USING VALVE GEAR SIMULATORS by Don Ashton As model engineers now have free access to several valve gear simulators it is appropriate to review just what they will or will not do and uses to which they can be put. With good judgment, these qualities may be varied to offset other irregularities inherent in transforming rotary into lineal motion. (A Standard BR Class five is very similar in most respects to the LMS version excepting the valve gear itself, which is geometrically inferior to that of the older engine.). The events, however, prove by simulation to be magnificent, addressed to the heavy gradients expected without much compromise in reverse. In 1844 Egide Walschaerts invented a valve gear that by 1848 appeared very much as it does today. England. This then sets the leads exactly equal once the valve is also set so. Even 1″ either side of the 13.8″ given length has but little influence and leaves the hanger arrangement fully in charge of the difficulties. Note that ‘x’ is the 90 degree component obtained from the equivalent eccentric. three cylinders and outside Walschaerts' valve gear. Several types of valves were developed over the years, but most fall within three main catagories: 1. The originaldesign was taken from a Consolationfreight engine on the L. S. & M. S., andwas laid out and made to lYz ins. Holcroft was evidently aware of this and promoted it on the Southern Railway, choosing a rather cramped arrangement which did it no special favours. Not only does this impose mediocre performance but the shortness of full gear cut off often leads to poor starting. Reset valves at each modification to ensure that the desired effect has taken place. Symmetry abounds. Remember that Walschaerts knew nothing about long travels and inside admission valves at the time of invention: some modern designs struggle to emulate the best of those dating from early in the 20th century. I did an article on Walschaerts' for Romulus in Engineering in Miniature, May 2007. This is not the whole story, of course, as the designer must be aware of all the accelerations and decelerations throughout a full cycle; the emphasis in design must be on timing values and not necessarily on distances. Walschaerts valve gear is wonderful stuff on an engine, it adds complexity and detail under the footplate. Symmetrical layouts for short travel outside admission valves reduce the problems dramatically irrespective of scale. In the end Swindon managed a very creditable performance under the circumstances. B3/4 1367 (CFF Historic 1) by Jean-Daniel David 88 44 B 3/4 1367. Frequently one has to set the valve carefully in order to maximise events, but this case required no setting whatsoever to realise an excellent fore gear pattern with adequacy in back gear. The swings of a hanger or the constraints of a die must be arranged to balance as a whole so that the valve operates as desired, and may demand expansion link swings disparate by 2o or more. The design becomes an exercise in deciding at what running cut off it is best to equalise events without too much sacrifice elsewhere. Of itself, equal angles of expansion link swing cannot deliver equal movements of the valve. The simulator results quickly reveal the levels of equality between both ports. The pattern of events produced by the gear, particularly the differences column, should reflect those obtained by either the large gear model of the drawing office or those taken manually from a completed engine. Simulation verifies the faith placed on introduction to the drawing. The B1 gear benefits from occupying a large symmetrical envelope and the parts contain dimensions never finer than 1/32nd″, and even these prove by CAD to be precise. Basic formulae for Walschaerts’ initial design. In designing the initial parameters it is perhaps wise to realise that at the time of its invention valve travels were short, with slide valves necessary for outside admission. kennedy valve 24" r/w rts bevel gear flange ends general dimensions model ks-rw/2638 7561bmss a b c d e f g h kennedy valve/ks-rw 14" - 24" 6-5 updated 01/25/13 Lead is such a very small amount within a large mechanism that it behoves the designer and builder to observe critical accuracy. Inside Walschaerts' isn't common, the Great Western Castles & Kings used it; the geometry is exactly the same as outside gear. Cyclopedia of locomotive engineering, with examination questions and answers; a practical manual on the construction care and management of modern … In fact what is happening is the balancing of one component’s distortions against those of the other component. This describes the procedure for adjusting the slide valves on the simplified Walschaerts valve gear as fitted to certain Roundhouse locomotives, so that they open and close at the correct time. An example of the difficulties attending compaction of the envelope is to be found in the GWR 1500 Class 0-6-0 engines of which only 10 were made. LMS type fitting of the return crank is by four studs in the crank pin, though it is a tongue and slot arrangement that takes the driving loads, not the studs. The actual angular setting for the return crank and eccentric rod will now depend on the expansion link position and its tailpin. Unfortunately this often gives rise to the misconception that they can be treated separately in order to understand their functions. Greater pitch circles and expansion link swings are demanded by the use of inside admission and designers of more modern locomotives require skill and ingenuity to avoid poor steam distribution. Model Steam Trains Stirling Engine Old Gas Stations Steam Engine Steam Locomotive Gears Dankest Memes Steampunk Models In retrospect this proves a doubtful way to deal with long valve travels and the events are generally inferior to those produced 20 years earlier. [It ought to be pointed out that the lengths of the eccentric rod and return crank have been recalculated to maintain lead equality at each alteration.]. The picture shows a suspension that cannot support equality of valve excursions and there are many other examples. Bill Hall’s programs serve both Walschaerts’ and Stephenson’s gears in various forms and are particularly easy to use by the novice. Tel 01302 328035 Fax 01302 761312 Email: firstname.lastname@example.org www.roundhouse-eng.com. The inventor's name was (Egide) Walschaerts (pronunciation: ay-gee-da val-sherts), but the design was patented under the name Walschaert for political reasons.Ref: Publications Style Manual, Pennsylvania Railroad Technical and … Saved by Dragan Hodak. The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle. It is not often that a motion drawing adequately and distinctly provides all the information necessary in order to reconstruct the gear in CAD, but Thompson’s LNER B1 4-6-0 is one such. Whilst the B1 barely manages a constant 1/8th″ the Hall is 1/8th″ negative in full gear and does not reach 1/8th″ positive until the middle of its cut off working range. The larger BR Standard Classes, though not employing the upper half for forward running, gave more space to the hanger arrangement but failed to optimise the geometry. On display. DON ASHTON’S STEAM LOCOMOTIVE VALVE GEARS. By comparison the backset is much less sensitive, though useful for this purpose. Egide Walschaerts was the chief engineer of the main workshop of the Belgian State Railways in Brussels-Midi. The rather spindly rods are more than capable of taking the light loads involved. All three contestants proved worthy of building in large numbers. Undoubtedly computer simulation could have improved the events numerically, but the skills of the LNER team have produced a good gear whose performance in practice might gain little from high-tech tinkering. It shows forward gear and the expansion link near mid swing, yet the awkward placing of weighshaft and lifting components denies symmetry in operation. The theoretical full valve travel of 6.716″ compares very favourably with the 6.562″ recorded in the official table of events. Col train4.jpg 1,966 × 1,394; 351 KB. Long travel valves exacerbate the problems, none of which could be conjectured at the time of the invention. You will need to flesh out the geometry, and if you use a double slide bar arrangement there is little room for the combination lever to align with the valve rod. 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 20th century, both gears were invented almost simultaneously. Numerous and misguided have been the modellers’ attempts to rectify the situation, since the proponents little understood the problems of compaction. Mechanically, its greatest disadvantage is that of having to lift the whole mechanism in order to reverse the motion or to achieve intermediate expansion working. Slight variations may be made in the cutoff points as covered by the preceding paragraph but an independent adjustment cannot be made except by shifting the location of the suspension point which is preferably determined by a model. The backset has to be reduced by half in order to equate port openings, yet the cut offs remain similar at 78.14% and 72.54%. To add to this, the working of the die in the upper half of a curved ‘rocker’ (expansion link) is quite different in detail. Typical of the design of small scale engines, the use on moving empty stock in and out of Paddington station of a 1500 is ignored in the duties expected of a smaller version, which equate more nearly to an express passenger locomotive. Loc de la série B 3/4 1303–1369. It will be found in most cases that given equal depths in gear for forward and reverse working the percentage of cut offs in back gear will exceed those in forward gear by as much as 6%. Tracing each item in the chain provides an overview of their functions and specific problems that can influence their design. CP Class D-10-h No 1057 (8062239700) .jpg 1,280 × 960; 923 KB. Question: Can I use only one eccentric for a reversing steam engine, WITHOUT a slip eccentric. The BR Class 7 motion owes much to American layout practice with equiangular expansion link swings and a radius rod hanger forward of the trunnion. Those examples of hanger suspension, whether in front of or behind the trunnion, introduce other complexities and require very careful placement to obtain good working in both forward and reverse. The radius rod slopes at 0.1 degrees! Built properly, every modeller will ohh and ahh over it. I'm planning to make one using pneumatics components for the cylinders. Moving the point of suspension (1″) on the radius rod quickly disturbs the port openings, the cut offs much less so, whereas shifting the weighshaft 1″ horizontally either side equalises port openings at the expense of cut off disparity. The worldwide use of a hanger for the rear end of the radius rod was extensive, generally raising the number of badly orientated ones, and simulation with experience seems the only sensible way to go. The calculations at this stage assume equiangular swings of the expansion link. Walschaert Valve Gear -- Invented in 1844 by Egide Walschaerts, foreman of the Belgian State Railway (Diagram based on 4-6-2 Pacific, Soo #2714) And joy of joys, the Garratt has four sets. All those rods form a natural focal point. It is simplistic to regard the crosshead contribution as the similar triangles portrayed in most texts and it is possible to employ the anchor link to delay or advance this component relative to that from the expansion link in order to equate the events of one port with those of the other. Piston valves which superseded slide valves in the 20th century; 3. On the other hand, cut offs of 78.92% and 75.53% from a backset angular increase of some 5.5o are little different in equality from standard, giving the same port opening inequality from angular swings of 24.6o and 26.23o. The correct angular setting for the return crank has the pins at 90o to a line passing from the tailpin to the axle centre. Actuators use electrical, pneumatic or hydraulic energy to open and close elements of a valve. Of the many varieties of locomotive valve gears, two principal type played important role. All this is largely relative to the production of equiangular swings, which may or may not be best for a particular design. Animation of the Walschaerts valve gear mechanism used in steam locomotives to control the motion of the drive wheels. It is a simple piece of geometry often ill-devised for no apparent reason and the gear’s ability to support equal leads, the smallest quantity in a large piece of machinery, is highly dependent upon this principle. Port opening as a distance, rather than time, is relatively unimportant, though it is interesting to see what it takes to remove this disparity and to reveal the relative insensitivity of backset angle. Some dimensions must be sourced from a drawing, and it is recommended that a CAD construction is maintained at the same time to provide other relevant entries. Notice particularly that the lead function normally associated with the crosshead and combination lever can be readily influenced by the parts of the 90o component – it is unwise to think of the two harmonic motions as separate entities. LBSC did not appreciate the problems. In the average inside admission arrangement there is therefore scope for reducing the pitch circle using a shorter leading return crank, such that an adequate foregear starting cut off is maintained. The top flange drilling is line with ISO 5211 standards and therefore fits a large range of gears and actuators. The valves on a steam engine control the flow of steam in and out of the cylinders. The error increases with pitch circle diameter increase, calling for the least that will provide sufficient travel to the valve. It may be noted that the return crank pin is the only one in the gear that revolves through 360o, hence the common use of a roller bearing, which is inappropriate for all the other pins. Model steam locomotive valve gear, Walschaert's valve gear for demonstration purposes, ex London & North Eastern Railway Mutual Improvement Coach series. The zero backset in the LNER B1 could hardly ‘work out’ to that figure – it is obviously implanted deliberately. The envelope of the gear is a squat rectangle containing a long anchor link, small pitch circle and minimal expansion link swings and one might expect little problem in attaining good event equality. This is important in two significant respects: firstly, the angularity problems are smaller and secondly the geometry dictates that the valve is driven from the upper pin of the combination lever, the ratio of which causes the radius rod to impart a relatively large movement of the upper pin. Model engineering owes so much to this great pioneer who, however, humbly stated his poor knowledge of valve gear design. This latter was more frequently a feature of Continental practice and has the admirable propensity, with a double arm, of providing the means of increasing valve travel without incurring objectionably large pitch circles and the angularity problems stemming therefrom. Increasing the lap introduces the opposite effect on the cutoff. The backset is a suitable modifier and will be found to be fairly insensitive, but the anchor link quickly alters the shape of the cut off curve as opposed to its position. Walschaerts’ gear readily satisfies this condition since only the raising of the radius rod is involved. Slide valves largely used in the 19th century; 2. It is of interest to investigate the points of relative sensitivity. The drawing should be constructed with the main crank on back dead centre. The illustration shows in detail an arrangement where equal swings are deliberate, and the resulting distances at the radius rod front pin reveal the linear discrepancies. He invented the valve gear that carries his name in 1844 and refined it further in 1848. In 1844 Egide Walschaerts invented a valve gear that by 1848 appeared very much as it does today. Little difference could be expected at most of the working speeds of a mixed traffic type, but the IHPs at the top end of any passenger work might well favour the Class 5. The first common principle, though not inviolate, is that at either dead centre position of the crank the return crank and eccentric rod pair render the reverser unable to impart any motion to the valve throughout its full working range. The events will never tie in exactly with results obtained by actual measurement, as the simulation contains exact dimensions without manufacturing tolerances, bearing clearances, etc. Enthusiasts, apart from partisanship, might be tempted to compare the LNER mixed traffic engine with the LMS Black Five and the GWR Hall. motions and in the case of Walschaerts’ these are from the main crosshead and the return crank. [HOME] [INTRODUCTION] [PROFILE] [WALSCHAERTS’ GEAR] [TIMING ERRORS] [STEPHENSON'S GEAR] [OTHER GEARS] [MORE CYLINDERS] [MINIATURES] [LEAD STEAM] [SIMULATION] [DOWNLOADS] [VALVE SETTING] [FAQ] [ANIMATION] [ANALYSES] [TRACTION & MARINE]. From the cylinder and port requirements feed the cells marked ‘enter’ in the spreadsheet and adjust lap, lead and port opening to obtain a suitable full gear cut off. The Class 5 reflects LMS general practice at ¼″ but is stated as being divided slightly unequally between the ports, though it is not specified whether this setting is hot or cold. A small discrepancy in the equality may be acceptable or even undetectable except by simulation, but working bearing clearances and subsequent wear could easily remove the desired lead altogether. The effect on reversing these pins for inside admission valves is to impart a slightly reducing ratio, necessitating a much greater influence from the radius rod and hence the return crank throw, with a consequent increase in expansion link swings of around 20%. This may be of some interest tothe readers of your paper. Modellers rarely potter about on shunting duties and should design as befits the new role. New Coolers Sets #CV1 (50's-80's) & CV2 (80's-90's) New USA Modern Gear Sets (Alice Packs 1973-Desert Storm) Sets 1-4 . It should be apparent at this stage that the reverser’s means of supporting the radius rod greatly influences the choices, some of which are illustrated. The primary reason for a more universal adoption of Walschaerts’ gear was its general suitability for mounting outside the frames, convenient for maintenance and permitting more strongly braced frames. All else is calculated automatically and the results shown for both inside and outside admission, including the 4 possible return crank lengths. Civilians, Warlords, Freedom Fighters, Terrorists & Running From Zombies. That the student should resist this temptation will soon become apparent; the alteration of a single part necessarily alters the whole. 4mm scale model locomotive Walschaerts valve gear. Pitch circle radiuses of 7″ or more compare ill with a Stephenson’s eccentric equivalent of only half of this. The spreadsheet cannot analyse other than equiangular expansion link swings, which mammoth mathematical exercise is best left to final adjustments in a simulator. The main differences are in design philosophy, particularly in the provision of lead. The .iam file contains also the Animation Timeline for the animation added. In right hand elevation the backset produces an anticlockwise angle of 24.43o and a clockwise one of 24.33o – essentially equal. There are, of course, many other design features that might influence a comparison. to I ft.scale. Proceed to the simulator, using the parameters generated in the ‘Data’ sheet. Also bear in mind that the simulator has no means of massaging figures! The spacious arrangement of the reversing gear gives full gear at the shallow lifting arm angle of only 24.5o to give very comfortable mechanics for the 6 21/32″ valve travel, albeit with an expansion link total swing fractionally under the advisable maximum of 50o. DN1 2TF. Walschaerts' gear has two distinct inputs, from the eccentric & from the crosshead. In this case the angle, length of return crank and eccentric rod length conform precisely and confirm the somewhat obscured pitch circle radius dimension. Walschaerts Valve Gear. More information is given on the LEAD page. Re: Walschaerts valve gear model Post by 52D » Wed Apr 18, 2012 6:12 pm I was about to reply in the same vein as James Brodie, im sure the Stephenson Railway Museum in Newcastle have a working set from North Blyth MIC. This is why tables of events list different figures for midgear at the minimum of the forward tabulation than those for reverse. As the usual combination lever ratio of pins is around 9:1 the anchor link provides an excellent and sensitive point of adjustment. Be aware of the much greater angles of swing required for inside admission cases. There is an apparent assumption that at dead centres the union link is parallel with the gear line which is proven in the reconstruction, though another that purports the radius rod top pin, expansion link trunnion and weighshaft all to be in line proves not quite so. All these programs are direct and convenient replacements for the drawing office large models and as such must be considered as confirmatory, and not design programs. Longer valve travels inevitably make this area more difficult to appease. Depending on control valve model, regulation of steam, liquids (in combination with KLINGER ball valves) and slurry, powder and paper pulp; Actuators. Walschaerts Locomotive Valve Gear Model - YouTube. You know, with an expansion link. I plan to use two of these, one over the other, for the cylinders, but I'm not quite sure how to assemble it. Swindon fought for decent results but LBSC was clearly out of his depth. The primary reason for a more universal adoption of Walschaerts’ gear was its general suitability for mounting outside the frames, convenient for maintenance and permitting more strongly braced frames. Poppet valves similar in principle to those used in internal combustion engines. Quite clearly the backset is shown to be relatively insensitive to adjustment, as expected. The inside gear of the GWR 4-cylinder 4-6-0s avoided this constriction to advantage. All gears have to provide the combination of two harmonic. The outside admission slide valves of short travel constitute exactly the sort of arrangement for which the invention was intended. When this condition become serious the Stephenson gear was abandoned in favor of the Walschaert type shown in this animation, … More surprising in this particular case is the resistance of the anchor link to affect results. Résumé historique. By the way, Walschaert gear is correct; Walschaerts gear is not (unless it is used in the possessive case, with an apostrophe, eg: "Walschaerts' design"). The combination lever and radius rod require support either by a valve crosshead guide or by a hanger. This required several weeks of trial and er… In full forward gear this accounts for 78.37% cut off (front) and 74% (rear) and a port opening disparity of almost 7/32″. I have seen it on som It is interesting to superimpose the model design over the Swindon drawing at the same scale (but without equating the valve and ports). This feature immediately contracted the combination lever to give pins so close to each other at the top end to warrant especially small pins and render it necessary to crank the front end of the radius rod for adequate clearances. Many designs tend to favour forward gear where more astute design work could have produced a better compromise. Although some engineers did not favour using the upper expansion link half for forward running because the drive is then indirect, the position is in fact little different from the many cases of rocker use in valve gears, though the results are not at 180 degrees. My goal was to try and build working valve gear with out modifying any parts, and to keep it as small and proportionate to the rest of the locomotive as possible. CP95 valve gear and motion.JPG 4,928 × 3,264; 4.02 MB. To be fair, if you ignore the connecting rods then the complexity is formed of only 6 parts. In practice the eccentric rod length is adjusted to maintain the principle even though veracity assumes that the return crank and its angular setting, together with the drive from the crosshead, are correct. The hump in the middle of the back gear cut off differences gives little concern for a 4-6-0 never expected to do serious work in reverse. My own design for Speedy clears the faults of the original without resort to a completely new layout in order to assist those who have already progressed too far down the LBSC road to contemplate total renewal. This therefore places the anchor link at the forefront of Walschaerts’ critical adjustment areas, greatly influencing the shape of the curves presented in the simulator. 2 years ago. The standard LNER reverser supports the radius rod extension by means of a slot and die allowing no adjustment to accommodate die slip but does not receive possible errors from a poor hanger arrangement. There are good examples of Walschaerts’ gear in a long travel context – the GWR King and the immaculate outside gear of the Bulleid rebuilds - yet in general it could prove better practice to use a mildly increasing element at the valve end, where a dual hanger would serve admirably to defeat enlarged angularities. 3D modeling with Autodesk Inventor 2014 of every part (.ipt) which compose the main mechanism of a Steam Locomotive - the ones presented in pictures and animation. If the ‘mid’ points coincide the angular extents will differ. It … the weighshaft and lifting arm and combination lever support where used, as being essential to correct functioning of the gear. Excepting the drop link the gears appear closely matched and shows just how so very near a design can produce hopelessly different results. The best examples use the suspending element to counter other inherent timing errors and this minimises die slip and wear. Even the apparently symmetrical LNER/LMS extended radius rod reverser with an equiangular lifting arm shows this trend. Thompson’s B1 does exactly what it says on the box, so to speak, and the irregularities of back gear mirror faithfully once the full gear parameters are set to the nominal figures on the drawing. Editor: I am sending you by same mail photo-graph of a model of Walschaerts ValveGear. Walschaerts Valve Gear Valve timing adjustment on Roundhouse locomotives. First the angular swings themselves. The primary reason for a more universal adoption of Walschaerts’ gear was its general suitability for mounting outside the frames, convenient for maintenance and permitting more strongly braced frames. If you are visiting to see this object, please contact … Most locomotives employing a leading bogie benefit from greater space in which to design the gear – all other six-wheeled engines of short wheelbase may suffer from compaction. The GWR 1500 tank and its 5″G Model ‘SPEEDY’. The leads cannot be set equal without this condition – attempts to set the valve to equal leads where the gear cannot support them simply destroys the equality of other events. Backset of the tailpin is clearly zero and we can expect that the expansion link swings are unequal, in fact by 2.11 degrees. In 1844 Egide Walschaerts invented a valve gear that by 1848 appeared very much as it does today. It is recognised as a major invention in the development of the steam locomotive. A sensible initial design may be had from the basic geometry shown in the diagram and the spreadsheet on the DOWNLOADS page quickly lays down the structure for both inside and outside admission simultaneously. That automatically means that a variable error exists at all other points by the transmission of rotary to linear motion. It is not difficult to conclude that the detailed design of Walschaerts’ gear is more complex than that of Stephenson’s gear, which has the advantage of combining the two components directly at the eccentric setting and merely requires that nothing in the subsequent chain of the mechanism should disturb its propensities. The valve gear on a 15" locomotive if accurately represented Walschaert gear. Could it have been better? Precisely as its name suggests, the combination lever combines the two essential components of the valve gear and in doing so takes its orders from both functions simultaneously – one cannot move without influence from the other. The difference between the two positions of the, A given lead determines the lap or a given lap determines the lead, and it must be divided for both ends as desired by lengthening or shortening the, Within certain limits, this adjustment may be made by shortening or lengthening the. And the less said about back gear the better! A spindle valve alternately applied high-pressure steam (red) to one side of the piston while simulataneously exhausting the steam (blue) from the other side. It is powered using magnets from the Electromagnets mod and is designed to run on 7u gauge tracks (tracks have 7 blocks between the rails). The return crank angle depends on the pitch circle and the distance and height of the expansion link tailpin relative to the axle at dead centres. Walschaerts Valve-Gear Roundhouse Engineering Co. Ltd Units 6 to 9, Churchill Business Park, Churchill Road, Wheatley, Doncaster. Walschaerts valve gear is one of the most extensively used gears of modern times; yet it was invented a long time before it came into general use, for the idea was evolved as far back as 1844. Rod is involved invention in the provision of lead the opposite effect on the L. S. & M.,... Though useful for this purpose eccentric rod will now depend on the L. S. & M. S., walschaerts valve gear model out... 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Fighters, Terrorists & Running from Zombies half of this combination with a long anchor link provides an overview their! As a major invention in the chain provides an excellent and sensitive point of adjustment refer to valve. Exacerbate the problems, walschaerts valve gear model of which could be conjectured at the of!
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