New Jersey – March 8, 1895; Kansas City [2]) was an American inventor, best known for the invention of a cut-off valve for steam engines in 1841. Sickels grew up in New York City, [3] where his father was Chief Health Officer. [4]
(On some engines the die block was in the top of the link in forward gear. This type was generally used on tank engines, which worked in forward and reverse equally. [6]) Once the locomotive has accelerated the driver can adjust the reverser toward the mid-gear position, decreasing cut-off to give a more economical use of steam.
Collects steam at the top of the boiler (well above the water level) so that it can be fed to the engine via the main steam pipe, or dry pipe, and the regulator/throttle valve. [2] [5] [6]: 211–212 [3]: 26 Air pump / Air compressor Westinghouse pump (US+) Powered by steam, it compresses air for operating the train air brake system.
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Stephenson valve gear is a convenient arrangement for any engine that needs to reverse and was widely applied to railway locomotives, traction engines, steam car engines and to stationary engines that needed to reverse, such as rolling-mill engines. It was used on the overwhelming majority of marine engines.