Edmund Heusinger von Waldegg: independently designed the Walschaerts valve gear (hence aka the Heusinger valve gear) Hermann Kemper: patent for maglev train technology Georg Knorr: considerably improved compressed air brake Georg Krauss: founder of Lokomotivfabrik Krauss & Co. in Munich, later part of Krauss-Maffei: Johann Friedrich Krigar The Walschaert valve gear, when correctly designed, provides constant valve lead irrespective of the chosen cutoff in both forward and reverse gear. Stephenson’s valve gear was not invented by George Stephenson but by two of Robert Stephenson’s employees, William Howe and William Williams (see, Walschaerts (no apostophe) valve gear invented by Belgian railway engineer Egide Walschaerts in 1844, gained near-universal acceptance in the early 20th century.  It is commonly externally mounted and driven by an eccentric crank mounted on the end of the locomotive crank-pin. The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. Piston valves which superseded slide valves in the 20th century; 3. A displacement of the union link end by half the piston travel must cause a valve rod displacement of the valve lead plus the valve lap. The valves on a steam engine control the flow of steam in and out of the cylinders. Next the fact that in midgear, the valve opening should be the same for the piston in both front and rear dead center positions is used to find the mid gear position of the pivot between the combination rod and reach rod. Fully operational, finely detailed Heusinger valve gear. In Germany, the Walschaert gear is often named the Heusinger valve gear after Edmund Heusinger von Waldegg, who invented the mechanism independently in 1849. To understand the operation, consider the cutoff in mid-gear. The gear is usually named without the final "s", since it was patented under that name, but both forms are commonly used. Note: Jamie Keyte of the 5AT Group is in the process of developing a new steam loco performance simulation package which he has appropriately named “STEAM” (see separate page of this website). The very high coupled wheel rotational speed at maximum train speed, limiting the time for lead steam to enter the cylinders. exceptions on rebuilt locomotives) the lag and lead motions must be reversed usually by placing the return crank 90 degrees in advance of the crank pin and the combination rod pivots on the radius rod above the linkage to the valve rods instead of below. But not answered there is the "why" of it. (SeeÂ. The pressure of this steam provides the driving fo… 6060 drive rod and valve gear (3812841990).jpg 2,398 × 1,503; 820 KB A steam tank locomotive from The Powerhouse Museum.jpg 1,024 × 783; 588 KB Ab class locomotive (New Zealand Railways, number 658, 4-6-2), closeup view of the link motion. The Walschaerts valve gear is a type of valve gear invented by Belgian railway mechanical engineer Egide Walschaerts in 1844 used to regulate the flow of steam to the pistons in steam engines. It is named after Robert Stephenson but was invented by his employees. They can be divided into those that drove the standard reciprocating valves (whether piston valves or slide valves), those used with poppet valves, and stationary engine trip gears used with semi-rotary Corliss valves or drop valves. In the 5AT FDCs, Wardale describes lead as follows: In practice the criterion to be satisfied by lead steam is to aid the obtaining of the least pressure drop between the steam chests and cylinders during the admission phase, and this is generally coincident with obtaining full steam chest pressure in the cylinder at dead centre. Valve Events may be defined as the four defining points in the cylinder power cycle – viz: These four points, in turn, define the four intervening periods as shown on the idealised Indicator Diagram (below) –  viz: 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. Motor with flywheel. For example, 'Southern' valve gear was found on Southern Railroad locomotives. In Germany and some neighbouring countries, like Poland and Czechoslovakia, the Walschaerts gear is generally named the Heusinger valve gear after Edmund Heusinger von Waldegg, who invented the mechanism independently in 1849. at the very start of a stroke, the valve opens to admit steam from the boiler into that space. Finally, some mathematical algorithms for estimating valve movements (ignoring angularity distortions) is presented in Appendix 1 of an instructive paper titled Predicting Locomotive Performance written by Prof. Bill Hall.  The algorithms can be used for predicing valve openings to steam and exhaust at any position (angle) of the main crank. PLEASE NOTE - this model and explanation contain a glaring error. 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. In this, Animation showing changes occurring to reverse, http://train.spottingworld.com/wiki/index.php?title=Walschaert_valve_gear&oldid=865, Articles lacking sources from August 2006. The Walschaerts valve gear is a type of valve gear invented by Belgian railway mechanical engineer Egide Walschaerts in 1844 used to regulate the flow of steam to the pistons in steam engines. To layout the Walschaert gear the proportions of the combination lever must be chosen. This is the case shown in the diagrams above. Walschaerts or Heusinger valve gear - most common valve gear on later locomotives, normally externally mounted. In the design of the 5AT, Wardale has adopted an exhaust lap of 18 mm compared to zero on the BR 5MT. This manipulates the valves. Heusinger's gear was closer to the form generally adopted, but most authorities accept Walschaerts' invention as sufficiently close to … The term is also used to refer to this particular type of Walschaerts valve gear system as a whole. The total movement of the valve rod in mid gear should be symmetric between front and back dead center. Cast metal chassis. In Germany, the Walschaert gear is often named the Heusinger valve gear after Edmund Heusinger von Waldegg, who invented the mechanism independently in 1849. However, only a small number of these saw any widespread use. The reversing rod, which connects to the valve gear, is attached to this lever, either above or below the pivot, in such a position as to give good leverage. En mecánica, la distribución de válvula de Walshaerts (distribución de válvula de Heusinger) de una máquina de vapor, es un tipo de mecanismo que acciona la válvula que regulan el paso del vapor de agua a los cilindros. The advanced compression resulting from the provision of exhaust lap is not necessarily a negative effect, since on a SGS design it compensates for the reduced pressure at which compression starts when the exhaust system is improved.  Locomotives with improved exhausts may otherwise suffer inadequate compression and consequently require too much lead steam thereby showing significant indicator “triangular losses” at the start of the stroke. THE ORIGINAL VALVE GEAR designed by the Belgian engineer, Egide Walschaerts, in 1844, employed an eccentric in conjunction with the crosshead to operate the valve. There are many different designs of valve gear, including the following more commonly used types: Valve ports are the slotted openings cast or cut into the circumference of each valve liner or sleeve at each end of the steam chest, though which high pressure steam passes on its way to the cylinder, and through which low pressure steam passes from the cylinder on its way to the blast pipe.  At each end of the steam chest, a single port consisting of several adjacent slots (marked A in the illustration below) carries both admission steam from the steam chest to the cylinder and exhaust steam from the cylinder to atmosphere. It was extensively used in steam locomotives from the late 19th century until the end of the steam era. The latter two effects can be seen as having “negative” effects on loco performance, however they can be counteracted by (a) the provision of large port opening (which are in any case necessitated by the provision of a long steam lap), and (b) a good exhaust system that generates high smokebox vacuum from the available exhaust steam. Purpose of Steam Lap: The longer the steam lap, the greater the distance that the valve has to travel in each direction to open the ports at each end of the valve chamber.  Long lap valves therefore require “long-travel” valves, which Gresley famously applied to his original A1 Pacific locomotives after the 1925 comparative trials with a GW Castle. Purpose. You can unlock your login by sending yourself a special link via email. In Germany, the Walschaerts gear is often named the Heusinger valve gear after Edmund Heusinger von Waldegg, who invented the mechanism independently in 1849. The term is also used to refer to this particular type of Walschaerts valve gear system as a whole. Factors on the 5AT favouring long lead are as follows. The Walschaerts valve gear is a type of valve gear invented by Belgian railway mechanical engineer Egide Walschaerts in 1844 used to regulate the flow of steam to the pistons in steam engines. The larger the magnitude of the superimposed component, the later the cutoff and thus the less expansion allowed for the steam in the cylinder. At any setting, the valve gear satisfies the following two conditions: 1. In practise the valve spindle length is adjusted to ensure this as part of setting the timing. It was slow to gain popularity. The valve gear operation combines two motions; one is the lead motion and the other is the directional motion required in full gear. Valve events from Walschaerts valve gear are indeterminate because of the angularity effect of both connecting and eccentric rods, but they can be approximated by geometric construction using Zeuner, Reuleaux or Bilgram diagrams.  Valve events can be more accurately determined by iterative computer programs such as: Charles Dockstader’s website also includes a program for constructing a Zeuner diagram which provides insights into the variables and how they affect valve events. The Stephenson valve gear remained the most popularly used valve gear on 19th-century locomotives. In Europe, its use was almost universal, while in North America, the Walschaerts gear outnumbered its closest competitor, the Baker valve gear, by a wide margin. The amount of lead provided is determined by the proportions of the combination lever and the lap designed into the valve. With the reverser in mid gear position since there should be no superimposed return crank motion, the expansion link die slot should be an arc of a circle centered on the pivot in mid gear and of radius equal to the length of the radius rod. and the valve heads were altered to give 5mm exhaust lap with a less rounded exhaust edge.  This was motivated principally by the need to reduce the intensity of the draught peaks as a further aid towards improving firebed stability.  However a little thought showed that there were other reasons why exhaust lap should be used.  2644 was generally worked at short cut-offs – 25% down to 15% and sometimes even less – at which the release was early, therefore exhaust lap was needed to lengthen the expansion period.  During the return stroke compression started from a low pressure due to the improved exhaust, which meant that too little steam was compressed.  Advancing the start of compression by means of exhaust lap was therefore also beneficial and it could be stated as a general rule that whenever the exhaust of a locomotive was improved there was a need far increase exhaust lap. Valve gear was a fertile field of invention, with probably several hundred variations devised over the years. This moves the valve in each direction by a distance which should be set equal to lap plus lead of the valve. Lengthening valve travel while keeping lap and lead unchanged, allows the port openings to be lengthened thereby increasing the area through which the steam passes on its way into and out of the cylinder and reducing the pressure drops in both directions.  Or, if the port length is unchanged, longer valve travel requires the use of longer lap. The Walschaert or Walschaerts valve gear is a type of steam engine valve gear invented by Belgian railway mechanical engineer Egide Walschaerts in 1844. • The valve operating mechanism (often known as the valve gear). Factors on the 5AT favouring limited lead are as follows. If this were the only motion made by the valve then the engine would only start if the piston were close to dead centre, and even then the direction in which the engined moved would depend upon whether it was fractionally before or after the dead centre point. Gab valve gear was an early form of valve gear used on steam engines. By choice of position of the reach rod the die block may be moved from top to bottom which superimposes a varying portion of this motion ranging from either 90 degrees in lag behind the crank (full forward gear) through none in midgear to 90 degrees leading the crank (full reverse gear). Low clearance volumes for the given level of internal streamlining. The valve slides back and forth along the machined surface between tapered edges C and D. The slots marked B are openings that allow exhaust steam to pass through the sleeve and into the exhaust passages leading to the blastpipe. The combination levers were driven, as normal, from the crossheads. In the design of the 5AT, Wardale has adopted a lead of 7.0 mm compared to 6.35 mm on the BR 5MT. A second motion is superimposed on the crosshead motion to the valve; the return crank provides a motion which lags the crankpin motion by 90 degrees. The gear is sometimes named without the final "s", since it was incorrectly patented under that name. The throw of the return crank must now be determined; it should be such as in full forward and reverse gear to cause a total movement of the valve rod equal to two times (valve lap plus port opening). This condition precludes adjustment of the valve gear by altering the length of the radius rod. At the instant when the space on one side of the piston starts to expand, i.e. The Walschaert gear had the advantage that it could be mounted entirely on the outside of the locomotives, leaving the space between the wheels and frames clear; this caused adoption first among some articulated locomotives. The combination levers were driven, as normal, from the crossheads. However, the Walschaerts valve gear had the advantage that it could be mounted entirely on the outside of the locomotives, leaving the space between the frames clear; which resulted in it being adopted in some articulated locomotives. Greenly, H., "Waelscharts Valve Gear", Marshall, From TrainSpottingWorld, for Rail fans everywhere, Animation of forwards motion of the gear. A supplementary benefit of exhaust lap is that when combined with valve exhaust diffusers and a Kordina at the exhaust passage junction below the blast nozzles, it helps to reduce the exhaust pressure peak at the blast nozzles during release and the consequent draught peak on the fire.  Wardale made this point in his book where he described his decision to introduce 5mm of exhaust lap on his modified 19D No 2644.  He wrote: During late May 1980 2644 was given an M repair …. Lengthening valve travel also increases the speed that the valve travels, which aids lubrication (even though it is unlikely to achieve hydrodynamic conditions) and also increases the speed with which the valve opens and closes, thereby minimising the amount of “wiredrawing” (and triangular losses) that occur just before the point of closure, and giving more clearly defined valve events. This criterion should be satisfied over the widest possible range of speeds and cut-offs. Drive on tender on 4 wheels with 4 traction tires. Slide valves largely used in the 19th century; 2. Generally low cut-off working (which increases the crank rotation during which the valve is open to lead steam). Purpose of Exhaust Lap: Exhaust lap is not so commonly used as steam lap, the majority of locomotives having zero exhaust lap. Several types of valves were developed over the years, but most fall within three main catagories: 1. It was extensively used in steam locomotives from the late 19th century until the end of the steam era. Each expansion link was driven from the crosshead on the opposite side of the engine. Extremely good internal streamlining at the valves and valve liner ports. [Note: in the case of a Uniflow engines, separate admission and exhaust ports are fitted.  The advantage gained is that the ports and cylinder surfaces are not subject to cyclical temperature fluctuations (and thus heat losses) caused by admission of hot high-pressure steam and the exhausting of cold low-pressure steam through the same openings.  One consequential disadvantage is that the greater temperature differential between the steam inlets (at the cylinder end) and exhaust outlet (at the centre centre) results in differential expansion which can cause excess ring wear and (in the extreme) siezing of the piston in the cylinder.]. Brake blocks between the wheels. Minimal heat transfer from the inlet steam to the cylinder and piston surfaces. The gear is sometimes named without the final "s", since it was incorrectly patented under that name. Walshaerts valve gear gives constrant, Caprotti valve gear invented by Arturo Caprotti, an Italian engineer, and gained some popularity in mid-20th century European locomotive designs.  Caprotti valve gear uses a rotary-drive from a gearbox mounted at the end of an eccentric crank on the end of the locomotive crank-pin. The Mason Bogie locomotive type was the first to use the Walschaert gear in North America. The gear is sometimes named without the final "s", since it was incorrectly patented under that name. The combination levers were driven, as normal, from the crossheads. “sharper” events during which the period of partial valve opening is shorter, thereby reducing the period of choking or “wire drawing”; for any given cut-off, the length (and area) of port that is opened will be longer thereby increasing steam flow into and out of the cylinder. Double headlights at each end coordinated with the direction of travel on tender. Heusinger's gear was closer to the form generally adopted, but most authorities accept Walschaerts' invention as sufficiently close to the final form. The necessity to get steam chest pressure in the cylinders at the start of each stroke over the widest range of speeds and cut-offs, which includes at relatively high cut-offs when maximum cylinder power is required for acceleration. It was extensively used in steam locomotives from the late 19th century until the end of the steam era. Walschaerts or Heusinger valve gear - most common valve gear on later locomotives, normally externally mounted. Close coupling between loco and tender. It can only be changed by changing the proportions of these components. The advantages of long steam lap (and therefore long valve travel) derives from the fact that the valve must travel further and therefore faster over the port, thereby delivering: In the design of the 5AT, Wardale has adopted a steam lap of 65mm thus giving the valve a mid-gear movement of 2 x (lap + lead) = 2 x (65 + 7) = 144mm compared to 98.4 mm on the BR 5MT giving a 46% increase. 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