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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.
The cut-off point determines the moment when the valve blocks a steam port, "cutting off" admission steam and thus determining the proportion of the stroke during which steam is admitted into the cylinder; for example a 50% cut-off admits steam for half the stroke of the piston. The remainder of the stroke is driven by the expansive force of ...
Definition of the part via a 3D CAD model rather than via a 2D engineering drawing. Drawings may be printed (plotted) from the model for reference use, but the model remains the governing legal instrument. MBP: measurement between pins: threads, splines, gears (internal, female) (synonymous with MBW) (see also MOP, MOW) MBW: measurement between ...
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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An oscillating cylinder engine cannot be reversed by means of the valve linkage (as in a normal fixed cylinder) because there is none. Reversing of the engine can be achieved by reversing the steam connections between inlet and exhaust or, in the case of small engines, by shifting the trunnion pivot point so that the port in the cylinder lines up with a different pair of ports in the port face.