To watch the flailing links and interactions of Stephenson’s gear belies its very simple concept. This forum is dedicated to the Live ... or a virtual one, there is no difference.. Click for a larger picture to view the offset trunnion. Later in life the rocker was eliminated by a successor with disastrous results not comprehended by the CME. Again, attention to symmetry and knowledge of the correct suspension was responsible for first class distribution. It is named after Robert Stephenson but was actually 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. Tom Stamey wrote the following description for setting Stephenson valve gear on Allen Models locomotives, 20 April 2014.. Often it is called Stephenson's Valve Gear. Straying from the correct driveline reverses the match of angularities to produce inferior valve events and is difficult to remedy. 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. For the steam techies: Modern valve gears like Baker, Walshaert, etc. Tom Stamey wrote the following description for setting Stephenson valve gear on Allen Models locomotives, 20 April 2014.. 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. Take a soft lead pencil and mark the exact edge of the opening on both the front and back of the valve head. Often it is called Stephenson's Valve Gear. Therefore the lifting link is highly unlikely to be vertical, though few traction engine designers seemed to realise this! Valve gears such as Stephenson's for example are variable lead valve gears. 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. Valve movement is … Welcome Guest. Applications. 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. 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. Locomotive Basics - valve gear Text and JavaScript diagrams of the Walschaert 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. The ‘Data’ sheet then has much of the simulator input material ready to transfer. 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. Note that launch links should never be end suspended on locomotives and as rarely as possible in marine practice. For reasons of practicality two significant deviations from the prototype have been made. Allan valve gear, a straight-link valve gear. 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. I don't know how he finds the time given all the other things he does. 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. Steam Locomotive Walschaert Valve Gear Animation Based on 4-6-2 Pacific, Soo #2714: images, data. Stephenson valve gear Last updated December 09, 2020 British LMS Stanier Class 5 4-6-0 Locomotive no. Whither had the basic design skills disappeared? 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 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. The employment of locomotive links involves larger eccentrics because the die never approaches the line of the eccentric rod pins, usually by a factor of almost 2. 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. are fixed in their construction. 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. 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. Resort to the simulator may then suggest minor diversion to suit the running range. 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. 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. If a final multiplying rocker ratio is contemplated these inputs must reflect that ratio. 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. 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 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. 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 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 … Which is the best way to re-adjust the valve gear? The lifting arm needs to be set oddly out of square in order to bias forward gear events at the expense of backward running. This is automatically incorporated into the spreadsheet, as is also the pin centre distance to prevent too much angular swing of the expansion link. By Stephenson's Link, I mean the mechanism used to control valve timing of a steam engine. Note the special form of combination lever placed horizontally. You can see what I mean at Wikipedia - Stephenson's Valve Gear. (See the previous illustration). Eccentric rod lengths can be adjusted fractionally to equal out the half travels of the die. The expansion links were somewhat hybrid, with pins offset in launch link fashion but too widely spaced to allow die alignment in full gear. 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. Finished a Simplex in 2008, gradually learning how to drive it. Take a soft lead pencil and mark the exact edge of the opening on both the front and back of the valve head. It is difficult to understand why so many poor examples were perpetrated. The valves on a steam engine control the flow of steam in and out of the cylinders. 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 following pic is the Stephenson valve gear that Gordon fitted to the 45mm gauge Philadelphia models that he built about 20 years ago. 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. They used saturated steam, had Stephenson valve gear and were built on plate frames. English examples for "Stephenson valve gear" - The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. 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. 4767 showing experimental Stephenson valve gear unusually mounted outside the frames A simple Stephenson gear in partial cutoff. All the proportions and details display a sound knowledge of Stephenson’s gear and the resultant steam distribution table bears this out. They used saturated steam, had Stephenson valve gear and were built on plate frames. Forward eccentrics are usually nearest to frame. 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. 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. Always put the weighshaft on the side away from the forward eccentric pin to bias fore gear. The gear can be properly designed to deliver incomparable steam distribution, highly dependent upon critical suspension. It ran fine until one strap broke and hit a sleeper. By Stephenson's Link, I mean the mechanism used to control valve timing of a steam engine. The amount of adjustment necessary to produce the finest of results should be very little, once the valve has been set. It is named after Robert Stephenson but was invented by his employees. 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. Stephenson valve gear: where to start? 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.. Some faults were found and improvements made which Don put in the Drawing Errors thread. English examples for "Stephenson valve gear" - The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. Slide valves largely used in the 19th century; 2. Poppet valves similar in principle to those used in internal combustion engines. 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. It was used on … 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. 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. 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. Once used, the Solver technique readily calculates all the gear trigonometry and the trunnion offset is the outcome. 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 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 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 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. Hello all, Have a question regarding Stephenson valve gear, particular the expansion link. 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. is 33mm and the cylinders are 7/16" dia. Sheet 2 needs inputs detailed in the downloadable supplement file. After that it quickly became the most popular valve gear on steam locomotives. 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. 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. Don Ashton gives several methods of doing this in his excellent book on the gear. John Baguley: 22/07/2010 09:40:07: 467 forum posts 50 photos: Valve setting was in Volume 96 Issue 2390. Once again, there is only one correct position for them. are fixed in their construction. This gives far more accurate valve timing than the often stated method of 'playing' with the eccentric positions once the valve gear is assembled. There are many designs which irrespective of age reveal a similar degree of design knowledge and execution. See also Valves. 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. 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. Chairman, Rivet Counters Fellowship. Setting Stephenson Valve Gear. Historical background . 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. 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. Timing Stevenson Valve Gear can be a real challange, especially when you do it the first time. 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.

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