Stupid Steam Questions

[Anonymous]

Common sense tells me that a steam locomotive ought to perform exactly the same way going in reverse as it does going forward.  Yet it seems the railroads made a lot of effort to insure that steam locomotives always faced "forward".  They built turntables, wyes, and balloon tracks just to turn the engine (or, sometimes, the whole train) around. Why did they do this?

Did steam locomotives perform any better going forward than in reverse?  Was the output of an SP "Cab Forward" any different than a similar steam engine facing "forward"?  Was there any difference in water flow from the tender when the locomotive operated "in reverse"?  (The reason I ask is this: I assume, probably wrongly, that the system of siphons "pulled" water from the tender into the firebox.  If the water "sloshes" back in the tender when the locomotive moves forward, then perhaps it "surges" when the engine is in reverse.)

Thanks!

[CSSHEGEWISCH]

A steam locomotive does not track very well at speed while shoving its tender in front of it and the cab-forward design works with oil fuel only.  Tank locomotives work well in either direction since they don't have a tender and Garratts are bi-directional by design.

[cprted]

The ability of the crew to see is also an issue. While the view out the front of the cab may not be great, it sure beats having to lean out to look around the tender.

[vsmith]

Engineer sits on the right side, seats faces forward, turn it around and now the fireman is one the engineers side, both are now sitting sideways on there seat looking back over the tender. Thats gets a bit uncomfortable for any lenth of extended time.  Switchers often had to endure sitting sideways for extended lenths of time but for the most part the reverse moves were short time wise. Dismal switchers had the same reversing problems as steam locos which is why side mirrors became common. I've read that some dismal switchers had seats that could be rotated 90 degrees so the engineer could sit and look both ways down the sides of the engine while still comfortably reaching the control stand during switching moves.

Water from the tender was pumped via a steam powered water pump into a preheater then direct into the boiler, so direction of travel was irrelevant.

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.

[Anonymous]

Good, sensible answers... thanks!

[marknewton]

Speaking only from my experience, the main reason for turning an engine was visibility. When running tender-first you can't see round the tender very well, and signal sighting becomes an real issue. As a result, the railway I work for has a blanket speed limit of 40 kph for tender first running. I once had to run tender-first from Gosford to Sydney, a distance of about 80 kilometres, and it was a real pain in the bum.

In Australia, Japan , the UK and Europe, many mixed traffic tender locos that were expected to spend a lot of time running trains tender-first had inset coal bunkers to allow better visibility in that direction. The same thinking is behind the so-called "clear-vision" tenders fitted to many US switchers.

I've never noticed any problem with the injectors picking up when running tender-first. If there's enough water in the tender, they'll work either way.

Cheers,

Mark.

[marknewton]

A steam locomotive does not track very well at speed while shoving its tender in front of it

I think that would depend on how the engine and tender were coupled. Most methods of coupling the two were designed to prevent slack, so running tender first shouldn't make any difference. The engines I used to work had Franklin radial buffers, and as long as the wedge was knocked up tight, the ride and tracking when running tender-first was not noticeably worse than engine-first.

Garratts are bi-directional by design

.

Yes, and depending on which Garratt you're on, the ride is either equally good or bad in both directions! The visibility from the cab on our AD60 class engines was better running bunker-first, and the smoke was behind you!

Cheers,

Mark

[Anonymous]

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....

[clash]

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.

[tomikawaTT]

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.

Chuck

[Anonymous]

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.

[wjstix]

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.

 

[Railway Man]

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

[Semper Vaporo]

If the cylinders were mounted directly over the drive wheels then track hammer would be equal in either direction of drive, but since they are mounted to one side there is a slight difference in hammer on the track based on direction of travel.  I remember reading (somewhere?) that the SP cab-forwards had differences in counterbalancing and suspension to account for the reversed operation of the engines.

[THE.RR]

I believe that the Santa Fe built the first 2-10-2's because of tracking, not weight distribution.  The trailing truck was added to a 2-10-0 to help guide it when backing down Raton Pass after its trip to the top as a helper.

[locoi1sa]

   I believe the main reason for piston on the front was for wear. the dust and dirt getting kicked up by the drivers getting into the valve gear would cause too much wear. Also do to width between the cylenders would limit firebox size. Look at the Pennsy Q1. But the Q2 was a dream but too much maintanance killed it.

[rrboomer]

I recall reading someplace, possibly an old ETT, that branch line backup moves (other than switching) were not to be made without over half a tank of water. I surmised this to mean that if the tender water level was low the rear tender truck would have less weight on it and more likely to derail.

[BigJim]

I'm sure that you will find different practices on different roads for different types of locos. On the N&W, engines on turnaround shifters (short run jobs where there was on means to turn the engine at the return point) were regularly run out of the initial terminal backwards in order to be facing forward on the return trip.

[J. Edgar]

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

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....

[J. Edgar]

and realy theres no such thing as a stupid steam question  

[route_rock]

  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.

[J. Edgar]

yea....rainy day as a utiltyman on a powerplant run.....expletitive deleted

[rrnut282]

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? 

[J. Edgar]

im no expert....but would they call that "nominal".....? granted im sure its there even measurable but not enough to hinder normal operation...IMHO

[selector]

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/

 

[Semper Vaporo]

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.

[dldance]

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

[tomikawaTT]

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

[Semper Vaporo]

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.

 

[rrnut282]

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.