pistons and rods on steam locos

[Anonymous]

Ok lets see

I noticed on my FEF-3 that the left and right set of pistons and rods are postioned differently for example while one piston is extended the other is exactly the opposite prototypically is this correct? I have never been able to see both sides of a steam engine at the same time to see if they are offset or identical to one another. In my mind I am imagining that steam would hit both cylinders right and left at the same time. Could someone plese let me know
and if the model is wrong why do manufacturers construct them this way?

[orsonroy]

The model is right. What you're seeing is called quartering. If both sides of the engine were in synch, not only would they pound the heck out of the rails but the engine would sieze up if standing with the rods in certain positions.

[howmus]

orsonroy and Alco GE are correct. The position of the piston in the steam chest should be quartered, that is 90 degrees off from each other. That way there is always steam driving the wheels from one chest or the other. It is also why there are 4 chuffs for each turn of the wheels (the piston is both pushed and pulled in the steam chest. If they were the same or 180 degrees off, they would both have full power one moment and then none a quarter turn away. There is a good explaination of how a steam locomotive works at Steamtown USA. This url gives most of the info they have on the display there: http://www.nps.gov/stea/locowork.htm

Chuff, chuff, Fwoooooooot, chuff, chuff.

Steam is way cool!

[Anonymous]

Except on the PRR, they used a left hand lead, and BLI did this incorrectly on their PRR models.

Also if a Three Cylinder Engine is modeled the crankpins are offset by I think 60 degrees to account for the third cylinder.

Rick

[twhite]

Yup, that's how they do it, all right--90degree quartering. Which gets even MORE interesting on a Mallet or simple articulated, because the two sets of drivers can get out of whack, depending on the steam pressure, so instead of having just two opposing revolutions, you get FOUR! That's why steamers always look so damn BUSY!
Tom[:P]

[dinwitty]

cool when you get one set on an articuleted spinning

if a model steamer's all wheels are geared for powering, it wont matter and the quartering as the loco power won;t be transmitted thru the rods,
so it wont matter on the rod positions.

if they are off, the model will still power thru the rods and thats a possibilty for
pinching and the engine will not run right period.

[tatans]

What is the clock position for the wheels? ? is it 12 o'clock AND 3 o'clock. if this is incorrect can you reply with the correct position. thanks

[mcouvillion]

Speaking of articulated engines, last summer I paced UP 3985 along the Sunset Route from Vinton, Louisiana to Dayton, Texas. I have video of it at speed (60 mph) where the front engine and the rear engine are in phase, then go out of phase, then back into phase over several minutes. I had heard that the front engines slipped on simple articulated engines but it was interesting to actually see the rods work together, then go out of phase. It is a scrambled mess, then in a few minutes, everything is "organized" again.

I videoed the engine from about the 4th car back and that pacing view is really unique. I also have about 10 minutes directly parallel to the engine and it is an awesome thing to see and hear.

Mark C.

[Anonymous]

QUOTE: Originally posted by Alco GE



On a 'Real' Two Cylinder Steam Locomotive the Right Crank Pin-Main Rod-Crosshead-Piston Leads the Left by Ninety 90 Degrees Going Forward.

In Basic Terms, this gives Four 4 Equally Spaced 'Chuffs' per Revolution of the Driving Wheels, Two Exhausts per Cylinder, 90 Degrees of Wheel Rotation apart.

Use an Internet Search Engine entering words 'Steam Locomotive' and search for Diagrams, etc.

Good explanation about the right leading the left, but there are exceptions. If you visit the Pennsylvania Railroad Muesum, you wil find all of the PRR engines have a left lead. The PRR was not the only one that used the left lead, but I cannot name the other road. None of the model engines that I have of the PRR are correct for the left lead.

If you have a three cylinder, you have still another set of rules, since 360 is divided by 6, the lead of those engines is 60 degrees, and not 90.

Just some facts that are interesting.

[Anonymous]

QUOTE: Originally posted by jesionowski

Except on the PRR, they used a left hand lead, and BLI did this incorrectly on their PRR models.

Also if a Three Cylinder Engine is modeled the crankpins are offset by I think 60 degrees to account for the third cylinder.

Rick

I inserted almost the same thing as you, before I read the rest of the comments.

Do you know of the other road that might have used a left lead? It would be a road that built their own of course, since all of the major builders did use the right hand lead as standard.
Sorry about the duplication.
You are correct about the 3 cylinder engines having 60 degree cranks.

Three of the 3 cylinder engines are preserved.

[Anonymous]

SInce the CNW was a left handed railroad, might they have had the left handed lead also?

I remember a discussion on this item somewhere but cannot remember where and they did list the other railroad.

Rick

[nfmisso]

3 cylinder locomotives usually have cranks offset by 120° (360/3) not 60°.

[twhite]

QUOTE: Originally posted by Alco GE




I may be wrong on this, but ONLY Compound Articulateds could be called Mallets from the name of their Inventor.

Simple Two-Engine Articulateds using Boiler Steam for BOTH Engines are NOT Mallets, as each Engine uses Steam Only Once. A Big Boy or Challenger are Simple, ( and NOT Mallets.)

Each Engine on a Simple Articulated will usually have same Cylinder Dimensions.

There will be Eight Exhausts for each Driver Revolution as BOTH Engines Exhausting up the Stack. Of Course the Exhausts will overlap as Drivers on each Engine Slip Slightly.

As Steam used only once, Exhausts will be louder than a Compound.

There are THICK Texts devoted to Valve Setting.

A Good Valve Setter was worth his weight in Gold, as his Ability affected the Operation of ALL the Locomotives in his care, resulting in Fuel and Maintenance Savings.

Right, Alco--Anatole Mallet's invention was for a compound engine with two sets of drivers and the steam used twice. A simple Articulated is just that--simple, even though it uses the Mallet's principle of two sets of drivers under one boiler, which causes a lot of confusion (did even back during the steam era--it wasn't unusual to hear an SP employee refer to the big cab-forwards as 'Mallets', even though they were simple articulateds). Most Mallet Compounds were used as helpers or drag freight locomotives, with 57" drivers, and 35 mph was about their top speed, otherwise the counter-balancing on the drivers would pound the track unmercifully. Simplifying the articulateds allowed for larger drivers, hence better speed. Driver size on simple articulateds was usually between 63-67 inches, with some of them going up to 70" (P&LE 2-6-6-4's). So theoreticaly, only an Articulated Compound was a "Mallet," even though the term was used pretty frequently for all articulateds during the Steam Era. Funny thing, even though Anatole Mallet was a French locomotive designer, the design took off in America much more than in Europe.
Tom [:D]

[Anonymous]

QUOTE: Originally posted by nfmisso

3 cylinder locomotives usually have cranks offset by 120° (360/3) not 60°.

You are correect about the 120 degrees. I was considering the puffing rate when I said 60 degrees. They puff six times per rev, but the actual offset for the cranks should be 120 degrees.

[pedromorgan]

i am not convinced about the agles on 3 cylinder loco's. there are many of these preserved in the uk and i will check the next time i see one.

p.s. the noise of a 4 cylinder loco with a heavy load is pure magic!
i was luckey enough to ride bahind an A4 pulling a heavy load last year on the great central line. there is supposed to be a 25mph speed limit on heretige lines! i think the driver was enjoying himself!

Peter

[Virginian]

Exhaust note on articulateds is more a factor of load and cutoff than compound or simple setup. The pressure and volume of the exhausting steam on each exhaust stroke, whether used once or twice, is the controlling factor. I never got to hear an A and a Y at the same point with a similar load, as the Y's were on the Shennandoah line and the A's were on the Norfolk line, but the results seemed similar, albeit different, no doubt due to smokebox and exhaust specific configurations.
A Y6b starting out simple, then going compound with the booster on was quite a symphony.

[pedromorgan]

i think i just misled you there i was talking about a brittish LNER A4! it is not articulated but is a 3 cylinder loco.

peter