I was taking water from my water cooler about 5 minutes ago and it led me to think of boiler explosions and water-injected boilers.
Question #1
My understanding of the system is: water is stored in the tender and fed into the injector, which in turn injects it in the boiler. Hypothetically speaking, if the tender runs out of water and—for whatever reason—there is no water to fill the tender, does the fireman have to just drop the fire to avoid a boiler explosion?
In the past, I always thought the steam engine would simply gradually lose power. However, it occurred to me now that the water line would dip below the firebox, causing the metal to be compromised, and the boiler would explode—hence, I think if a steamer were running low on water, the fireman would have to drop the fire to avoid a boiler explosion?
Question #2:
Speaking of boiler explosions, is it just me or did boiler explosions seem more common on larger locomotives? I know of instances where the water line dipped below the firebox in smaller locomotives, and there was no explosion—though the boiler was finished. But, in larger locomotives: finito. Is this my imagination, or is there a reason for this (higher psi maybe?)
Question #3:
God forbid a boiler explosion on one of today’s steamers. I really hope every excursion railroad is careful about this and knows that the future of steam excursions rests in their hands. One explosion = no more steam excursions. Darn lawyers [;)]. Do current excursion locomotives carry any modern or advanced equipment to avoid a boiler explosion/detect a drop in water in the boiler?
Question #4
Is it possible for an engineer to rapidly “drop,” for lack of a better term, his boiler pressure? If he suddenly realizes his water is too low, does he have an emergency recourse?
Good questions Gabe. Again, I’m no expert but I do know that if the crown sheet is exposed and heats up when water does again hit it , well say bye bye.
I think boiler explosions were more dramatic on bigger locos because of greater pressure being allowed to build up before catastrophic failure of the pressure vessel. I have read about the great distances a locomotive can be launched. I used to have a book on train disasters that had many photographs of boiler explosions. Some real wild stuff.
I would be interested in hearing what the old heads have to say about this.
Rule 1: Do not run low on water. Make sure the gauges (water glasses) are working properly and the injectors are working. There are two, normally only one is used, the other is a back up or used for short periods when the main one cannot keep up.
Rule 2: If rule 1 is violated, drop the fire, now, not later.
Rule 3: Keep the steam pressure you have, if you reduce it quickly the water boils faster lowering the level in the boiler even more exposing even more firebox and tubes. Do not apply cold water if the crown sheet is exposed.
Rule 4: Stop the train and get clear of the locomotive.
Actually, most so-called boiler explosions are crown sheet ruptures. Excessive uncooled heat has caused the crown sheet to soften to the point where the boiler pressure forces the top of the firebox (crown sheet) to collapse down into the firebox and vent the boiler out through the firebox and taking the fire right along with it. Unfortunately for all involved, this includes the cab of the locomotive. The engine crew may never know what happened. For a certainty, they won’t know it when it does happen.
If coal fired, you will have to drop the fire onto the ties. This causes Mudchicken fits, but lets you live to hear his fits. I prefer to listen. But Mudchicken is going to have to replace everything for several hundred feet, and like I said, he won’t be happy.
If oil fired, simply turn off the oil. It won’t take long for the fire to go out. You can aid the process by closing off all combustion air going into the firebox. Close the throttle and stop the train. Keep the pressure up as arbfbe said. Let the pops handle the situation.
And be patient. The Dispatcher is going to have to call out a tow for you and he is not going to be very happy. About as happy as Mudchicken. You just shut his railroad down for about 8 hours and took a locomotive out of service for at least two months or perhaps forever.
Hopefully, you got to the situation prior to the crown sheet being exposed. Remember also, that you can have several inches of water over the crown sheet and still have it exposed if the boiler pressure is permitted to drop - water will be making steam faster than liquid can flow in to replace the vanished liquid.
If you ran a water plug that you were supposed to fill up at, you won’t be working for a steam operation ever again. They may be impressed by your action in saving lives and machinery, but the fact you permitted this to happen in the first place … well.
There was an incident with a locomotive boiler explosion about 10 years ago in Pennsylvania. Here is the NTSB report on the incident if anyone is interested.
Yeah, on the Gettysburg Railroad, near Gardners, Pennsylvania. Take a look at the link I posted in my previous post. It goes to the NTSB report on that explosion.
The incident at the Gettysburg was actually a RELATIVELY minor boiler explosion. (locomotive stayed on the track, boiler did not go airborne, no one was killed) As the NTSB report points out, what prevented a full fledged explosion from happening was the Canadian boiler design of alternating straight thread and button head crown stays. (see p22 of the report) In effect what happened was more of a controlled release rather than an explosion.
Regardless, the reason why the water level dropped so low in the first place was due to crew negligence and a false reading on the water glass due to scale blockage. This incident would have been avoided if the locomotive had been properly maintained and the crew had known what they were doing. In this case you cannot solely blame the firemen (there were 2)because the engineer is ultimately responsible for the water level on a steam locomotive.
Actually, the locomotive at Gettysburg was not equipped with fuseable plugs. What happened was a crown sheet failure. Read the report for the full story. (not as dry as you might think)
#1. Keep in mind that the tender doesn’t need to be “empty” to break flow to the injector or feedwater-heater lines. Likewise, grade can affect the working water level in the boiler (at least one class of locomotive, the NC&StL Dixie, had a plaque in the cab indicating the ‘right’ water level for working a grade). As indicated by previous replies, it isn’t the tender water that matters, it’s the boiler water. And it’s the crown sheet that usually fails – this sees by far the most heat from the fire, and for a variety of reasons isn’t tolerant of overheating even for relatively short periods or over relatively small areas. Supposedly, thermic syphons a la Nicholson help keep water over the crown sheet when working low water, but in at least one explosion, 2-6-6-6 #1642 in 1953
the Nicholson syphons kept pumping water over the crown sheet, but did so in an irregular pattern, leading to thermal cycling and quench cracking which may have accelerated the catastrophic failure when it started.
Yeah, the ‘right’ thing to do is drop most of the fire as soon as you recognize there’s a problem with low water. Probably wise (especially with '40s-style weird nickel-alloy construction) to leave some heat going through the boiler structure to let it cool down and equalize instead of ‘shocking’ with a quick dump and open firedoor. (Also leave some heat in cold weather!)
More on this point in #4, but venting boiler pressure in ways available from the cab isn’t going to help you much (and only if you’ve already dumped the fire). Remember that there is a large mass of overcritical water sitting in the boiler below effective crown level. If you start relieving the pressure, this will obediently start flashing to steam, giving a nice mass flow at 1500 to 1800 times volumetric expansion, until the heat in All That Water drops down to allow the pressure to fall. Meanwhile, the
Overmod – sounds to me as though you have some practical experience with this kind of catastrophe? Hope not… but a superb explanation.
One thing for the rest of us to remember – clearly – is sort of buried up there, though: if you let the pressure off the boiler, boiling will occur throughout the boiler, not just at the top of the water. And enough water will boil until the water temperature is dropped to whatever pressure is maintained – in the case of a crown sheet or substantail tube failure, atmospheric. Which will be most of the water. His bottom line advice – if things look like they’re getting out of hand, kill the fire, keep the firedoor closed, set the air, and get the h_ll out of Dodge – is right on!
One might add that in modern haz-mat and fire work, there is a closely related catastrophe which is, if anything, worse and more spectacular: a BLEVE (Boiling Liquid Expanding Vapour Explosion). It has all the benefits of a boiler explosion, plus the resulting vapour cloud isn’t steam, it’s explosive.
My recollection is that the SP cab-forwards were peculiarly subject to boiler explosions, as the crown sheet was, of course, on the ‘uphill’ end of the engine and there were real difficulties in keeping enough water in there to keep it covered when working wide open.
The Uintah Railroad’s #50 was a 2-6-6-2T articulated narrow gauge engine built by Baldwin for use on 7.5% grade and 66 degree curves. Baldwin built a special section of track to test the 66 degree curve capability, but had no way to test it on 7.5% grades. The first run of #50 up Baxter pass was uneventful and proved that #50 was a powerful, flexible performer.
However, its first trip down from the top of Baxter pass was much more exciting. As the engine transitioned from lesser grades to the 7.5% grade, the engineer and fireman both noticed the water guage showing less and less water until it showed the crown sheet might be uncovered. In the words of the engineer, they opened the feedwater pumps to force as much water into the boiler as possible, while at the same time he dumped steam to lower boiler pressure. That allowed sufficient water into the boiler to show on the glass. He limped the engine to the yard at the bottom of the grade and quit the railroad.
(I know that this is at odds with your recommendations, Overmod, but he had a full water tank t work with.)
The engine was immidiately embargoed. The railroad’s own shops and Baldwin staff started with a drawing of the engine and drew a 7.5% grade line across the boiler and firebox. They determined that the crownsheet had not been uncovered - even though it looked that way on the glass.
The railroad shops then lowered the crown sheet by “several inches” and added a new steam dome near the rear of the boiler. Uintah’s undelivered #51 was so modified at the factory by Baldwin. Both engines ran well through their remaining Uintah career and then the Sumpter railroad in Oregon, finishing life in Central America.
My understanding of the system is: water is stored in the tender and fed into the injector, which in turn injects it in the boiler. Hypothetically speaking, if the tender runs out of water and—for whatever reason—there is no water to fill the tender, does the fireman have to just drop the fire to avoid a boiler explosion?
If the tender was suddenly found to be out of water and there wasnt a hole in the tank, the train crew would get fired. Even assuming a water line breakage, if their is sufficient water in the boiler continue for a short distance, the loco could be brought onto a siding and its fire quenched there. Dumping the fire was a big to-do, and was no gaurentee that it wouldnt blow because steel tends to stay hot once it gets hot
In the past, I always thought the steam engine would simply gradually lose power. However, it occurred to me now that the water line would dip below the firebox, causing the metal to be compromised, and the boiler would explode—hence, I think if a steamer were running low on water, the fireman would have to drop the fire to avoid a boiler explosion?
What your describing, the technical name I dont remember, is when the crown sheet is exposed due to low water, gets super heated, then either was water sloshed back onto it or the metal fatigues and fails resulting in a quick trip to heaven for the crew, there is nothing in the performance of the engine to indicate this as long as their is sufficient boiler pressure, the engine will perform normally, right up to the big kabloo-ee!
Question #2:
Speaking of boiler explosions, is it just me or did boiler explosions seem more common on larger locomotives? I know of instances where the water line dipped below the firebox in smaller locomotives, and there was no explosion—though the boiler was finished. But, in larger locomotives: finito. Is this my imaginatio
If a boiler did experience a crown sheet exposure , even for just a short time, its boiler was considered compromised and would have to be rebuilt, and the engineer and fireman would be in deep poop.[:0]
There was a story in TRAINS a few years back about explosions and their causes. I think the name of it was “Big Bang - No Theory”.
As I recall, the story was reprinted in the National Board Bulletin, the magazine of the National Board of Boiler and Pressure Vessel Inspectors. If you’re interested, maybe you could get a reprint from either source.