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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.
This will suddenly and violently throw the lever into the full cut-off position, carrying with it the real danger of injury to the driver, damage to the valve gear and triggering wheel slip in the locomotive. The only way to prevent this is to close the regulator and allow the steam pressure in the valve chest to drop.
As built the Pennsylvania's I1s 2-10-0 had lap 2 inches, lead 1/4 inch and valve travel 6 inches in full gear. In full gear the two angles are 48.19 deg and 41.41 deg and the maximum cutoff comes out 49.65% of the piston stroke.
In the simple case, this can be a relatively simple task as in the internal combustion engine in which the valves always open and close at the same points. This is not the ideal arrangement for a steam engine, though, because greatest power is achieved by keeping the inlet valve open throughout the power stroke (thus having full boiler pressure, minus transmission losses, against the piston ...
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. The engine's tractive effort is then less than it was at starting, but its power is greater.
Subclass I1sa increased maximum steam cut-off to admit steam for 78% of the piston stroke (rather than the original 50%), boosting low speed tractive effort from 90,000 to 96,000 pounds-force (400 to 430 kN). There was no obvious external difference, except for a revised builders' plate and combination lever.
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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]