A Primer on the Lempor Exhaust

While we have mentioned the Lempor in some of our White Papers, and we will focus a new White Paper specifically on exhaust systems in the near future, the CSR Team thought it might be helpful to give some insights into the physics given that both Grand Canyon Railway steam locomotives No. 29 and No. 4960 are now back in service and that both have Lempor Exhausts designed by Nigel Day. 

This video, courtesy of Chris Zahrt, shows GCRy No. 29 hustling a train under stormy skies. The 1906-built 2-8-0 burns used vegetable oil and employs a Lempor Exhaust to use steam as efficiently as possible within the constraints of the historic locomotive.

Understanding drafting in steam locomotives starts in the cylinder at the point of release [C on the following diagram]. This is when the valve first opens to let exhaust steam out of the cylinder. The pressure in the cylinder at release depends largely on the cutoff selected. A long cutoff means that the cylinder has been filled with near-boiler pressure steam for the majority of the stroke, which prevents the steam from expanding much before exhaust, therefore leading to a higher pressure at release. A short cutoff allows steam to enter the cylinder for a shorter percentage of the stroke, providing a proportionately longer percentage of the stroke for the steam to expand and, thus, exhausting with a lower pressure. Regardless of the pressure at the release point, the steam pressure in the cylinder drops quickly as the steam flows out and fills the exhaust steam passages [E]. The pressure at the cylinder exit [C] will eventually stabilize to a level determined by the total cross-sectional area of the exhaust nozzle(s) and the mass flowrate of steam. This stabilized pressure is known as "back pressure."

CLICK TO ENLARGE This diagram compares a "Normal" U.S. exhaust nozzle system with the advanced "Lempor" system, as equipped on GCRy Nos. 29 and 4960. Both types share similar components of: 1) Branch Pipes [live steam]; 2) Valves [live and exhaust stem]; 3) Piston [live and exhaust steam]; and 4) Exhaust passage. Where they differ is the design of: 4A/4B) the exhaust paths; 5A/5B) the type of nozzle; 6A/6B) the design of the petticoat; and 7A/7B) the refinement in design of the stack.

Between the cylinder [3 in the diagram above] and the exhaust nozzle [5A], some of the energy left in the steam will be lost due to factors such as: passages being too small; turns being too sharp; sudden changes in passage size; passages walls being too rough; or excessive heat loss due to design / lack of insulation. In some very poorly designed locomotives, the exhaust passages can be joined in ways such that the exhaust pressure pulse from one side of the cylinder can be "seen" by the opposite cylinder which creates an artificially higher back pressure [as exhibited above near the number 4A].

Bernoulli's equation helps us understand the relationship of pressure and velocity in fluid flows. Without delving too deeply into the details, the equation tells us that a high speed flow equates to a lower pressure and a low speed flow leads to higher pressure. Taking a look at the locomotive exhaust nozzle [5A], the idea is to transfer the "pressure energy" of the steam into velocity to create a low pressure region just outside the nozzle which will suck the exhaust gasses from the firebox through the flues. For a given back pressure, a smaller nozzle opening (aka "cross-sectional area") will give a higher velocity flow and, thus, a strong draft on the fire. However, that back pressure may become high enough to start limiting the power that can be produced in the cylinders. This is exhibited in the relationship between the difference in pressure going in and going out of the cylinders. 

Normally, to get more power, one would simply increase the cross-sectional area of the nozzle opening, lowering the back pressure at the same cylinder inlet pressure and cutoff. While this may increase power, it decreases the velocity of steam exiting the nozzle and, in turn, also decreases the draft acting on the fire and drawing hot gasses through the boiler. The result would be a poorly-drafting locomotive that would have difficulty making steam to meet the improved power from the cylinders.

Whereas the above describes a traditional single nozzle exhaust, a Lempor nozzle splits the total steam flow between four separate, smaller nozzles [5B]. Assume that the total cross-sectional opening for the four Lempor nozzles is the same as a single nozzle [5A]. Under the same inlet pressure and other conditions, the local speed of the steam jet exiting the smaller openings of the four nozzles will be a fair bit higher that that of the single, larger nozzle, simply because of the relationship between opening size and velocity. This creates a stronger draft with the same back pressure. The steam locomotive designer now has more options for finding an optimal balance between cylinder power and draft.

Steam locomotive mechanical engineer L.D. Porta also introduced a converging-diverging, or DeLaval, nozzle to steam locomotive design [5B]. In all other steam locomotive exhaust nozzles that we are aware of prior to his application, the exit walls were essentially parallel to the direction of steam flow. Under subsonic conditions, the converging or narrowing section works to speed up the flow. Once the flow reaches choked conditions, basically a velocity of Mach 1, no further acceleration can be obtained and thus no more improvement in draft. The diverging, or widening, portion of the nozzle under subsonic conditions actually serves to slow down the flow and increase the pressure. However, things flip-flop once the flow goes supersonic and by allowing the nozzle to widen to the outlet, the steam jet can continue to accelerate leading to draft improvement.

The multiple nozzles also help with mixing of the steam and flue gas as they lead to more surface area of steam at high velocity in contact with the flue gas. [Note that without good mixing of the two streams, the flue gas would mostly just stay in the smokebox instead of exiting the stack and its velocity through the flues and tubes would be much lower, resulting in poor heat transfer and thus poor steaming.] While mixing takes place as soon as the steam exits the nozzle, the first section of the petticoat [6B] is specifically thought of as a mixing chamber and its proportions in concert with those of the nozzles help assure good mixing/momentum transfer from the high velocity steam to the lower velocity flue gas.

Once mixed, the steam and flue gas is in the subsonic flow region but still has a fair bit of energy left and is still flowing at a fairly high velocity. If it was just allowed to go up a straight stack to the atmosphere [7A], that energy would be lost. Therefore, the latter part of the Lempor petticoat widens out [7B], which slows the flow and increases its pressure back to that of atmospheric. This characteristic, widening stack can be seen in the diagram of No. 29 below.

As in much of fluid mechanics, it takes very careful calculation and proportioning to maximize the benefit of the system which can be significant compared to other known exhausts. Failure to do so, either through poor engineering or when physical or other constraints restrict the designer's ability to implement a properly sized system will lead to a poor performing product.

Upcoming White Paper

The CSR Team is working on a White Paper dedicated to the development of advanced steam exhaust systems, from the traditional U.S. designs through Chapelon to Giesel and Lempor. Expect more information on that in the coming month. To stay up to date on CSR, consider signing up for our email list at the bottom of this page.

How it Works - Phoenix Log Hauler

A typical"tech tuesday" video post has received a great deal of attention in the past week. Posted Tuesday, July 12, on CSR's Facebook Page, the video [embedded below] of Wabeno's Phoenix Log Hauler has received, as of Friday, more than 170,000 views in three days. The unique vehicle, largely unknown to those outside of rural northern Wisconsin, is most likely why the video has been so popular.

That uniqueness is also what attracted CSR President Davidson Ward to visit Wabeno and attend its annual "Steam Up Days" festival the weekend prior.

"I had run across the Phoenix Log Hauler parked and under cover when driving through the town on a road trip two years prior," explained Ward. "When the opportunity arose to visit friends in the region and see the 'Phoenix' in action, I couldn't say no."

The Phoenix Manufacturing Company of Eau Claire, Wisconsin, manufactured the unique piece of steam history in the early 1900's for use by the G.W. Jones Lumber Company at its mill from 1909 to 1935.

The machine is a unique mixture of steam locomotive, steam tractor, and treaded-excavator that was used to haul long sleds of logs from the forests to the lumber mill in Wabeno, Wisconsin. It was used in both summer and winter, with two skis attached in place of the wheels for winter operations. Interestingly enough, the device burns hardwood scraps and uses water picked up along the way (or from snow), and it could thereby be an example of "old school sustainability." Click on the diagram below to get an enlarged view of the machine.

The "Phoenix" was donated to the Town of Wabeno in 1944 by the lumber company, and a group of citizens restored it to operation in 1965. The unique machine is one of only a few similar to it operating today, with the majority of other surviving machines having been made by Lombard in Maine (Lombard licensed components of its invention to Phoenix for the manufacture of this and about 200 other units made by the company).

Each year on the weekend after the Fourth of July, Wabeno hosts a "Steam Up Days" to show off its unique, operating piece of history and host a bunch of other lumberjack-related equipment. It is a good time and an event not to be missed!

Be sure to follow CSR to stay up-to-date on interesting innovation and preservation news:

Axles vs. Axis - Memorial Day 2016

The U.S. railroads banded together with the nation to help win the Second World War, and a large portion of that included promoting war bonds and recognizing the accomplishments of the railroad in supporting the Allied war effort. This ad shows many pieces of the "Axles vs. Axis" of the ATSF, including an engineman lubricating the driving box pedestals of ATSF 3460. 

On this Memorial Day, CSR remembers and honors the ultimate sacrifice given by so many in support of freedom - from those who rode to the front lines behind ATSF steam locomotives to those who have defended our freedom before and since. To all, we are forever grateful.

New Mainline Steam in the South?

New not-for-profit seeks to rebuild unique steam locomotive, CSR's Ward assists in the process

The Nashville Steam Preservation Society announced today its intentions to seek a lease agreement with Metro Nashville to move, inspect, and rebuild to operation Nashville, Chattanooga & St. Louis 4-8-4 type steam locomotive number 576. The newly-formed group is comprised of some of the most respected and experienced steam preservationists in the industry.

CSR President Davidson Ward has assisted the group from its nascence. In addition to designing the logos and graphic standards of NSPS, Ward has been involved in negotiations with Metro Parks regarding 576, has served as a strategic advisor to matters ranging from fundraising strategy to facilities designs, and is involved in many of the strategic planning matters undertaken by NSPS.

The "Stripe" with a few of the NSPS folks in front of its 70" driving wheels. From left to right: Jim Wrinn [Editor of Trains Magazine & NSPS Board Member], Shane Meador [NSPS President], Jason Sobzynski [Steam Mechanic and NSPS Advisor] and Davidson Ward [CSR President and NSPS Advisor]. Photo: S. Ward

The "Stripe" with a few of the NSPS folks in front of its 70" driving wheels. From left to right: Jim Wrinn [Editor of Trains Magazine & NSPS Board Member], Shane Meador [NSPS President], Jason Sobzynski [Steam Mechanic and NSPS Advisor] and Davidson Ward [CSR President and NSPS Advisor]. Photo: S. Ward

Built in 1942, locomotive No. 576 was designed and built utilizing the most modern technology of the day. Before its preservation, it roamed the southeast pulling freight and passenger trains, most notably during the busy years of World War II.

The restoration of No. 576 will enhance the locomotive’s value to Nashville and the region as a living historical artifact instead of a static park display. Passengers and spectators will be able to ride behind it and experience the sights, sounds, and impressions of a major steam locomotive in operation.

To reach this goal, the organization must reach a lease agreement with Metro Nashville, move the engine to a shop at the Tennessee Central Railway Museum, and raise a significant amount of money before embarking on the work.

NSPS President Shane Meador also serves as a  technical advisor  to CSR. Photo: D. Ward

NSPS President Shane Meador also serves as a technical advisor to CSR. Photo: D. Ward

“We are excited about this proposal to help secure locomotive No. 576’s future, and are looking forward to working with Metro Parks, the Tennessee Central Railway Museum, and the Nashville and Eastern Railroad to bring this Nashville Icon back to life to educate and operate it for the good Citizens of Nashville,” said President Shane Meador of the preservation society. “As a native of Nashville, I am thrilled to have the opportunity to pursue returning this one-of-a-kind locomotive to operation.”

Once operational, No. 576 will pull the Tennessee Central Railway Museum’s restored passenger cars on the Nashville & Eastern Railroad, also used by Nashville’s “Music City Star” Commuter operation. Excursions would originate downtown.

A 14 car-long matching stainless steel TCRM railway excursion, behind its fleet of first generation diesels, rounds the curve near Mt. Juliet in March 2016. It would look nice with a 4-8-4 on the point. Photo: D. Ward

“The locomotive 576 has been an important part of Centennial Park since 1953. The Park Board will be thoughtful in their assessment to ensure that any lease honors the intent of the original donors, retains public access, and provides for responsible stewardship going forward. The opportunity to ride a steam train out of Riverfront Park could be a much richer experience than the current static observation available in Centennial Park and is worthy of consideration,” said Parks Director Tommy Lynch. If approved by the Park Board, the agreement would next go to Metro Council for approval.

“Having worked on more than 20 steam locomotive restoration projects, I am excited about this proposal to return such a unique technological marvel to operation for the Citizens of Metro Nashville,” said steam locomotive expert Gary Bensman, a member of the organization’s board of directors. “Given the condition and disrepair of the locomotive following more than 60 years of being exposed to the elements, this proposal comes at a critical time to ensure the locomotive can be preserved for future generations.”

NSPS plans to raise $3 million to restore the locomotive, which will take place just a couple of miles from downtown Nashville. The organization is also seeking an additional $2 million to construct a permanent, visitor- friendly home and facility for the locomotive that will allow for its continued maintenance as well as to provide an interactive educational environment.

The organization has already received pledges of more than $200,000 to launch this campaign, and will continue seeking private and corporate supporters. After an agreement is reached with Metro, the locomotive will not be moved out of Centennial Park until an initial capital goal of $500,000 is reached to ensure funding throughout the first phase of this six phase project. In addition, the Nashville & Eastern Railroad has sent a letter of commitment stating that it will allow the locomotive to run on its tracks, and the Tennessee Central Railway Museum has pledged the use of its fleet of vintage, restored passenger cars. This proposal also provides a set number of free tickets, annually, to children and seniors of Metro Parks sponsored Community Centers for excursion trains once the 576 is operational.

Diametral Speed for Pi Day

Today is "Pi Day" - the date of 3-14.16. Pi was very important to railroad engineers of yesteryear, and not just the dessert-type.

Balancing of steam locomotive driving wheels was an engineering exercise subject to much trial and error (and some success). One term often thrown around in steam locomotive technical pieces is "Diametral Speed," or the the speed when the diameter of the driving wheel (in inches) equals the speed (in mph). This “Diametral Speed” occurs at 333RPM thanks to the relationship between the circumference of the driving wheel (2πr).

Thus, when the 84” diving wheels of an ATSF 4-6-4 are rotating at 333 RPM, the locomotive is traveling at 84 mph. Likewise, when the 60” wheels of a Chinese QJ are spinning at 333 RPM, that locomotive is traveling 60 mph, and so on. Since a steam “engine,” like an automotive “engine,” is limited by maximum rotational speed (read: “redline”) at approximately 550 RPM, the larger the wheel, the higher the speed. But, since the power range of steam locomotives depend partially on the flow of steam through the pistons at certain RPMs, the smaller-wheeled locomotives develop maximum horsepower at lower speeds, which is why small driving wheels were used on freight locomotives moreso than passenger locomotives.

As to this advertisement, when cast steel wheels of Boxpok and Baldwin Disc variety came onto the scene in the late 1930’s, they allowed railroads to improve balance and reduce dynamic augment (track forces attributable to overbalance) since they were significantly lighter (and stronger!) than the traditional spoked wheel. This 1937 Baldwin ad outlines the significant improvements. More info on balancing can be found in CSR's White Papers on Steam Locomotive Balancing -www.csrail.org/whitepapers

Regardless, we hope you had a chance to eat some “pi” yesterday. Enjoy your ‪#‎techtuesday‬!

History of the 141 R - A Precursor to CSR's New White Paper

Preserved 141-R 1199 sits at the Vailleneuve-Saint-Georges on May 5, 2007. Didier Duforest Photo - Wikimedia Commons

Preserved 141-R 1199 sits at the Vailleneuve-Saint-Georges on May 5, 2007. Didier Duforest Photo - Wikimedia Commons

CSR will be releasing its newest White Paper, the Development of Modern Steam 4: Advanced Internal Water Treatment, to its Supporters later this week (one benefit of being a CSR Supporter is receiving advanced copies of White Papers). The paper will be released to the public in mid-February.

On this #TechTuesday, we wanted to take a moment to discuss the unique history of French State Railways'(SNCF) Class 141-R, a series of more than 1,300 U.S.- and Canadian-built 2-8-2's used overseas. Covered in greater detail in the upcoming White Paper, the 141-R served as test bed locomotives for an advanced internal boiler water treatment that eventually led the way to that which CSR's Director of Engineering Shaun McMahon has been utilizing in locomotives for the past 24 years. Of note is that this predecessor treatment resulted in a 90% reduction in boiler maintenance, allowing the locomotives to operate in excess of 1,000,000 kilometers with next-to-no boiler maintenance issues!

General Steel Castings advertisement from the era - click to enlarge.

When the French entered the World War II, the country had more than 17,000 operable steam locomotives to haul its trains - shortly after Liberation, however, only 3,000 remained in operation. The SNCF needed a rugged, light-weight, and powerful dual-purpose locomotive to aid in reconstruction, and they turned to North America for a solution.

That solution evolved into the 141-R, a 256,000 pound 2-8-2 (known as 141 in France where steam engine configurations are designated by axles not wheels) that could pump out 44,500 pounds of tractive force through its 65 inch driving wheels. These locomotives were without a doubt the most advanced 2-8-2's ever manufactured in mass quantity (1,340 were manufactured by a combination of ALCO, LIMA, Baldwin, and MLW between 1945 and 1947, but 17 were lost at sea with their ship during a storm).

This comparison of drawbar horsepower between Kylchap and standard exhaust speaks to the benefits of proper steam handling - click to enlarge.

Locomotives 141 R 1 - 141 R 1100 featured traditional U.S.-style bar frames, spoked driving wheels (save for the main drivers, which were Boxpok) and roller bearings on lead and trailing trucks, as well as on the tender trucks. The exciting developments came with 141 R 1101 - 141 R 1340, which were equipped with the latest in technologies, including:

  • One-piece cast steel frame;
  • Roller bearings on all engine and tender axles;
  • Boxpok wheels on all driving wheels;
  • Chapelon-invented "Kylchap" Exhausts straight from the factory;
  • Open-type feedwater heaters;
  • North American multiple throttle front end; and
  • All other advances afforded to larger locomotives in the U.S. and Canada at the time.

The photographs below, courtesy of Creative Commons, show many of the advanced features of the 141-Rs.

The locomotives were found to be incredibly reliable and robust by many at SNCF. At the time, many locomotives previously in service in France had been of more-than two cylinder design, often compounded with inside and outside cylinders (see CSR White Paper on Chapelon), which often led to higher maintenance costs.

By means of comparison, the following table shows the difference between the SNCF 141-R and Southern Railway 4501 here in the U.S.

CATEGORY SNCF 141-R 1199 SOU 4501
General Classification 2-8-2 2-8-2
Service Dual Service Freight
Fuel (Current) Oil Coal
Builder Baldwin Baldwin
Year Built 1947 1911
Tractive Force, lbs. 44,500 53,900
Weight in Working Order, lbs. 256,000 272,900
Length, Wheelbase, locomotive, ft.-in. 79-2 77-1
Boiler Pressure, lbs. (Designed) 220 205
Firebox Grate Area, Sq. ft. 55.5 54
Engine (Bore x Stroke), in. 23.5 x 28 27 x 30
Driving-wheel Tread Diameter, in. 65 63

The 141-R locomotives operated on SNCF from 1945 until 1975. Fortunately a number of 141-R's have been preserved, of which at least six, four in France and two in Switzerland, are in operational condition. The video below shows one of the Swiss locomotives in service a few years ago.

Check Out 141-R 1244 In Action in 2012

Stay tuned for the release of CSR's newest White Paper in mid-February.