Walschaerts Valve Gear

Last revised: February 10, 2024

The Walschaerts valve gear, named after its inventor Egide Walschaerts, is a mechanism that found commonality in steam locomotives due to its brilliant design and efficient functionality.

Egide Walschaerts, a Belgian mechanical engineer, first conceived and designed this intricate system in 1844 while employed as a shop foreman at the Belgian State Railways. Walschaerts' mechanism anchored itself prominently in history due to its profound influence on the evolution and operation of steam locomotives.

To understand the popularity of this valve gear, we must first comprehend how it functions. At its essence, the gear is a valve-controlled system employing an intricate blend of kinetic and steam interactions to dictate the steam flow in locomotive cylinders.

Photos

Virginia & Carolina Southern 4-6-0 #34, sporting Walschaerts valve gear, is seen here in Hope Mills, North Carolina on June 12, 1955. The V&CS was leased to the Atlantic Coast Line in 1922, at which time it operated from Fayetteville to Lumberton, North Carolina, with a spur to Elizabethtown. Homer Newlon, Jr. photo. American-Rails.com collection.

History

Central components of the Walschaerts valve gear system include the main rod, expansion link, union link, return crank, and lifting arm, amongst others. These components work together harmoniously, amalgamating the seemingly erratic energy of the piston into a controlled, powerful force ideal for propulsion.

The momentum accumulated across these components is channeled towards the eccentric crank and link hanger. Here, an interaction of the angular movements of these parts determines the opening, closing, and overall operation of the locomotive exhaust port.

American Use

In America, the Walschaerts valve gear grew in popularity due to its mechanical ingenuity and resilience. It was essentially a smarter, sturdier design that enhanced locomotive reliability and control.

In his book, "The American Steam Locomotive In The Twentieth Century," author Tom Morrison notes European railroads had been widely using the Walschaerts valve gear throughout the 19th century.

However, it failed to catch on in America during this time. In 1876 locomotive builder William Mason of Taunton, Massachusetts showcased a locomotive equipped with Walschaerts at the Centennial Exposition of 1876 at Philadelphia's Fairmount Park.

In addition, he equipped 100 other locomotives with the gear. However, American lines continued to largely use Stephenson valve gear. In 1904 Walschaerts was reintroduced in the U.S. as interest in the Stephenson waned. As the 20th century progressed, the former became the preferred valve gear.

A 1904 entry in Railway Age noted the following:

"The Stephenson link motion has been the standard valve gear on American locomotives since the beginning of railroading in this country, the chief reason for this being that it combines simplicity and reasonable efficiency.

Simplicity has been the keynote of all progress in locomotive design in the United States rather than extreme economy either of fuel or water.

Because of this fact, the deficiencies of the Stephenson valve gear, with its irregularity of steam distribution under various conditions and its excessive weight of moving parts, are complacently put up with, and, of course, freely admitted; nevertheless it is used to the practical exclusion of every other kind."

Furthermore, the Walschaerts valve gear showcased an upgrade in the manipulation of valve events when compared to previous models such as the Baker valve gear. The Walschaerts had the advantage of separate and more accessible adjustments for the locomotive operator.

While the Baker valve gear was also a notable player in the field, boasting its own inherent strengths and benefits, it had a more complex configuration leading to potential difficulties in maintenance. On the contrary, the simplicity and robust design of the Walschaerts elevated it above other competitors.

The pistons of the steam engine are a pivotal element of the Walschaerts. Specifically, the reciprocating motion of the piston is what the valve gear leverages to achieve the desired control over the steam exhaust valve.

A common misconception is that the Walschaerts solely controls the flow of steam into the engine pistons. In reality, its influence extends further, playing a significant role in directing the exhaust steam out of the pistons too.

From an economic perspective, the Walschaerts could be constructed with foundry, or fabricate-formed components, enhancing its affordability, ease of manufacture, and repair in comparison to more sophisticated designs.

Popularity

In the history of steam locomotives, the early 20th century saw the birth of the articulated/Mallet compound concept (1904), which required a more efficient valve gear. In the 1920s, the Super Power design was born.

These more powerful steam locomotives drastically increased the adoption of the Walschaerts valve gear in the United States.

Despite the advent of diesel and electric locomotives reducing the prominence of steam engines, the brilliance of the Walschaerts has ensured that it remains an integral part of historical and operational steam locomotives globally into the modern era.

Egide Walschaerts

Egide Walschaerts, born in Mechelen, Belgium, in 1820, was a quiet but creative man, growing to become a notable figure in the field of mechanical engineering.

The seed of the Walschaerts valve gear idea planted itself in young Walschaerts' mind while he was still a teenager. By the time he was 24, Walschaerts had designed and prepared detailed drawings of this unique valve gear for steam locomotives.

Interestingly, Walschaerts did not seek a patent for his valve gear, choosing instead to share his idea openly with the world—an act that has undoubtedly had significant repercussions on the steam locomotive industry.

Walschaerts' invention focused on two key problems previously seen in the valve gear systems of steam engines – inefficiency and unreliability.

The main drawback for earlier builds, such as the Stephenson valve gear, was the difficulty and complexity involved in any form of positional adjustment or tweaking. Understanding that this was a major shortcoming, Walschaerts sought to create a more functional and adjustable system.

The Walschaerts valve gear stands as a testament to the simplicity and genius of foundational engineering, which sought to augment existing capabilities by refining old ideas and repackaging them into a more workable solution.

The mechanism proved to be a pivotal asset during the industrial expansion of the 19th century, primarily due to its ability to safely harness the immense power of steam and convert it into potent, controlled motion.

The valve gear is reliant on the principle of converting the back-and-forth linear motion of pistons to a rotary motion on the wheel axle. While it seems a simple concept, the successful and efficient execution of this idea is more complex than it appears, defying the principles of direct motion conversion.

With the Walschaerts valve gear system, this motion conversion is achieved by allowing an appropriate mix of radial and linear forces to operate in cohesion.

As steam from the boiler enters the steam chest, the valve, under the control of the Walschaerts gear, directs it to one end of the cylinder. The high-pressure steam pushes the piston, converting the linear motion into rotary motion through the main rod.

This precise control over the piston movements supplies a measured degree of force to the wheels at exactly the right moments. This characteristic is essential for the correct operation and efficiency of the locomotive.

Every component in the Walschaerts is meticulously designed for a specific function. The main rod connects the driver with the pistons, transmitting piston motion to the driving wheels.

The expansion link, a critical component of the system, is responsible for controlling steam exhaust direction and timing. It rotates back and forth following the main rod's motion and, with the help of the union link, powers the valve rod.

Wabash 4-6-2 #675 is seen here in Decatur, Illinois, circa 1950. This was one of sixteen examples acquired new in 1912; list as Class J1 they were the last new passenger steamers the railroad purchased. The fleet consisted of ten examples built by Alco's Richmond Works (660-669) and another six manufactured by Baldwin (670-675). All carried Walschaerts valve gear. The fleet was later superheated and classed as J1s. In addition, the Wabash converted some of its 2-6-2s into Pacifics in 1916; listed as Class J2 they were numbered 683-699 and 1676-1681. Fred Byerly photo. American-Rails.com collection.

The union link, another vital cog in this mechanical ensemble, transfers power from the expansion link to the valve rod. Its role ensures a balanced control over the valve's slide movements, contributing its part to the symphony of parts that constitute the Walschaerts.

The return crank, integral to the gear's operation, sits on the main driver axle. It transfers motion to the combination lever, thus contributing to the overall objective of valve movement control.

The lifting arm is primarily responsible for adjusting the valve gear's cut-off, thereby altering the steam distribution in the cylinder, changing the steam locomotive's power, speed, and efficiency.

The operator can control the cut-off, which means the locomotive is not reliant on a fixed setting and can be adjusted depending on the required operating conditions.

Faced with challenging terrains, climbs, or heavy loads, the Walschaerts allowed operators to manipulate the cut-off and effectively deal with such situations, an advantage that was not possible with many other valve gears.

The American love for the Walschaerts arouse primarily due to its reliable performance, more accessible adjustments, and simpler construction. For an expanding nation keen on exploring the limits of its industrial capabilities, the Walschaerts was an almost poetic fit.

Light and speedy passenger locomotives and giant freight haulers alike reflected the influence of Walschaerts' design, as the versatility of the valve gear made it a practical option for a broad spectrum of applications.

However, the journey of the Walschaerts was not a straight path to victory. Along the way, other valve gears like the Baker, emerged challengers.

Baker Valve Gear

The Baker valve gear, patented in 1909 by Akron, Ohio-based inventor Abner Baker, found notable favor with many railroads in the U.S., presenting Walschaerts with some genuine competition.

The Baker boasted the use of more lightweight parts, but the assembly was more complex, leading to potential difficulties in operation, maintenance, and repair. It had a larger number of smaller parts which increased the chances of wear and required more frequent maintenance.

Comparatively, the Walschaerts, while deemed more "old-fashioned," showcased robustness and relative simplicity. Its sturdy design and ease of operation and maintenance helped to retain its popularity against the likes of the Baker.

The Walschaerts offered a relatively easier adjustment mechanism for cutoff and lead, made possible by its lifting arm. This feature enabled the locomotive operator to control these aspects independently, a major advantage absent in most other valve gears.

Its brilliant design allowed for more accuracy and consistency in controlling the steam distribution in the cylinder, which translated to better responsiveness, power delivery, and overall performance from the steam locomotive.

This efficiency and performance advantage played a crucial role in securing the popularity of the Walschaerts valve gear in America.

At the heart of a steam engine, and by extension, the Walschaerts valve gear, lays the piston. In its simplicity, a piston is essentially a cylinder filled with high-pressure steam that moves back and forth.

The piston in a steam locomotive is directly linked to the movement of the wheels. The back-and-forth movement is converted to a rotary one, thereby propelling the locomotive. The role of the Walschaerts in facilitating this process is fundamentally irreplaceable.

The steam admission to the piston is afforded by a slide valve, an integral component of the Walschaerts, and it is a testament its engineering brilliance.

Its operative advantage comes to the fore in this aspect. As steam fills the piston cylinder and the piston commences its stroke, the Walschaerts aids in the careful management of the steam exhaust, ensuring smooth and efficient operation.

As the piston is pushed by high-pressure steam, it initiates its return stroke by steam being admitted to the opposite side of the piston. Simultaneously, the steam from the first side is exhausted.

The orchestrated dance of steam admission and exhaust in the cylinder, as controlled by the Walschaerts, is thus instrumental in converting the piston’s linear motion into powerful rotary motion to drive the wheels of the locomotive.

The gear also proved economical to manufacture, maintain, and repair due to its simplistic design and sturdy constitution. Unlike its challengers which had a connectivity of smaller pieces, the Walschaerts' major components are robustly built, providing longevity and reliability.

With the advent of bigger, more potent boilers during the 20th century, there was a need for a more effective and potent valve gear mechanism to harness and control this newfound power.

In these circumstances, the attributes of the Walschaerts valve gear clearly stood out. Its advanced design, offering separate control over steam admission and exhaust with a relatively easy adjustment mechanism, was perfect for the Super Power locomotives.

These began with the testbed 2-8-4 #1 manufactured by the Lima Locomotive Works. Listed as Class A-1 it tested on the Boston & Albany in the spring of 1925. Its notable upgrades included a larger firebox, larger boiler, sufficient air-intake, booster, and limited cutoff.

The extraordinary success and longevity of the Walschaerts valve gear in the face of the relentless tide of technological advancements bear testimony to its intrinsic quality and design.

Today, the bulk of operational steam locomotives still use Walschaerts or derived valve gears, including most heritage and touristic trains retaining steam locomotion.

While modern transportation has largely migrated away from steam power, the principle of the Walschaerts valve gear is still applicable and beneficial. Its concepts are used in a variety of functions, even in sectors not directly related to locomotion.

The beauty of Walschaerts' design lies in its versatility. Beyond steam locomotives, valve gears based on the Walschaerts design have been used in mechanical music instruments like the barrel organ and even certain makes of car engines.

Despite the overall decline in the use of steam engines, be it for locomotives or factories, the Walschaerts valve gear continues to serve as a fascinating study for mechanical engineers and train enthusiasts.

Conclusion

Ultimately, the Walschaerts is a coveted specimen of 19th-century mechanical engineering, conceived by a mind for whom limitations were merely challenges to be overcome. A testament to ingenuity, adaptability, and resiliency, it continues to be a significant part of the rich tapestry of locomotive history.

The Walschaerts, undeniably, illustrates the beauty of form meeting function, mechanical simplicity converging with high-level performance. Its design, unaffected by the passage of time, remains a timeless symbol of the Atomic Age and carries on influencing the way we perceive, understand, and engineer motion even today.