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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Tue Jul 17, 2012 11:52 pm 

Joined: Fri Mar 03, 2006 1:45 am
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Location: Skagway, Alaska
Ok, here is a further question if you catch my drift. (no pun intended) How do you convince others that you aren't "wasting steam"?

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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 12:20 am 

Joined: Fri Mar 05, 2010 3:41 am
Posts: 3971
Location: Inwood, W.Va.
I just got to looking at this thread, and as so often happens, it tickled my brain cells into remembering an article in Trains years ago. It was an account of what it would have been like to run the then recently restored 3985 in regular service, and was written, if I recall correctly, by none other than Steve Lee.

His comments about drifting the Challenger stood out. As I recall, the technique would have been, as the engine would go into some phase that required drifting, would be to close the throttle briefly, then open the cylinder cocks. Crack the throttle until you had just a bit of steam showing at the cocks, then close the cocks and adjust the reverse to reduce rod noise to a minimum.

What this did was to maintain a steam flow through the superheater, supply lubricant to cylinders and valves (which was implied as the most important thing), and also to obtain a cushioning effect for the running gear. I seem to recall he commented that a steam locomotive should normally never be drifted with the throttle closed, unless just about to stop, largely to maintain lubrication in the cylinders.

At least that's how I remember the piece; someone else may have that digital copy of Trains handy, and be able to look it up quicker than I can among my "musty magazines" (what my wife calls them) to make sure my memory is right.


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 12:49 am 

Joined: Wed Aug 25, 2004 11:16 am
Posts: 767
Hi All

On locomotives with a mechanical lubricator for the valve and cylinders they keep pumping as the locomotive moves. On SP 3420 which is equipped with a hydrostatic lubricator the oil is inputted into steam flow in the branch pipe before the valve to lubricate both the valve and the piston. In this arrangement steam is critical at all times to atomize the oil so it spreads evenly.

The other thing to keep in mind with the throttle closed is you actually create a vacuum in the piston as it pulls away from the cylinder head creating new forces on packing and other seals and when the valve travels to exhaust the side the vacuum sucks in matter (gas and solids) from the smoke box to fill the vacuum. The hot gases this action draws in can carbonize the valve oil due to temperature or if it is solid in state it can act as sand paper. Furthermore one must remember that if the locomotive is working hard with exhaust gas temps over 2500 F and superheat temps approaching 640 F you have the potential to soften the steel in the superheater units if they see some more heat without the heat draw from the steam flowing through the superheaters. With 18 and 4960 at GCR I saw temperatures of over 600 F for the better part of the trip over the road. There we drifted with the valves at or near full motion and about 20 psi of steam pressure in the cylinder chest.

When I went to work for another line they wanted you to go downhill with the locomotive hooked-up. This created a hopping sensation (on a rod locomotive) if there was not enough steam to the cylinders and if there was enough it took more brake to hold the train back than if the gear was in full travel creating a longer input pulse at a lower pressure. The other advantage to drifting with a full valve travel with minimum steam input is the valves travel into areas that they did not reach when hooked-up and they might pick up any lubrication that had been thrown onto those surfaces. While I was there, the only time we did not drift with full valve motion at GCR is when we were trying to reduce rod slap and we found if we hooked-up the locomotive 3 or 4 notches from full travel we eliminated at lot of noise without much additional braking force.

Robby Peartree


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 1:34 am 

Joined: Wed Oct 22, 2008 8:18 pm
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I'm a little aghast at the thought of "cooling" the superheaters, when the purpose is to heat the steam further that creates more power, the superheaters have to be able to withstand higher temperatures than just the boiler. Given temperatures in the coal fire may get hot enough to melt metal it just does not happen due to heat transfering.
I understand about the "why" effect of keeping the steam moving to prevent an overheating of the tubes. But the whole purpose of the superheater is to get that extra POP to the engine. ..now that I think about it...NNNnoooo, you can't really hurt the superheaters like this when the flues have to be treated red hot in an oven to make them spread for flaring the ends, you will never get the superheaters to that temperature. You'd have to pitch them into that oven to do that.
If they couldn't withstand this extra heating, you have the wrong superheaters.
I think simply heat wear and acidic gasses are your worst enemies here and that takes time over your normal boiler use.

Drifting downhill or even at speed cutting off the throttle to coast or braking you will still tweak the throttle open to pass steam to send the lubrications thru and as already noted prevents the reverse vacuuming. The reverse valve "Johnson bar" has more to do with when the steam is cutoff to the cylinders, the throttle effects the -volume- of steam admitted. This is where running a steam engine becomes an art form a bit learning how to work the two with different train sizes and speeds and grades up/down for the most effective operation. Your "bar" will be full forward when starting and at speed is cut back because you don't need that starting power to maintain speed and may actually be an operational hinderance full open at speed.
With the "bar" back a bit you let the normal steam expansion to do its powering than continuing to admit more steam.

Aside from that even when braking you may still power the throttle to keep your train "stretched". Or face the broken knuckle wrath.


feel free to correct me or enhance :D


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 6:33 am 

Joined: Sun Aug 22, 2004 8:31 am
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Location: South Carolina
Regarding the original post in this thread, which includes a link to the 5AT website, including comments on drifting by UK steam designer David Wardale:

Wardale conclusively determined that the optimum way to drift a steam locomotive is with the reverser centered and the throttle cracked. He did this by testing- using an indicator on a locomotive and by testing all the "popular" suggestions for drifting steam locomotives. The indicator diagrams showed that reverser centered/throttle cracked prevented any vacuum in the cylinders which the other settings did not.

Robert's photo clearly shows there are other reasons this is the best way to drift as well.

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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 9:11 am 

Joined: Sat Feb 05, 2005 1:05 am
Posts: 482
When steam flow ceases in a superheater, the tube almost instantaneously achieves the temperature of the flue gasses. At the firebox tubesheet at high firing rates the temperatures will be between 1500F to 1700F. For locomotive superheater materials, at temperatures over 850F the carbon will start to migrate out of the grains to the grain boundaries resulting in loss of tensile strength. At about 1100F the degradation is measured in hours.

Powerplant superheaters have a safety valve set to a lower pressure than the drum such that if the turbine trips, it always pops before the drum to maintain flow through the superheater tubes.

Note than my superheater tubes are bent more than Bob Y.'s are......
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Attachment:
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bentsuperheaters2.jpg [ 50.92 KiB | Viewed 13655 times ]


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 10:58 am 

Joined: Fri Aug 27, 2004 4:02 pm
Posts: 1841
Location: Back in NE Ohio
I come at this as a latter day dismal engineer (and, until recently, the subsequently minimal training in anything but the use of dynamic braking). I've had some experience running steam over nearly four decades, only one small part of that on a mainline at speed (The Wolsztyn Experience). Over the years I've heard brief explanations before about the problems of drifting a steam locomotive. One of the surprising things about the operating practices at Wolsztyn is the amount of the trip (at least on the line to Poznan) spent coasting. My guess is that nearly 25% of the trip is spent coasting at speed, throttle totally off (get the train up to 50 mph, then coast several minutes before braking for the next station - 17 stops in 52 miles). The engine crews there would be either puzzled or horrified at the idea of "stretch" or "power braking", since with European style couplers there is virtually no slack in a train to keep stretched. It's really hard for me to know, since most of their crew's English was not much better than my Polish (non-existant), but they seem to have next to no concern about possible harm to the cylinders or superheaters from so much drifting. Anybody here familiar with Polish/European drifting appliances on those locomotives (I was running 2-6-2 Class OL49 #59 with Russian Tropinov[sp?] valve gear for anyone familiar with them)?

Also, the thought occurs to me that knowing how fast a short train (like a steam excursion train) heading downgrade gains speed, the engineer must be incredibly busy opening cylinder cocks to check for steam flow, while adjusting the throttle and oh, by the way, not letting the speed get out of control, and also remembering to blow for grade crossings, etc. It really isn't just a matter of drifting at a given speed, trains gain momentum downgrade at a surprisingly fast pace, and with modern brake shoes, will slow down way too much in fairly short order, even with only a minimum service application on them. So, it must be a fairly constant cycle of adjusting the throttle, playing with the cylinder cocks, and setting and releasing brakes? Any of the experienced steam hoggers here care to comment?


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 11:16 am 

Joined: Fri Dec 03, 2004 9:42 pm
Posts: 2953
dinwitty wrote:
I'm a little aghast at the thought of "cooling" the superheaters, when the purpose is to heat the steam further


It does sound a bit odd to think of keeping them "cool" with steam, but it works. The reason why it works is that they heat the steam, just as you said. Since the steam is absorbing that heat, then the tubes themselves don't get overheated.

Quote:
the superheaters have to be able to withstand higher temperatures than just the boiler. Given temperatures in the coal fire may get hot enough to melt metal it just does not happen due to heat transfering.


Think about it for a moment... The firebox is kept cool by having water on all sides. If you remove that water, things get ugly pretty quickly. (Don't try this at home!)

Quote:
the flues have to be treated red hot in an oven to make them spread


The difference between an oven and a hot firebox, especially one full of coal that can't simply be "dialed down" would be what? The end of the tubes are quite near that firebox.


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 11:29 am 

Joined: Fri Dec 03, 2004 9:42 pm
Posts: 2953
PaulWWoodring wrote:
Also, the thought occurs to me that knowing how fast a short train (like a steam excursion train) heading downgrade gains speed, the engineer must be incredibly busy opening cylinder cocks to check for steam flow, while adjusting the throttle and oh, by the way, not letting the speed get out of control, and also remembering to blow for grade crossings, etc. It really isn't just a matter of drifting at a given speed, trains gain momentum downgrade at a surprisingly fast pace, and with modern brake shoes, will slow down way too much in fairly short order, even with only a minimum service application on them. So, it must be a fairly constant cycle of adjusting the throttle, playing with the cylinder cocks, and setting and releasing brakes? Any of the experienced steam hoggers here care to comment?


Yep, you've got it about right, especially on a line with lots of grades and curves. One of our engineers used to joke "They do engineer training for this line on the Roller Coaster at Coney Island!" It's not really that bad, but we do have our share of ups and downs.

Oh, you forgot a few things... Keep an eye on your fireman, you want to verify that he's (most, but not all, are male) got enough water in the glass, and also what the boiler pressure is. You also need to communicate with him about what you're doing, if the track is clear etc. Keep an eye on the lubricator as well, being sure it's feeding OK. Listen to your engine, is it making any unusual noises or doing anything else that may be of concern? Monitor the radio, and keep an eye on the train. Look out for fallen trees, deer or other animals, slides and washouts etc. Keep the schedule in mind too. I'm sure I've also forgotten a few things, if not more.

A couple things help out though. By the time you're promoted to engineer, you already know the line like the back of your hand. You're been firing for a while, most likely a couple years if not more, and then spent more time as a student engineer. By then grade crossings don't "sneak up on you", any more than the intersections on your drive to work do. You know the grades, you know the curves, you're familiar with the territory. (We're talking typical tourist railroad, not mainline excursions, but in that case you'd have a pilot)

You also get to know the equipment, so after a few times of opening the cylinder cocks to check how much steam flow you have while drifting, you get to know "OK, so if I notch out two notches I'll have what I need" and so you don't have to check it constantly. You might check it a time or two, then be comfortable. You also get to the point where can feel what's right. The engine drifts easier when she's getting a touch of steam in the cylinders. Too much steam? You'll really start to pick up speed and you'll hear it in the stack.

Short trains do make for challenging braking, especially when the profile changes a lot. The slow speeds most tourist railroads operate at can also make it difficult, since you end up with a pretty narrow window to keep the speed in, for example at least 10mph but not more than 15mph.

The slow speed does help in one regard, things don't happen quite so quickly.

But yes, on some railroads the engineer is pretty busy. With practice, a lot of it becomes second nature.


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 12:20 pm 

Joined: Sun Aug 22, 2004 7:19 am
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Location: southeastern USA
I'm struck by the loss of basic operating practices evidenced by this thread......or by the loss of actual experienced practitioners who now post to RyPN in proportion to others. This is steam 101 information, people....don't argue with the pros who are advising you on this or any other technical topic just because you don't understand it.

Heating tubes in an oven to make them spread? Good lord......annealing newly safe ended tubes or swaging superheater flues is not at all relevant, assuming that's what was meant.

I'm starting to get very scared.....

dave

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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 2:33 pm 

Joined: Fri Dec 17, 2010 2:41 pm
Posts: 166
JohnHillier wrote:
Ok, here is a further question if you catch my drift. (no pun intended) How do you convince others that you aren't "wasting steam"?



Tell them to leave railroading to the professionals and stop bugging you with senseless banter...sorry I couldn't resist!

Simply tell them to watch the pressure gauge, water and fireman to dispel that accusation. If they continue to rant, show them one of the photos Mr. Yuill or Mr. Austin has kindly put up here. If that still isn't enough, there's quite a few items that others have brought up in this thread worthy of noting to convince them otherwise also. Whether it is lubrication, the vacuum effect that draws flue gases and cinders into the cylinders(sans relief valves), overheating dome-throttled superheaters, keeping the running gear quiet, more controlled station stops associated with proper train-handling etc. each has their own validity


Best,
DC


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 4:11 pm 

Joined: Thu Aug 26, 2004 2:50 pm
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Location: Northern Illinois
JohnHillier wrote:
Ok, here is a further question if you catch my drift. (no pun intended) How do you convince others that you aren't "wasting steam"?


Tell them you are expending a little steam to keep from wasting the life of the locomotive.

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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 4:52 pm 

Joined: Mon Aug 23, 2004 2:14 pm
Posts: 618
Location: Essex, Connecticut, USA
Greetings:
A couple of comments.
Two of our steam locomotives are superheated with dome throttles.
The older one has steam chest relief ("snifter") valves. On this one we train our crews to drift with the engine in full gear in the direction of travel with the throttle opened just enough to keep the snifter valves closed. Having the engine in full gear keeps it from pounding. Having the throttle opened slightly insures that there is a flow of steam to keep the superheater units (relatively) cool and positive pressure at the exhaust nozzel keeps cinders and such from being sucked into the valves.
Our newer one (Chinese class SY) is equipped with Trofimov valves, which are a "poor man's" drifting valve. Locomotives with Trofimov valves are drifted with the throttle fully closed (steam chest pressure "0") and the reverser on center. Steam/air trapped in the cylinders moves back and forth from one side of the piston to the other until the throttle is again opened. Locomotives with Trofimov valves have extra lubricator lines and mechanical lubricators set to a bit higher feed rate to issure sufficient lubrication while drifting.
The question, of course, is what about overheated superheater units on Trofimov equipped locomotives? Having seen many (over 100) Chinese steam locomotives torn apart being rebuilt at various Repair Factories throughout the country, and never seeing a superheater unit in the condition show in the first photo above, I have two thoughts: since Chinese steam locomotives were "over maintained" (totally rebuilt every 300,000 KMs), perhaps the superheater units were never allowed to get thinned to the point that they would warp and/or they were using heavier and/or different material in the first place. My recollection is that the material for the superheater units came from the same mill that made the tubes and flues.
I would note that on the JiTong Railway going north, there was a downgrade of perhaps 30 miles. Decending this grade (cycle braking with No.6ET, if interested) the throttle was never opened.
J.David


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 6:59 pm 

Joined: Sat Jul 25, 2009 9:49 pm
Posts: 36
Dave wrote:
I'm struck by the loss of basic operating practices evidenced by this thread......or by the loss of actual experienced practitioners who now post to RyPN in proportion to others. This is steam 101 information, people....don't argue with the pros who are advising you on this or any other technical topic just because you don't understand it.

Heating tubes in an oven to make them spread? Good lord......annealing newly safe ended tubes or swaging superheater flues is not at all relevant, assuming that's what was meant.

I'm starting to get very scared.....

dave


Very well stated Dave! You must have a background in operating steam. To further your point, the first seemingly entirely unknowledegable response to this thread from "hadder" is from the shop foreman at the Grand Canyon Railway. The individual on the front line for the mechanical care and operating crew over-site of their steam locomotives.

John


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 Post subject: Re: Throttle/Valve Settings While Drifting on Steam Locomoti
PostPosted: Wed Jul 18, 2012 7:07 pm 

Joined: Fri Nov 16, 2007 10:21 pm
Posts: 174
J. David's comments on the Chinese engine have me thinking about the AT&SF.... Didn't some of their locomotives have a drifting valve? I'm not that familiar with the operation of those, and don't know if the throttle is closed normally while drifting. Also, were those only on locomotives with front end throttles, or were there some on locomotives with dome throttles?

My main interest is on locomotives with water brakes. My understanding of the operation of the water brake is - the throttle is closed, the reverser placed in oposite direction, and hot water is supplied to the exhaust cavity to break the vacuum between the smokebox and cylinders. I believe there were superheated locomotives that also had water brakes. Did they just have much more failures of the superheaters?

In response to John Creasing, GCR practice has always been to run downgrade with a drifting throttle with the reverser in full gear so that the cylinders receive lubrication, there is no exaust sucked back into the cylinder cavity, and there is some cushion for the rods. However, I realize that other Railroads have other practices, and I am trying to play devil's advocate to understand why they though those practices were better than others.


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