Mechanics of MachinesFinal Project

Group Members:Khurram Mehdi 120403Nauman Rasheed 110547

Project :Steam Engine Locomotives Driving Mechanism

History: In 1781 James Watt patented a steam engine that produced continuous

rotative motion.[1] Watt's ten-horsepower engines enabled a wide range of manufacturing machinery to be powered. The engines could be sited anywhere that water and coal or wood fuel could be obtained. By 1883, engines that could provide 10,000 hp had become feasible.[2] Steam engines could also be applied to vehicles such as traction engines and the railway locomotives. The stationary steam engine was a key component of the Industrial Revolution, allowing factories to locate where water power was unavailable.

Working: Steam engines are external combustion engines,[3] where the working fluid

is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be used. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In the cycle, water is heated and transforms into steam within a boiler operating at a high pressure. When expanded through pistons or turbines, mechanical work is done. The reduced-pressure steam is then condensed and pumped back into the boiler.

Application: In general usage, the term steam engine can refer to either the

integrated steam plants (including boilers etc.) such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine. Specialized devices such as steam hammers and steam pile drivers are dependent on steam supplied from a separate boiler. Reciprocating piston type steam engines remained the dominant source of power until the early 20th century, when advances in the design of electric motors and internal combustion engines gradually resulted in the replacement of reciprocating (piston) steam engines in commercial usage, and the ascendancy of steam turbines in power generation.[4] Considering that the great majority of worldwide electric generation is produced by turbine type steam engines, the "steam age" is continuing with energy levels far beyond those of the turn of the 19th century.

Different types of this mechanism

Stephenson valve gear was invented by employees of the Stephenson's Locomotive Works during the 1840's. The design used eccentrics on the driving axle of the locomotive to control valve motion. In the USA it quickly became the most popular valve gear through the 1800's. However, because the valve gear mechanism was located between the wheels, it was difficult to maintain

Stephenson Valve Gear

Walschaerts Valve Gear

Walschaerts valve gear was invented around the same time as Stephenson valve gear but did not become popular until the very late 1800's. After that it quickly became the most popular valve gear on steam locomotives. It's main advantage was that it was located completely outside the wheels and therefore was much easier to maintain than Stephenson valve gear.

Baker valve gear was similar to Walschaerts valve gear except that it replaced the slider and expansion link with a pin-joint mechanism. In most linkage mechanisms, a sliding joint will be the source of most problems. The Baker valve gear did not have any slider/block joints. It was made up completely of pin joints, thus requiring less maintenance.

Baker Valve Gear

Southern valve gear was designed by engineers from the Southern Railway (thus the name). It was similar to Walschaerts except that it did away with the combination lever and union links connected to the crosshead. It had a curved expansion link (like on Walschaerts) except that it was mainly horizontal instead of vertical like on Walschaerts.

Southern Valve Gear

Young valve gear was invented by an employee of the C&NW named O. W. Young. This valve gear was first applied to a steam locomotive on the Grand Trunk in 1915. Young valve gear eliminated the need for the eccentric crank. It took advantage of the quartering of the drivers by using the piston rod motion on one side of the locomotive to control the steam valves on the other side of the locomotive. As a result, it was said to have put less dynamic loads on the main driver. It was also

purported to produce better valve timing events which resulted in more power.

Young Valve Gear

Progress in our Project