# Steam engine question



## Mister Bill (Jan 30, 2014)

I have never seen this question asked. 

I think it is the steam pressure that pushes the drive rod connected to a tire.

What makes the tire continue to revolve after the drive rod reaches its most forward or backward position? The way I imagine things, the tire would just be stuck in that far position and would not rotate or move any further.

Is it inertia, or is there another set of rods that pushes or pulls the tire in a complete circle?

It is just an amazing contraption.

Bill


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## DonR (Oct 18, 2012)

Been a long time since I last saw a steamer on
the rails, but to me the way it works is quite
similar to the action in a two cylinder motor.
The loco wheels are the ' crank shaft' with the off set
crank bearings. When one goes down the other goes
up. The rotational energy smooths the
action.

Don


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## Big Ed (Jun 16, 2009)

The answer is the steam pressure strokes.


http://trumpetb.net/loco/rodsr.html


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## Big Ed (Jun 16, 2009)

Another explanation with a moving diagram here,

http://www.animatedengines.com/locomotive.html


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## Big Ed (Jun 16, 2009)

*More wheels? (click on the image and it moves for you.)
Steam Locomotive Walschaert Valve Gear Animation,








*


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## MtRR75 (Nov 27, 2013)

Mister Bill said:


> I think it is the steam pressure that pushes the drive rod connected to a tire.
> 
> What makes the tire continue to revolve after the drive rod reaches its most forward or backward position?
> 
> Is it inertia, or is there another set of rods that pushes or pulls the tire in a complete circle?


The diagrams that Big Ed posted and linked, show how you get two power strokes per revolution of the drive wheels. But these diagrams only show one side of the loco. On the other side of the loco is another set of cylinders, rods and drive wheels -- which are set at a 90 degree angle from the wheels on the side shown in the diagrams. Because of this 90 degree offset, the two power strokes of the drive wheels on the other side occur exactly in between the two power strokes shown in the diagram

So there are four power strokes per revolution of the drive wheels -- one power stroke every 1/4 turn -- on alternating sides.


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## highvoltage (Apr 6, 2014)

The rest of the answer is rotational inertia. See the large counterweights on the tires? Those provide centrifugal force to keep them rotating, the power strokes do the rest.


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## santafe158 (Jul 14, 2010)

highvoltage said:


> The rest of the answer is rotational inertia. See the large counterweights on the tires? Those provide centrifugal force to keep them rotating, the power strokes do the rest.


Maybe in part, but they're mainly to balance out the weight of the rods hanging from the crank pins. If they weren't there the thing would be way out of balance and would rattle down the tracks like an unleveled washing machine. It's the 90 degree offset that keeps things moving when one side reaches the extent of each piston stroke.


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## wvgca (Jan 21, 2013)

when people mention steam loco drive 'quartering' , that simply means one side is a quarter turn out from the other side ... when one side is at either end of power stroke, the other is halfway in the power stroke ..
in real loco's this matters a great deal, in models that are electric motor drive, it's just for realistic appearance


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## thedoc (Oct 15, 2015)

santafe158 said:


> Maybe in part, but they're mainly to balance out the weight of the rods hanging from the crank pins. If they weren't there the thing would be way out of balance and would rattle down the tracks like an unleveled washing machine. It's the 90 degree offset that keeps things moving when one side reaches the extent of each piston stroke.


As Santafe158 posted the counter weights are there primarily to balance the moving parts, but this balance is only good to a set speed. Most steam engines have a speed limit set by the operating dept, based on the balance provided by the counter weights, though the extra weight will certainly add to the centripetal force. 

Once on the B&O, the superintendent decided to suspend an engineer for some infraction, and informed him of that decision with the instructions to return from Garrett Pa to Rockwood Pa. He was driving a steam engine and was a bit angry about the situation, so he drove the engine over the speed limit for that engine from Garrett to Rockwood. The result was that by driving the engine at a speed over the limit, the rotating parts were out of balance and with every revolution the wheels kinked the rails for almost the whole distance.


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## gunrunnerjohn (Nov 10, 2010)

wvgca said:


> when people mention steam loco drive 'quartering' , that simply means one side is a quarter turn out from the other side ... when one side is at either end of power stroke, the other is halfway in the power stroke ..
> in real loco's this matters a great deal, in models that are electric motor drive, it's just for realistic appearance


Not true, most steamers drive a majority of the drivers using the rods. If they were at 0 degrees or 180 degrees out, the wouldn't work. I've actually seen this, it stops in it's tracks! In addition, the left/right quartering is critical as well for models.

I agree they don't always have to be exactly quartered like a real steamer, but you can't just stick them on.


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## wvgca (Jan 21, 2013)

gunrunnerjohn said:


> If they were at 0 degrees or 180 degrees out, the wouldn't work. I've actually seen this, it stops in it's tracks! In addition, the left/right quartering is critical as well for models.
> 
> I agree they don't always have to be exactly quartered like a real steamer, but you can't just stick them on.


i can see if they were close to identical , from side to side, where that might cause problems, especially with multiple part drive rods, so far i have been lucky not to get any that were far enough out of quarter to bind, or other wise give problems, bent or binding valve gear i have seen occasionally , weird waddling motion ..


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## gunrunnerjohn (Nov 10, 2010)

I've fought the good fight with a number of them, the side-to-side quartering is key, if one wheelset is different than the others, bad news!


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## alaska railroad (Oct 20, 2015)

gunrunnerjohn said:


> Not true, most steamers drive a majority of the drivers using the rods. If they were at 0 degrees or 180 degrees out, the wouldn't work. I've actually seen this, it stops in it's tracks! In addition, the left/right quartering is critical as well for models.
> 
> I agree they don't always have to be exactly quartered like a real steamer, but you can't just stick them on.


Exactly.when the quartering is thrown off on my bachmann steamers due to cracked axles, the drive wheels bind and lock up immediately.


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## Lemonhawk (Sep 24, 2013)

In a model, its because the left and right wheel sets are connected by a solid axle that quartering becomes necessary. Since the drive rods connect all the wheels, if not quartered then they will bind as the fight to get past the same end of piston movement.


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## gunrunnerjohn (Nov 10, 2010)

Which is why I specifically mentioned left/right quartering. That's actually the most critical as all the wheels have to have the same left/right orientation or you just won't go. However, even dismissing the left/right issue, quartering does have to be observed for the one side. As I said, if you have them either together or 180 out, you'll have problems. You don't have to have them precisely on like a real steamer, although you'll get the smoothest running if they are quartered properly.


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## 400E Blue Comet (Jul 11, 2014)

I've wondered this too. If the connecting rod goes to the back of the wheel, how would it move forward when the piston goes forward if it's not really on one side of the wheel or the other? What stops it from just going the other direction? One thought I've had is that the connection points aren't really opposite of each other on both sides of the wheel. Imagine this plus + If the connection points on the wheels at the right side of the train are at the bottom, maybe the connection points for the wheels on the left side of the train aren't actually on the top of the plus but are at the right or left if the plus, so while one connecting rod is at the back of the wheel, the other can't be and the piston still works on it.


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## Kelpieflyer (Jan 9, 2012)

I learned this when I was 10 years old and took my American Flyer steam engine apart for an overhaul not paying attention to the wheels. My first attempt was to put them back on 180 degrees from each other. Definatley did not work. Took a trip to the encyclopedia and a few attempts to get the quartering right.


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## MtRR75 (Nov 27, 2013)

400E Blue Comet said:


> Imagine this plus + If the connection points on the wheels at the right side of the train are at the bottom, maybe the connection points for the wheels on the left side of the train aren't actually on the top of the plus but are at the right or left if the plus, so while one connecting rod is at the back of the wheel, the other can't be and the piston still works on it.


Correct. When the connecting points (of the rods to the wheels) are at the bottom of the wheel on the right side (at 6 o'clock), the connecting points on the left side are at 3 o'clock or 9 o' clock.


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## sajan (Oct 1, 2010)

Right dide left side sequences is the trudt in opposite direction drive of the said mechanism

Sent from my GT-I9060 using Tapatalk


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## gunrunnerjohn (Nov 10, 2010)

Lemonhawk said:


> In a model, its because the left and right wheel sets are connected by a solid axle that quartering becomes necessary.


Drive wheels sets are connected by a hard axle in a real prototype as well.


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## shaygetz (Sep 23, 2007)

Get and operate a model one...you'll never look at your electric ones the same way again...


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## wvgca (Jan 21, 2013)

in the summer of 1966, i was taught how to fire and run a couple of steam traction engines, a few times, and then they were loaded on to trailers and hauled to winnipeg for scrap, same summer he sold his old 26 model t for $75, and the new owner drove it home .. 
the old water tanker made from a riveted boiler from a traction engine is still out on the farm in the tree line in the yard ..
when the same farm yard has been in the family since the late 1890's, it tends to collect some wierd old junk,


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## time warp (Apr 28, 2016)

Good topic! Remember also that quartering is necessary for the locomotive to START moving the load, it's one thing to keep it moving, but it has to be able to "pick up" the load. I could be wrong but I believe the RH stroke leads the left.
Have you ever heard a steamer gather slack to start? They slowly push the train backwards to push the couplers together, then when they start em rolling, you here the bang, bang , bang of the couplers tightening up as the train moves forward. Gives them some advantage starting.


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## gunrunnerjohn (Nov 10, 2010)

I would assume that the position of the piston in the cylinder would determine how it gets started. But you are certainly correct, you need the quartering to be correct to actually move the load.

As for coupler slack, we do that with O-gauge when pulling a real long consist, it actually makes the difference between being unable to start the train moving and starting up quite easily.


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## DonR (Oct 18, 2012)

GRJ

Speaking of coupler slack:

Maybe you recall the video one of the members posted
a year or so back. He had a very long train. He posed
the loco at the head on one track and you saw the
caboose on another. He did this to illustrate the
coupler slack. You saw the loco start, but it was
several seconds later that the caboose began to move.

Maybe you can find tht video.

Don


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## gunrunnerjohn (Nov 10, 2010)

I've witnessed it a number of times, last Monday we had a 100 car train on the club layout, and the only way to get it moving was to backup first to compress all the couplers.


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## Lemonhawk (Sep 24, 2013)

A singe wheel steam engine uses a large flywheel to get past the ends of the piston travel. In a steam loco you would not want a large fly wheel operating so you must quarter. I saw an old single cylinder Fairbanks Morse diesel operating a small stamping plant (used to crush ore) in Nelson NV at Murel Emory's Museum. To start it Murel just turned the big flywheel then the diesel would fire about every 4 rotations, as controlled by a rod that held the exhaust valve open when the crankshaft was spinning too fast. You could see that as the crankshaft slowed, suddenly the rod would let the exhaust valve shut and you got a power cycle that sped up the crankshaft to await another cycle. It was fascinating to watch.


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## time warp (Apr 28, 2016)

So what if it's a 3 cylinder steamer? Would the crank throws be "thirded"?:dunno:


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## DonR (Oct 18, 2012)

Those old John Deere farm tractors that had the
familiar chug a chug sound were started by
hand twirling their engine's flywheel. A friend of
the family collects them and demonstrated
it start process recently.

Don


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## sanepilot (Mar 11, 2012)

*hit and miss engine*

Hi,all...my 2 cents,if I may. I worked for a man that had what [around here anyway] was called hit or miss engine like the tractor with the big flywheel. It would run on kerosene or gas. Fired every fourth stroke. Most any old antique engine show or farm show will have one or more at them. In Columbus,Ohio every year they have a big farm show with all kinds of old timey engines,big and small.

The one he had was horizontal and the flywheel was about 2 feet. 
We would spend all day playing with it and I got the honor of spinning the flywheel. I was getting paid good,LOL They are very pricey,that is the reason I don`t have one..

I`m gonna ebay it and google,Have a good evening,everyone,Everett


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## thedoc (Oct 15, 2015)

time warp said:


> So what if it's a 3 cylinder steamer? Would the crank throws be "thirded"?:dunno:


On a Shay there were usually 3 cylinders and the crank was divided into thirds, On a conventional steam engine with the third cyl. in the center, I would assume that drive rods were connected on thirds, otherwise you would have uneven power strokes applied to the wheels.


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## thedoc (Oct 15, 2015)

DonR said:


> GRJ
> 
> Speaking of coupler slack:
> 
> ...


I did that once with a string of hopper cars, it was on a friends layout, which was 2 times around the outside and one loop in the center. I had 3 engines on the head end, all with flywheels, and over 100 hoppers. I backed the train a little and then slowly started out so that you could hear the slack running out. The big advantage to this was that you would start one car rolling at a time. BTW, the train was so long that for most of the loop the engines were running alongside the caboose.


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## time warp (Apr 28, 2016)

thedoc said:


> On a Shay there were usually 3 cylinders and the crank was divided into thirds, On a conventional steam engine with the third cyl. in the center, I would assume that drive rods were connected on thirds, otherwise you would have uneven power strokes applied to the wheels.


I'm gonna say a three cylinder conventional would start a load moving easier and run smoother, saving on track maintainence.


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## time warp (Apr 28, 2016)

sanepilot said:


> Hi,all...my 2 cents,if I may. I worked for a man that had what [around here anyway] was called hit or miss engine like the tractor with the big flywheel. It would run on kerosene or gas. Fired every fourth stroke. Most any old antique engine show or farm show will have one or more at them. In Columbus,Ohio every year they have a big farm show with all kinds of old timey engines,big and small.
> 
> The one he had was horizontal and the flywheel was about 2 feet.
> We would spend all day playing with it and I got the honor of spinning the flywheel. I was getting paid good,LOL They are very pricey,that is the reason I don`t have one..
> ...


Hey,Everett. How close are you to Dayton?


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## sanepilot (Mar 11, 2012)

*dayton*

Hi,Time, I`m about 2hrs 20 minutes from dayton. Been there a lot of times. Awesome airplane collection and shows. at wright pat field. Been to wright state university and the trade show they have every year at that large complex north of dayton.I hauled tires out of there in 1955. The old man I was talking about died on the outskirts of dayton. He hit a truck head-on,killed jis wife also. Bad,bad.We usta camp at Indian lake every year.

Here is a photo of the fairbanks-morse I was talking about.,What part of dayton you at? Have a good evening,Everett


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## time warp (Apr 28, 2016)

I have some accounts in Dayton and I work there quite a bit, also the Cleveland area.
I'm headed over to Newcomerstown, OH to work most of next week, just South of West Philly.
Interesting note: I just completed a job in Corry PA, in a factory where the old Climax locomotive works used to be. 
Anyway, I thought I might catch up to you before long when I'm bouncing around Ohio. Maybe get some supper.


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## sanepilot (Mar 11, 2012)

*supper*

Hi,Time.. Sounds like a plan. Newcomerstown. That`s over near zanesville,isn`t it?..You ever get into southern ohio. We use to go to chillicothe to eat at a nice resturant on east main street quite a few times. Can`t remember the name,maybe Golden corral. MY wife doctored at Adena hospital for awhile.

We`ll try to meet up or you can come to the house.

What kinda work you do? Everett


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## time warp (Apr 28, 2016)

North of Cambridge, I 77 & Hwy 36. There's a place up there called Unusual Jct., It's an old train station turned restaurant with several passenger cars and a caboose. I eat there from time to time. Chillicothe is only a little over an hour from Dayton, I can drive that like nothin'. I go to the Springfield Antique malls all the time hunting choo choos. I'll be in touch. Messing up this thread.Sorry guys:goofball:


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## thedoc (Oct 15, 2015)

time warp said:


> Messing up this thread.Sorry guys:goofball:


For me, don't mind at all, I sometimes think that off topic comments are more interesting that those that are strictly on topic.


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## sanepilot (Mar 11, 2012)

*messing up*

Hi,fellas.. Me ,too. I know better but sometimes my manners get left behind.

Have a good weekend,Everett:smilie_auslachen:


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## shaygetz (Sep 23, 2007)

thedoc said:


> For me, don't mind at all, I sometimes think that off topic comments are more interesting that those that are strictly on topic.


...one of the reasons MTF is so appealing...


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## mesenteria (Oct 29, 2015)

highvoltage said:


> The rest of the answer is rotational inertia. See the large counterweights on the tires? Those provide centrifugal force to keep them rotating, the power strokes do the rest.


Those weights merely balance the rotating mass to control dynamic augment...rail hammer. What keeps the steam locomotive moving forward is the 'quartering' of the rods, and the resultant timing of the valve gear openings on the opposite side of the axles...the opposite piston.


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## dinwitty (Oct 29, 2015)

answering the first question directly, the later pics dont fill the answer fully.

one side of the piston stroke is 2 direction unlike an automobile which is only one sided, why cars usually need 3 or more cylinders and usually they spin all the time.

whats missing in some of the explanations is the other side of the engine, the other set of drivers, they are 1/4 turn out of position from the other side. When one side is out of "push" the other side is "kicking" so you have a continuous exertion of force.

If you have ever been to an exhibition of steam threshing engines used on farms often someone has a display of single cylindered gas engines...these rely on rotational momentum to keep running as they have "flywheels", they have governors on them. one loud POP they spin faster as the flywheel keeps it turning, then as it slows the governor kicks it and it gets another gas charge and KAPOW!!! its kicked again spinning faster.

A steam locomotive does not rely on the flywheel effect for its momentum, its pure force, but the inertia of the engine like any other train you can "coast". The counterbalances on the wheels are NOT there for the flywheel effect, they are there to counter the weight of the drivers so the rails do not get "pounded" by the drivers and balances the weight of the siderods so the whole engine doesnt go flying off the rails by all the poor balancing without the counterweights. The counterweights have holes in them you can add lead or remove to balance the wheels, like you do on car tires when the auto mechanic pops these little weights on the tires, same effect. Balances the wheels.

Hope this clears some confusions.


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## mesenteria (Oct 29, 2015)

gunrunnerjohn said:


> I would assume that the position of the piston in the cylinder would determine how it gets started.....


Not really. It is the position of one of the two _valves_ that determines IF you can reverse the engine or get it to move forward. The pistons themselves act in two directions unlike an internal combustion engine's pistons. If steam can be admitted to one of the two/three cylinders such that the piston is driven to force the main rod in the correct direction, the locomotive must reverse. However, the valves and piston rods are linked by several levers, and with the quartering of the main cranks (to which the main rods are linked), one of the valves will have an inlet port open that will admit steam to the face of the piston that forces its main rod to force the drivers to turn rearward.

So, the engineer has to elect to move the loco one direction or the other. This election is possible upon stopping only because he can place the valves in a position to let steam into the cylinders in the volume of the cylinder that will cause the cylinder to move in the correct direction. This, in turn, is afforded by the quartering of the drivers _which places one of the two pistons halfway along it's path in its cylinder_.


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