This one cost £13,278, which was about £600 more than those built at the same time with Walschaerts' valve gear. Valve gears such as Walschaert's are said to be constant lead valve gears. Stephenson Valve Gear Computer Simulation Program Charles Dockstader has created an excellent program that simulates the operation of Stephenson Valve Gear action. Steam Engine Valve Gear On The Computer Downloadable freeware simulations of every kind of valve gear you've ever heard of by Charles Dockstader (CA). The Gooch gear gave constant lead at whatever cutoff. To give you some sense of scale, the coupled wheelbase is 53mm, the driver dia. Longer eccentric rods and a shorter link reduce this effect. STEPHENSON'S LINK VALVE GEAR - 28xx 2-8-0 This kit is designed to accurately produce in 4mm scale a working model of the Stephenson's link valve gear. As with other computer modelling start with something easy before attempting a complicated gear. Launch-type links were pretty well universal for American locomotives right from the 1850s but, in Europe, although occurring as early as 1846, they did not become widespread until around 1900. Holcroft, Harold (1957). After enough years to be accused of approaching senility, and no engineering training, I cannot recall how I devised my formula, but you have kindly verified that it produces exactly the correct answer. First, you want to set the cams. 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. Walton J.N. I own a 5" Hunslet Don Young design, had it for close to 3 yrs and currently have the boiler off and remaking some of the valve gear as it very loose and worn. "Light Steam Power" Isle of Man, UK; p. 196. 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 engine. It is named after Robert Stephenson[2] but was invented by his employees. I'll demonstrate how any valve gear can be animated logically. It is named after Robert Stephenson but was actually invented by his employees. Property Value; dbo:abstract: The valves on a steam engine control the flow of steam in and out of the cylinders. See also Valves. A Note on Stephenson’s Valve Gear and its Analysis in the 1850s. One consequent disadvantage of the Stephenson gear is that it has a tendency to over-compression at the end of the stroke when very short cut-offs are used, and therefore the minimum cut-off cannot be as low as on a locomotive with Walschaerts gear. Larry suggests adding up to 0.002 inches to the Throw of Eccentric value for each pin in the valve gear (including the eccentric, too) because, even when new, there will be lost motion, possibly enough to eliminate the lead. The Throw of Eccentric formula, below, applies only to locomotives using Stephenson valve gear. These became known respectively as the 'locomotive link' and the 'launch link'. The initial stage of the analysis which determines the details of the 'equivalent eccentric' is the same as for Walschaerts gear. It may be calculated from the physical dimensions of the gears, or it may Slide valves largely used in the 19th century; 2. 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 kinds of steam engines. Professor Bill Hall devised two simulators, one for Stephenson's and one for Walschaert's, and these are quite easy to use requiring only basic dimensions. The cams For reasons of practicality two significant deviations from the prototype have been made. To change direction, the link and rod ends were bodily raised or lowered by means of a counterbalanced bell crank worked by a reach rod that connected it to the reversing lever. July 24, 2009 Previous Next Go to Decoders for HO Atlas Genset: November 1, 2010 Wishlist Data. 4767, had Stephenson valve gear mounted outside the wheels and frames. is 33mm Instead of eccentrics, double return cranks were used to drive the eccentric rods, and a launch-type expansion link was used. Stephenson's valve gear was invented by Wiliams and Howe, introduced in 1842 by Stephenson & Co.,and it was used on many locomotives for many decades. This concept can be used on other valve gears. In early locomotive practice, the eccentric rod ends were pivoted at the ends of the link while, in marine engines, the eccentric rod pivots were set behind the link slot (or below on a vertical engine). Valve … First, you want to set the cams. Although a brief glance into history (except on the Continent) might place Stephenson’s gear as being largely replaced by Walschaerts’ gear around the turn of the 20 th century, both gears were invented almost simultaneously. Its use on engines in which all the cylinders lie in one plane, represents, in the belief of the writer, the best choice." Preparation. Historical background. This was observed to be a disadvantage when similar locomotives fitted with either Gooch or Stephenson gear were compared in service[10] Gooch gear was never popular in Britain except with one or two engineers down to the 1860s, but it was quite common in France. This paper is a report on work in progress. In the United Kingdom, locomotives having Stephenson valve gear normally had this mounted in between the locomotive frames. It can be a very simple valve gear and still be very accurate, but its great advantage is that its accuracy is self-contained, for the exact relationship between its points of support (eccentrics on shaft, valve crosshead, and link hanger arm) have but little effect on the motion of the valve. Sketches showing arrangements of Stephenson valve gear on Great Western Railway locomotives Click on the sketches to enlarge them. In 1947, the London, Midland and Scottish Railway built a series of their Stanier Class 5 4-6-0 locomotives, most of which had the Walschaerts' valve gear that was normal for this class, but one of them, no. During the 1830s the most popular valve drive for locomotives was known as gab motion in the U.K. and V-hook motion in the U.S.A.[3] The gab motion incorporated two sets of eccentrics and rods for each cylinder; one eccentric was set to give forward and the other backwards motion to the engine and one or the other could accordingly engage with a pin driving the distribution valve by means of the gabs: - vee-shaped ends to the eccentric rods supposed to catch the rocker driving the valve rod whatever its position. The eccentics are split and keyed to the crank axle so I need to know the angle of advance to cut the eccentric keyway in the correct position. Stephenson gear. Moreover, the straight expansion link simplified manufacture. Based on 4-6-2 Pacific, Soo #2714: images, data Here's a larger version , … Angle of Advance of the Eccentric calculator uses Angle of advance of the eccentric=asin((Steam lap+Lead)/The eccentric centre line) to calculate the Angle of advance of the eccentric, Angle of advance of the eccentric is the angle in excess of 90° that a steam-engine valve gear is in advance of the crank. The following pic is the Stephenson valve gear that Gordon fitted to the 45mm gauge Philadelphia models that he built about 20 years ago. STEAM ENGINE VALVE GEAR ON THE COMPUTER Windows Version by Charles Dockstader HCR 69 Box 3111 California Valley CA 93453 805 475 2519. Another benefit of the Stephenson gear, intrinsic to the system, is variable lead: usually zero in full gear and increasing as cutoff is shortened. It is named after Robert Stephenson[2] but was invented by his employees. 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. is 33mm and the cylinders are 7/16" dia. The simulators ask … Timing Stevenson Valve Gear can be a real challange, especially when you do it the first time. However, in this case it is less easy to relate the valvegear mechanism to the equivalent eccentric. This will help you to decide. Once again, the Allan gear was not often used in the UK but fairly common on the Continent. Notable UK examples are the Great Western Railway's 1361 and 1366 classes, and the narrow-gauge Ffestiniog Railway's 0-4-0TT class (which were produced by George England and Co.) and the narrow-gauge Talyllyn Railway's original locomotives, Talyllyn and Dolgoch (which were produced by Fletcher, Jennings & Co.). The Great Western Railway used Stephenson gear on most of its locomotives, although the later four-cylinder engines used inside Walschaerts gear. It became the practice to start the engine or climb gradients at long cutoff, usually about 70-80% maximum of the power stroke and to shorten the cutoff as momentum was gained to benefit from the economy of expansive working and the effect of increased lead and higher compression at the end of each stroke. Note you need to download all of the individual zip files or the one large one. An outline of Great Western locomotive practice, 1837-1947; Locomotive Publishing Co Ltd, London, U.K. p.20. A loco with decent valve gear is a delight to watch. These valve gear programs were written betweem 1986 and 2000 by Charles J. Dockstader P.O. Note the special form of combination lever placed horizontally. Animated GIF diagrams of steam locomotive rods, drivers, and Walschaert valve gear. This not only simplified reversing but it was realised that the gear could be raised or lowered in small increments, and thus the combined motion from the “forward” and “back” eccentrics in differing proportions would impart shorter travel to the valve, cutting off admission steam earlier in the stroke and using a smaller amount steam expansively in the cylinder, using its own energy rather than continuing to draw from the boiler. Quarter Turn Worm Gear Box Series 15/16 Date: August 2014 Page 1 of 1 Formulae and Conversion Quarter Turn Worm Gear Box ... Flow Line Valve and Controls, LLC P.O. As a harmonic valve gear, the Stephenson arrangement may be considered as optimum. Box 677; 110 Main Project Road, Schriever, LA 70395 Phone: (985) 414-6004 Fax: (985) 414-414-6072 www.flowlinevalves.com. The aim of the experiment was to find out if a valve gear having variable lead (as opposed to the constant lead of the Walschaerts' motion) would affect performance. On trial, it proved to have no advantage, although in normal service it did gain a reputation as a good performer on banks.[5][6][7][8][9]. The amount of lead remains constant over the whole range of cut offs that the gear is designed to provide. The first drawing is for Juliet with Stephenson's valve gear and shows the position of the weighshaft and link hanger pivot as given on the drawings. The Stephenson valve gear or Stephenson link or shifting link is the oldest and simplest standard design of steam locomotive valve gear.The design is normally attributed to George Stephenson.. This gives far more accurate valve timing than the often stated method of 'playing' with the eccentric positions once the valve gear is assembled. Apart from the usual couple of hours worth of tweeking to get it to run to my satisfaction, I am sure the valve gear has something missing. That's what results from simply letting my design spreadsheet (downloadble, etc.....) cope without mental exertion on my part. It is named after Robert Stephenson but was invented by his employees. Don quotes the formula for eccentric rod length to give equal lead as t+X^2/2t (Where t is the distance from the axel centre to a defined point relative to the centre of the link). The Poppet Valve gear doesn't count because it wasn't used nation wide like the Baker, Walschaerts, Stephenson valve gear. A further intrinsic advantage of the Stephenson gear not found in most other types was variable lead. It was used on the overwhelming majority of marine engines. Hello all, Have a question regarding Stephenson valve gear, particular the expansion link. For reasons of practicality two significant deviations from the prototype have been made. It is normally driven from “eccentrics” mounted on one of the drive axles and located inside the loco’s frames. Piston valves which superseded slide valves in the 20th century; 3. Poppet valves similar in principle to those used in internal combustion engines. For reasons of practicality two significant deviations from the prototype Valve gears such as Walschaert's are said to be constant lead valve gears. Depending on how the gear was laid out, it was possible to considerably reduce compression and back pressure at the end of each piston stroke when working at low speed in full gear; once again as momentum was gained and cutoff shortened, so lead was automatically advanced and compression increased, cushioning the piston at the end of each stroke and heating the remaining trapped steam in order to avoid temperature drop in the fresh charge of incoming admission steam. Tom Stamey wrote the following description for setting Stephenson valve gear on Allen Models locomotives, 20 April 2014. Stephenson Valve Gear for Climax Loco Post by peterseager » Tue Feb 09, 2010 11:04 am I am looking into building Kozo's Climax scaled X 1.5 for 5" Gauge. In mid gear the die block is in the centre of the expansion link, and experiences much less horizontal movement so insufficient motion is transferred to the extension rod to open the valves to admit steam. The cams consist 4 individual cams. Stephenson gear. Stephenson Valve Gear Computer Simulation Program Charles Dockstader has created an excellent program that simulates the operation of Stephenson Valve Gear action. The missing parts appear to be the valve stem and rocker arm. 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 all kinds of steam engine. If you haven't already done so, before you make any final decisions try to run a 7 1/4" (7 1/2") locomotive with well set valve gear (there are lots of them around). This setting information is the same for all Stephenson link valve gear. You can see what I mean at Wikipedia - Stephenson's Valve Gear. STEPHENSON’S LINK VALVE GEAR – GWR HALL 4-6-0 This kit is designed to accurately produce in 4mm scale a working model of the Stephenson’s link valve gear. Because valve gears in Britain were generally placed between the frames beneath the boiler, the extremely cramped conditions made the valve gear inaccessible for servicing. Hi, I have just received an HO Bachmann Spectrum 2-8-0 with Stephenson valve gear. Nevertheless, the fact the link needed to be bodily displaced in order to reverse meant that it required considerable vertical clearance. Check between the first and second drivers for another hole. Steam engines with Stephenson link valvegear, https://en.wikipedia.org/w/index.php?title=Stephenson_valve_gear&oldid=993139941, Creative Commons Attribution-ShareAlike License, This page was last edited on 9 December 2020, at 00:42. 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