Italy's Bizarre double-boiler steam trains - "Franco-Crosti" Boilers

In today's video, we take a look at the Franco-Crosti boiler, the reason why some Italian steam locomotives have more than one boiler
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[@enrique5167]

Here you have an article about the spanish locomotive, with an explanation of why the peculiar shape: historiastren.blogspot.com/2020/03/una-locomotora-unica.html Piero Crosti had completely redesigned the entire system, solving one of its biggest drawbacks: the location of the exhaust just in front of the driving cabin, which made it difficult for the driver to see the track and, in addition, caused the entry of large amounts of smoke at your workplace. This new development was carried out in collaboration with the Officine Meccaniche Reggiane firm, which is why it received the name Reggiane-Crosti and, thanks to the recirculation of the gases through the new preheater, the exhaust could be placed in the usual location of the chimney of steam locomotives.

[@javiermedina9080]

I guess another factor was that at the time the locomotive was going through trials, RENFE was receiving several of the new Renfe Class 141 ( one of the most mass produced steam locomotives in the history Spanish railway) in addition to several new diesel engines and the electrification of both old and newer sections of the network. So with the problems of rolling stock being solved, converting several of the steam locomotives to oil burning( as well as fixing a bit the problem of the coal supply) and the incorporation of Diesel and electric, it’s not hard to see why no more where built. A bit of a shame, as it seemed like a rather interesting and effective locomotive.

[@gitgut4977]

I really would like to see a newly build steam loco just to see how much of an efficiency gain we could reach with modern technology

[@caledonianrailway1233]

The advanced steam trust and mackwell locomotive company are doing this

[@Leonardo-cw1dd]

@@caledonianrailway1233nice. i prefer steam trains over diesel trains mainly due to having grown up watching thomas and friends. however i dont have a problem with diesels

[@kanehood3478]

@@Leonardo-cw1dddeisel locomotives just seam a little….. whats the word, soulless, the driver turns up in the morning 10 mins before his/her shift and turns a key to get it running, a steam loco requires hours of preparation to get it up and running, and watching the con rods and cylinders do their thing along with the sound and smell is a whole different experience that you cant get from any other machine, however my next door neighbour owns an old transit that sounds and smells shockingly just like a diesel locomotive, nothing to special bout that, but all this is just my opinion and is not a knock in what people like just my personal perspective.

[@kkobayashi1]

I suspect the highest efficiency steam locomotive would use a steam turbine and a hybrid electric drivetrain (turbine spinning at constant speed, and battery assisting when needed).

[@caramelldansen2204]

I've always wondered if it's feasible to build or convert a steam loco to operate on electricity, replacing the bunkers or tenders with batteries and the firebox with heating elements through the boiler. It would certainly help heritage railways, who can often find buying coal expensive and troublesome.

[@atshinkansen7439]

Franco-Crosti engines are a prime example of real life steam locomotives being even more steampunk than many fictional designs.

[@hedgehog3180]

We've had one boiler, but what about a second?

[@mnsv10]

I like how locomotive engineers try the simplest answers first. This channel always teaches me things I would have never found out about trains.

[@Bragbigfoot_2]

As an Italian, i can say that this was a very interesting video. Not only because i know now why those boilers are for, but also because Italian locomotives always looked so cool on my opinion and the creativity Italy have is so underrated. I especially love the locomotives (683, 741, 743) they really fascinate me. So yea, good job

[@olic9804]

Love Italy! Also, always had a soft spot for the Crosti 743 2-8-0s - they have a lot of character! (Though no idea as to what they were like to work on or how forgiving they were to operate) glad to see a few still about in museums and the like

[@Bragbigfoot_2]

@@olic9804 same as any other engines i think, i'm from the south and all of these locomotives are in the north of Italy, i don't think we have Crosti locomotives here on Sicily

[@deez8202]

I love italian vehicles, designs etc especially The Caproni Jet

[@hedgehog3180]

One thing I've noticed that's kinda peculiar is that seemingly Italy, Austria and Denmark were the only places where cone shaped smokebox doors were common. I have no idea why that is the case because it's not like there's any connection here.

[@olic9804]

@@Bragbigfoot_2 Yeah I think you're right, most of the Italian steam loco info I got comes from the Northern areas for definite - once saw a couple of 740s in a siding on the outskirts of Florence when taking the train to Tuscany - still have the photos somewhere...

[@user-cw9qn1nb2n]

The weight of an engine has got nothing to do with the loading gauge, which is something of a misnomer. The loading gauge refers to how high or wide you can make an engine or train and still fit it under bridges, through tunnels, and through station platforms. The curved gauges themselves could often be seen hanging from a gantry at the exit from goods sidings. If the whole train passed safely under the gauge without touching it, that train was good to go. Anything fouling the gauge would need to be repositioned and placed lower down.

[@4ntig3n]

Interesting Video :) Just for anyone curious, the loading gauge doesn't refer to the weight, but rather the overall space required / available for the locomotive above the rails. It's the clearance to trackside obstacles such as platforms, signage, tunnels.. etc.

[@1258-Eckhart]

Yes indeed, the loco's weight is one of the factors needed to ascertain its RA (route availability), minimum track curvature is another. The term "loading gauge" comes from those suspended iron bars which open wagons had to pass under when fully loaded.

[@kkobayashi1]

Right, he should have said axle loading, not loading gauge. Though of course loading gauge is a problem with these preheat systems too.

[@simonwass6315]

@@kkobayashi1 his technical knowledge is grade 1 level, 10 for effort but research needs more work!

[@royreynolds108]

In the US, we use the term "load diagram" or "Clearance diagram" instead of "loading gauge". There are many different terms used around the world that mean the same thing when talking about the same subject.

[@itsnic2295]

Ah, I remember first seeing the weird, side-mounted smokestack on the Italian FS 741 engine and being extremely confused at first.

[@javiermedina9080]

Honestly im just glad Spain got mentioned. Spain actually made a large amount of rather effective and interesting locomotives, that honestly don’t get as much recognition as they should.

[@GuretoSefirosu]

Seriously, scenes from "The General"? That is awesome. I love Buster Keaton!

[@Tom-Lahaye]

Had the preheaters been made of stainless steel it would have helped to keep maintenance cost down, initial cost would be higher but the reduced maintenance requirements would outweigh this over the locomotive's life. Downside of any system taking energy from exhaust steam is that it increases back pressure and so it will induce less air flow trough the fire.

[@anthonyjackson280]

stainless steel is poor for power boilers, it has a relatively high thermal resistance.

[@RainShadow-yi3xr]

Huh, I never realised that the reason Franco-Crosti boilers caught on in Italy but not so much elsewhere was that they had to import they're own coal so any savings were worthwhile. Whilst in other countries that experimented with it (and other systems intended to save fuel) found that the increased maintenance costs usually offset the reduced fuel costs.

[@lucagentile4674]

Yes! As an Italian I’m happy that the bizarre Franco Crosti systems finally got some recognition! Believe it or not, there is another Italian class steam locomotive that had a singular Franco Crosti boiler underneath the primary one. It’s called the FS class 741 and there’s one that is still in running condition today (number 741.120) In fact, it is the only Franco crosti steam locomotive that is still functional in the world

[@trainman1ish]

The German class 50.40 was put out of service in the middle of the 1960s due to the build-up of sulphuric acid in the pre-heater boiler which destroyed the flues over time. Even stain-less flues didn't solve the problem. One of the class was even fitted with a fuel burner and was nearly as powerful as a 2-10 class 44 with 3 cylinders.

[@Iron_Blood_Enjoyer1933]

In my TTTE head-canon, after an accident where Murdoch is pushed into the sea at Brendam Docks by some troublesome trucks, The Fat Controller sends Murdoch to the mainland to be repaired at Swindon Works (Where some of the the Topham family had worked in the past). When he returns, Murdoch had been given a "Franco-Crosti" boiler as a way of introducing the idea to the NWR.

[@1258-Eckhart]

Thanks for this excellent explanation! French and Italian engineers were also keener on complexity than German or British engineers, who liked to keep things simple wherever possible.

[@Xalerdane]

The K.I.S.S. Principle.

[@historynerd88]

Debatable. As a rule, as soon as superheating became feasible Italian designers almost always chose to discard compounding, for example.

[@1258-Eckhart]

For the simple reason that both compounding and superheating are expensive, and the efficiency gains from fitting both to an engine are negligible compared with fitting just one of the two, and they don't justify the extra cost. I wasn't claiming that Italian engineers went complicated just for the sake of it. @@historynerd88

[@nikospapageorgiou57]

Boiler pre heaters are a common thing on ships. I didn't know they were tested on steam locomotives as well. Great video!

[@lukechristmas3951]

I always like the bizarre appearance of the Franco-Crosti boilered engines. I don't know how to describe it much but they were quite the design and look even if not conventional. Also, it gives a special uniqueness to Italian steam seeing how Italy was the only country where it saw the most success. A native invention solution for a native problem.

[@LemonSpacebirb]

Glad you finally covered this

[@chriswade7470]

Remember that a standard steam locomotive injector has to use cold water otherwise it won’t function correctly.

[@iansinclair521]

Worth mentioning... almost all post 1820 US and Canadian steam engines had feedwater heaters which did much the same job -- but without the complexity or the detrimental effects on draught in the boiler.

[@historynerd88]

For far less fuel savings, though. That's the point - complexity for less coal burned.

[@FlyingFishVans123]

I really love this channel. I learn so many things about my trains!

[@TrainMaster04]

Interesting video. The US used many different types of feed water heaters that used exhaust steam to heat the feed water. Some of these heaters include Worthington, Elesco, and Coffin.

[@00Zy99]

The Santa Fe, in the US, had mallets with "articulated boilers" that seem to have actually been precursors to the Franco boiler-the front half was a feed water heater. They were retired early due to issues with maintaining the joints and cinder build-up in said articulation, but they predated Franco by several years.

[@user-xsn5ozskwg]

Such clever innovations. And as always you've done a great job telling us about it.

[@BulletWanderer]

Watching this video, and seeing one in it, reminded me of the film Von Ryan's Express. It has a Franco-Crosti steam engine driven by the SS at the end, chasing after Frank Sinatra's train. Didn't know at the time why it looked so odd and didn't have a funnel at the front, but seeing it in this video cleared up why! Good video 👍

[@historynerd88]

It was indeed a Class 743. That film did little justice to either her or the Class 735 pulling the main train, however, especially the latter with its hideous props.

[@stormgamingtv6096]

Using the song Gustavo from Pizza Tower was a great touch of detail

[@dustin_4501]

Unlike some people think the Franco-Crosti 9F were constructed with them from the star, also thanks to inferior performance to the Standard 9F they were classified to 8F and crews hated them so much they nickname "Frankly Crusty".

[@historynerd88]

They actually weren't derated, turns out. It's just an urban legend

[@victorcontreras3368]

By now I've seen many different,, interesting locomotives with features that tried ideas for improvement. It would have been a great idea to save at least one from being scrapped. This would create revenue and would make museums grow in popularity as well as get people thinking on how to make improvements on existing ideas. I mean there are so many unique models made and tried from many different lands!

[@harrymu148]

I gotta admit, the feather in the cap looking chimney for the german one looks flippin cool

[@alanbates1471]

Interesting and Informative video, thank-you.

[@astridvallati4762]

The Franco-Crosti additional " boilers" were actually water Pre-heaters, using expended steam from cylinders and added Draught for Firetubes. After experimental 683 series, 741 and 743 Series were made in large numbers. The added Performance however, was minimal, and added cost and increased maintenance. A solution searching far a problem.

[@garryferrington811]

I've always wondered what the Franco-Crosti boiler was. Thanks for the explanation.

[@awesomecronk7183]

This is genuinely impressive

[@giuseppecaponigro533]

Grazieeeeee millee per il video i tuoi video sono molto interessanti e molto dettagliati 😊 wonderful🙏

[@C.A.A93]

Just a weekly comment to feed the algorithm and to say keep up the great work

[@CrystalClearWith8BE]

In Thomas and Friends in the BWBA Series, as we introduce to Lorenzo and Beppe, I noticed that Lorenzo aka the Lost Engine is a Franco-Crosti engine.

[@historynerd88]

Just two details: In 1939 the system was trialled at the same time on five 685s and five 743s, as was often the case on the most widespread passenger and freight designs of the time. It is not quite right to say that "new locomotives were built"; all of them were rebuilt from existing locos. Because of the lack of coal and the feasibility of electrification, for its own state railways Italy had stopped building new steam locomotives a long time before, with the last ones being outshopped in 1928.

[@davidthebeaststudious2960]

Steam engine past ideas are getting crazy

[@MatthewsBranchLine]

Wow, this was a really interesting one! Thanks ToT! Also, I’m guessing the idea behind this video is (at least partly) from cursed trains?

[@Dudeface167]

I wonder why they couldn't just make the heater a continuation of the boiler, putting it in between the boiler and the smokebox with the firetubes running through it?

[@francescogiuseppearagona1109]

Did you know that a class 741 locomotive has been kept operational and you can still see it towing touristic trains? 740 class locomotives have been the work horse of italian railways since their introduction in early 1910s. Some of those were modified with Franco-Crosti boilers giving birth to the 741 and 743 class locomotives. 743s had two boilers, one on each side of the main one, 741s had only one mounted under the main boiler. In the end the lack of coal mines in Italy also explains the early end of stem engines here: we started electrification very early, and by 1930s there was no need for faster and more powerful locomotives anymore. It's a great luck that some of those were preserved in working order, so than we can appreciate 1900s engineering up to these days. Check it out: kzbin.info/www/bejne/hpjLh5iArJmrftk

[@IlikeTitanic]

I haven't seen the video yet! But after the last stream, and how everyone in the comments reacted, i am legitimately happy to see you are alright!

[@420sakura1]

Im out of the loop. What happened?

[@IlikeTitanic]

@@420sakura1 he was streaming "cursed trains" with mike, and at the very end he started to cough. A lot. Quite a lot. And suddenly the streaming ended. Everyone in the comments wondered what happened, asking if he was alright. That got me somewhat worried, nit gonna lie. I have no idea if he talked on discord saying if he was fine or not. But seeing him uploading videos again makes me feel at ease

[@andrewadams3894]

A number of USA built Mallets in the pre-superheater era had economizers hidden in plain sight, appearing as just the front few courses of the boiler behind the smokebox. At least some of these, called separable boilers, were arranged to be unbolted and separated from the boiler proper for tube and flue-sheet replacement. Most notorious were the Santa Fe's flexible boilers with ball or metallic bellows between the boiler and the economizer. Most were, however, rigid and outwardly unremarkable for large early Mallets. These disappeared with the introduction of superheaters. One wonders if the USA builders were aware of Franco? Or if Franco was aware of the USA Mallets? None of these survive, either as constructed or as rebuilt with superheaters replacing the economizer.

[@ComradeMeow]

That is such a Kerbal approach to things, haha. If something doesn't work? Just add more boosters!

[@Pyrotrainthing]

I just had an image in my head of a Class A Shay with a Franco-Crosti boiler mounted on the open space of the running board, it was so cursed but hilarious to think about.

[@scotthamp384]

If you haven't, can you talk about the tank engine in Hungary that was an express engine?

[@dragonblaster-vu8wz]

Now I want to see a Big Boy equipped with one of these boilers

[@laurenceskinnerton73]

interesting.

[@kevinthomson8282]

Thank you for this v.useful article - I never previously understood the features and purpose of the Franco-Crosti system. Slightly puzzled at time = 374 secs (6 min 14 secs), there's a mention of "Loading Gauge" in relation to WEIGHT of the loco and its weight distribution. I've always assumed "Loading Gauge" defines the DIMENSIONS of a railway vehicle (i.e. will it fit through tunnels, under bridges, through station platforms, round double-track curves etc). Does this detail maybe need some thought ? But returning to the main point - thank you for presenting this mini-docu👍👍 Kevin Thomson

[@albertobonaiuti8746]

Can you do next "il pendolino" an ETR 450

[@Ice_Karma]

I thought "loading gauge" had to do with the shape and size of rolling stock, not its weight.

[@rafchris]

2 things I am thinking about here is injectors. Normal injectors as part of the process of brining cold atmospheric water up to a higher pressure, the feed water gets heated. So the tempersture drop in the boiler isnt as drastic as putting cold water in already. Secondly traditional injectors do not like warm feed water and often fail or have low performance on hot days. Having never worked on a crosti boiler im assuming that feedwater to main boiler might have used a pump or some form of different injector? As a fireman on some days its hard enough to get one boiler to play ball. Now you have 2 water levels to worry about it must have been abit more taxing on the fireman keeping a mental track of water states, fire bed state amongst all the other duties!

[@sierkdejongh8984]

What about having the preheater always full and having the injector feeding into the preheater? That would solve your problem. You only need a non-return valve between the preheater and the boiler.

[@rafchris]

@sierkdejongh8984 true but thats assuming that exhaust gases on their own could get the feedwater boiler up to a pressure equal to or higher than the main boiler. Assuming for most mainline locos that somewhere between 180psi and 250psi then thats quite high. And what if your main boilers full? A one way return valve wont on its own control the rate or stop the water if needed. A variable rate feed water pump sounds more useful but again vastly more complicated. Im guessing theres a few more details in the design and operation that I havent found online yet to understand the ins and outs! But great video!

[@zaku32888]

Any chance of a video on Elesco feedwater heaters?

[@Alessandro_Gorini]

As an Italian and a railfan that didn't know this fact, it is very interesting indeed

[@andrewrife6253]

Ah, Italy, always making things way more complicated than they need to be at the cost of reliability. Never change

[@nicoferguson1215]

Could you please do a video on subway "money trains"? I just heard of them in New York city, and was curious if other cities had similar trains

[@lunathegolden2076]

I' m from italy

[@SodorStudiosAndCoProductions]

ITALIAN TECHNOLOGY MENTIONED 🔥🔥🔥🔥🔥🔥🔥🔥🔥

[@frankthediesel102p6]

Lorenzo basis mentioned

[@SteamboatWillie1233]

Is ThAt ThE PAstA Boiler 3000

[@abloogywoogywoo]

They should’ve made the 9F spaceships longer, having the preheater in the tender, or 2nd tender.

[@hawkerhellfire9152]

I wonder if a contributing factor was that the Crosti Boilered locos operating had Italy had less work to do in heating the feedwater in Italy with its much hotter climate than up north where the feed water would be colder when being fed into the tank.

[@historynerd88]

Italy can be quite cold in winter, too. Check out some videos of Class 741s at work in the Val Pusteria/ Pustertal line.

[@22pcirish]

William Stroudley fitted feed water heating to his minute ‘Terrier’ locomotives in the 1870’s.

[@terrier_productions]

Could you do the APT-P? The story of the APT is very interesting.

[@420sakura1]

I thought Brits hated it

[@davidty2006]

The prototype? thats for sure interesting.

[@terrier_productions]

@@420sakura1no, day-drinking media people did.

[@Hard-Boiled-Bollock]

4:27 - That looks a bit like Nicholas Lyndhurst

[@harrisonallen651]

This is why every steam engine only has one boiler

[@roadtrain_]

Good lord the stacked boilers look cursed

[@brenlc1412]

He really just said “Boiler x2”

[@sebastianthomsen2225]

how about a "Franco-Crosti-fairlie" locomotive? 🤔 😊🚂👍

[@alicehodges9964]

My Friend Luke We Talk About Steam Engines Its Fun

[@FreighttrainDaniel1225]

So are there gonna be more steam engines built and with substitute fuels for coal

[@0fficialdregs]

If the steam is exhaust, maybe take a vacation lol

[@tred6292]

I wonder which engines with "Franco-Crosti" Boilers were preserved, and where I might be able to see one in person?

[@sandrodunatov485]

There are some in the National Railway Museum of Pietrarsa on the former Napoli-Portici railway. Locomotive 741.137 is exposed there.

[@tred6292]

@@sandrodunatov485 Thank you.

[@pauljensen5699]

Basically an early Co-generation system.

[@microbusss]

didn't they use a reheated steam design on locos that went across deserts?

[@b43xoit]

A feedwater preheater is not an "additional boiler". It does not boil the water.

[@tim3172]

A boiler is a common term for a device used to heat water, even if not to the point of boiling. Many furnaces use a boiler for radiators without boiling the actual water. Definitions of boiler: a fuel-burning apparatus or container for heating water. (Heating, not boiling) A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. (All pre-heaters for liquids are boilers.) Let me know if you're still (somehow????) confused. Step one of correcting someone: making sure they're wrong. Step two of correcting someone: making sure you're right.

[@b43xoit]

@@tim3172 The specific context here is the design of steam locomotives. Readers make certain associations between terms and how they are generally used when talking about that subject.

[@faragar1791]

Why did they put the Franco-Crosti boiler underneath the main boiler? Wouldn't it make more sense to have the Franco-Crosti boiler on top of the main boiler? Hot gases naturally rise up. So, if you have the Franco-Crosti boiler on top of the main boiler, the hot gases would go up into the Franco-Crosti boiler. Then, the pre-heated water in the Franco-Crosti boiler can just drain down into the main boiler.

[@neiloflongbeck5705]

That would mean the feed water would get hotter than the boiler and would affect the water injectors feeding water into the water heater.

[@davidty2006]

there generally tends to be quite a bit of space under engines. Because the boiler is generally bigger than the frame is wide it sits ontop of the frame leaving a empty gap under it. Also tunnels are a thing meaning putting it ontop would cause issues.

[@ShinGhidorah17]

I heard that there’s a steam locomotive that runs on vegetable oil in the United States, the Grand Canyon Railway 4960. So I was wondering, is it possible to make an environmentally friendly steam locomotive? Is it a good or bad idea?

[@davidty2006]

well steam engines can run on litterally anything that burns.

[@lukechristmas3951]

Oh yeah, ex-Burlington O Class 2-8-2 No. 4960

[@Machodave2020]

SMU exist?

[@IsaacDaBoatSloth]

its a chimney not a funnel (or in america a smoke stack) i can tell you used to watch thomas the tank engine/read the books

[@simonsadler9360]

Didn't at one time the pressure injection of coal dust increase performance ?

[@ryleeculla5570]

So this is we’re that lost Italian engine was based off of 4:00

[@duncanharris9479]

Ships have funnels - steam locomotives have chimneys.

[@saraihooper75]

I don't think you know how steam engines work-

[@simonwass6315]

@@saraihooper75 what the item is called varies from country to country, questioning knowledge on that basis is pretty childish..... smokestack, chimney, funnel, probably others....

[@tim3172]

My name is Duncan and my localization of words represents the entire world because I'm 5 years old and myopic. They are called: funnels, stacks, smokestacks, smokestack pipes, smokepipes, ejectors, chimneys, and smoke tubes. I'm sure there's a long list outside of that as well. Ships have: funnels, stacks, chimney, smokestack. Again, likely others as well.

[@loanedengineproductions]

So if that engine was a TTTE character, would it have 2 faces like MightyMac and the CFR fleet?

[@sunnygappy9717]

No, both MightMac and CFR fleet are single boiler But Crosti boiler loco does exist in TTTE tho but I forgot the name (he's Italian)

[@albertobonaiuti8746]

Yes, but in real Life, Is black, not Blue, and i am someone the Who know something, cause im italian 🇮🇹

[@loanedengineproductions]

@@albertobonaiuti8746 Lorenzo?

[@sunnygappy9717]

@@loanedengineproductions yes

[@sunnygappy9717]

@@albertobonaiuti8746 they would have 2 faces tho

[@AlexRails]

LORENZO

[@ethribin4188]

18-20% furl saving sounds modest... But just think of it compaired to, for example, airplanes. 95% of an airplanes lifetime costs is fuel. Thus, the mahority tickets pay for is fuel. Thus a reduction of 18-20% fuel consumption means anywhere from 10-15% reduction of airplane ticket prices. Suddenly, flying usa europe for 500-800$ costs 425-720 instead. Or if the full 20% translates all to tickets, you get tickets that cost "only" 400-640$ instead. This is huge. Suddenly, tickets arent half 1k to 1k, but half 1k, give or take hundred. These kinds of numbers chamge how many people can afford flights. Which changes demand, which changes income for air companies, which lets them grow. Not to mention, fuel will be left for other things, and the envitoment will be impacted less due to less exhaust. Naw, translate that to rails. Both passanger and cargo. Even if its only half, these kinds of savings on the scale of a nations economy, can decide between a nation becoming a first world nation, or being stuck as a second world nation.

[@magdos7160]

3678th

[@joshuaW5621]

The 9Fs look ugly with the Crosti design.

[@davidty2006]

good thing it was a freight engine

[@TitopsCanvas]

Megamind spanish train

[@N330AA]

That is not a boiler, a boiler has to boil a liquid by definition. What that is is an economiser, fair enough though that's a less exciting title. Also i wouldn't say that adding cold water to a boiler is a problem per se as it is added at a constant rate so temperature of the boiler should stay the same. What this essentially does is allows you to capture colder flue gasses. The boiler is pretty much at constant temperature throughout which is dictated by the pressure. For example at 10 bar the temperature will be around 180C. This is due to the latent heat of evaporation meaning liquid/steam mix will not rise in temperature as you add more energy, until the steam is completely dry (at which point it heads into the superheater). That also means that the flue gasses exiting the boiler can't be any colder than 180C, which is a whole load of energy that you're just chucking out the chimney. But you can use that energy to preheat the cold water before it enters the boiler meaning the boiler doesn't have to do that works itself and the whole process is more efficient. Viola!

[@historynerd88]

Since especially the first Franco-Crosti locomotives, as the video mentions, other than the preheater drums also got various enhancements to the boiler, British speaking literature has taken to calling it "Franco-Crosti boiler". I agree it isn't quite right.

[@simonwass6315]

They are pre-heaters, not boilers. Clue is in the name. They are designed to heat the feed water before it enters the main boiler. It is not a loco with 2 boilers. The 9f didn't use both chimneys. Where do you get your info from!

[@tim3172]

A boiler is a common term for a device used to heat water, even if not to the point of boiling. Many furnaces use a boiler for radiators without boiling the actual water. Definitions of boiler: a fuel-burning apparatus or container for heating water. (Heating, not boiling) A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. (All pre-heaters for liquids are boilers.) The 9F did use the second chimney. It was used as an ejector. Something is still used, even if it isn't for whatever narrow view you have defined as a use for it. For example: it's a common mistake that the Titanic didn't use its fourth funnel. It was, in fact, used for ventilation.

[@simonwass6315]

@@tim3172 the 9f smokebox chimney on a crosti was only used for lighting up, once in steam a hinged lid sealed it. If you think your ejector point through, the ejector exhaust is not powerful enough to overcome cylinder exhaust, the cylinder exhaust would pull air down instead of through the boiler. Just think before posting! A pre heater is not a boiler, is is best described as an economiser. A feed heater is designed not to create steam, a boiler is.

[@CampDweller]

Do a history of Americans steam engines