JoAnne K I have followed this forum for quite some time and have never felt any need to post, until now. The tail of this thread had nothing to do with the head, and i would prefer you guys keep your name calling to yourselves. I may be a girl -I like that word, it makes me feel young again- but i do work with steam. I am currently employed by the Commonwealth of Massachusetts, Department of Public Safety, Division of Inspection of Testing as a boiler inspector. What Toot Toot has written is correct and no it does not violate the laws of physics, but he -I'm assuming he- has done a remarkably poor job of explaining what does happen. Steam is not like water. It does not flow like water. When the throttle valve is opened steam from the boiler EXPANDS into the piping and whatever is beyond. When it does so, the temperature of the steam drops measurably, even though the pressure may not appear to change, it does. In response to this stimili, steam pockets form spontaniously throughout the water, increasing the apparent volume of same as the boiler replenishes. By how much the water level changes is depend on what kind of boiler, but an inch is not impossible. No magic, no smoke or mirrors and no rewriting the laws of physics. Now please play nice. JoAnne
I have followed this forum for quite some time and have never felt any need to post, until now. The tail of this thread had nothing to do with the head, and i would prefer you guys keep your name calling to yourselves. I may be a girl -I like that word, it makes me feel young again- but i do work with steam. I am currently employed by the Commonwealth of Massachusetts, Department of Public Safety, Division of Inspection of Testing as a boiler inspector. What Toot Toot has written is correct and no it does not violate the laws of physics, but he -I'm assuming he- has done a remarkably poor job of explaining what does happen. Steam is not like water. It does not flow like water. When the throttle valve is opened steam from the boiler EXPANDS into the piping and whatever is beyond. When it does so, the temperature of the steam drops measurably, even though the pressure may not appear to change, it does. In response to this stimili, steam pockets form spontaniously throughout the water, increasing the apparent volume of same as the boiler replenishes. By how much the water level changes is depend on what kind of boiler, but an inch is not impossible. No magic, no smoke or mirrors and no rewriting the laws of physics. Now please play nice.
JoAnne
First JoAnne, you must be new to the forum if you've never seen a topic change from heading to the latest post. The longer a thread gets, the more likely this is to happen. Sometimes several times. And this is not the first time I've been called a troll by a newcoming poser. What I said is Toot-Toot's conclusion is correct, but how he got there in his long winded explanation on the first page is, at best, confusing and misleading, or as you say, "done a remarkably poor job in explaning." This is what I've called him to task about. Your explanation is much better and easy to understand.
I've worked with steam at both Steamtown NHS and at the East Broad Top Railroad. Before rebuilding the fire and steam pressure in the morning at Steamtown, it's quite normal to see the water in the glass fluctuate slowly by an inch or more, even after the locomotive sat still all night.
toot toot So how often does this boiler blow up when the temperature drops that much? Boiler temperature and pressure constantly fluctuate during operation and don't cause the boiler to explode. Loss of containment cause explosions. That's what I said. Now go back under your bridge.
So how often does this boiler blow up when the temperature drops that much? Boiler temperature and pressure constantly fluctuate during operation and don't cause the boiler to explode. Loss of containment cause explosions.
That's what I said.
Now go back under your bridge.
"Superheated" as applied to a steam locomotive means a boiler that is equipped with a clever device called a superheater, which differentiates it from a saturated steam boiler. We use railroad terminology, just in case you didn't notice the "Trains" logo at the top of the page.
Easily said by Mr. 139 posts with a juvenile name. Let me get out of the way while you make up your own laws of physics and dream up new uses for railroad terminology.
toot toot lets say that a boiler is operating at 200 psi g. the temperature of water in the boiler is 381.79 * F. open the throttle. steam from the boiler fills the dry pipe and whatever appliance is being run. let's say its a turbine, since i happen to have one right in front of me. The temperature of the steam measured at the nozzle is 368.41 * F. Difference of 13.38 * F. i have 22 years in as a steam plant operator. i have run ships, a hospital, a power plant, and a few locomotives. if you want to discuss this further i'd suggest you read Steam Plant Operation by Woodruff and back channel me afterwards.
lets say that a boiler is operating at 200 psi g. the temperature of water in the boiler is 381.79 * F. open the throttle. steam from the boiler fills the dry pipe and whatever appliance is being run. let's say its a turbine, since i happen to have one right in front of me. The temperature of the steam measured at the nozzle is 368.41 * F. Difference of 13.38 * F.
i have 22 years in as a steam plant operator. i have run ships, a hospital, a power plant, and a few locomotives. if you want to discuss this further i'd suggest you read Steam Plant Operation by Woodruff and back channel me afterwards.
This psuedo-science is almost as entertaining as Toot-Toot's screen name. If the volume of water is going to suddenly increse due to the change in temperature, what causes this temperature change in large enough margin to cause this so called "swell?" Still not explained by the Physics of the situation.
As I said, your last sentence is correct, but the question is in how you got there.
TomDiehl toot toot the term superheated means only that a substance has absorbed enough energy to change from one state of matter to the next, it doesn't matter if we're talking about water or iron. Now as for a boiler, any uncontrolled venting of the contents of the pressure vessel is called an explosion. In a boiler when you open the throttle the pressure doesn't drop measurably (at first) but several things happen. First the volume of water in the boiler will suddenly increase. if you watch in the water glass you will see the water level suddenly rise by a half to a whole inch! this is normal and we call it "swell." As steam is drawn off through the throttle you don't suddenly run out of steam because the water in the pressure vessel is still water only because it is under pressure. As steam is drawn off additional water converts into steam to take the place of the steam being drawn off. This also is normal and is called "replenishment." Why doesn't a boiler explode when steam is drawn off? because when steam is drawn off there is restriction called back pressure from whatever work is being done. In an uncontrolled venting of the pressure vessel there is no back pressure, there is nothing to prevent the contents from converting itself in its entirety from water to steam, to get an idea of how much power we're talking about here watch a boiler being blown down sometime, and don't stand too close!. In the case of an explosion, lets use a recent example. about 10 years ago a steam traction engine operating at 40 psi blew up from a thinned and leaky crown sheet. There was a tiny leak of water coming through the crown sheet where it had eroded from old age, the water converted into steam and replenishment began inside the boiler, the leak became a vent and steam began to exit in an uncontrolled manner. it only took a few seconds for the vent to become a tear and the entire contents of the boiler converted itself to steam in an almost instantanious manner. It was calculated by the state boiler inspector that the pressure exceeded 10,000 psi as the boiler blew itself apart killing four unfortunate bystanders including the fool that had been operating a red tagged boiler. it isn't a drop in pressure that causes an explosion, it is the loss of containment. All this sounds like an Alchemy class and should continue on how to turn lead into gold. Water, in the liquid state, will not compress or expand, regardless of how much pressure or vacuum is applied. How the "volume of the water will suddenly increase" when the throttle is opened is not supported by the Physics. The increase or "swell" you're seeing in the water glass is more likely from the locomotive starting to move forward and the inertia of the water surging back until it also starts to move forward. A boiler doesn't explode when steam is drawn off because a decrease in pressure will not cause an explosion. The explosion is caused by a sudden increase in volume when the water suddenly flashes to steam. Your example shows an explosion happening because the containment vessel ruptured and the rupture suddenly increased in size allowing the uncontrolled flashing to steam. Your last sentence is correct but how you got there....
toot toot the term superheated means only that a substance has absorbed enough energy to change from one state of matter to the next, it doesn't matter if we're talking about water or iron. Now as for a boiler, any uncontrolled venting of the contents of the pressure vessel is called an explosion. In a boiler when you open the throttle the pressure doesn't drop measurably (at first) but several things happen. First the volume of water in the boiler will suddenly increase. if you watch in the water glass you will see the water level suddenly rise by a half to a whole inch! this is normal and we call it "swell." As steam is drawn off through the throttle you don't suddenly run out of steam because the water in the pressure vessel is still water only because it is under pressure. As steam is drawn off additional water converts into steam to take the place of the steam being drawn off. This also is normal and is called "replenishment." Why doesn't a boiler explode when steam is drawn off? because when steam is drawn off there is restriction called back pressure from whatever work is being done. In an uncontrolled venting of the pressure vessel there is no back pressure, there is nothing to prevent the contents from converting itself in its entirety from water to steam, to get an idea of how much power we're talking about here watch a boiler being blown down sometime, and don't stand too close!. In the case of an explosion, lets use a recent example. about 10 years ago a steam traction engine operating at 40 psi blew up from a thinned and leaky crown sheet. There was a tiny leak of water coming through the crown sheet where it had eroded from old age, the water converted into steam and replenishment began inside the boiler, the leak became a vent and steam began to exit in an uncontrolled manner. it only took a few seconds for the vent to become a tear and the entire contents of the boiler converted itself to steam in an almost instantanious manner. It was calculated by the state boiler inspector that the pressure exceeded 10,000 psi as the boiler blew itself apart killing four unfortunate bystanders including the fool that had been operating a red tagged boiler. it isn't a drop in pressure that causes an explosion, it is the loss of containment.
the term superheated means only that a substance has absorbed enough energy to change from one state of matter to the next, it doesn't matter if we're talking about water or iron. Now as for a boiler, any uncontrolled venting of the contents of the pressure vessel is called an explosion. In a boiler when you open the throttle the pressure doesn't drop measurably (at first) but several things happen. First the volume of water in the boiler will suddenly increase. if you watch in the water glass you will see the water level suddenly rise by a half to a whole inch! this is normal and we call it "swell." As steam is drawn off through the throttle you don't suddenly run out of steam because the water in the pressure vessel is still water only because it is under pressure. As steam is drawn off additional water converts into steam to take the place of the steam being drawn off. This also is normal and is called "replenishment." Why doesn't a boiler explode when steam is drawn off? because when steam is drawn off there is restriction called back pressure from whatever work is being done. In an uncontrolled venting of the pressure vessel there is no back pressure, there is nothing to prevent the contents from converting itself in its entirety from water to steam, to get an idea of how much power we're talking about here watch a boiler being blown down sometime, and don't stand too close!. In the case of an explosion, lets use a recent example. about 10 years ago a steam traction engine operating at 40 psi blew up from a thinned and leaky crown sheet. There was a tiny leak of water coming through the crown sheet where it had eroded from old age, the water converted into steam and replenishment began inside the boiler, the leak became a vent and steam began to exit in an uncontrolled manner. it only took a few seconds for the vent to become a tear and the entire contents of the boiler converted itself to steam in an almost instantanious manner. It was calculated by the state boiler inspector that the pressure exceeded 10,000 psi as the boiler blew itself apart killing four unfortunate bystanders including the fool that had been operating a red tagged boiler. it isn't a drop in pressure that causes an explosion, it is the loss of containment.
All this sounds like an Alchemy class and should continue on how to turn lead into gold.
Water, in the liquid state, will not compress or expand, regardless of how much pressure or vacuum is applied. How the "volume of the water will suddenly increase" when the throttle is opened is not supported by the Physics. The increase or "swell" you're seeing in the water glass is more likely from the locomotive starting to move forward and the inertia of the water surging back until it also starts to move forward. A boiler doesn't explode when steam is drawn off because a decrease in pressure will not cause an explosion. The explosion is caused by a sudden increase in volume when the water suddenly flashes to steam. Your example shows an explosion happening because the containment vessel ruptured and the rupture suddenly increased in size allowing the uncontrolled flashing to steam. Your last sentence is correct but how you got there....
Water, in the liquid state, will not compress or expand, regardless of how much pressure or vacuum is applied. How the "volume of the water will suddenly increase" when the throttle is opened is not supported by the Physics.
water in the liquid state does not change due to pressure or vacuum AT A CONSTANT TEMPERATURE. water does, however, change volume when heat is applied. when steam is drawn the temperature of the steam is minutely lowered compared to the temperature of the water.
The increase or "swell" you're seeing in the water glass is more likely from the locomotive starting to move forward and the inertia of the water surging back until it also starts to move forward.
swell is caused by that difference in heat, which is also the process that propells the replenishment. swell happens in stationary boilers, and it also happens in train locomotives operating in reverse
A boiler doesn't explode when steam is drawn off because a decrease in pressure will not cause an explosion. The explosion is caused by a sudden increase in volume when the water suddenly flashes to steam. Your example shows an explosion happening because the containment vessel ruptured and the rupture suddenly increased in size allowing the uncontrolled flashing to steam.
THAT'S WHAT I SAID
the example given is of a boiler which was not in motion and was not being drawn on. it exploded because of a failure of containment.
Thank You.
TomDiehl Also, your use of the term "superheated" in reference to steam locomotives is misleading. The water in the boiler will convert to steam at a higher temperature because of the pressure in the boiler, so its boiling point is above 212 degrees.
Also, your use of the term "superheated" in reference to steam locomotives is misleading. The water in the boiler will convert to steam at a higher temperature because of the pressure in the boiler, so its boiling point is above 212 degrees.
Sorry, my last class in thermodynamics was over 30 years ago. 8-)
Dave H. Painted side goes up. My website : wnbranch.com
Depending on date, size and location steam loco boilers mostly work at between 120 amd 250 lbs pressure. To get from even the lower pressure to a negative pressure sufficient to cause an implosion without the crew noticing would be quite an achievement. If it were possible through the fast action of a valve or whatever the design would be prohibited. It would, after all,mean that a loco boiler could implode without warning at any time.
Look at it another way. When a tank car is discharged without the lid being opened or relief valves set then the whole body collapses inwards as can be seen in various pics on the web. The visible damage is entirely different from a boiler explosion. Imploded cars do not get launched hundreds of yards... even if the employee that caused them does - by his supervisors boot...
Unfortunately firebox crown failure does not always result in instant death for the footplate crew. I have read several accident reports in which crews died several days later from their burns. This was the principle reason why British loco cabs largely remained open cabs until about 1940-45. The crews prefered putting up with the weather and being able to get out fast - or even to be blown out - rather than the risk of being boiled alive.
dehusman I have been told the reason boilers explode is not a rise in pressure, but a sudden drop. The water when heated absorbs a lot of energy. But the increase in pressure in the boiler keeps the water in a liquid state, a condition called super heated, it is liquid but hotter than the boiling point. The throttle lets some of the steam out, lowering the pressure in the boiler slightly, allowing some of the superheated water to turn into steam. When a portion of the metal boiler fails, it leaks and actually drops the pressure in the boiler quickly. At the lower pressure the superheated water cannot remain liquid and ALL the water instantly turns to steam and expands tremendously, causing the boiler to explode.
I have been told the reason boilers explode is not a rise in pressure, but a sudden drop.
The water when heated absorbs a lot of energy. But the increase in pressure in the boiler keeps the water in a liquid state, a condition called super heated, it is liquid but hotter than the boiling point. The throttle lets some of the steam out, lowering the pressure in the boiler slightly, allowing some of the superheated water to turn into steam.
When a portion of the metal boiler fails, it leaks and actually drops the pressure in the boiler quickly.
At the lower pressure the superheated water cannot remain liquid and ALL the water instantly turns to steam and expands tremendously, causing the boiler to explode.
Even with the throttle wide open you cannot lower the pressure in the boiler fast enough to cause that kind of hyper-steaming (I don't know the real phrase) As is stated earlier, if a flue tube or crown sheet would ever become not covered in water it would almost instantly turn plastic and rupture and allow the boiler to fail. Crown sheet failures would be much more impressive then say a flue tube or stay-bolt failure.
More often, a boiler will explode because of a rupture in the boiler. The explosion is energized by the fact that you have a large quantity of water suddenly flashing to steam when the water escapes from the pressure vessel into the atmosphere. The expansion rate when water goes from liquid to steam is around 1:1600, where 1 gallon of water will become 1600 gallons of steam. The drop in pressure doesn't cause the explosion, but once initiated, it adds the energy to it.
Superheating as I understand it is actually more a process where the steam in the steampipes is sent thru the firebox a second time. This second heating causes the steam to change from "saturated" or "wet" steam to become superheated or "dry" steam.
Adding superheating to an engine could increase it's power by IIRC 10-20% with no other modifications.
Thanks Dave & ChuckVery informative replies. I was trying to explain to a non modeling friend how the boilers work. We were looking at a boiler with the smoke box off and he ask me about the tubes. Thankfully I had the correct answers even though I started second guessing myself later.
Lee
Howdy, Lee,
That's a typical fire-tube boiler, the type originally designed by George Stepehenson and brought close to to perfection by the N&W Roanoke design team. Note the two sizes of tubes - the larger ones are called flues and were intended to contain superheater loops.
The two 'bugeye' tubes at the top carried steam from the superheater header (that boxy-looking thing to which they are attached) to the valve chambers above the cylinders.
A very few locomotives were built with either water tube boilers or water tube fireboxes. While ideal for fixed installations or maritime use, water tube boilers proved unable to stand the slam-bang rigors of rail service without frequent (expensive) maintenance. I would guesstimate that well over 99% of the world's steam locos were of the type seen here.
As for the tendency to explode, there were several common reasons:
The answer was to adopt very conservative design standards [a boiler designed to operate at 300psi would be static tested (completely filled with water, no steam) at 700psi.] More recently, the ex-V&T loco occasionally steamed by the Nevada State Railroad Museum is only allowed to develop a steam pressure of 40psi, out of deference to the age of the boiler.
Chuck (Modeling Central Japan in September, 1964 - with teakettle tank locos with fire tube boilers)
Heat (hot gases from the firebox). They increase the "heating area" of the boiler. making it more efficient.
Good morningI have a quick (dumb) question. Do the tubes in the picture carry water or heat?The reason I ask, is that a long time ago I remember something about the tea kettle style locos had a tendency to blow up and that water in tubes aleviated that problem.
Thanks Lee