|
Johnson Bar (locomotive)
A Johnson Bar is a control lever on a steam locomotive, used to control the timing of the admission of steam into the locomotive's cylinders. By controlling this timing, the amount of power delivered to the wheels is regulated, as is the direction that the wheels rotate, giving the lever the alternate name of the reversing lever. This is the term employed in British English, while the term 'Johnson Bar' is the norm in the United States. History Historians have not identified the reasons why engineers called the reversing lever a Johnson Bar, but the reversing lever is described in both British, and American railway journals of the time. The best accreditation of the invention is documented under the Walschaerts valve gear. Reversing The reversing lever in locomotive history is documented from about 1842. The American Railway Master Mechanic's Association had members that published illustrations. Parts for the reversing lever are drawn in the "Locomotive Dictionary", 1st e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steam Locomotive
A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomotive's boiler to the point where it becomes gaseous and its volume increases 1,700 times. Functionally, it is a steam engine on wheels. In most locomotives, the steam is admitted alternately to each end of its cylinders, in which pistons are mechanically connected to the locomotive's main wheels. Fuel and water supplies are usually carried with the locomotive, either on the locomotive itself or in a tender coupled to it. Variations in this general design include electrically-powered boilers, turbines in place of pistons, and using steam generated externally. Steam locomotives were first developed in the United Kingdom during the early 19th century and used for railway transport until the middle of the 20th century. Richard Trevithick ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slack Action
In railroading, slack action is the amount of free movement of one car before it transmits its motion to an adjoining coupled car. This free movement results from the fact that in railroad practice cars are loosely coupled, and the coupling is often combined with a shock-absorbing device, a "draft gear", which, under stress, substantially increases the free movement as the train is started or stopped. Loose coupling is necessary to enable the train to bend around curves and is an aid in starting heavy trains, since the application of the locomotive power to the train operates on each car in the train successively, and the power is thus utilized to start only one car at a time. United Kingdom The UK formerly used three-link couplings, which allowed a large amount of slack; these were soon replaced on passenger stock by buffers and chain couplers where the couplings are held tight by buffers and shortened by a turnbuckle while in most other parts of the world automatic couplings, su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lever
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or ''fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is divided into three types. Also, leverage is mechanical advantage gained in a system. It is one of the six simple machines identified by Renaissance scientists. A lever amplifies an input force to provide a greater output force, which is said to provide leverage. The ratio of the output force to the input force is the mechanical advantage of the lever. As such, the lever is a mechanical advantage device, trading off force against movement. Etymology The word "lever" entered English around 1300 from Old French, in which the word was ''levier''. This sprang from the stem of the verb ''lever'', meaning "to raise". The verb, in turn, goes back to the Latin ''levare'', itself from the adjective ''levis'', meaning "light" (as in "not heavy"). The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Switcher
A switcher, shunter, yard pilot, switch engine, yard goat, or shifter is a small railroad locomotive used for manoeuvring railroad cars inside a rail yard in a process known as ''switching'' (US) or ''shunting'' (UK). Switchers are not intended for moving trains over long distances but rather for assembling trains in order for another locomotive to take over. They do this in classification yards (Great Britain: ''marshalling yards''). Switchers may also make short transfer runs and even be the only motive power on branch lines and switching and terminal railroads. The term can also be used to describe the workers operating these engines or engaged in directing shunting operations. Switching locomotives may be purpose-built engines, but may also be downgraded main-line engines, or simply main-line engines assigned to switching. Switchers can also be used on short excursion train rides. The typical switcher is optimised for its job, being relatively low-powered but with a high ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interstate Commerce Commission
The Interstate Commerce Commission (ICC) was a regulatory agency in the United States created by the Interstate Commerce Act of 1887. The agency's original purpose was to regulate railroads (and later trucking) to ensure fair rates, to eliminate rate discrimination, and to regulate other aspects of common carriers, including interstate bus lines and telephone companies. Congress expanded ICC authority to regulate other modes of commerce beginning in 1906. Throughout the 20th century, several of ICC's authorities were transferred to other federal agencies. The ICC was abolished in 1995, and its remaining functions were transferred to the Surface Transportation Board. The Commission's five members were appointed by the President with the consent of the United States Senate. This was the first independent agency (or so-called ''Fourth Branch''). Creation The ICC was established by the Interstate Commerce Act of 1887, which was signed into law by President Grover Cleveland. The cr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Servomechanism
In control engineering a servomechanism, usually shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the action of a mechanism. On displacement-controlled applications, it usually includes a built-in encoder or other position feedback mechanism to ensure the output is achieving the desired effect. The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position, speed, attitude or any other measurable variables. For example, an automotive power window control is not a servomechanism, as there is no automatic feedback that controls position—the operator does this by observation. By contrast a car's cruise control uses closed-loop feedback, which classifies it as a servomechanism. Applications Position control A common type of servo provides ''position control''. Commonly, servos are electric, hydraulic, or pneumatic. They operate on the principle of negative feedback, wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Priming (steam Locomotive)
Priming (foaming in North America) is a condition in the boiler of a steam locomotive in which water is carried over into the steam delivery. It may be caused by impurities in the water, which foams up as it boils, or simply too high a water level. It is harmful to the valves and pistons, as lubrication is washed away, and can be dangerous as any water collecting in the cylinders is not compressible and if trapped may fracture the cylinder head or piston. Causes The most frequent cause is running the locomotive with too high a level of water in the boiler and is most apparent when the regulator is opened sharply or steam demand is high. Thus, sensible locomotive management by the operators will help to prevent the occurrence. The phenomenon is particularly evident in areas of impure water, where boiled water creates a foam, or a mist of droplets, filling the space that collects steam at the top of the boiler, to be drawn down the steam collector pipe in the form of slugs of w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Screw Thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a ''straight'' thread and the latter called a ''tapered'' thread. A screw thread is the essential feature of the screw as a simple machine and also as a threaded fastener. The mechanical advantage of a screw thread depends on its ''lead'', which is the linear distance the screw travels in one revolution. In most applications, the lead of a screw thread is chosen so that friction is sufficient to prevent linear motion being converted to rotary, that is so the screw does not slip even when linear force is applied, as long as no external rotational force is present. This characteristic is essential to the vast majority of its uses. The tightening of a fastener's screw thread is comparable to driving a wedge into a gap until it sticks fast thro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reversing Gear
On a steam locomotive, the reversing gear is used to control the direction of travel of the locomotive. It also adjusts the cutoff of the steam locomotive. Reversing lever This is the most common form of reverser. It consists of a long lever mounted, parallel to the direction of travel, on the driver’s side of the cab. It has a handle and sprung trigger at the top and is pivoted at the bottom so as to pass between two notched sector plates. The reversing rod, which connects to the valve gear, is attached to this lever, either above or below the pivot, in such a position as to give good leverage. A square pin is arranged so as to engage with the notches in the plates and hold the lever in the desired position when the trigger is released. The advantages of this design are that change between forward and reverse gear can be made very quickly as is needed in, for example, a shunting engine. Disadvantages are that, because the lever must rest at one of the notches, fine adjustment ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slide Valve
The slide valve is a rectilinear valve used to control the admission of steam into and emission of exhaust from the cylinder of a steam engine. Use In the 19th century, most steam locomotives used slide valves to control the flow of steam into and out of the cylinders. In the 20th century, slide valves were gradually superseded by piston valves, particularly in engines using superheated steam. There were two reasons for this: * With piston valves, the steam passages can be made shorter. This reduces resistance to the flow of steam and improves efficiency. * It is difficult to lubricate slide valves adequately in the presence of superheated steam. Murdoch's D slide valve The D slide valve, or more specifically Long D slide valve, is a form of slide valve, invented by William Murdoch and patented in 1799. It is named after the hollow central D-sectioned piston. This valve worked by "connecting the upper and lower valves so as to be worked by one rod or spindle, and in maki ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steam
Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Steam that is saturated or superheated is invisible; however, "steam" often refers to wet steam, the visible mist or aerosol of water droplets formed as water vapor condenses. Water increases in volume by 1,700 times at standard temperature and pressure; this change in volume can be converted into mechanical work by steam engines such as reciprocating piston type engines and steam turbines, which are a sub-group of steam engines. Piston type steam engines played a central role in the Industrial Revolution and modern steam turbines are used to generate more than 80% of the world's electricity. If liquid water comes in contact with a very hot surface or depressurizes quickly below its vapor pressure, it can create a steam explosion. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Valve Gear
The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle. It can also serve as a reversing gear. It is sometimes referred to as the "motion". Purpose 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 throughout the stroke) while peak efficiency is achieved by only having the inlet valve open for a short time and then letting the steam expand in the cylinder (expansive working). The point at which steam stops being admitted to the cylinder is known as the '' cutoff'', and the optimal positio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.jpg "Click for more on -> Slide Valve")
