The lifting arm needs to be set oddly out of square in order to bias forward gear events at the expense of backward running. It is based on the eccentric rod valve gear developed for stationary steam engines, but with the added complexity that unlike a stationary steam engine, a steam locomotive needs to reverse. This picture shows a working demonstration model of the gear in the Science Museum, South Kensington. Long travels are better accommodated by rocker arm enhancement in the manner of GWR locomotives and this keeps the eccentric throws at manageable dimensions. Forward eccentrics are usually nearest to frame. The reversing shaft goes across the frames and activates both sets of valve gear, (and there is no reach rod on the left hand side of course) but the rock shafts and rock arm assemblies are on both sides of the locomotive and independant of each other. It was used on … The amount of lead changes as the cut off point changes. They used saturated steam, had Stephenson valve gear and were built on plate frames. Where convenient, placing the weighshaft ahead of the link can be advantageous, as revealed by the excellent equality to be found on the old LNWR Coal tank 0-6-0s. Click for a larger picture to view the offset trunnion. Similarly, the eccentrics for Stevenson link valve gear can be set once and for all before the axle is even fitted in the loco. 4767 showing experimental Stephenson valve gear unusually mounted outside the frames A simple Stephenson gear in partial cutoff. Improper suspension will counter any good initial design. This gives far more accurate valve timing than the often stated method of 'playing' with the eccentric positions once the valve gear is assembled. The placement of the weighshaft and the lengths of the lifting components will alone determine the best events. Finished a Simplex in 2008, gradually learning how to drive it. if i were doing my BOXHILL cylinders again i would set the bores 1/8" further apart and make the outer crank webs 1/4" thick and take a 1/16" off the axlebox width. First, you want to set the cams. English examples for "Stephenson valve gear" - The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. The Stephenson valve gear or Stephenson link or shifting link is a simple design of valve gear that was widely used throughout the world for all kinds of steam engines.It is named after Robert Stephenson but was actually invented by his employees. This setting information is the same for all Stephenson link valve gear. John Baguley: 22/07/2010 09:40:07: 467 forum posts 50 photos: Valve setting was in Volume 96 Issue 2390. The expansion links were somewhat hybrid, with pins offset in launch link fashion but too widely spaced to allow die alignment in full gear. It is named after Robert Stephenson but was invented by his employees. (See the previous illustration). Yes, Don will be along soon to confirm! To watch the flailing links and interactions of Stephenson’s gear belies its very simple concept. Triangle M,X,R shows the setting and advance for a locomotive link eccentric to achieve the identical performance, superimposed on the launch link eccentric. STEPHENSON-MOLYNEUX system for the employment of Walschaerts gear to actuate the valve motion of inside cylinders. These calculations merely appear on the sheet so that the user may see when cells contain either # marks or minus signs, which must be absent before Solver is invoked. My question is that by having 2 eccentrics that could be set at any position on the axle in the shop, could the Stevenson valve gear be "tweaked" to make a certain engine perform For some more sophisticated understanding of valve gears I suggest Don Ashton's Steam Locomotive Valve gears site, especially in this context the page on Stephenson's gear. Please Login or Register. My question is that by having 2 eccentrics that could be set at any position on the axle in the shop, could the Stevenson valve gear be "tweaked" to make a certain engine perform Expansion links should not swing more than 25 degrees for mechanical exigency. The suspension positioning is also determined. Stephenson’s valve gear was extensively used worldwide throughout the 19th century and through the first half of the 20th Century on Great Western Railway 2-cylinder locomotives. Setting Stephenson Valve Gear. Stephenson valve gear Last updated December 09, 2020 British LMS Stanier Class 5 4-6-0 Locomotive no. Therefore the lifting link is highly unlikely to be vertical, though few traction engine designers seemed to realise this! Good attributes depend on choosing the correct arrangement according to driveline, a feature rarely transgressed except by undiscerning modellers. Larry also points out the fact that Cut-Off is always 75% when Lap equals Port Width, for all values of Port Width. Initial design work can be achieved very quickly using a spreadsheet such as that found on the DOWNLOADS page, enabling simple juggling of the lap/lead to address port requirements. The following pic is the Stephenson valve gear that Gordon fitted to the 45mm gauge Philadelphia models that he built about 20 years ago. The gear can be properly designed to deliver incomparable steam distribution, highly dependent upon critical suspension. For the steam techies: Modern valve gears like Baker, Walshaert, etc. In 1844 Egide Walschaerts invented a valve gear that by 1848 appeared very much as it does today. BOXHILL and METRO use the same cylinder layout though the stroke on METRO is longer. Tom Stamey wrote the following description for setting Stephenson valve gear on Allen Models locomotives, 20 April 2014.. Click here to remove banner ads from this forum. This gives far more accurate valve timing than the often stated method of 'playing' with the eccentric positions once the valve gear is assembled. The intermediate valve spindle worked by the eccentric and carrying the left- hand end of the combination lever is clearly seen alongside the rectangular guide bar in the centre of the picture. The Stephenson valve gear or Stephenson link or shifting link [1] is a simple design of valve gear that was widely used throughout the world for various … is 33mm and the cylinders are 7/16" dia. The eccentric advance angle is critical to the lead function and correct valve setting is also crucial, but since the two harmonic elements are already fixed in the eccentric setting there can be none of the distortions found in Walschaerts’ gear. It is fitted to 0-4-0WT "Dolgoch", preserved on the Talyllyn Railway. Historical background . Note the special form of combination lever placed horizontally. In the absence of other means of countering the effects of angularity it has to be accepted that perfection is unavailable and that back gear may suffer somewhat in order to satisfy forward running. Often it is called Stephenson's Valve Gear. The heavy traction engine flywheel is intended to smooth out the uneven torque of the single cylinder and ought not also to be encumbered with greatly unequal power production between one end and the other. Not designing a gear with the finest of results should be set on their spindles by provided,. 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