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stephenson valve gear calculation

29th Dec 2020

It is named after Robert Stephenson[2] but was invented by his employees. To give you some sense of scale, the coupled wheelbase is 53mm, the driver dia. STEPHENSON-MOLYNEUX system for the employment of Walschaerts gear to actuate the valve motion of inside cylinders. This concept can be used on other valve gears. 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. It is normally driven from “eccentrics” mounted on one of the drive axles and located inside the loco’s frames. 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. The valves on a steam engine control the flow of steam in and out of the cylinders. The Throw of Eccentric formula, below, applies only to locomotives using Stephenson valve 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.. Of the many varieties of locomotive valve gears, two principal type played important role. 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 entire wiki with photo and video galleries for each article The cams STEAM ENGINE VALVE GEAR ON THE COMPUTER Windows Version by Charles Dockstader HCR 69 Box 3111 California Valley CA 93453 805 475 2519. In the United Kingdom, locomotives having Stephenson valve gear normally had this mounted in between the locomotive frames. The amount of lead remains constant over the whole range of cut offs that the gear is designed to provide. A Note on Stephenson’s Valve Gear and its Analysis in the 1850s. The Baker valve gear had one operating advantage over the Walschaerts in that it could be set up for a larger valve w/longer valve travel, 8-1/2" vs. about 7" for Wal., and was generally more rugged and could operate a heaver valve better. The valve gear is for an Isle of Wight O2 loco. Stephenson Valve Gear Computer Simulation Program Charles Dockstader has created an excellent program that simulates the operation of Stephenson Valve Gear action. 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. 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. Tom Stamey wrote the following description for setting Stephenson valve gear on Allen Models locomotives, 20 April 2014. Slide valves largely used in the 19th century; 2. 1920 Purdue University treatise on locomotive boiler and engine design, construction, and operation. 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. In order to address these problems two main variants were developed: In the Gooch valve gear (invented by Daniel Gooch in 1843) the reversing and cut-off functions were achieved by raising or lowering a radius rod which connected the valve-rod to a "stationary" link pivoting around a fixed point. Abner Doble[4] 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. Its use on engines in which all the cylinders lie in one plane, represents, in the belief of the writer, the best choice." Another benefit of the Stephenson gear, intrinsic to the system, is variable lead: usually zero in full gear and increasing as cutoff is shortened. Once again, the Allan gear was not often used in the UK but fairly common on the Continent. 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. 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). In my previous post, I mentioned Harry Allin's locomotives, a Dart and a Virginia, both in 7 1/4" gauge and both with Stephenson's valve gear. Another valve gear animation in Blender: a Stephenson valve gear based on the Furness Railway K2. 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 following pic is the Stephenson valve gear that Gordon fitted to the 45mm gauge Philadelphia models that he built about 20 years ago. Model that took me ~20 hours for doing it and 3 hours for making the movie. pressure relief valve orifice area and maximum available flow. It is named after Robert Stephenson but was actually invented by his employees. Piston valves which superseded slide valves in the 20th century; 3. 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). This picture shows a working demonstration model of the gear in the Science Museum, South Kensington. Share: Go to Turbine Lift Off! 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. 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. 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. Longer eccentric rods and a shorter link reduce this effect. 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. VALVE GEAR PROGRAM INSTRUCTIONS RUNNING IN MICROSOFT WINDOWS These Windows valve gear programs were written betweem 1998 and 2007 by Charles J. Dockstader HCR 69 Box 3111, California Valley, CA 93453 The Allan straight link valve gear (invented by Alexander Allan in 1855) combined the features of the Stephenson and Gooch gears. Lesson 1: Gear Pump Basics Displacement (D) – The displacement of a rotary gear pump is the volume displaced during one complete revolution of the gears. Stephenson Valve Gear Computer Simulation Program Charles Dockstader has created an excellent program that simulates the operation of Stephenson Valve Gear action. Details of the gear differ principally in the arrangement of the expansion link. Note the special form of combination lever placed horizontally. 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