Search results
Results From The WOW.Com Content Network
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.
Control is by a small three-way steam valve (“forward”, “stop”, “back”) and a separate indicator showing the position of the rod and thus the percentage of cutoff in use. When the steam valve is at “stop”, an oil cock connecting the two ends of the locking piston is also closed, thus holding the mechanism in position.
The valve itself can be a drop valve or a Corliss valve. Trip valve gear was applied to larger stationary engines. It was not used in transport applications, [ft 1] as it was not suitable for high speed. [1] The trip point of the valve mechanism, and therefore the cut-off, would be adjusted either manually or automatically by the governor.
The valve gear, actuated by connection to the driving wheels, ensures that steam is delivered to the piston with precision. Types are slide valves, piston valves or poppet valves. [2] [3]: 62 Valve chest / Steam chest Valve chamber next to the cylinder (24) containing passageways to distribute steam to the cylinders. [6]: 41 [3]: 75 Firebox
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 ...
Diagram showing lap and lead and their relation to valve travel When on the move, a steam locomotive requires steam to enter the cylinder at precise times relative to the piston's position. [ 3 ] This entails controlling the admission and exhaust of steam to and from the cylinders with a valve linked to the motion of the piston.
Gooch outside valve gear as applied to a French 2-4-0 outside cylinder express locomotive (Midi no. 51) in 1878. In the Gooch valve gear (invented by Daniel Gooch in 1843) the reversing and cut-off functions were achieved by raising or lowering a radius rod which connected the valve-rod to a "stationary" link pivoting around a fixed point. The ...
Cylinder, with slide valve removed to show ports A double-acting slide valve cylinder. Steam enters via the steam port SP, and is admitted by the slide valve SV through the upper passage S to push down the piston P. At the same time, exhaust steam from below the piston passes back up the lower passage S, via the valve cavity, to exhaust E. As ...