heusinger valve 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. “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. 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. Walschaert's valve gear: lt;p|>The |Walschaerts valve gear| is a type of |valve gear| invented by |Belgian| railway |mecha... World Heritage Encyclopedia, the aggregation of the largest online encyclopedias available, and the most definitive collection ever assembled. To understand the operation, consider the cutoff in mid-gear. 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. 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). Deeley valve gear - fitted to several express locomotives on the Midland Railway. 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. Drive on tender on 4 wheels with 4 traction tires. (SeeÂ. Minimal steam leakage past the piston rings and piston rod and tail rod packings. It can also serve as a reversing gear.It is sometimes referred to as the "motion". The larger the magnitude of the superimposed component, the later the cutoff and thus the less expansion allowed for the steam in the cylinder. However, only a small number of these saw any widespread use. 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. This criterion should be satisfied over the widest possible range of speeds and cut-offs. 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). 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. 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. Generally low cut-off working (which increases the crank rotation during which the valve is open to lead steam). 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. 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 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 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. Valve gear was a fertile field of invention, with probably several hundred variations devised over the years. The Kuhn slide is part of a modified Walschaerts (German:Heusinger) valve gear on steam locomotives and is named after its inventor, Michael Kuhn (1851–1903). Walschaerts or Heusinger valve gear - most common valve gear on later locomotives, normally externally mounted. 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 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. Factors on the 5AT favouring limited lead are as follows. The combination levers were driven, as normal, from the crossheads. The term is also used to refer to this particular type of Walschaerts valve gear system as a whole. The gear is sometimes named without the final "s", since it was incorrectly patented under that name. The Stephenson valve gear remained the most popularly used valve gear on 19th-century locomotives. Much has been written about the comparative trials conducted in 1925 between a GWR Castle 4-6-0 and the much larger LNER A1 Pacific 4-6-2 when the diminutive Castle walked away with all the honours, bettering the Pacific in time-keeping and (by a long margin) fuel consumption.  The immediate result was the start of a programme of rebulding the A1s into A3s, having higher boiler pressure and long-travel valves which transformed their performance.  Yet, the precise advantages that the use of long-travel valves confers has seldom been clearly explained. 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. 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. 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. Piston valves which superseded slide valves in the 20th century; 3. reduce the exhaust steam pressure (because of the extra expansion); advance the start of compression and thus the amount of compression; reduce the port opening available for the passage of exhaust steam; shorten the period of exhaust steam flow and thus reducing the draught on the fire. The gear is sometimes named without the final "s", since it was incorrectly patented under that name. Walschaerts or Heusinger valve gear - most common valve gear on later locomotives, normally externally mounted. 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. http://www.timewarp.demon.co.uk/ned/howebiog.html, “WValve” created by Dr. Allan Wallace and downloadable from his own, Two spreadsheets (one for Walschaerts simulation, the other for Stephensons) by Don Ashton and downloadable from, Several programs created by Charles Dockstader and downloadable from his, delay the point of steam release thereby extending the period of expansion and getting more “work” from the steam. In the 20th century, the Walschaert valve gear was the most commonly used gear, especially on larger locomotives. In the design of the 5AT, Wardale has adopted an exhaust lap of 18 mm compared to zero on the BR 5MT. The Walschaerts valve gear is an improvement on the earlier Stephenson valve gear in that it enables the engineer to operate the steam engine in a continuous range of settings from maximum economy to maximum power. Lag and lead of these motions are always described relative to the engine moving forwards. Motor with flywheel. Minimal heat transfer from the inlet steam to the cylinder and piston surfaces. The total movement of the valve rod in mid gear should be symmetric between front and back dead center. 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. It was extensively used in steam locomotives from the late 19th century until the end of the steam era. 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. of them on a great website, www.steamlocomotive.com, showing in motion details of the differing styles of valve gear used in the US, including Stevens, Baker, Southern, Young and Walschaerts. Greenly, H., "Waelscharts Valve Gear", Marshall, From TrainSpottingWorld, for Rail fans everywhere, Animation of forwards motion of the gear. The terms “Lap” and “Lead” are often used together as if they are closely associated.  However they describe very different phenomena as described below: The illustrations below are taken from “Locomotive Valves and Valve Gear” by Yoder and Warren first published in 1921 and republished by Camden Miniature Steam. Factors on the 5AT favouring long lead are as follows. Purpose of Lead: Increasing lead is comparable to advancing the ignition on a petrol engine.  With positive lead, the admission occurs before the piston reaches dead centre, thus ensuring that the steam has time to begin applying pressure to the piston as it begins it “power” stroke.  High speed steam engines require a long lead whereas low speed freight engines require short or even negative lead.  The analogy with petrol engines remains the same. But not answered there is the "why" of it. 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. 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. Low clearance volumes for the given level of internal streamlining. Gab valve gear was an early form of valve gear used on steam engines. In Germany, the Walschaert gear is often named the Heusinger valve gear after Edmund Heusinger von Waldegg, who invented the mechanism independently in 1849. For internal admission valves (most piston valves, but there are some Cast metal chassis. Each expansion link was driven from the crosshead on the opposite side of the engine. The term is also used to refer to this particular type of Walschaerts valve gear system as a whole. For example, 'Southern' valve gear was found on Southern Railroad locomotives. The Kuhn slide (German: Kuhnsche Schleife) is part of a modified Walschaerts (German:Heusinger) valve gear on steam locomotives and is named after its inventor, Michael Kuhn (1851–1903). The very high coupled wheel rotational speed at maximum train speed, limiting the time for lead steam to enter the cylinders. The Mason Bogie locomotive type was the first to use the Walschaert gear in North America. The Walschaert valve gear, when correctly designed, provides constant valve lead irrespective of the chosen cutoff in both forward and reverse gear. 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. 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. Slide valves largely used in the 19th century; 2. The actual throw required from the crank is determined from the dimensions of the expansion link. 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 1844 Egide Walschaerts invented a valve gear that by 1848 appeared very much as it does today. With the piston in the front or rear dead centre positions, the expansion link should be vertical and moving the die block up and down should not alter the valve spindle position. This manipulates the valves. Tutorial on setting Walchaert Valve gear on a live steam locomotive. Fully operational, finely detailed Heusinger valve gear. Heusinger's gear was closer to the form generally adopted, but most authorities accept Walschaerts' invention as sufficiently close to … This condition precludes adjustment of the valve gear by altering the length of the radius rod. 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 combination levers were driven, as normal, from the crossheads. Minimal slackness in the valve gear, due to the extensive use of roller bearing joints, a very important factor in the ability of the valve gear to deliver the correct motion over a long period of time. PLEASE NOTE - this model and explanation contain a glaring error. At any setting, the valve gear satisfies the following two conditions: 1. But what were the advantages and disadvantages of each compared … 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 gear is usually named without the final "s", since it was patented under that name, but both forms are commonly used. [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.]. The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. Your IP address 103.56.70.111 has been flagged for potential security violations. This moves the valve in each direction by a distance which should be set equal to lap plus lead of the valve. Heusinger's gear was closer to the form generally adopted, but most authorities accept Walschaerts' invention as sufficiently close to … The combination levers were driven, as normal, from the crossheads. In the US, the Combination Lever in Walschaerts valve gear is usually called the “Lap and Lead Lever” since its geometry defines the amount of lead that is given to the valve.  The amount of valve movement that is derived from the Combination Lever equates to 2 x (lap + lead). 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. It was extensively used in steam locomotives from the late 19th century until the end of the steam era. Purpose. Methods of constructing of Zeuner, Reuleaux and Bilgram diagrams is outlined at the SE Lounge website, and a step-by-step procedure for constructing a Reuleaux diagram (as used by Porta for preliminary estimates of valve events) is provided on the next page of this website. Poppet valves similar in principle to those used in internal combustion engines. Brake blocks between the wheels. Consider the case of outside admission valves such as slide valves. The gear is sometimes named without the final "s", since it was incorrectly patented under that name. In practise the valve spindle length is adjusted to ensure this as part of setting the timing. Porta also explains the purpose of lead in his “Compounding” paper as described in the “Triangular Losses” page of this website. Heusinger's gear was closer to the form generally adopted, but most authorities accept Walschaerts' invention as sufficiently close to the final form. 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. Close coupling between loco and tender. • The valve operating mechanism (often known as the valve gear). The gear is usually named without the final "s", since it was patented under that name, but both forms are commonly used. Extremely good internal streamlining at the valves and valve liner ports. Walschaerts or Heusinger valve gear - most common valve gear on later locomotives, normally externally mounted. The Walschaerts valve gear was slow to gain popularity. 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. 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. 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). 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 …. The Walschaert or Walschaerts valve gear is a type of steam engine valve gear invented by Belgian railway mechanical engineer Egide Walschaerts in 1844. In Germany, the Walschaert gear is often named the Heusinger valve gear after Edmund Heusinger von Waldegg, who invented the mechanism independently in 1849. You can unlock your login by sending yourself a special link via email. It was extensively used in steam locomotives from the late 19th century until the end of the steam era. A simple Stephenson gear in partial cutoff 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. Deeley valve gear - fitted to several express locomotives on the Midland Railway. 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.

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