4767 sho... World Heritage Encyclopedia, the aggregation of the largest online encyclopedias available, and the most definitive collection ever assembled. It is obvious that there is less to-and-fro movement at this point of the link than at the ends. At first sight, a non-technical or lay reader might wonder why a reversing gear is necessary. The die block works on a swinging arm pivoted to the inside of the frame, and movement is transmitted from this to the inner pendulum lever by an inclined coupling-rod. The action of the gear is simplicity itself. Share: Go to Turbine Lift Off! Google Both the B class and E class Double Fairlies wer… Piston valves which superseded slide valves in the 20th century; 3. A Stephenson link motion locomotive, running at high speed with the gear notched well up and the die blocks almost in the centre of the links, presents a striking parallel. Return to the GWR Information Index Page. DOUBLE GABS on the valve spindle were used in the final development of the gab gear, and the two eccentric rods were connected by a bar as shown in this diagram. 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. The locomotive is a parallel instance; taken as a whole it appears formidable and complicated, yet any average person can easily understand it if the component parts are separately considered. Steam Locomotive Walschaert Valve Gear Diagram Walschaert Valve Gear --Invented in 1844 by Egide Walschaerts, foreman of the Belgian State Railway (Diagram based on 4-6-2 Pacific, Soo #2714) 1. When the engine is moving slowly, the port need not open so soon; but when it is running quickly it is obvious that an early opening of the steam ports will help to ensure full pressure on the pistons at the beginning of the stroke, not only maintaining the speed, but also enabling an early cut-off to be made, thus utilizing the steam's expansive properties to the utmost. The idea and principles of the Stephenson link motion have been applied to other forms of valve gear. This picture shows a working demonstration model of the gear in the Science Museum, South Kensington. It is, for example, extensively used on the Great Western for two-cylinder tender and tank engines, the general efficiency of which is above question. Once the general principles are understood the various means of applying them will present no difficulty. Category: Tony's Tips, Locomotives & Miscellaneous. is no reach rod on the left hand side of course) but the rock shafts Some had the gabs pointing downwards towards the valve spindle; some had them pointing upwards; and some had one above and one below, so that they faced one another, and one engaged directly the other disconnected. Wonderful it certainly is; but complicated - certainly not. The “ahead” and “astern” positions of the eccentrics were, of course, exactly opposite, and so the treadle could not be operated unless they were moved half a turn, or the engine moved to suit. Where the cylinders are inside the frames, with valves between, or with outside cylinders having valves inside the frame, direct connexion is possible. No lap or lead could be given to the valve with this gear. This enabled them to be combined on a sleeve, which was loose on the axle. The valves on a steam engine control the flow of steam in and out of the cylinders. of the expansion link and only the reverse rod contributes to © Railway Wonders of the World 2012-20  |  Contents  |  Site Map  |  Contact Us at info@railwaywondersoftheworld.com. used here are consistent with late GWR and BR(W) usage. Eccentric Crank 2. This had projecting pins at either end, and the eccentric rod had a double “gab”, resembling two V-forks placed back to back, at the end. STEPHENSON VALVE GEAR, the joint invention of Williams and Howe in 1842, was first applied to locomotives by Robert Stephenson & Co, and is still in use throughout the world. The farther out it is the more the eccentric will “wobble” or “tumble”. form, or if you prefer use Linked In or even Facebook. Valve gears site, especially in this context the page on Stephenson's Previous owner's marks include name and date on the front end paper. It enables parts of the gear to be removed without dismantling it all, saving much time in running-shed repairs. Valves at that time had no lap; that is, they just spanned the steam ports and no more; the eccentric was therefore placed at right angles to the main crank. Piston valves which superseded slide valves in the 20th century; 3. A typical example of this was to be found in the old Stroudley “Gladstones” of the London, Brighton and South Coast Railway, where the piston rods passed over the leading coupled axle, and the valve spindles below it, the former inclining downward and the latter upward, the centre lines meeting at the middle of the crank axle. The opening time, however, still had to be the same - that is, with the crank on dead centre; and therefore, the eccentric had to be moved on ahead of the 90 deg. when the locomotive is put into forward and reverse.The 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). When the position of the expansion link This lay-out of the Stephenson link motion is used largely on the Great Western locomotives, and gives every satisfaction. The oldest diagram in the book. Daniel Gooch, the first locomotive superintendent of the Great Western, devised a link motion in which the link itself was not raised or lowered for reversing, but swung from stationary hangers in what would be mid-position in the Stephenson motion. This minimizes “lost motion” due to any wear or slackness in the parts, and also gives better valve movements when the engine is running notched up, as there are no “offset” connexions for which allowance would have to be made. 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.It is named after Robert Stephenson [2] but was actually invented by his employees. The “Rocket’s” gear worked on this principle. A short shaft with two pendulum levers is carried in a substantial bearing on top of the frame; the outside lever is connected to the valve spindle by a short link. 1.1 Indicator diagram of steam cycle 4 2.1 Newcoman atmospheric engine 9 2.2 Green steam engine 10 2.3 Jensen steam engine 12 2,4 Watt steam engine 13 2.5 Stuart steam engine 14 2.6 Stephenson Valve Gear 16 2.7 Walschaert Valve Gear 17 2.8 Flywheel 18 2.9 Sliding valve 18 2.10 Piston and piston rod 19 2.11 Crosshead 20 3.1 Project flow chart 23 Some engines will run in either direction, with the lever in the middle, and die blocks in the middle of the link; the advance of the eccentrics, due to the valve lap, is responsible for this apparent paradox. Stephenson valve gear: | | | British LMS Stanier Class 5 4-6-0 Locomotive no. On the “Rocket” and its contemporaries, this was accomplished by leaving the eccentric loose on the axle, and driving it by means of stops, one set for either way. The easiest one to use for Stephenson's is Bill Hall's. In this position, the maximum movement is transmitted to the valve spindle. Another variation derived from the Stephenson gear was the Allan straight link motion. (A Walschaert Gear section starts on page 87.) The eccentric rods were connected to the top and bottom of the link, but the link itself was placed the other way round, with the concave side towards the steam chest. This diagram shows the Stephenson link motion reversing gear, with the reverse lever set for running forward. 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). Although a Zeuner diagram is an approximation it is most useful for those wishing to see proportionally the connection between the piston and valve parameters. Its simply to enable the reader to identify and name the key parts. THE STRAIGHT LINK of Allan’s valve gear, here shown set for forward running, is moved upwards to reverse the direction of travel, and at the same time the valve-rod die block is moved downwards in the link. the reversing shaft by the lifting link, and is moved up and down Reverse Arm & Shaft 7. It is fitted to 0-4-0WT "Dolgoch", preserved on the Talyllyn Railway. When the die block is in the middle of the link it escapes the “wobble”, but is moved by the bodily swing of the link; and, this being just sufficient to move the valve and open the port at either end, steam enters the cylinders and the engine keeps going. Nutty is a valuable text and Stephenson's Link Motion. The rear end of the cylinder is open to the exhaust, the spent steam passing away by the cavity in the slide valve. FULL FORWARD. William T. James valve gear 1832, used first by Baltimore and Ohio Railroad, United States. The “box” link has no open slot, but a curved groove machined out on one side of it, in which the die block works; the eccentric rods, which are not forked, work on pins fixed in the plain side. In this position, the maximum movement is transmitted to the valve spindle. July 24, 2009 Previous Next Go to Decoders for HO Atlas Genset: November 1, 2010 Wishlist Data. (and almost everything else) on GWR Locomotives "GWR Two Cylinder This diagram shows the Stephenson link motion reversing gear, with the reverse lever set for running forward. Don Ashton's Steam Locomotive Walschaerts Valve Gear. The Stephenson valve gear remained the most popularly used valve gear on 19th-century locomotives. Link (Expansion Link) 8. [From parts 26-27, published 26 July-2 August 1935], [Read the previous article in part 26]     [Read the next article in part 27]. Check between the first and second drivers for another hole. independant of each other. Yet another arrangement is needed when the cylinders are outside and the valves on top of them. 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. Williams's idea in its original form could not be carried out, as it was mechanically impossible to couple the eccentrics themselves by a link; but “two heads are better than one”, and a Stephenson pattern-maker named Howe made the idea a working pro position by shifting the link to the ends of the eccentric rods. In 1874, New Zealand Railways ordered two types of Double Fairlie locomotives from Avonside. The next step was to provide an eccentric for each direction of movement, and fix a single gab on the end of either rod, connecting up by suitable rods to a lever on the footplate, so that the driver could engage either gab at will, with a pin in the valve spindle. gear. ALLAN’S STRAIGHT LINK MOTION, designed in 1855, made use of two eccentrics for forward and reverse gear. One advantage of this type is that the pins line up with the die blocks in full forward or backward gear, so that the movement of the valve rod follows the movement of the eccentric rod exactly; just the same, in fact, as though they were directly connected. As soon as it gets under way the driver “notches up” by bringing the reverse lever a little towards the middle. cylinders. The piston moves up and down the cylinder, in exactly the same way, whichever way the engine runs. is intermediate between mid gear and full gear then the locomotive is ahead of the crank, the engine ran forward; if 90 deg. It is fitted to 0-4-0WT "Dolgoch", preserved on the Talyllyn Railway. By Steammechanic Watch. with Already a deviant? Thus, the link motion came into being. A plate with a hole in it was fixed to the outside of each eccentric, and a collar on the axle outside of this carried a peg which fitted the hole. Gooch valve gear GOOCH’S GEAR. Slide valves largely used in the 19th century; 2. This piston-rod is moved back and forth by a piston, which is a disk moving up and down in a circular chamber closed at the ends and called a cylinder. The very earliest valves were operated by a simple tappet gear. William T. James valve gear 1832, used first by Baltimore and Ohio Railroad, United States. A similar arrangement was widely used in America when the Stephenson link motion was in vogue, before the advent of the radial gears. If the crank is on “dead centre” - that is, at the extreme end of the stroke - and the piston is up against one end of the cylinder, it must move away from that end, whether the engine goes ahead or backs. There is the regular “open” locomotive link, which has an open slot, and the fork-ended eccentric rods are coupled above and below it. #267B in the International Library of Technology. Valve gears such as Walschaert's are said to be constant lead valve gears. Steam is admitted and exhausted from either end of the cylinder by a valve, which may be of the slide or piston type. Stephenson's Valve Gear: 7mm cast white-metal kit 19 th Century swing-link version - non-working, cosmetic only Instructions HEALTH & SAFETY: The castings contain some lead. See also Valves. By means of a lever and rod, the eccentric rod could be made to engage with either pin at will; so that the eccentric either moved the valve rod direct, when the engine went ahead, or moved it through the rocking lever in the opposite direction, when the engine, of course, went backwards. Spend a bit more time with the valve gear program. This fine model in the Science Museum, South Kensington, can be operated by the public and clearly shows the application and working principles of the Gooch gear. Allan valve gear, a straight-link valve gear. You may order it from here. The original articles on these pages are mainly contractions from my book, "An Introduction to Great Western Locomotive Development", a That should be where the rocker shaft would be on a locomotive with the main driver in the third position. 1K Views. 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