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. Walschaerts’ gear readily satisfies this condition since only the raising of the radius rod is involved. Egide Walschaerts was the chief engineer of the main workshop of the Belgian State Railways in Brussels-Midi. This required several weeks of trial and er… 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. from Kieran Jones. It is interesting to superimpose the model design over the Swindon drawing at the same scale (but without equating the valve and ports). 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. In full forward gear this accounts for 78.37% cut off (front) and 74% (rear) and a port opening disparity of almost 7/32″. 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. That the student should resist this temptation will soon become apparent; the alteration of a single part necessarily alters the whole. Tracing each item in the chain provides an overview of their functions and specific problems that can influence their design. 2 years ago. 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. 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. Résumé historique. Built properly, every modeller will ohh and ahh over it. On modern large-wheeled engines little latitude for ideal placement may be available for a shaft which of necessity passes through the frames and beyond. Hi all, I'm wondering, has anyone attempted to build a lego Walschaerts Valve Gear, and what were the results? 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. The Stephenson gear located between the wheels, this gear was successful up to the time when modern developments in locomotive practice crowded the space between wheels. 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. Only if the anchor link assumes the same angle at each stroke end can it impart the same amount as the crosshead stroke itself, in which case the ‘mid travel’ points will not coincide. 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. Bear in mind that these areas of adjustment refer to the design stage. 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. In this case the angle, length of return crank and eccentric rod length conform precisely and confirm the somewhat obscured pitch circle radius dimension. Quite clearly the backset is shown to be relatively insensitive to adjustment, as expected. I'm planning to make one using pneumatics components for the cylinders. 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. 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. to I ft.scale. 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. 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 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. Piston valves which superseded slide valves in the 20th century; 3. That automatically means that a variable error exists at all other points by the transmission of rotary to linear motion. Where pure analysis of an existing gear is contemplated a CAD construction will prove invaluable in discovering those items either missing from a drawing or found to be incorrect. 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. Unfortunately this often gives rise to the misconception that they can be treated separately in order to understand their functions. Symmetry abounds. 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. Walschaerts valve gear is wonderful stuff on an engine, it adds complexity and detail under the footplate. The rather spindly rods are more than capable of taking the light loads involved. 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. Proceed to the simulator, using the parameters generated in the ‘Data’ sheet. [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.]. It is of interest to investigate the points of relative sensitivity. This is a 4-6-4 Hudson type Steam Locomotive equipped with a fully functioning Baker Valve Gear. Slide valves largely used in the 19th century; 2. Editor: I am sending you by same mail photo-graph of a model of Walschaerts ValveGear. 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. Jun 21, 2019 - What has turned out to be the most difficult part of building these models is the working Walschaerts Valve Gear. 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. 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 Question: Can I use only one eccentric for a reversing steam engine, WITHOUT a slip eccentric. If the ‘mid’ points coincide the angular extents will differ. I also favour a substantial cross brace across the frames to unite the motion plates and to provide for the expansion link brackets. Simulation verifies the faith placed on introduction to the drawing. Basic formulae for Walschaerts’ initial design. 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. Poppet valves similar in principle to those used in internal combustion engines. The lead may be increased by reducing the lap, and the cutoff point will then be slightly advanced. Much of the compaction arises from the proximity of the cylinder to the driving axle and use of the trailing axle to originate the drive (like the USA Dock Tanks) would have created a better envelope. Increasing the lap introduces the opposite effect on the cutoff. 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. The front end of the radius rod operates the valve through the combination lever, so proportioned that it provides the lap and lead via the main crosshead. Col train4.jpg 1,966 × 1,394; 351 KB. 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. Walschaerts Valve Gear Valve timing adjustment on Roundhouse locomotives. Excepting the drop link the gears appear closely matched and shows just how so very near a design can produce hopelessly different results. LBSC did not appreciate the problems. Short wheelbase tank engines often suffer badly from compacted restrictions, making equality difficult to obtain. The valve gear on a 15" locomotive if accurately represented Walschaert gear. 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%. Inside Walschaerts' isn't common, the Great Western Castles & Kings used it; the geometry is exactly the same as outside gear. A helper who offered some help last week, long story short he determined that the trunnions on the valve gear frame seemed to not be correct as that frame seemed to be bent a bit. In 1844 Egide Walschaerts invented a valve gear that by 1848 appeared very much as it does today. 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. CP95 valve gear and motion.JPG 4,928 × 3,264; 4.02 MB. 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. It is tempting to accord this excellence to the small pitch circle and short valve travel but due praise of the design details should be recorded. Even the apparently symmetrical LNER/LMS extended radius rod reverser with an equiangular lifting arm shows this trend. All three contestants proved worthy of building in large numbers. This is deceptive, as the angular discrepancy is a mere 1.38o due to the short travel and squat envelope. Cyclopedia of locomotive engineering, with examination questions and answers; a practical manual on the construction care and management of modern … It is recognised as a major invention in the development of the steam locomotive. This may be of some interest tothe readers of your paper. The calculations at this stage assume equiangular swings of the expansion link. Only the 1/8th″ lead is somewhat optimistic. 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. This feature was ignored by LBSC in his design for Speedy, a drop link being provided, and there are other quite small divergences which plunge the model design into trouble. Civilians, Warlords, Freedom Fighters, Terrorists & Running From Zombies. And joy of joys, the Garratt has four sets. [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]. The drawing should be constructed with the main crank on back dead centre. Symmetrical layouts for short travel outside admission valves reduce the problems dramatically irrespective of scale. 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. 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. I plan to use two of these, one over the other, for the cylinders, but I'm not quite sure how to assemble it. Reset valves at each modification to ensure that the desired effect has taken place. The top flange drilling is line with ISO 5211 standards and therefore fits a large range of gears and actuators. 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. Walschaerts' gear has two distinct inputs, from the eccentric & from the crosshead. Walschaerts Locomotive Valve Gear Model - YouTube. The expansion link must sit square to the radius rod in mid gear and the so-called backset of the tailpin theoretically lessens as the inclination of the eccentric rod increases, and in many inside gear arrangements where the eccentric diameter might be excessive the pin may be well up towards the expansion link trunnions and cause the backset to become positive. 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. Old and delightfully quirky though they appear, these locomotives provide a shining example of early excellence in Walschaerts’ gear design. 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. I did an article on Walschaerts' for Romulus in Engineering in Miniature, May 2007. 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 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. 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. Holcroft was evidently aware of this and promoted it on the Southern Railway, choosing a rather cramped arrangement which did it no special favours. The best examples use the suspending element to counter other inherent timing errors and this minimises die slip and wear. It shows forward gear and the expansion link near mid swing, yet the awkward placing of weighshaft and lifting components denies symmetry in operation. B3/4 1367 (CFF Historic 1) by Jean-Daniel David 88 44 B 3/4 1367. There are, of course, many other design features that might influence a comparison. If you are visiting to see this object, please contact … 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. 2 Construction If constructing your own frames, ensure that the rear axle hole, expansion link mounting hole and cylinder mounting holes are … The inside gear of the GWR 4-cylinder 4-6-0s avoided this constriction to advantage. In the case of the ‘B’ Class the tailpin is placed exactly on the expansion link’s central curve – also deliberately so and producing unequal swings as a direct result. 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. motions and in the case of Walschaerts’ these are from the main crosshead and the return crank. Loc de la série B 3/4 1303–1369. Could it have been better? The design becomes an exercise in deciding at what running cut off it is best to equalise events without too much sacrifice elsewhere. National Railway Museum: Warehouse . All gears have to provide the combination of two harmonic. The Walschaerts valve gear on a steam locomotive (a PRR E6s). You can intervene and change the movie by entering Environments / Inventor Studio. The events, however, prove by simulation to be magnificent, addressed to the heavy gradients expected without much compromise in reverse. The purpose of this website is not to discuss basics, either of the cylinder or valve gear, but to help readers interested in the finer points of design, particularly with regard to the two primary gears used universally – Walschaerts’ and Stephenson’s gears. CP Class D-10-h No 1057 (8062239700) .jpg 1,280 × 960; 923 KB. Best resolved by computer simulation, where the results are assessed quickly combustion engines error exists at all points. 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