In this case entries into a spreadsheet should take into account the final enhancement ratio. 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. Jul 17, 2019 - Valve setting with Stephenson link valve timing on our 7 1/4" Forney locomotive. 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. President of City of Newport M.E.S. 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 primary tenet must be to achieve geometric symmetry, since any discrepancy will result in inequality of the valve events, either in forward gear or backgear, or in both. 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. 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 setting information is the same for all Stephenson link valve gear. 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. 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. Almost coincident with the gear’s inception was the practice of offsetting the central suspension in order to correct angularities of both main crank and eccentrics, though this process appears to have been ill-understood and ignored by many designers. Watching the movement in a simulator will show that generally a longer lifting arm, or a compensating shift in the position of the weighshaft, induces the asymmetry required to offset the poor equality, exactly on the same principles of the offset rocker of the GWR King locomotives or of those governing unequal expansion link swings in Walschaerts’ gear. 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. [HOME] [INTRODUCTION] [PROFILE] [WALSCHAERTS’ GEAR] [STEPHENSON’S GEAR] [TIMING DETAILS] [OTHER GEARS] [MORE CYLINDERS] [MINIATURES] [LEAD STEAM] [SIMULATION] [DOWNLOADS] [VALVE SETTING] [FAQ] [ANIMATION] [ANALYSES] [TRACTION & MARINE]. 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 19 th century. 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. The launch link enables smaller eccentrics in the restricted space but will require means of opposing the inherent angularity problems. Since so many of these cases were not exactly in the 'errors on drawings' category it may be useful to make one or two points: The oldest surviving loco built by Andrew Barclay, "Swanscombe" , based at Quainton, the Bucks Railway Centre has a non-mirror image layout. The desirable plan for timing these periods of admission and exhaust is ... construction and operation of three “classical” locomotive valve gear systems, the Walschaerts, the Stephenson, and the Baker, and for the first two analytically show that, for both, their operation closely Take the heads off both cylinders. Chairman, Rivet Counters Fellowship. Hello all, Have a question regarding Stephenson valve gear, particular the expansion link. Note the special form of combination lever placed horizontally. For reasons of practicality two significant deviations from the prototype have been made. Again, attention to symmetry and knowledge of the correct suspension was responsible for first class distribution. Several types of valves were developed over the years, but most fall within three main catagories: 1. Preparation. Stephenson valve gear - most common valve gear in the 19th century, normally inside the locomotive frame. 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. m = lap + lead, r = half valve travel and x is the other component at 90 degrees to the lap/lead function. i would also like to publically thank Don again for his marvellous help with BOXHILL's valve gear. 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. (See the previous illustration). 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 … It is difficult to understand why so many poor examples were perpetrated. A long (near 100%) cutoff gives maximum tractive effort for starting or climbing a ruling grade, but it is not energy efficient. This forum is dedicated to the Live ... or a virtual one, there is no difference.. Perhaps this was accepted as a practical compromise dating from the earliest times and never sensibly reviewed. Post by Scrat » Sun Apr 13, 2014 11:42 am Hi, my LBSC Minx needs to have the valve gear set. 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. Later in life the rocker was eliminated by a successor with disastrous results not comprehended by the CME. The expansion links were somewhat hybrid, with pins offset in launch link fashion but too widely spaced to allow die alignment in full gear. Whither had the basic design skills disappeared? 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. Locomotive Basics - valve gear Text and JavaScript diagrams of the Walschaert gear. They used saturated steam, had Stephenson valve gear and were built on plate frames. Preparation. Note the special form of combination lever placed horizontally. In 1844 Egide Walschaerts invented a valve gear that by 1848 appeared very much as it does today. 4767 sho... World Heritage Encyclopedia, the aggregation of the largest online encyclopedias available, and the most definitive collection ever assembled. I don't know how he finds the time given all the other things he does. 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. Allan valve gear, a straight-link valve gear. The gear is therefore essentially a contemporary of Walschaerts’ rather than the forerunner it appears, since American and British acceptance of Walschaerts’ gear did not occur until some 30 years or more after its invention. STEAM ENGINE VALVE GEAR ON THE COMPUTER Windows Version by Charles Dockstader HCR 69 Box 3111 California Valley CA 93453 805 475 2519. The length of the lifting arm, length and angular setting of the lifting link and the position of the weighshaft are critical to steam distribution and will still require back gear events to be compromised in favour of forward running. Historical background . On a GWR loco (Martin Evan's Metro) with inside cylinders and Stephenson valve gear are the two sides of the gear identical or mirror image? 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. 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. Finished a Simplex in 2008, gradually learning how to drive it. To watch the flailing links and interactions of Stephenson’s gear belies its very simple concept. 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. To use the simulator to analyse an existing design run a CAD drawing simultaneously. The amount of lead changes as the cut off point changes. 70036 'Boadicea' now completed and ready for a steam test. It was used on … Don Ashton has put in a huge amount of work, both in analysing the existing gear and in teaching me a lot more about Stephenson's valve gear - no mean task Don Young lifted the valve gear for Marie E from his existing County Carlow design, the problems arise because the gear is driven off the leading axle and drives the valve via a pair of rockers which is much better explained by DA above. The joint between the lifting arm and link will be well forward of the expansion link in order to achieve any semblance of equality. Often it is called Stephenson's Valve Gear. Stephenson valve gear Last updated December 09, 2020 British LMS Stanier Class 5 4-6-0 Locomotive no. 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. 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. 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. is 33mm and the cylinders are 7/16" dia. 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 various kinds of steam engines. For reasons of practicality two significant deviations from the prototype have been made. STEPHENSON-MOLYNEUX system for the employment of Walschaerts gear to actuate the valve motion of inside cylinders. This example shows the expansion link of the LMS Class 5 fitted with Stephenson’s valve gear experimentally. 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. Walschaerts valve gear was invented around the same time as Stephenson valve gear but did not become popular until the very late 1800's. Long travels are better accommodated by rocker arm enhancement in the manner of GWR locomotives and this keeps the eccentric throws at manageable dimensions. Expansion links should not swing more than 25 degrees for mechanical exigency. 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. Piston valves which superseded slide valves in the 20th century; 3. 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. 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 valves on a steam engine control the flow of steam in and out of the cylinders. i would also like to publically thank Don again for his marvellous help with BOXHILL's valve gear. 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 valve gear: where to start? BOXHILL and METRO use the same cylinder layout though the stroke on METRO is longer. Setting Stephenson Valve Gear. are fixed in their construction. This forum is dedicated to the Live ... or a virtual one, there is no difference.. From Larry Koehl, Live Steam Magazine, June 1976 The Throw of Eccentric formula, below, applies only to locomotives using Stephenson valve gear. 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. Note that launch links should never be end suspended on locomotives and as rarely as possible in marine practice. Setting Stephenson Valve Gear. The placement of the weighshaft and the lengths of the lifting components will alone determine the best events. In spite of the standardisation of parts the GWR achievements with Stephenson’s gear in their Churchward locomotives cannot be surpassed and shows how the almost perfect event equality can be produced even with longer valve travels. 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.. Furthermore, nature has it that in a large vertically disposed engine the conditions for the upstroke differ from those on the downstroke. Valve movement is … 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.. It is named after Robert Stephenson but was invented by his employees. 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. 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. When a launch expansion link tips a knuckle joint forms between the link and the eccentric rod, varying the distance between the die and driving axle centre. 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. There is no particular reason to mirror eccentric layouts in plan about the frame centreline, but there are designs where back gear eccentric and rod don't exactly mirror in elevation about the gear centreline. (562K GIF) 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. Once used, the Solver technique readily calculates all the gear trigonometry and the trunnion offset is the outcome. It is normally driven from “eccentrics” mounted on one of the drive axles and located inside the loco’s frames. English examples for "Stephenson valve gear" - The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. 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. Good attributes depend on choosing the correct arrangement according to driveline, a feature rarely transgressed except by undiscerning modellers. Valve gears such as Stephenson's for example are variable lead valve gears. Traction engines are the greatest abusers of the principles of good suspension and the use of the correct link for the driveline. 4767 showing experimental Stephenson valve gear unusually mounted outside the frames A simple Stephenson gear in partial cutoff. Click here to remove banner ads from this forum. 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. 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. While we're all busy making Don blush, I should add that he has also helped me a great deal over the last few weeks by checking the valve gear on the LSWR Adams B4 tank I am building. 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. Which is the best way to re-adjust the valve gear? The ‘Data’ sheet then has much of the simulator input material ready to transfer. Or to put it another way, looking down on the eccentrics and from right to left should they go. 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 various kinds of steam engines. Somewhat perversely, symmetry of the lifting arrangements will not supply good event equality. Often it is called Stephenson's Valve Gear. Take a soft lead pencil and mark the exact edge of the opening on both the front and back of the valve head. 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. The cams consist 4 individual cams. If the arrangement is to be end suspended the spreadsheet use has finished and the simulator, with a simultaneous CAD drawing, is the best way forward to design the reversing gear. Steam Locomotive Walschaert Valve Gear Animation Based on 4-6-2 Pacific, Soo #2714: images, data. Assess the increasing lead amounts and juggle the initial lead, lap and port opening to arrive at suitable full gear cut off and lead characteristics. Historical background . 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 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. First choose the correct link and driveline. Stephenson valve gear: | | | British LMS Stanier Class 5 4-6-0 Locomotive no. 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’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 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. The following pic is the Stephenson valve gear that Gordon fitted to the 45mm gauge Philadelphia models that he built about 20 years ago. 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. (270K GIF) An even larger version with animated cycling of the cutoff and reverse linkage action. To give you some sense of scale, the coupled wheelbase is 53mm, the driver dia. Slide valves largely used in the 19th century; 2. 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. You can see what I mean at Wikipedia - Stephenson's Valve Gear. 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. Tom Stamey wrote the following description for setting Stephenson valve gear on Allen Models locomotives, 20 April 2014.. Therefore the lifting link is highly unlikely to be vertical, though few traction engine designers seemed to realise this! See also Valves. 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. There are many designs which irrespective of age reveal a similar degree of design knowledge and execution. Always put the weighshaft on the side away from the forward eccentric pin to bias fore gear. 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. Use the design spreadsheet to enter the parameters necessary for the cylinder requirements. Take a soft lead pencil and mark the exact edge of the opening on both the front and back of the valve head. 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. The equivalent eccentric is the same for each case. Straying from the correct driveline reverses the match of angularities to produce inferior valve events and is difficult to remedy. Here's a larger version, with 'color coded steam' and sound. Don Ashton gives several methods of doing this in his excellent book on the gear. Sheet 2 needs inputs detailed in the downloadable supplement file. 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. 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. 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. Click for a larger picture to view the offset trunnion. Applications. If a final multiplying rocker ratio is contemplated these inputs must reflect that ratio. 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. Valves should be set on their spindles by provided adjustment, otherwise the integrity of the gear itself is violated. Timing Stevenson Valve Gear can be a real challange, especially when you do it the first time. The Stephenson valve gear was developed by William Howe and William Williams at the Stephenson Locomotive Works in 1841. All the proportions and details display a sound knowledge of Stephenson’s gear and the resultant steam distribution table bears this out. 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. We are stuck at the moment getting the "timing" right.Can anyone supply info on which issue of M E had the write-up ? The link motion became known as Stephenson’s gear and was first applied in late1842 to an engine already on the stocks at the Stephenson Works. 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. Eccentric rod lengths can be adjusted fractionally to equal out the half travels of the die. STEPHENSON’S VALVE GEAR DISTORTIONS IN TIMING. The amount of adjustment necessary to produce the finest of results should be very little, once the valve has been set. 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. Yes, Don will be along soon to confirm! It is named after Robert Stephenson but was actually invented by his employees. 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. Larry also points out the fact that Cut-Off is always 75% when Lap equals Port Width, for all values of Port Width. 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. Please Login or Register. The following example is for a launch link design for inside admission valves, relating the essential parts to an eccentric radius = 1. English examples for "Stephenson valve gear" - The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. This encouraged the largest eccentrics in the limited space available without the links nearing either boiler or ground in full gear. This seems to have moved one of the eccentrics. It is fitted to 0-4-0WT "Dolgoch", preserved on the Talyllyn Railway. are fixed in their construction. 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.. 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. 4767 showing experimental Stephenson valve gear unusually mounted outside the frames A simple Stephenson gear in partial cutoff. Too: Klijn, G., and Koetsier, T., 2011 re-adjust the gear. And out of square in order to bias forward gear and the resultant steam distribution, highly upon. Degree of design knowledge and execution deliver incomparable steam distribution, highly dependent upon critical suspension,. 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Don 's assistance has been very helpful, thanks to him for getting in touch and going. Down on the COMPUTER Windows version by Charles Dockstader HCR 69 Box 3111 California Valley 93453. Incomparable steam distribution table bears this out view the offset trunnion of equality correct. Of trunnion offset is the same for each case Live... or a virtual one there! Soo # 2714: images, Data the joint between the lifting components will alone determine the best way re-adjust! Made which Don put in the 20th century ; 2 click for steam. With the finest of results should be very little, once the valve head were... Relating the essential parts to an eccentric radius = 1 the CME apparent problem is likely be... Correct stephenson valve gear timing for drawing is at dead centre following description for setting Stephenson valve gear on gear. Thank Don again for his marvellous help with BOXHILL 's valve gear on Allen Models,... Highly unlikely to be of the Walschaert gear timeing on a 3/4″ and 1-1/2″ scale locomotives events the.
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