I found the follwing in an old post. I assume many of these issues as posted by Mr. Anderson will still exist in some form with 3985 with the new exaust?

Robby Peartree


Mr. Anderson's post


John E. Rimmasch wrote:
Dave,


Last year the Grand Canyon Railway applied some of Mr. Porta’s technology. What was the result? The result was a stronger more powerful locomotive that pulls more cars and burns less fuel……..who would have thought!

What operation out there would not want to pull more people, do less maintenance, burn less fuel and spend less money over-all?

The technology is here. Our company holds many of the keys to implementing the technology. This issue (the issue of fuel consumption, locomotive power and over all cost)

John E. Rimmasch


As far as overall operating/maintenance costs over the long term, making a locomotive more powerful using Mr. Porta’s techniques is a double edged sword. While reducing fuel consumption should have the effect of reducing boiler maintenance if operating under the same load as before the modifications were made, or at least not increasing boiler maintenance if the new found extra capacity is utilized, the life span and reliability of the driving gear will drop like a rock down a well if the locomotive is regularly loaded to its new limits.

All indications are that driving gear maintenance (and cost) goes up at a geometric rate depending on the load the locomotive is under. At Strasburg, our locomotives are generally loaded to about 1/3 of their “traditional” tonnage ratings as derived from Ralph Johnson’s book (IIRC #90 should be pulling twenty nine of our coaches every day. I’d like to see that!) Generally, they will run 31 days between inspections with little more than replacement of a cotter pin or two being required. D&S runs their locomotives at their traditional maximum capacity every day, and both Steve Jackson and Bernie Watts have said that there is usually something broken every day, sometimes something pretty major. In their off season, they will run a 2/3 length train to cascade wye, and back, and report the locomotive will often run day in and day out with nothing being written up.

That the Red Devil was as successful as it was is in part due to its having a one piece cast engine bed, as well as roller bearing axles and rods, in other words it was built like a tank. Even so, they had considerable trouble with the piston to piston rod, and/or the piston rod to crosshead connections failing. These failures were not present in other unmodified locomotives of this class and were attributed to the extra loading made possible by the modifications. Had the Red Devil been an engine with a fabricated frame and friction bearings I have little doubt that it would have beaten itself to death in short order. Accordingly, I believe that the Grand Canyon should be careful about taking advantage of any increase power available in #4960. Serious breakdowns may result.

How does the lempor exhaust work to make a locomotive more efficient?

Robert T.

[quote="Robby Peartree"]
As far as overall operating/maintenance costs over the long term, making a locomotive more powerful using Mr. Porta’s techniques is a double edged sword. While reducing fuel consumption should have the effect of reducing boiler maintenance if operating under the same load as before the modifications were made, or at least not increasing boiler maintenance if the new found extra capacity is utilized, the life span and reliability of the driving gear will drop like a rock down a well if the locomotive is regularly loaded to its new limits. (end quote)

Which has everything to do with operating strategies and nothing to do with exhaust design. The back pressures inherent in a less efficient exhaust also affect the running gear. The practical limit of power at the running gear is the pressure and volume. Same pressure and volume, whether loaded on both sides of the piston or just one, equally stresses the parts, although in different ways. I see a freer flowing exhaust with commensurate lower back pressure allowing the power to flow more easily through the running gear out to the wheels.

Does this ean that stress which would have been dealt with in the cylinder is now moved into the rods? Sure - but the rods can handle it.

dave

In simple terms, they use a larger nozzle size, thus reducing backpressure, but create a stronger draft.

The complicated answer is a debate that even people who are very knowledgeable on the topic will debate the finer points of.

Roger

All Lempors use a petticoat.

Roger

Dear Dave,

That quote is not mine. Please reread the post.

Robby

Sorry Robby, just hit quote and your name popped up.

dave

Dave:

I have a question.......the Lempor exhaust will give you more horsepower and be easier on fuel and water. Someone here said that it would give 4960 the ability to pull another car. The way I see it,that's not true. What might be true is whatever train the 4960 can handle,she can handle it faster on less fuel and water than she could previously. Since I assume the valves or their passages were not changed, nor the tractive effort changed, she will be more efficient, and have more horsepower,but not be able to pull any more than she could previously. Am I mistaken in that line of thinking?

Go to the link below and at the bottom of the page are Excel Spreadsheet Hyperlinks. Have not tried them since I do not have Excel.


http://www.livesteaming.com/Lempor.htm

Mr. Anderson is correct. It has everything to do with steam circuit design and nothing to do with operating strategies, as some simple "back of the envelope" calculations can easily prove. Traditionally, for calculating starting tractive effort, maximum pressure in the cylinders was taken as 85% of boiler pressure, to account for pressure drop through the throttle, superheater and branch pipes. Much effort was spent on the Red Devil to mitigate this pressure drop: larger superheater header, redesigned branch pipes, redesigned valve and radiused steam ports. It was the equivalent of a "port and polish" for a hot rod. Say for the sake of arguement that all this work gave just a five percent increase in maximum cylinder pressure, raising it from .85*200=170 to .9*200=180psi (I'm using a 200psi boiler for the sake of argument). That is an extra 10psi available at the cylinders. At the same time, improvement in exhaust flow has lowered the exhaust pressure (back pressure) on the other side of the piston from a traditional 15psi to around the 7psi. The cumulative effect is to raise cylinder pressure 18psi. Force is pressure times area, so for a 27" cylinder such as found on 4960, the area is (pi r^2) 572.6 in^2. 18psi * 572.6in^2=10305lbs. The running gear will see five tons more force, regardless of the operating strategy employed. Hope this helps.
-Stu

Mr. Anderson’s previous post is not arguing thermal efficiencies but rather discussing the material limitations of a given steam locomotive. A loss in the mechanical world (particularly at the University level) is an understanding of materials and their behaviors. Many engineering programs do not instill an understanding of material science to their students. As a result we have a lot of material failures that happen because of ignorance created by a lack of education that could have been avoided. There are a lot of designs that we can consider today that we do not have the materials to accomplish them. As man continues to make discoveries in material science impractical designs will become reality. After all who would have considered in 1920 that within 100 years man would have cars made largely of plastics or the carbon fiber materials used in aircraft today?

A PhD in Mechanical Engineering with an emphasis in Materials Science once described Metallurgy as a black art. We understand far less about materials than we think we do. Materials need to be considered with any design or design change. After all history is filled with material failures that resulted in significant economic impact.

Respectfully,

Robby Peartree

Hi Tex.

There's a lot more than the front end to be considered - the ability of exhaust steam passages not to choke the exhaust, the valves ability to do so, and the admission side as well - so consider that back pressure against the piston caused by the exhausting steam being forced through passages takes power to shove out. This power comes from the steam being admitted and expanded on the other side of the piston. If we lower the back pressure by improving the vacuum in the front end (to help suck it out) without further constricting the nozzle to give it a stronger blast (which prevents it from being readily pushed through) more of the power from the admitted steam can be used for things apart from forcing the exhaust - generally it runs out the back end along the rods to the wheels.

Lempor design makes a larger nozzle that creates a higher vacuum - through black magic that only an arithromancer of engineering can comprehend. Like many puzzling things in the universe, I know it works but can't tell you why - but Jos Koopmans can, if you read his book. Or Nigel Day, Hugh Odom, and a few other great minds who, like Porta, transcend the theoretical into the practical. I just read about it, try to follow the developments, and appreciate it with a bit of covetousness.

Point being, if the margin of additional power required to pull the additional car is more than compensated for by the greater amount of the potential total power now available at the wheels, and created by the greater ability of the stronger draft to force a more productive fire, the additonal car can be pulled. If the additional gains are not greater than that critical margin, no more cars but greater efficiency.

Cool stuff, but too occupied with bad fuel, leaky packings, healing up the latest fingertip I cut off, etc to work on the esoteric stuff now. Maybe someday........

Materials science is something we have lost, or cut up into so many specialized bits its almost impossible to find anybody under 65 that can deal with a wide range of practical applications today - much like a good manual machinist. Can't help but agree with Robby that we are poorer for its loss. BTW, steam circuit design isn't front ends - they overlap a bit at the end of the circuit, however. It is interesting to consider how much more could be gained by an organic complete steam circuit / combustion system design as opposed to retrofitting as best we can on existing technology.

dave

In an effort to settle this story just a bit, here are a few facts about the 3985 and the work that has been done and is yet to be finished.

Indeed, Mr. Matt Janssen and Nigel Day have modified the exhaust system on the 3985. It is noted here however that these are not the only modifications that have been made. The 3985 has also had some very significant work performed in the firebox as well. The details of this work as well as the front end work are not ready to be divulged.

The 3985 is nearing completion. The work performed by Wasatch Railroad Contractors is finished, however the other UP oriented work is not yet done. I can tell you that when the 3985 makes its first test run we will keep everybody posted as to how well the new technology is working.

It benefits nobody at this stage to overly speculate on what has been done, why or how it works. The truth is, the results have been proven, the work that has been done is quality work and you will be the first to know how it works. Stay tuned and you may want to watch the WRC web page for updates as we make them available.

www.wasatch-rr-contractors.com

Respectfully,


John E. Rimmasch
Wasatch Railroad Contractors

Here are a couple of points about the fluid mechanics behind the Lempor from what I have gleaned from some folks who have worked with them.
My apologies to those who are already familiar with this material or for any mistakes in my interpretation.

It is not just a matter of enlarging the nozzle to reduce the backpressure. There are a detailed set of calculations required that size the drafting system (which actually starts at the air openings in the firebox) to the locomotive. Optimally this would be done, as Dave said, from a clean sheet, but as the Grand Canyon, Mt. Washington Cog, Red Devil and many other modified locomotives have shown it can do very good things to extract the most out of the energy available from most any locomotive.

The simplest way to think of what makes a drafting system work was captured in the Bernoulli principle: an equation that describes the physics of how a high speed flow results in a localized low pressure region. In a locomotive, the nozzle takes the exhaust steam and creates the high speed flow. This creates a localized vacuum in the petticoat drawing the heated gasses of the fire through the boiler and out to the atmoshpere. The shape of the petticoat, like a carburetor, plays a role in how the steam and flue gas mix as well as how much vacuum can be produced.

A smaller nozzle opening will create a faster flow and thus a better vacuum to draw the flue gasses through the boiler. However, it also puts backpressure against the cylinders, which as others have pointed out, reduces the power that can be produced by the cylinders (work is achieved in the cylinders through pressure differential - the bigger the difference in starting and ending pressure, the more work).

However, at some point the nozzle size, backpressure and volume of steam combine such that the speed of the steam through the nozzle can go supersonic. Just like in a jet fighter, shock waves (think of breaking the sound barrier) are then produced. These shock waves momentarily disturb the vacuum therefore harming the draft on the fire.

A properly designed Lempor sizes and shapes the nozzles and petticoat to the energy available in the boiler and power possible in the cylinders such that the steam exhausts the nozzles as fast as possible without producing the supersonic shock waves that limit the draft. It makes use of a few aerodynamic tricks well known to designers of fighter jets which relate to the number and total area of the nozzles as well as the physical shaping of the nozzles.

Hope that helps those of you unfamiliar with the topic.

Wolf

Would using a Lempor change the sound of the exhaust?