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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.
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.
where d is the bore of the cylinder (diameter) in inches, s is the cylinder stroke, in inches, P is boiler pressure in pounds per square inch, D is the diameter of the driving wheel in inches, and c is a factor that depends on the effective cut-off. [83] In the US, c is usually set at 0.85, but lower on engines that have maximum cutoff limited ...
A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be transformed by a connecting rod and crank into rotational force for work.
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The WHE-25 engine has a 34% cutoff. [4] This allows for the remaining 66% of the piston stroke to expand the steam, extracting work from it and causing the pressure to drop. The figure to the right shows how pressure in the cylinder of a steam engine drops after the cutoff point. The WHE-DR must have a much later cutoff to allow it to self-start.