Steam shoots out and why?

Hello once agian im rather new to the hobby of collecting steam locomotives. I have read a couple books so far on them but there are a few questions that have not been answered, so i figured i would ask the experts. When an steam train starts up why does it blow all that steam out of the cylinders, wouldnt it be loosing power? Sames goes for when it slows down or stops. Why does it blow steam out of the safety valve on the top of the boiler and also out the cylinders when slowing down, staring up or stopping. Help on this would be greatly appreciated thanks agian!

The steam you see coming out from the cylinders is actually controlled by the engineer, via what are called the "cylinder cocks". These are ports in the cylinder that can be opened to allow steam and/or water to escape, and the reason you would want to provide them is simple. When starting, a locomotive's cylinders are relatively cool compared to the incoming steam, and water, liquid water, will condense out in the cylinders. These cylinder cocks allow the liquid water, along with some steam of course, to escape, preventing the cylinder heads from damage or being blown off, as liquid water does not compress!

By the way, welcome to the forum and to the very rewarding hobby of locomotion! I hope this answered your question!

David A. Davis

I see!!! That makes alot sense. Thank you for your reply and your right it an awsome hobby and very addictive. Thanks agian for explaining this to me and Happy New Year!

With respect to the safety valve, for a given amount of fire heat a specific amount of steam is produced. The goal for efficiency is to have the amount produced equal that needed for propulsion and auxiliaries. When the engine slows, or starts downgrade, less steam is consumed so boiler pressure increases and the safety valve will relieve that pressure to keep it within design limits. A fireman will try to anticipate stops and downgrade and fire accordingly but control is not perfect.

Another reason for steam coming from lower regions is for the fireman to blow down the boiler to remove scale and sediment that accumulates.

Regarding opening the cylinder cocks to blow them out.....I have seen many movies of such near or at stations (or on rail excursion trains)...what, if anything, prevents person/s standing near the loco from getting scalded? Or does the engineer have a whistle signal to signify he is going to blow the cylinder cocks?

Thank you for the information regarding the safety valve. I really do appreciate it but regarding to what CarterB said if steam from the cylinder cock could possibly harm bystanders, i honestly dont think it can hurt anyone. I have a small video of some people getting blasted by the steam coming off the cylinder cock as a steam engine is beginging to depart. Here i linked it for ya, i hope that this might help answer your question.
http://www.youtube.com/watch?v=wxaTEJBU ... re=related

escaping steam cools and condenses rapidly. furthermore the cylinder cocks are generally directed downward, so the steam hits the ground, then wafts away harmlessly in all directions. Also, railroad locomotives run on fairly feeble boiler pressures or a few hundred psi, and moderate superheat.
In stationary practice, there are tales of highly superheated steam which, being invisible, an undetected leak could pose a terrible hazard etc.
Well I have spent many years in power plants and gotten pretty close to roaring steam leaks, super heater outlet safety valve flanges, throttle seat drains, and various other chronic leakage points, pressures of 1300psi and temperatures of 1000F, and I can tell you, you can get you hands in there within a few feet without it being injurious. closer than that and you can get burned, certainly.

The worst burn I ever got wasnt from live steam, but from reaching into the steam space of a heating boiler that was cooling down, but not yet drained, taking out the manhole cover from the top of the shell. I had a glove on , and I had buttoned my shirt sleeve and tucked it into the glove, but the gap in the bottom of the sleeve opened as I was turning the cover to fit it out through the hole, and that exposed oval patch on the back of my forearm got a pretty bad 2nd degree burn in the three of four seconds it took to get that cover out. that was just from the 200 or so degree vapor and low infrared radiant heat from the hot water a couple feet down from the manhole.

By the way, what is commonly mistaken as steam is actually water vapor which you see. "Steam" is invisible and is what drives the engine. "Water vapor" is a by-product of steam.

CarterB, I agree with Eliphaz that the steam coming out of the cylinder cocks doesn't pose any risk. While working on the loco or acting as shunter on the ground I have often stood in that cloud of steam (or water vapour). It's noisy, impressive and harmless.

The blowdown cocks mentioned by Ken are different. We tend to give them a wide berth when they are operating. The South African rule book says that the driver must check for people and livestock before operating them, and they are only to be operated by the driver, not the fireman. Old drivers will wedge eggs or corn on the cob in the blowdown cocks to boil them; old firemen tell me of irresponsibly packing track ballast in there to see it shoot out in all directions when the cocks are operated.

Hello Rail-Gun,
just some impressions from Germany:
The cylinder drain cocks are explained before, and usually the driver holds the locomotive with the air brake, opens the throttle a little bit, just enough to close the self-idle meachnisms and thus letting steam into the cylinder. Now he quickly moves the valve gear a couple of times from full ahead to full backwards.... So steam passes into the space of the cylinder, fills it and before getting serious, the valves moves to backwards, letting the steam drain through the exhaust and steam will flow to the opposite part of the piston surface, also to fill this space. This should be done, before the locomotive is start up, just to preheat the cylinders and avoiding massive steam condensation.
After this, the fireman has to operate the cylinder / valve lubrication pump certain times manualy, just to ensure a good oil supply to the stroke boxes. Now the engine can move.

Drivers are told, not to open the drain cocks on stations, even if neccessary. Because the Steam form the drain cocks will blow down to the tracks, can whirl up dust and dirt and maybe affect passengers or spectators, this should be avoid.
So advanced drivers do the preheating carefully and often, sometimes with open drain cocks, and thus helping to avoid the full pressure getting out of the drain cocks.

In Germany, the valve gear has self-opening piston valve drain cocks. Two tubes run down from the valve stroke box in front and on the rear of the cylinder block. If the engine is running under cylinder pressures above a certain pressure, these cocks open and let a little amount of steam bypass through this tubes, just to ensure a good and still drainage of condensing water form the exhaust chambers of the piston valve.
You can see this well in my u-Tube Video of the departure of 18 201 from Kranichstein (Kranichstrein = crane stone ;o) ) museum back to their home at Dresden east Germany:
http://www.youtube.com/watch?v=2p_fv_m1M0M
The engine starts moving, now the drain cocks are opened and cover the front of the engine in steam. The engine moves on more, and as it comes closer, the drain cocks are cloesed and now you can see with every beat of the exhaust steam is pressed out the piston valve drain tubes, giving small steam clouds close to the cylinders.

All this is harmless and normal.

Serious is the boiler blowdown valve.
In Germany this wasn't allowed in stations, because not to disturb passengers or to disturb the free sight of staff to signals and along the station site.
Also, because scale deposits were removed by this procedure, it wasn' t allowed to do this in switches, only on free straight tracks. So one will often notice this after the engine departed from the station, reaches the open track - and the blow down valve is opened, just to remove the muds, which had aggregated in the area before the blow down valve.
Huge amounts of steam quickly arise, usually from between the wheels. The Blow Down Valve is under the boiler and has an exhaust deflector mounted to the exhaust tube, which would prevent the rushing power of the steam/water jet from the boiler damaging the track bed. Because of having inside the boiler hot water under pressure, this will rapidly turn into steam, if the blow down is opened, thus the stream of water rushed throught the tube and turn into huge amounts of steam, which than cover engine in a massive shield of steam. This can result in a limited sight of fireman and driver to signals and track, thus it should only be done on moving engines, just to ensure to get quick to normal unlimited sight by the huge amounts of steam.
So for fotograph works, this valve can be opened, to get a nice steam cover effect...

3rdrail wrote:By the way, what is commonly mistaken as steam is actually water vapor which you see. "Steam" is invisible and is what drives the engine. "Water vapor" is a by-product of steam.

We in Germany to not make real difference betwen steam and water vapor. There are locomotives, which operate only with the steam from the boiler, without any superheating, we call this "wet steam".
Other locomotives run with superheaters and thus we call those "hot steam" Locomotives.

And: During the start, through the drain cocks comes live and superheated steam, because this the same steam used to move the piston - it's not exhaust steam or simple water vapor - this is steam driving the engine, pressure of up to 217 psi and 570 up to 715° F...

Steffen wrote:And: During the start, through the drain cocks comes live and superheated steam, because this the same steam used to move the piston - it's not exhaust steam or simple water vapor - this is steam driving the engine, pressure of up to 217 psi and 570 up to 715° F...

Pure steam is a transparent gas.

3rdrail wrote: Pure steam is a transparent gas.

Yes, and no...
As long as under pressure, steam is a transparent gas, as lower the pressure, as more droplets occur, but also: As more volume and light, as more visible.
What color has sugar? Most of us thinks it's white, but pure sugar is transparent. Even brilliants are transparent in high quality, but a bunch of it, well, and the look white. Glass, we all know is transparent, because our windows show us, but shatter this glas in pieces, and you get a white coloration, of something, which was before transparent and it get nearly intransparent. But take only a small piece, and you will see transparency again.
This has something to do with multible light reflections. So the light cannot easy pass the mass, is reflected, and because of this mass reflection it appears white, because transparency means: Light passes the mass, and the reflections from the background pass trough it and we see only the background reflections, from the light rays reflected, hitting our visual sensors.
So now the mass becomes so massive like shattered glass, so many small water droplets: Reflections of light occur and something transparent appears now white.

Steam from the safety valve for example: In your water gauge glass the steam is transparent, but the safety lifts and we have the same steam, which is in the gauge now free and unbound. Massive and quick condensation occurs, as massive parts of steam molecules crowd together, forming an intransparend cloud.
Is this steam? Yes! It's hot and very dangerous. So sitting next to a safety and get hit by the exhaust can seriously injure human, tearing of flesh before burning the tissue.
As higher the temoperature of the steam and as higher the pressure, as less this effect.
Superheated steam from a stationary power plant has temperatures of around 960 up to 1000° F and pressures of around 1750 psi up to 2200 psi. This steam is so high in pressure, it takes a little time, before a mass occurs were the light reflection appears. This has only secondary to do with condensation and appearance of droplets, it has more to do with pressure and the possibility of light reflection.
During our boiler safety course in Spring 2002 we got from our state boiler inspector a superslow motion of the shatter of a water gauge glass. First, the water remains quite and nothing, then a crack appears. What do you thinks happens next? Sure: The former transparent water gas, called steam, get quickly into a milky fog, next the water levels rises and all bursts by a huge mass expansion into pieces.
So a former transparent thing gets into something intransparent not only by lossing temperature and condensation, also quick loss of pressure will lead the this intransparence effects.

And water vapor is, if you boil water, maybe for your breakfast egg, what raises from the surface of the boiling water. Clouds are water vapor and fog is water vapor... but steam is water vapor under temperature. This has something to do with enthalpie and entrophie.

Look water vapor in form of fog. Fog appears, if there is more humidity in air than the air can bind. So there is more mass of humidity and thus the humidity gets visible. Now every fog is in so huge droplets that this is wet, sometimes thick and dense fog is rather cold and less wet, than the less dense but damp fog. But both appear without pressure.
If we have the possibility, for example to catch fog in a glass cylinder, seal it and apply pressure with a piston, it won't take long and the fog gets less and less dense till it disappears. So here less the thermal effect, as the pressure is what makes the difference in transparence.
The next thing to get this fog transparent is the seal our virtual glass and get a burner blow and heat up the things inside the cylinder: Again, the fog disappears and get's to a transparent gas.
The last we know from fog mornings: As the day break and sun appears, the fog disappears, because the increased temperature make now the fog more and more invisible (as the suround air can bind much more water, as under low temperatures)...
Also:
If you have oxygen bottle or a carbondioxid, if the bottle would be transparent, the gas inside wold be transparent, too.
But think on a bottle sparkling water. If you open it quickly, for a blink of an eye you can see the transparent gas over the water surface to the lid will get foggy, before the pressure is released and the gas is transparent again. This has only to to with pressure, not with temperature and the massive pressure breakdown will result in this effect, which is only visible for a very short moment.
But back to our gas bottles: Open the ventile of both, very quickly! In both cases you will see the gas as a foggy white haze, before the gas get's back to transparent. The simple pressure breakdown atop of the opened valve results in this haze, making our gas visible.
Again, this has nothing to do with the state of the oxygen, because the oxygen does not condensate, it remains still a gas. But the pressure break down and the massive amount of molecules result in visibility, because of light reflection: The same as with brilliants or sugar crystals.

So yes: Steam is a transparend gas, and no: Not allways this gas is transparent.

So for me, out of the drain cocks comes no vapor, this is life steam!

Part of our training in steam service was to avoid opening the cylinder cocks in the station area if at all possible. You warm up the cylinders before you moved for the first time at the start of the day. While at the station, you could open the cocks with no annoyance to anyone, to let any condensation run out, and you closed them before you started up. Opening the cylinder cocks while drifting into the station was not necessary, although doing that wouldn't produce much vapor as the throttle was shut off.

Blowdowns were done in an area away from people and anything that could be damaged or blown over by the blast of steam and hot water. Our engines all had blowdowns that exhausted outward from the fireman's side. Lots of noise and clouds of vapor that was very impressive...from a safe distance.

Another thing we tried to avoid was to start the injector on the engineer's side while at the station. While priming, the injector would spill out hot water just below the cab, possibly making a mess or splashing someone. The fireman's side was used then.

A good fireman would try to avoid having the safeties lift. You let them lift to make sure they worked, usually while firing up, but having them go off during the day was annoying, hard on the boiler in the long run due to unnecessary stresses on the metal due to pressure changes, and a waste of the fuel used to heat that wasted water in the first place. Keeping a steady steam pressure was the most efficient way to fire a boiler.

Like someone's signature above suggests, keeping a 2/3 glass of water and a nice clean white fire, thicker on the edges and corners, keeeps the engineer happy.