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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]
Piston Produces the motion for the locomotive from expansion of the steam. Driven backward and forward within the cylinder by steam delivered alternately, in front and behind, by the valve. [1] [3]: 61 Cylinder Chamber that receives steam from the steam pipe. [2] [3]: 23 Valve Controls the supply of steam to the cylinders.
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 ]
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 ...
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..
The final 97 locomotives had piston valves mounted outboard of the cylinders, instead of inbound as previously built, giving the cylinder assemblies an outward cant at the top, rather than inward. All B6sa and B6sb locomotives were retrofitted with power reverse to make the frequent back-and-forth of switching quicker and easier.
Especially in steam days, wheel arrangement was an important attribute of a locomotive because there were many different types of layout adopted, each wheel being optimised for a different use (often with only some being actually "driven"). Modern diesel and electric locomotives are much more uniform, usually with all axles driven.
Oppose An indicator diagram would very rarely have the mechanism drawn. The piston position doesn't match any of the possible positions indicated by the diagram. Additionally, an indicator diagram is a plot of pressure vs volume (P-V) not pressure vs piston position. This distinction is important for calculating the work done in each cycle.