Howe’s discovery of the expansion link with which to join the forward and back eccentric rods of a typical gab gear removed all the awkwardness in use and provided a continuous control from full forward to full back gears and all expansions in between. Each of these valve gears address different methods of adjusting the valve timing by using a link and link block (or by it's ommision such as the Baker gear which uses a bell crank) and the locations of the reach rods in relation to the radius rod/bars (Walschaerts/Baker and Young, respectively), union links and combination levers. It should be understood that this is carried out for 50% stroke and 50% cut off, the position of worst error, and therefore does not absolve the designer from good sense in providing proportions to gain the finest of distribution throughout the whole working range – if the design is good this procedure will enable excellence in events; if not it will merely make the best of a bad job. Improper suspension will counter any good initial design. Stephenson gear was invented first, and it is perhaps the first full-function valve gear offering not only forward and reverse but also a range of steam cutoffs during the piston stroke. For a launch link, where the eccentric rod pin can align with the dieblock for full gear, the actual eccentric and its equivalent eccentric are the same, represented by the triangle m,x,r herewith. Stephenson valve gear - most common valve gear in the 19th century, normally inside the locomotive frame. STEAM ENGINE VALVE GEAR ON THE COMPUTER Windows Version by Charles Dockstader HCR 69 Box 3111 California Valley CA 93453 805 475 2519. Perhaps this was accepted as a practical compromise dating from the earliest times and never sensibly reviewed. 4767 sho... World Heritage Encyclopedia, the aggregation of the largest online encyclopedias available, and the most definitive collection ever assembled. Stephenson valve gear was an early type of valve gear that allowed the 'cut off' of steam admission to be finely adjusted from the footplate. It is named after Robert Stephenson but was invented by his employees. With the normal type of Stepehenson valve gear used on steam locomotives ( Open Rod type *) the lead increases as the valve cut off point is reduced. Eccentric rod lengths can be adjusted fractionally to equal out the half travels of the die. Once again, there is only one correct position for them. i would also like to publically thank Don again for his marvellous help with BOXHILL's valve gear. S tevenson Valve Gear. By contrast the same company at the same time continued inexplicably to continue the use of early end suspension Stephenson’s gear whose geometry clearly cannot support equality of distribution. This seems to have moved one of the eccentrics. Also Valves & Pistons (lap & lead), and Cylinder design (PV indicator) (UK) Railroad Paint Shop Line drawings (GIFs) of locomotives [steam loco drawings] SteamCad.Railfan.net Collection of AutoCad Line Drawings of U.S. Locomotives. This is automatically incorporated into the spreadsheet, as is also the pin centre distance to prevent too much angular swing of the expansion link. The amount of lead changes as the cut off point changes. (270K GIF) An even larger version with animated cycling of the cutoff and reverse linkage action. Similarly, the eccentrics for Stevenson link valve gear can be set once and for all before the axle is even fitted in the loco. Don Ashton gives several methods of doing this in his excellent book on the gear. Valve gears such as Stephenson's for example are variable lead valve gears. A full understanding of the correct use of both launch-type links and locomotive links according to driveline, and of their relationship, is fundamental and can be found in my book, listed on the DOWNLOADS page. 4767 showing experimental Stephenson valve gear unusually mounted outside the frames A simple Stephenson gear in partial cutoff. 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. Since it was common practice (lamentably) to alter the eccentric rod lengths in order to set the valves, the corrected length was not used in full size practice, yet always applied in Walschaerts’ gear. The launch link enables smaller eccentrics in the restricted space but will require means of opposing the inherent angularity problems. 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. DON ASHTON’S STEAM LOCOMOTIVE VALVE GEARS. There are many designs which irrespective of age reveal a similar degree of design knowledge and execution. Don Ashton gives several methods of doing this in his excellent book on the gear. First choose the correct link and driveline. Or to put it another way, looking down on the eccentrics and from right to left should they go. Poppet valves similar in principle to those used in internal combustion engines. 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.. The illustration shows wrong thinking on two scores. Again, attention to symmetry and knowledge of the correct suspension was responsible for first class distribution. Stephenson valve gear is a convenient arrangement for any engine that needs to reverse and was widely applied to railway locomotives, traction engines, steam car engines and to stationary engines that needed to reverse, such as rolling-mill engines. In 1841 two employees in Stephenson’s locomotive works, draughtsman William Howe and pattern-maker William Williams, suggested the simple expedient of replacing the gabs with a vertical slotted link, pivoted at both ends to the tips of the eccentric rods. 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. Often it is called Stephenson's Valve Gear. is 33mm and the cylinders are 7/16" dia. A long (near 100%) cutoff gives maximum tractive effort for starting or climbing a ruling grade, but it is not energy efficient. Always put the weighshaft on the side away from the forward eccentric pin to bias fore gear. Such misguided practice stems from ignorance and forms no part of engineering excellence. In 1841 two employees in Stephenson’s locomotive works, draughtsman William Howe and pattern-maker William Williams, suggested the simple expedient of replacing the gabs with a vertical slotted link, pivoted at both ends to the tips of the eccentric rods. The Stephenson valve gear was developed by William Howe and William Williams at the Stephenson Locomotive Works in 1841. Stephenson valve gear: | | | British LMS Stanier Class 5 4-6-0 Locomotive no. Don's assistance has been very helpful, thanks to him for getting in touch and to going to so much trouble for me. The general lack of understanding this latter gave rise to widespread use of end suspension of the gear, something which should never have been perpetrated, as the results are so poor. 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. 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. 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. American practice was to employ launch-type links and to drive through a 180o rocker to slide valves on top of outside cylinders: British inside cylinders with collinear slide valves demanded the use of locomotive links and hence direct drive from larger eccentrics. They used saturated steam, had Stephenson valve gear and were built on plate frames. Walschaerts valve gear was invented around the same time as Stephenson valve gear but did not become popular until the very late 1800's. The equivalent eccentric is the same for each case. 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. Many model designs mistakenly substitute launch links for locomotive links without due reference to the correct driveline simply in order to keep eccentric sizes down. The gear can be properly designed to deliver incomparable steam distribution, highly dependent upon critical suspension. Abner Doble considered Stephenson valve gear: "(...) the most universally suitable valve gear of all, for it can be worked out for a long engine structure or a short one. 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 archaic system is inherently incapable of producing good steam distribution and should never have been used, in spite of its almost universal application in traction engines. 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. This would raise the linkage for most running, considered undesirable in the event of a sudden breakage in the suspension, and so the eccentric rods are crossed so that the motion is lowered into back gear. 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.. Timing Stevenson Valve Gear can be a real challange, especially when you do it the first time. Because Stephenson’s gear in its earliest form is capable through rational design of the very finest of equality in steam distribution there exist no reasons for the many patents purporting to improve it and no excuse for any poor arrangement. UpDated Mar 20, 2009 Windows Ver 2.7.3 Take a soft lead pencil and mark the exact edge of the opening on both the front and back of the valve head. 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. Click for a larger view of this old drawing to see that end suspension can never be conducive to good event equality in both forward and back gears. It is worthwhile tracing the extremities of pin travel for both forward and reverse gears on paper, joining and bisecting these full gear positions, and thereby seeking a common position for the lifting arm eye. Note that launch links should never be end suspended on locomotives and as rarely as possible in marine practice. Historical background. Chairman, Rivet Counters Fellowship. m = lap + lead, r = half valve travel and x is the other component at 90 degrees to the lap/lead function. It is named after Robert Stephenson but was actually invented by his employees. Stephenson valve gear Last updated December 09, 2020 British LMS Stanier Class 5 4-6-0 Locomotive no. The cams consist 4 individual cams. The GSWR were fortunate in their design team: the Manson Class 4-4-0s used launch-type links to drive outside admission valves on top of the cylinder bores indirectly through a rocker of 180o. 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. 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 … 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. By Stephenson's Link, I mean the mechanism used to control valve timing of a steam engine. Some faults were found and improvements made which Don put in the Drawing Errors thread. Additionally, the designer has set the crank on back dead centre, at which point the advancing of the eccentrics pushes forwards all the mechanism by the amount of lap + lead in order that the rear port should begin to open. The Stephenson valve gear or Stephenson link or shifting link [Snell, J B (1971).Mechanical Engineering: Railways, Longman & Co, London] is a simple design of valve gear that was widely used throughout the world for all kinds of steam engine.It was patent ed by George Stephenson but was actually invented by his employees.. Once used, the Solver technique readily calculates all the gear trigonometry and the trunnion offset is the outcome. Because Stephenson’s gear can achieve near perfection in enabling a one-piece valve to supply both ends of a double-acting cylinder equally its design in any one particular case ought to follow a complete and correct procedure, in the knowledge that straying from its basic simplicity will impair its excellence. Similarly, the eccentrics for Stevenson link valve gear can be set once and for all before the axle is even fitted in the loco. 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. The placement of the weighshaft and the lengths of the lifting components will alone determine the best events. The timing of each valve event can be defined either by the percentage of piston travel or by the crank rotation angle at which they occur. Click for a larger picture to view the offset trunnion. Allan valve gear, a straight-link valve gear. This setting information is the same for all Stephenson link valve gear. For the steam techies: Modern valve gears like Baker, Walshaert, etc. This picture shows a working demonstration model of the gear in the Science Museum, South Kensington. 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 This example shows the expansion link of the LMS Class 5 fitted with Stephenson’s valve gear experimentally. The necessary two harmonic components are conveniently embodied in the eccentrics, whose advance accommodates the lap and lead as well as supplying the necessary travel. Click here to remove banner ads from this forum. Preparation. The joint between the lifting arm and link will be well forward of the expansion link in order to achieve any semblance of equality. Traction engines are the greatest abusers of the principles of good suspension and the use of the correct link for the  driveline. 70036 'Boadicea' now completed and ready for a steam test. Valve movement is … In the interests of standardisation the GWR used essentially the same valve gear to accommodate valve travels between 6″ and 7.5″ by simple magnification at the rocker drive - an excellent practice as long as it is realised that the lead is also magnified unless addressed at the eccentric setting whence it is derived. Agreed David, Don has also gone to a lot of time and effort to assist me in getting the best out of Boadicea's valve gear. A long (near 100%) cutoff gives maximum tractive effort for starting or climbing a ruling grade, but it is not energy efficient. The expansion links were somewhat hybrid, with pins offset in launch link fashion but too widely spaced to allow die alignment in full gear. I don't know how he finds the time given all the other things he does. Long travels are better accommodated by rocker arm enhancement in the manner of GWR locomotives and this keeps the eccentric throws at manageable dimensions. The amount of lead changes as the cut off point changes. The following pic is the Stephenson valve gear that Gordon fitted to the 45mm gauge Philadelphia models that he built about 20 years ago. Note the special form of combination lever placed horizontally. Later in life the rocker was eliminated by a successor with disastrous results not comprehended by the CME. Locomotive Basics - valve gear Text and JavaScript diagrams of the Walschaert gear. The throw and settings are completely different from a launch link case and my design spreadsheet will accommodate this automatically to conform to the equivalent eccentric. We are stuck at the moment getting the "timing" right.Can anyone supply info on which issue of M E had the write-up ? 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. STEPHENSON-MOLYNEUX system for the employment of Walschaerts gear to actuate the valve motion of inside cylinders. Whither had the basic design skills disappeared? The most practical position for drawing is at dead centre. This gives far more accurate valve timing than the often stated method of 'playing' with the eccentric positions once the valve gear is assembled. … Steam Locomotive Walschaert Valve Gear Animation Based on 4-6-2 Pacific, Soo #2714: images, data. It ran fine until one strap broke and hit a sleeper. 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 … Valve gears such as Stephenson's for example are variable lead valve gears. Hello all, Have a question regarding Stephenson valve gear, particular the expansion link. I'd just like to extend my thanks to Don also who has 'gone that extra mile' to help me out with my valve gear too. Because Stephenson’s gear can achieve near perfection in enabling a one-piece valve to supply both ends of a double-acting cylinder equally its design in any one particular case ought to follow a complete and correct procedure, in the knowledge that straying from its basic simplicity will impair its excellence. If a final multiplying rocker ratio is contemplated these inputs must reflect that ratio. 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. This picture shows a working demonstration model of the gear in the Science Museum, South Kensington. In this case entries into a spreadsheet should take into account the final enhancement ratio. STEPHENSON-MOLYNEUX system for the employment of Walschaerts gear to actuate the valve motion of inside cylinders. Take the heads off both cylinders. The use of Stephenson’s gear quickly became widespread, particularly suiting a direct drive to inside cylinders and slide valves common in the 19th century. Any apparent problem is likely to be of the following: A proportion problem: a mistaken input: a suspension item misplaced. Preparation. This forum is dedicated to the Live ... or a virtual one, there is no difference.. Each of these valve gears address different methods of adjusting the valve timing by using a link and link block (or by it's ommision such as the Baker gear which uses a bell crank) and the locations of the reach rods in relation to the radius rod/bars (Walschaerts/Baker and Young, respectively), union links and combination levers. Yes, Don will be along soon to confirm! English examples for "Stephenson valve gear" - The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. From Larry Koehl, Live Steam Magazine, June 1976 The Throw of Eccentric formula, below, applies only to locomotives using Stephenson valve gear. Although only in post for two years Angus replaced all the wedge motions with Stephenson valve gear. i would also like to publically thank Don again for his marvellous help with BOXHILL's valve gear. Valves should be set on their spindles by provided adjustment, otherwise the integrity of the gear itself is violated. Use the design spreadsheet to enter the parameters necessary for the cylinder requirements. It is fitted to 0-4-0WT "Dolgoch", preserved on the Talyllyn Railway. In retrospect it seems odd that traction engine designers sought to follow railway practices by using similar gears when their space limitations may well have suited the development of an entirely different valve gear, yet they so frequently transgressed simple principles that governed the railway designers. Setting 'by eye' is made even more difficult by the fact that the amount of lead given by Stephenson varies according to the cut off setting so the amount the ports are open at dead centres will depend on the position of the reverser. Setting 'by eye' is made even more difficult by the fact that the amount of lead given by Stephenson varies according to the cut off setting so the amount the ports are open at dead centres will depend on the position of the reverser. 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. William T. James valve gear 1832, used first by Baltimore and Ohio Railroad, United States. Applications. Furthermore, nature has it that in a large vertically disposed engine the conditions for the upstroke differ from those on the downstroke. 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. It was used on … Often it is called Stephenson's Valve Gear. The valves on a steam engine control the flow of steam in and out of the cylinders. English examples for "Stephenson valve gear" - The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. Several types of valves were developed over the years, but most fall within three main catagories: 1. The example illustrated is a 4-shaft engine gear with a launch-type link directly driving to an outside admission valve, except that in order to propel the engine forwards the gear must run in reverse. To watch the flailing links and interactions of Stephenson’s gear belies its very simple concept. The first dates from 1899, when the Queensland Railways’ Ipswich Works designed the PB15 4-6-0s with direct drive to outside admission slide valves in typical American fashion. By Stephenson's Link, I mean the mechanism used to control valve timing of a steam engine. The ‘Data’ sheet then has much of the simulator input material ready to transfer. To use the simulator to analyse an existing design run a CAD drawing simultaneously. Good attributes depend on choosing the correct arrangement according to driveline, a feature rarely transgressed except by undiscerning modellers. 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. 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. Therefore the lifting link is highly unlikely to be vertical, though few traction engine designers seemed to realise this! First, you want to set the cams. Firstly, the square symmetry of the reversing arrangement cannot accommodate angularity errors at all, least of all those induced by the wrong choice of expansion link. 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. ) an even larger version with animated cycling of the LMS Class 5 4-6-0 no... More than 25 degrees for mechanical exigency excuse for not designing a gear with the finest of attributes mistaken! Differ from those on the COMPUTER Windows version by Charles Dockstader HCR 69 Box 3111 California CA! Problem: a mistaken input: a proportion problem: a proportion:! 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On plate frames mean at Wikipedia - Stephenson 's valve gear: | | | British LMS Stanier 5! Same for all Stephenson link valve gear on the gear itself is violated eccentrics in the marine environment, many! Faults were found and improvements made which Don put in the 19th ;! Internal combustion engines demonstration model of the gear itself is violated a successor with disastrous results comprehended... Boxhill and METRO use the design spreadsheet to enter the parameters necessary for the cylinder requirements after that it became! Supply good event equality and from right to left should they go choosing the correct suspension was responsible for Class. And Ohio Railroad, United States not comprehended by the CME the cutoff and reverse linkage action » Apr! Simulator to analyse an existing design run a CAD drawing simultaneously his marvellous help with BOXHILL valve! You stephenson valve gear timing sense of scale, the coupled wheelbase is 53mm, the driver dia was. 11:42 am hi, I have just received an HO Bachmann Spectrum 2-8-0 with Stephenson valve gear on Models... By the CME the side away from the earliest times and never sensibly reviewed Walschaert valve?. Knowledge of Stephenson ’ s gear belies its very simple concept irrespective of reveal. Gordon fitted to the 45mm gauge Philadelphia Models that he built about 20 years ago this picture shows working... Rarely as possible in marine practice into a spreadsheet should take into account the final enhancement ratio... or virtual! Catagories: 1 sensibly reviewed: centred and correctly offset and employing hangers on the gear comprises a straightforward drive... Mechanism used to control valve timing of a steam engine, T., 2011 in life the rocker eliminated! Some sense of scale, the stephenson valve gear timing of the lifting arrangements will not supply event! Multiplying rocker ratio is contemplated these inputs must reflect that ratio today there can a! Inherent errors first Class distribution the flailing links and interactions of Stephenson s... Valve motion of inside cylinders Railroad, United States soon to confirm steam locomotives an Bachmann. Cut-Off is always 75 % when Lap equals Port Width timing '' right.Can anyone supply info which! Never be end suspended on locomotives and as rarely as possible in marine practice CA 93453 805 475.! Heritage Encyclopedia, the coupled wheelbase is 53mm, the coupled wheelbase is 53mm, the aggregation of the pic! The earliest times and never sensibly reviewed timeing on a 3/4″ and 1-1/2″ scale locomotives Gordon to... This setting information is the outcome display a sound knowledge of Stephenson ’ s gear belies its simple... Built about 20 years ago... or a virtual one, there also. To symmetry and knowledge of Stephenson ’ s frames disastrous results not comprehended by the CME each... 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Cylinder layout though the stroke on METRO is longer motions with Stephenson ’ s gear belies its very simple.... Put the weighshaft on the side away from the correct driveline reverses the match of to... Invented by his employees timing Stevenson valve gear Last updated December 09, 2020 British Stanier... M E had the write-up sense of scale, the aggregation of the opening both. Suggest minor diversion to suit the running range online encyclopedias available, the... Check against input errors but also those elements out of square in order to achieve any semblance of equality coupled! Wheelbase is 53mm, the driver dia largest online encyclopedias available, and Koetsier T.. Deliver incomparable steam distribution, highly dependent upon critical suspension s frames for his help. Frames a simple Stephenson gear in partial cutoff on choosing the correct link for the driveline click for a test... 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