wjstix wrote: Remember that the wheel arrangement of a steam engine was there for a purpose. An 0-6-0 would be limited in speed even if it had large driving wheels, because the drivers would have a harder time going into a curve and would be more likely to derail. Engine designers found early on that putting a two wheels in front to make a 2-6-0 or later 2-8-0 helped the engine run considerably. As speeds increased, passenger engines got a four wheel truck which tracked even better at high speed, creating the 4-4-0 and 4-6-0, later the 4-6-0 etc. Trailing trucks came in to help carry the ever-growing firebox, first two wheels, then four, even six.So if you have say a 4-6-0 with tender and you turn it around to run it backwards, you have the engine pushing it's tender at speed (increasing the risk of a derailment) and the big drivers digging into the rail with no lead wheels to help ease the transition into the curves. Even a 4-6-4 would still have to deal with having the tender in front. (BTW a NYC Hudson would have a hard time taking on water from the water pans on the mainline if running backwards, since the tender scoop would be backwards too!)There were some engines designed to go both ways, like a 4-6-4T, and on some branchlines it wasn't unusual for an engine to pull a train facing backwards at slow to moderate speeds. But particularly at speed steam worked best going forward.
Remember that the wheel arrangement of a steam engine was there for a purpose. An 0-6-0 would be limited in speed even if it had large driving wheels, because the drivers would have a harder time going into a curve and would be more likely to derail. Engine designers found early on that putting a two wheels in front to make a 2-6-0 or later 2-8-0 helped the engine run considerably. As speeds increased, passenger engines got a four wheel truck which tracked even better at high speed, creating the 4-4-0 and 4-6-0, later the 4-6-0 etc. Trailing trucks came in to help carry the ever-growing firebox, first two wheels, then four, even six.
So if you have say a 4-6-0 with tender and you turn it around to run it backwards, you have the engine pushing it's tender at speed (increasing the risk of a derailment) and the big drivers digging into the rail with no lead wheels to help ease the transition into the curves. Even a 4-6-4 would still have to deal with having the tender in front. (BTW a NYC Hudson would have a hard time taking on water from the water pans on the mainline if running backwards, since the tender scoop would be backwards too!)
There were some engines designed to go both ways, like a 4-6-4T, and on some branchlines it wasn't unusual for an engine to pull a train facing backwards at slow to moderate speeds. But particularly at speed steam worked best going forward.
IIRC, the Prairie type's trailing truck was generally more important for reverse operation than it was for firebox support. As I understand it, since Prairies were used on logging railroads and such where the track wasn't always the greatest, the rear truck functioned essentially like a pilot truck, except that it was on the rear of the locomotive.
-ChrisWest Chicago, ILChristopher May Fine Art Photography"In wisdom gathered over time I have found that every experience is a form of exploration." ~Ansel Adams
JamesP wrote:Stephenson valve gear (on a road locomotive) was typically set with more lead in the forward direction than in reverse. The old-timer's saying was "Forward motion line-to-line, backward motion 1/4" blind," referring to where the edge of the slide valve was in relation to the edge of the port when the engine was on dead center.
You're saying if you stop the engine with one piston all the way to the front end of the cylinder, and throw the reverse lever full forward, the front steam port will be just barely closed, and if you shift to full reverse the valve will have moved forward a quarter-inch? Where will the valve be when the reverse lever is set for short cutoff in forward gear-- we want it to have shifted rearward from line-and-line, don't we? (To get some lead, I mean.)
It is true that "modern" valve gear such as Walschaerts and Baker do not favor one direction of travel. However, Stephenson valve gear (on a road locomotive) was typically set with more lead in the forward direction than in reverse. The old-timer's saying was "Forward motion line-to-line, backward motion 1/4" blind," referring to where the edge of the slide valve was in relation to the edge of the port when the engine was on dead center. This means that a Stephenson road engine would not have as much power or be quite as efficient when running at speed in reverse. However, I do not believe that was the primary reason for turning locomotives - visibility and tracking are the important reasons. From experience with 7.5" gauge and 12" gauge live steam, there isn't any doubt that tracking is an issue. These locomotives are usually built with suspension identical to the prototype engines. I have spent a lot of time at the throttle of a 7.5" gauge K-28 that has prototypically accurate leading and trailing trucks. The lead truck has the typical equalizing suspension that transfers more weight to it when the locomotive is in a turn, thus helping guide the engine into the curve and making the truck want to track straight. The trailing truck has a pivot just behind the last driver axle with the suspension designed to carry the weight of the firebox without a link type suspension like the front truck... this is normal practice for an American steam locomotive designed for running over the road (as opposed to a switch engine). The "K" tracks wonderfully when moving forward at any speed. However, the trailing truck has a tendency to find any defect in the track when moving backward, even at slow speeds. If I remember my history right, SP had some derailing trouble with the first cab-forwards since they basically turned a conventional articulated around without revising the trailing truck suspension to lead instead. Later versions of the cab-forwards had proper swing link suspension on what was now the lead truck and tracked just fine (for more information, see "Those Amazing Cab Forwards" by George H. Harlan). One more thing, and I promise to stop beating this dead horse. I have a 12" gauge 4-4-0, and it definitely exhibits a preference for running forward when pulling a train. The four wheel lead truck guides the engine around curves just great running forward with a train in tow - the drawbar from the tender is mounted close to the rear driver axle, so although the tension from the drag of the train would want to make the locomotive nose to the outside of a curve, the lead truck way out front easily nudges the front of the engine around the curve so that the flanges of the drive wheels don't "climb the rail". In reverse, with a train coupled to the coupler on the pilot beam, the drag of the train again wants to straighten out the locomotive in the curve, but now it has the leverage to do so since the coupler is so far from the drivers, and the lead truck now has forces acting in the opposite direction of what it is designed to do. This tends to make the flanges on the rear drivers (leading the engine in reverse) climb the rail due to their angle in relation to the rail itself. When switching with the locomotive, the combination of low speed and light loads (just one or two cars on the front) makes this a non-issue. But couple a heavy train to the pilot and try to run backward at speed upgrade through a curve, and you are asking for trouble! By the way, this is not a stupid question at all - as you can see, there are a variety of reasons with some fairly complex issues involved to answer it!
vsmith wrote: Same with fuel from the tender on cabforwards, it was pumped via a steam powered oil pump from the tender all the way up to the front of a cabforwards firebox.
Same with fuel from the tender on cabforwards, it was pumped via a steam powered oil pump from the tender all the way up to the front of a cabforwards firebox.
Uhh...no. The tender on the cab forwards used a pressurized compartment, under 5-8 lbs of pressure, that in turn caused the heated oil to flow to the burner control. Look at the tender pictures of cab-forwards, you'll see a a clamped lid on the oil fill location.
rrnut282 wrote: Selector,Your explaination just made me think it through and (duh) there are four power strokes per revolution of the driving wheels. This means that both pistons have to be pushed forward and backward to complete a revolution. So the face with the rod is inconsequential with respect ot direction of travel, except when starting out. I'm going to hang my head in shame for a while.
Selector,
Your explaination just made me think it through and (duh) there are four power strokes per revolution of the driving wheels. This means that both pistons have to be pushed forward and backward to complete a revolution. So the face with the rod is inconsequential with respect ot direction of travel, except when starting out. I'm going to hang my head in shame for a while.
No, no!!! Please...I have been there myself. I can't tell you how many times I have had someone gently point out something as clear as an old oak on the prairie to me when I walked right past it...on things steam.
Not shame, just share...quite a difference in that one consonant.... Others have done it for me, and I just pass it on...with full respect.
-Crandell
tomikawaTT wrote: There's a BIG loose link in the, "Piston rod versus no piston rod," discussion. Many steam locomotives had so-called balanced pistons; with a piston rod, connected to nothing, sticking out of the front cylinder head of each cylinder. One class of Japanese locomotive (JNR 4110 class 0-10-0T) actually had the forward cylinder heads just aft of the pilot beam - and a 660mm length of rod housing sticking out almost to the coupler knuckle on each side.Obviously, balanced-piston locomotives had equal thrust on both faces of the piston, inlet steam pressure and cutoff being equal.Chuck
There's a BIG loose link in the, "Piston rod versus no piston rod," discussion. Many steam locomotives had so-called balanced pistons; with a piston rod, connected to nothing, sticking out of the front cylinder head of each cylinder. One class of Japanese locomotive (JNR 4110 class 0-10-0T) actually had the forward cylinder heads just aft of the pilot beam - and a 660mm length of rod housing sticking out almost to the coupler knuckle on each side.
Obviously, balanced-piston locomotives had equal thrust on both faces of the piston, inlet steam pressure and cutoff being equal.
Chuck
This is true, but the reason was not so much to balance the thrust of the piston, but rather to support the piston itself so that the piston rings would not wear on the cylinder due to the weight of the piston resting on the lower portion of the cylinder wall.
Semper Vaporo
Pkgs.
At Golden Spike the engines spend 1/2 their time running in reverse with no discernable difference. However, visibility in reverse is a concern - especially on the Jupiter with a full load of wood. We have to spot the engines in precise locations. During the day, at the viewing stands, and at night we spot the smoke stack on the engine under the smoke jack in the engine house. So we stop at the needed location and ignore the position of the rods. One thing I have noticed is that the Johnson bar has twice as many notches in the forward direction as in reverse. While not an operating issue today - more notches would have given an 1869 engineer more control.
dd
I have read that there is a difference in starting a locomotive as to which end of the cylinder the steam is FIRST admitted.
Assuming a locomotive with the Right side leading the Left side, if the engine is stopped with the rods at the lowest position of the rotation of the wheels, then when starting, steam would be admitted to the front of the right side cylinder and pressure would be applied to the face of the piston (no surface lost due to the rod connection). After 1/4 revolution of the wheels, the left side would have steam admitted to the front of the cylinder, where again the pressure would be applied to the face of the piston. Thus you would get 1/2 of a revolution of the wheels using the full surface of the front of the two pistons to obtain greatest force. The second 1/2 revolution would be using the rod side of the piston which has a slightly smaller surface area for steam to apply pressure to.
Assume the rod is 2 inches in diameter and the piston is 20 inches, then the front surface is:
Pi * 20^2 =1256.64 Sq.In.
and the rod side surface is:
Pi * 20^2 - Pi * 2^2 = 1256.64 - 12.57 = 1244.07 Sq.In.
If you are running 200psi then the power of the front surface is 251328.lbs and the rod side surface is 248814.lbs. A difference of 2511.lbs or about 1 ton.
Not a great advantage, just 1 percent. But any advantage is an advantage!
I have read (I remember from THIS website a few years ago) that engineers tried to stop their engine with the rods down on their side of the engine (assuming right side leads, or rods forward for Left side leads), but I have always wondered if the engineer really had that much control over where the rods were when the engine stopped.
rrnut282 wrote:What about the area lost on the face of the piston by the piston rod? IIRC F=pA which means the pressure exerted over an area equals the force available. With a smaller area for the steam to push upon, wouldn't the power output of a steamer be less when going backwards?
Just trying a logical approach to answering you...but in what way would it be different from the other direction? No matter which way the engine is moving, pick one, each piston, shaped like the other, rodded like the other, does exactly the same thing....slide back and forth exerting the pressure on the rod that it can by design and function.
Steam enters each end of the cylinder one end at a time, expands, and does its work on the available surface area.....direction of travel doesn't change that.
It occurs to me that you are not aware that, regardless of the direction of motion, the valve gear and the cylinder let steam do its business on both their ends....alternately. When the steamer is runing pilot and stack forward, it is not only one side of the piston face that ever gets steam. The piston is blown away on both sides of it as steam is allowed into each end of the cylinder, but in a timed stroke...hence the purpose of the eccentric valve motion, with variance allowed by the Johnson bar to adjust the valve to let steam in the appropriate side of the cylinder on the first stroke such that the cylinder wanting to flee the steam drives its rod on the right side of the drivers' centres to force the desired rotation about the axle.
I don't know it that is very clear.
Here is a site that explains it with an animation. There is a link that takes you to a reversing depiction that shows how the Johnson bar lifts the link, bringing back the valve stem and thus causing the valve to admit steam to the other side of the cylinder that last received it ...which causes the reversing.
http://home.new.rr.com/trumpetb/loco/
Amen J Edgar!! Also from some stories from old Railroad Magazines and first hand accounts. Crews would rather the tender follow them on coal burners. No matter how much water you soaked into the pile they say you always got a dusting of coal.
I have had coal dust in my boxers all day once and it SUCKS!!You sweat and it turns to mush and itches and just makes one miserable.
Yes we are on time but this is yesterdays train
Railway Man wrote: wjstix wrote: Remember that the wheel arrangement of a steam engine was there for a purpose. An 0-6-0 would be limited in speed even if it had large driving wheels, because the drivers would have a harder time going into a curve and would be more likely to derail. Engine designers found early on that putting a two wheels in front to make a 2-6-0 or later 2-8-0 helped the engine run considerably. As speeds increased, passenger engines got a four wheel truck which tracked even better at high speed, creating the 4-4-0 and 4-6-0, later the 4-6-0 etc. Trailing trucks came in to help carry the ever-growing firebox, first two wheels, then four, even six.So if you have say a 4-6-0 with tender and you turn it around to run it backwards, you have the engine pushing it's tender at speed (increasing the risk of a derailment) and the big drivers digging into the rail with no lead wheels to help ease the transition into the curves. Even a 4-6-4 would still have to deal with having the tender in front. (BTW a NYC Hudson would have a hard time taking on water from the water pans on the mainline if running backwards, since the tender scoop would be backwards too!)There were some engines designed to go both ways, like a 4-6-4T, and on some branchlines it wasn't unusual for an engine to pull a train facing backwards at slow to moderate speeds. But particularly at speed steam worked best going forward.That's how I understand it too. The suspension of a locomotive can be designed for either-or, or favor one direction or the other. If you know can acheive superior tracking and geometry by designing the locomotive to favor one direction, then by definition it's not going to be very good in the other direction.I think I recall seeing timetable special instructions about speed limits on reverse moves on helper locomotives dropping down hills. I have to think that is a suspension geometry question rather than a visibility question, because the way railroads think, if you have a tender in the way you're expected to just stick your head out farther.RWM
That's how I understand it too. The suspension of a locomotive can be designed for either-or, or favor one direction or the other. If you know can acheive superior tracking and geometry by designing the locomotive to favor one direction, then by definition it's not going to be very good in the other direction.
I think I recall seeing timetable special instructions about speed limits on reverse moves on helper locomotives dropping down hills. I have to think that is a suspension geometry question rather than a visibility question, because the way railroads think, if you have a tender in the way you're expected to just stick your head out farther.
RWM
the type of mounting system for either leading or trailing wheels makes a difference in how it will track in relation to direction and stability....most trailing trucks are merely pivoted on pintels with friction plates to support weight and running backward at speed would likely cause the truck to wobble.... some early Atlantics and other wheel types had a ridged mounted trailing wheel....ridged in name only as it would be mounted with bearing boxes in frame slots and sprung to the rear driver......this trailing wheel was to support weight and guide the engine in reverse.....most superpower leading trucks are radially connected to the main driver equalizing system .....to support weight and guide the drivers into curves....some early engines...1800's..........had nothing more then a true truck pivoted on a kingpin sprung to the main drivers..............to support weight and guide the drivers into curves.......going back to the early greats in locomotive building they figured out pretty quick that guiding the engine in the forward direction and spreading the weight was as important as keeping up steam.... early track construction wasnt the greatest for a budding industry.....once it was known what worked things didnt change for over 100 years of steam locomotive construction......other then the size....
.
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
Timber Head Eastern Railroad "THE Railroad Through the Sierras"
Some Steam engines "Trip" and sway off the track without a trailing truck supporting the cab/firebox to guide the engine backwards. Switchers dont suffer because of low speed but road work killed them and wore the crews out.
Im going to say it first before anyone else on the West does, the Cab Forwards were a example of direction of travel being irrevelant and everything to do with giving the crew a chance at the fresh air inside the tunnels before the smoke. Going in smoke first probably hurt the crew and rendered them either dead or ineffective.
Turntables for the engines. Wyes were convient when they are used but more for returning a train to home base after a turn or similar.
Keep in mind the steam engine worked steam both ways inside the cylinder. That is why we get the familar 4 beat in the USA steam.
clash wrote:Itf I remember correctly, a certain amount of valve "advance" is built into a steam locomotive valve gear through the combination lever and combination link . I presume this designed in valve advance is only in the forward direction and ,when moving in reverse, the valve motion is actually retarded. This probably is'nt very noticable as steam locomotives usually operate much slower while running in reverse.I am only speculating on this and would appreciate the opinion of someone who has more knowledge on the subject.
Steam locomotive valve gear is perfectly symmetrical in its relationship to piston positon and cutoff - there is no bias in favor of one direction of travel. Reverse operation is lower speed for the reasons previously cited, visibility and railroad rules.
The double-ended tank locos I am familiar with (JNR C11 and C12 classes) ran at equal speeds in both directions. If anything, the C12 in pusher service between Agematsu and Kiso-Fukushima ran faster bunker first - downgrade, light - than smokebox first - with a freight train between it and the road loco on a 2.5% upgrade. The C11s running out of Hakata on a couple of country branches were given equal running times between stations in both directions.
Thanks, Mark. I think the two best answers that make the most sense are the visibility issues and the tracking issues, visibility being the most obvious. I am not so sure about whether steam locomotives track better with the tender in front or in the rear... but when folks talk about tank engines, or the mighty Garrett in South Africa, it makes sense that they, being unibody locomotives, would function equally well going either way.
Did the Garrett have visibility issues? Seems to me I recall that one end was taken up with a large coal bin....
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