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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. [3]
The connection between piston and main rod is a crosshead, which slides on a horizontal bar behind the cylinder. [2] [5] [3]: 55 Piston rod Connects the piston to the cross-head. [2] [3]: 61 Piston Produces the motion for the locomotive from expansion of the steam.
The cylinder is made pressure-tight with end covers and a piston; a valve distributes the steam to the ends of the cylinder. Cylinders were initially cast iron , but later made of steel . The cylinder casting includes other features such as (in the case of Stephenson's Rocket ) valve ports and mounting feet. [ 1 ]
For a period of the crank cycle, steam is admitted, and the poppet inlet is then closed, allowing continued expansion of the steam during the stroke, driving the piston. Near the end of the stroke, the piston will uncover a ring of exhaust ports mounted radially around the centre of the cylinder.
An indicator diagram is a chart used to measure the thermal, or cylinder, performance of reciprocating steam and internal combustion engines and compressors. [1] An indicator chart records the pressure in the cylinder versus the volume swept by the piston, throughout the two or four strokes of the piston which constitute the engine, or ...
Schematic indicator diagram of pressure in a steam locomotive cylinder. The pressure in the cylinder declines after cutoff as the steam pushes the piston down its bore. Cutoff is one of the four valve events. Early cutoff is used to increase the efficiency of the engine by allowing the steam to expand for the rest of the power stroke, yielding ...
The main moving parts of a steam locomotive with Walschaerts valve gear: 1 - Link, 2 - Eccentric crank, 3 - Radius rod, 4 - Lap/lead lever, 5 - Crosshead, 6 - Valve, 7 - Cylinder, 8 - Reach rod. A detailed animation of the exterior working parts of a steam locomotive. This animation is from the commons, and is already a featured picture there..
Indicator diagram for steam locomotive [3] Specifically, the diagram records the pressure of steam versus the volume of steam in a cylinder, throughout a piston's cycle of motion in a steam engine. The diagram enables calculation of the work performed and thus can provide a measure of the power produced by the engine. [4]