(But moderators, if this is inappropriate, please feel free to take it down.)

A lot of you know I write fiction in addition to being a flaming steam fan. I'm looking at a scene that makes me uneasy because I may be making a major Hollywood mistake.

Let's assume that a large steam engine (coal-fired Mallet, to be exact) is sitting in the yards, with a move contemplated in an hour or two. She doesn't have a full head of steam, but has enough to move her around for the needs of the moment since she isn't coupled to anything.
Were it necessary to make a very quick forward move, followed by a sharp stop, a reverse move of about a hundred feet, and another quick forward move of a quarter-mile or so, what damage might result? I'm thinking holes in the fire, but would anything more serious be apt to happen?
If it helps, the situation in the scene is extremely urgent and there is no choice but to move her immediately--at least on the forward leg of the trip. (And no, she's not about to be, er, Unstoppable.)

Thanks in advance,

Becky

On low pressure, it won't do ANYTHING quickly. Mallets in particular, or actually any compound engine, since the high pressure engine needs to move a couple strokes before the LP cylinders get their secondhand steam. Which steam, already low pressure and expanded once in cool cylinders enters another set of cool cylinders, turns into a warm wet fog and rains out the stack until the cylinders get hot. There MAY be a simpling valve, but not on every example.

OTOH, nothing raises steam pressure better than moving a bit since the draft fans the fire - until the fuel is burning out rather than burning hotter.

No air pressure to brake with for the fast reverse move either, which leaves a slowish Johnson Bar stop followed by a short pause while the steam exhausts from the end in which it is trapped by the compression braking and the other end of the cylinders fill to start up in the opposite direction. Power reverse needs air to work, unless you run it on emergency steam, BTW, which tends to fry the air oil into nasty clogging junk if it doesn't wash it away first.

So, I'd spend a bit of the hour or two raising steam with some coal and blower and make some air before starting to move, if I understand the scenario correctly. Alternatively, the scene will be slow and soggy rather than fast and dramatic.

Best wishes.

dave

I think you need to define enough steam to move around. She would probably move on much less steam than what is required to run the compressor to have fully operational brakes and power reverse. If the engine is hot enough to have 50PSI steam you could have full pressure in an hour or so although most operators today would not push it that fast. In the 1940's they probably would have on a regular basis.

A-HA! Thank you.
I may have to have them doing some switching with her or moving her around the yards just before the big event to make the relatively quick move plausible. (I mean railroad-quick, not airplane-quick.) She has to back through a switch, pick up another piece of equipment and get out of the way in a (relative) hurry.

Yeah, that's the key. If the engine had just come in from a run, she'd have full pressure and a decent fire... likewise, if the engine was scheduled to go out in an hour, the hostler would have the blower on and be getting the fire in shape. But if she'd been sitting all night banked, nothing dramatic is going to happen.

Thanks. I knew she couldn't have been sitting overnight, but I wondered about the hour or so. For the purposes of the big event, she has to be the only piece of big power outside, so she may be the default switcher of the moment. That would give me an excuse to have her sitting in harm's way with a decent head of steam. I'm trying to eliminate the "Hey, WAIT a minute!" reaction. Not even a diesel fires up fast enough for what has to happen.

I thought the incident was really clever when I made it up, only to find that something very close to it, differing only in tiny detail, really happened. At least I found out that it wasn't impossible.

I like the "just come in off a run" idea. Still good pressure in the boiler, a bit of a scramble to get a few scoops of coal on the banked fire and the blower on and the air pump started, but moving off within a couple minutes.

dave

This reminds me of what I think is a true story from about a hundred years ago in Mexico. A train had stopped for water in this small town in a mining district. Nothing out of the ordinary. Then the engineer noticed flames coming from a boxcar loaded with explosives. The town didn't have a fire department, so the engineer took action. He pulled the pin at the rear of the car, shoveled some more coal into the firebox, and highballed out of town. Just a few minutes later an explosion echoed over the landscape. The engineer had perished, but he kept the town from being blown off the face of the earth. Reportedly, visitors to this town can still see the monument erected in his memory.
(one might call this story the antithesis of railway preservation, but it's part of the vast lore of our favorite system of transportation)

The "operative" word here is air. It usually takes 175 psi or above to keep the air pumps running enough to keep the main res charged. Moving isn't the problem, stopping is.

Here's another thing I hadn't thought of: if she isn't coupled to anything, she should have enough air for her independent brake, correct?
I'm going to go with she's just come down off the hill and has been shuffling cars around the yards while she's waiting to go out again. That would leave her fired up and ready to roll. All she has to move in a hurry is a very small, old 4-4-0.

OK, about 100 PSI left in her, on a banked fire, been home for about an hour or so off a run, hostelers just done with beddie-bye. Uncap the stack, spread the bank out, throw in a few scoops of coal, open blower valve. Open lubricator valve, then start air pump. 70-75 PSI air will actuate the independent air brake and power reverse just fine, 100 PSI steam will make 75 PSI air. 3-4 minutes and you are slowly moving while warming up with cylinder cocks open. A few minutes of getting warmer and building some steam while going to the pickup and you are at 120 - 125 PSI and ready to hook up to the dead engine and haul it away.

dave

this makes me think of the Star Trek last second moment, you have an opportunity of dramatic moments here. Scotty, the Fireman and Jim, the Engineer
have to try to do things given restrictive things that barely make to happen.
On the average Hollywood always gets it wrong, but if you know your thing, it gets lots better dramatically, say your crew knows they need to do something fast, they have to fuel the fire on low pressure to get things to work right, air, moving, at the last second the pump gets enough pressure to work the brakes. etc etc.

As far as damage goes, you can have driver slippage, that tears the rail a little, or hard brake application that freezes the drivers/wheels skidding, there is some potential derailment issues, turning the rail over, maybe a weak spiking joint spreading the rails , engine too heavy for the track as the rail is to light for its weight, so your "big event" can lead to plenty of dramatic moments.

When you understand your steamer better you can have better ideas how to impliment your story.

I think the best most accurate Hollywood train film is the Great Train Chase.

No, the first half of "Our Hospitality." "The General" comes pretty close.

dave

Thanks again for all the help. I have a couple of stories about this particular engine up online (unless the mods say it's OK, I won't link to them), but they mostly deal with regular excursions or the occasional dogcatch. This has to be more detailed. I did fudge by having an outside observer see what happens (steam crew member who can't get over to the engine to help) so what's going on the the cab won't be on camera, so to speak. The scenario is that the engine shop is on fire from a lightning strike and the paint locker may blow at any minute. The fire department hasn't made it to the yards yet and the engine is beside the burning building. I can always say a couple of the nearly unused tracks into the shop are old light rail because the small old engine never moves. (She's chained down, but if a heavily modified EM-1 cranks up I don't think either the chains or the rail will be a problem.)

ETA: In the real-life incident, a piece of historic equipment--I forget who--was saved from a shop fire because someone backed full tilt into the door behind which the old engine was parked. The sheet metal gave way enough to allow a coupling, however shaky and definitely not FRA-authorized, and it stayed hooked long enough to get both engines out of danger. It wasn't a sane thing to do, but a lot of things we do for the love of old iron aren't sane :)

good luck on your writings, feel free to work out details with us.