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Steam engines laid the foundation for the rapid development of mechanical parts and machinery mechanisms and were the precursors of numerous sophisticated machines still in use today.

Concurrently, the development of the railway and telegraph networks began, leading to faster information, people, and goods flow, boosting the economy, and creating new values as never before in human history. The steam engine provided a significant impetus to the industrial revolution in Europe.

## Why was the steam engine invented?

The beginning of the idea of a device using the power of steam to replace human labor is attributed to [Heron](https://www.smith.edu/hsc/museum/ancient_inventions/steamengine2.html), who constructed the first primitive machine. Throughout history, many people worked on developing this idea, and the first recorded successful application was achieved by [Thomas Savery](https://www.britannica.com/biography/Thomas-Savery) in 1698 when he created a steam pump.

When the steam engine was invented, the production of goods at that time largely operated on the principles of manufacturing and small family crafts. 
The main function of the initial steam engines was to power pumps that drained water from mines.

Coal mining and the extraction of various metals were enormously important economic sectors in 18th-century Great Britain.

The steam engine was constructed in 1712 by [Thomas Newcomen](https://www.britannica.com/biography/Thomas-Newcomen) to power water pumps in coal mines.

He aimed to harness the machine's power to replace horses that were used to operate primitive water pump mechanisms in mines. Horses were expensive, and coal was cheap.

Newcomen's steam engine was fairly simple and consisted of a cylinder with a piston. The image shows a cross-section of Newcomen's simple steam engine.

![Thomas Newcomen's Steam Engine](https://strapi.metrikon.io/uploads/Parni_stroj_Thomasa_Newcomena_430c3a962e.png)
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Image: Thomas Newcomen's Steam Engine ([Source](https://www.britannica.com/biography/Thomas-Newcomen))

Atmospheric pressure would push the piston downward after water vapor condensed in the cylinder, creating a vacuum. The power obtained in this way was transmitted further through a mechanism.

A significant amount of coal was required for heating the water and generating steam to power the piston in Newcomen's steam engine.

As mines grew larger, more and more water needed to be pumped out. Newcomen's steam engine was not up to the task in terms of its working capacity.

Maintenance of machines and equipment was an unknown concept in the 18th century.

If water constantly flooded the mines, the steam engine would stop working, causing a halt in mining operations.

[James Watt](https://en.wikipedia.org/wiki/James_Watt), by 1764, was already known for his skill in crafting and repairing mechanical devices such as compasses, scales, quadrants, small mechanical toys, and musical instruments.

James Watt was also very frustrated and annoyed by the frequent need to repair damaged Newcomen steam engines brought to him by mine owners in northern England.

After each repair of a Newcomen steam engine, like any conscientious mechanic, James Watt would run the machine for a test to check its functionality.

The steam engine barely worked.

## How did James Watt improve the steam engine?

Extremely frustrated that all his efforts to repair existing steam engines resulted in meager progress, James Watt began experimenting.

In the process, he discovered that roughly 75% of thermal energy was spent heating the cylinder during each working cycle.

Thermal energy was wasted because cold water was injected later in the cycle to condense the steam, reducing pressure.

By repeatedly heating and cooling the cylinder, the steam engine had low efficiency because most of the thermal energy was spent on heating rather than converting into usable mechanical work.

He realized that the biggest drawback of Newcomen's steam engine was the amount of latent heat lost during the change of water's phase from liquid to steam.

Therefore, water condensation had to be separated from the steam phase in a [separate chamber](https://www.britannica.com/video/180124/James-Watt-steam-engine) connected to the steam cylinder. James Watt aimed to improve the existing steam engine and came up with the idea of creating a separate condenser. The cylinder's dimensions were 127 cm, and the entire machine's height was 7 meters.
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![James Watt's Steam Engine](https://strapi.metrikon.io/uploads/Parni_stroj_Jamesa_Watta_9eba0d02f7.png)
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Image: James Watt's Steam Engine ([Source](https://www.worldhistory.org/Watt_Steam_Engine/))
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Due to the constant threat of a steam boiler explosion, which was very primitively regulated, and frequent malfunctions such as leakage and scale buildup, James Watt restricted his machine to operate only using atmospheric-pressure steam.

In addition, he added numerous other improvements: a rotating shaft, a pressure-regulating valve, and a speed governor.

He obtained a patent in 1769 but did not make further efforts to commercialize his invention.

Now enters the scene Matthew Boulton, a wealthy manufacturer and owner of a factory producing fasteners, buckles, and simple tools.

The machines in his factory were powered by hydropower, which posed a particular problem during the summer when the river's water level decreased.

As a result, production had to adapt to the available energy supply.

Matthew Boulton realized that applying the steam engine for water pumping or powering machines would provide the necessary production capacity and continuous operation.

James Watt and Matthew Boulton became business partners in a joint venture, with Watt responsible for the technical aspects and steam engine development, and Boulton for finances.

They hired master founder John Wilkinson, who was highly successful in casting cannons, to make a steam cylinder.

It was essential for James Watt that the cylinder casting was free of impurities and porosity to achieve optimal heat transfer and minimize the risk of an explosion.

The machine was four times more powerful compared to Newcomen's.

The company bought machine parts from numerous suppliers, and then employees assembled steam engines under the supervision of engineers.

The profit was made based on a nearly 30% difference in the amount of coal used by the less efficient Newcomen steam engine compared to the more efficient Watt steam engine.

Buyers of steam engines were mine owners who needed to continually pump water and owners of textile manufacturing factories.

The versatility of steam engines proved so great that Matthew Boulton later used them to power coin minting machines.

In the period 1783-1800, over 500 steam engines were produced and used in Great Britain.

## How do steam locomotives work, and what are their main components?

[William Murdoch](https://en.wikipedia.org/wiki/William_Murdoch) was an employee of the Watt-Boulton company, responsible for installing and repairing steam engines in factories and mines of customers.

Continuously working on steam engine mechanisms, he made certain improvements that so impressed James Watt and Matthew Boulton that they took him as a third partner in the company.

William Murdoch came up with the idea of using the steam engine for transportation and thus created the prototype of the first steam locomotive. Many others later improved and developed this invention.

During the 19th century, steam engines were widely used to power locomotives for transporting goods and passengers over longer distances.

Although steam locomotives are now museum pieces, they can still teach us and remind us of the basics of mechanical devices.

During a visit to the technical museum, I saw and studied one of the largest exhibits, a steam locomotive with an exposed steam boiler due to the removed casing and open cylinders and auxiliary systems.

This is a Prussian locomotive model S 10, which was produced between 1910 and 1914 when a total of 202 locomotives were built.
The next image shows a locomotive model S with the outer casing removed
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![Screenshot 2024-02-03 at 20.08.35.png](https://strapi.metrikon.io/uploads/Screenshot_2024_02_03_at_20_08_35_1726636f1e.png)
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Image: Steam locomotive with removed casing, cross-section of the steam engine (Source: Author's Archive)
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Below the casing or steel cylindrical shell, you can see the cross-section of the steam boiler and pipes, the steam cylinder with piston, the front part of the boiler for exhaust gases, and the transmission mechanism.

In the next picture, you can see the locomotive from the other side with the complete casing, and part of the drive mechanism connected to three pairs of driven wheels.

![Parna lokomotiva sa cjelovitom oplatom](https://strapi.metrikon.io/uploads/Parna_lokomotiva_sa_cjelovitom_oplatom_59036c3181.png)
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Image: Steam locomotive with complete casing (Source: Author's Archive)
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The steam locomotive **model P8** was produced in 1919 for hauling freight and express passenger trains and was used until the 1970s.

In the following picture, the portal or cover of the P8 model locomotive is open.

The front part of the smoke gas boiler is visible, where the **heat exchanger tubes** are located.

![Prednja strana lokomotive](https://strapi.metrikon.io/uploads/Prednja_strana_lokomotive_c001341556.png)
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Image: Front view of the locomotive (Source: Author's Archive)
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Over the past 200 years, the principle of steam engine operation and energy conversion for locomotive propulsion has remained unchanged, although the locomotive's design has undergone numerous changes.

Every steam locomotive fundamentally consists of two parts: the **steam boiler** (firebox, tubes, preheater, valves) and the **power unit** (cylinders with pistons, crossheads, transmission mechanism, wheels).

The simplified cross-section of the locomotive and its main components are shown in the illustration.

The basic operation of every steam locomotive is for steam under pressure, ranging from 14 bar to 22 bar, to enter the cylinder space with a piston, expand, and push the piston.

![steam-engine.webp](https://strapi.metrikon.io/uploads/steam_engine_0805c3feb6.webp)
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Image: Parts of a steam locomotive ([Source](https://straction.wordpress.com/how-the-steam-engine-of-the-locomotive-works/))
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The **piston connected to the crosshead** translates the translational motion to the crosshead of the drive mechanism connected to the drive wheels.

This leads to the transfer of translational motion to rotational, or the locomotive's wheels start moving.

Steam expands in the **cylinder** until it reaches atmospheric pressure.

At the bottom of the steam boiler's firebox, there is a grate where fuel combustion occurs. Hot combustion gases rise to the upper part of the firebox, the combustion chamber.

**Fireboxes** where coal is burned have ash pans at the bottom to collect ash, which can be shaken down using a lever.

**Smoke gases** leave the combustion chamber with turbulent flow through a system of pipes in a water-filled boiler.

The heat of the smoke gases heats the water until it evaporates.

Steam is created, and under pressure, it rises towards the dome and then goes to the steam cylinders through a system of parallel pipes. 

The steam quantity is regulated by a control valve located in the dome.

Another set of pipes **transports the steam to a superheater**, where the steam is further heated to a higher temperature before entering the steam cylinders.

Using superheated steam, as opposed to saturated steam, increases the efficiency of a steam locomotive's operation by 25% to 30% (refer to the Mollier h-s diagram for water vapor).

When we examine the boiler with its pipes more closely, does it remind you of the precursor to today's modern [shell-and-tube heat exchangers](https://en.wikipedia.org/wiki/Shell-and-tube_heat_exchanger)?

Furthermore, the steam locomotive's boiler is essentially a pressure vessel that needs careful regulation.

Safety valves are designed and adjusted to automatically open and release steam if the pressure in the steam boiler exceeds the allowed limit.

The space above the firebox must always be filled with water. If the water level falls below the height of the firebox's crown sheet (right side of the image), the boiler overheats, and the risk of a boiler explosion increases.

**Water level gauges or sight glasses** are installed to monitor the water level.

Steam passes through steam pipes and enters the steam cylinders, where it expands and moves the pistons.

Once the steam has transferred its energy and done useful work by moving the pistons, the valve system allows the subcooled lower pressure steam to escape through an exhaust pipe located in the boiler filled with smoke gases.

The locomotive's wheels start moving as a result of the motion transfer from the pistons through the crosshead and crosshead guide, and the motion of the power mechanism is controlled by a lever located in the locomotive's cab at the rear.

The same lever is used to control the direction of locomotive movement, as well as to accelerate or decelerate.

Once the steam has driven the piston to the end of the cylinder, the crosshead, crosshead guide, and the connecting rod's pivot system convert the piston's translational motion (back-and-forth) into the circular rotation of the wheels.

Counterweights or counterbalance weights positioned at the opposite ends of the connecting rod and wheel joint allow for maintaining a balanced position during movement.

Early locomotives had one pair of driven wheels, and more complex mechanisms with a larger number of wheels were developed later, with the largest number of wheels driven from a single cylinder assembly being six (6) pairs.

Due to the large diameter and the need for flexibility in movement, numerous locomotives featured two steam engines and two sets of driven wheels.

The arrangement, number, and construction of wheels and the drive mechanism depended on the locomotive's purpose.

After the steam has transferred its energy in the cylinders, it exits through an exhaust pipe and mixes with smoke gases.

This creates a draft that further pulls the smoke gases through pipes into the front part of the boiler.

Fresh air enters the firebox through openings or ports on the front and bottom of the firebox.

The mixed exhaust steam and smoke gases exit through the locomotive's chimney with fast, turbulent flow.

The flow of the resulting mixture enters the chimney pipes, leading to a sudden decrease in speed, creating the well-known sound of the locomotive.

Since the amount of exhaust gas depends on the consumed steam leaving the cylinders, it must be anticipated when the engineer closes the valve.

For this purpose, a group of small nozzles, known as steam jets or blast pipes for directing steam, is placed at the front of the smoke gas boiler.

In the smoke gas boiler, partially burned coal particles from the firebox collect in the mixture of smoke gases.

When a sufficient amount of particles accumulates to impede gas flow, vortexing of the particles and their expulsion in the form of cinders occurs through the chimney, along with a mixture of steam and smoke gases.

## Which parts of a steam locomotive are most susceptible to failures?

A steam boiler can **explode** if the steam exceeds the maximum allowed pressure.

Steam boilers were riveted together until the discovery of welding and its widespread use in joining metal materials.

Riveted joints have lower strength compared to well-executed welds, so as steam pressure increased, the load on riveted joints also increased.

Furthermore, pressure tests as a method of [testing pressure vessels](https://narodne-novine.nn.hr/clanci/sluzbeni/2020_07_75_1450.html) only became widespread in the 20th century, so it's questionable how thoroughly the original steam boilers were tested before being put into operation.

**Fires** in the firebox are another potential danger, occurring when overheating and a lack of water in the space above the firebox would take place.

Early locomotives had no fire protection systems.

**Breakage of parts in the transmission mechanism** could occur due to poor manufacturing or the use of low-quality materials for making the driving axles, crossheads, piston rods, or connecting rods.

**Tube ruptures** through which smoke gases pass occurred due to material fatigue in the tubes or the presence of excessively hot gases.

**Failure of safety valves** or loss of functionality is another potential failure, given that there were no legal regulations for regular service and testing of safety valves at that time.

Other **potential problems** encountered by locomotive engineers included reduced combustion efficiency due to poor-quality coal and lower efficiency, significant mechanical losses, heat losses due to inadequate steam utilization, insufficient steam superheating, excessively stiff or ruptured springs, water leakage from the steam boiler, clogged steam pipes, and reduced heat transfer due to scale buildup on pipe surfaces.

## Conclusion

The invention of the steam engine was revolutionary for industrial production and led to fundamental changes in all aspects of society.

The steam locomotive is an excellent practical example of how the steam engine improved and developed the transportation of people and goods, with numerous mechanical mechanisms finding application in various industrial sectors.

Great Britain paid tribute to its two giants, Watt and Boulton, who laid the foundations of modern industry by featuring their portraits on the reverse of the £50 note.

![Matthew-Boulton-and-James-010.png](https://strapi.metrikon.io/uploads/Matthew_Boulton_and_James_010_af2472c4d4.png)

Slika: Back of the £50 note with portraits of Matthew Boulton and James Watt ([Source](https://www.theguardian.com/business/gallery/2013/apr/26/banknotes-winston-churchill-predecessors-in-pictures))

Underneath their portraits, the following quotes appear:

Sir, I sell here what all the world desires to have – POWER (Boulton, on the left side)
I can think of nothing else but this MACHINE (Watt, on the right side)

The SI unit for [power](https://hr.wikipedia.org/wiki/Snaga) is named Watt in honor of James Watt and is defined as the work of 1 Joule done in 1 second. It is equivalent to 1/746 horsepower (hp) for determining mechanical and electrical power.

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Water vapor isn't a miracle, but its thermal energy has created wonders by powering the steam engine, an invention that revolutionized the industry.

Parni strojevi su udarili temelj naglom razvoju mehaničkih dijelova i strojnih mehanizama te bili preteča brojnih sofisticiranih strojeva koje i danas koristimo.

Paralelno je krenuo razvoj željezničke i telegrafske mreže, što je dovelo do bržeg protoka informacija, ljudi i dobara te uzdiglo gospodarstvo i stvorilo nove vrijednosti kao nikada do tada u ljudskoj povijesti. Parni stroj je dao je veliki poticaj razvoju industrijske revolucije u Europi.

## Zašto je nastao parni stroj?

Začetak ideje o uređaju koji koristi snagu vodene pare da bi zamijenio ljudski rad pripisuje se [Haronu](https://www.smith.edu/hsc/museum/ancient_inventions/steamengine2.html) koji je konstruirao prvi primitivni stroj. Tijekom povijesti puno ljudi se bavilo razradom ove ideje a prvu zabilježenu uspješnu primjenu ostvario je [Thomas Savery](https://www.britannica.com/biography/Thomas-Savery) 1698 napravivši parnu pumpu.

Kada je izumljen parni stroj, onovremena proizvodnja dobara je uvelike funkcionirala po principu manufaktura i malih obiteljskih zanata.
Glavna funkcija prvobitnih parnih strojeva bila je pokretati pumpe koje su ispumpavale vodu iz rudnika.

Rudarenje ugljena i raznih metala bilo je u 18. stoljeću enormno važna gospodarska grana u Velikoj Britaniji.

Parni stroj konstruirao je 1712. [Thomas Newcomen](https://www.britannica.com/biography/Thomas-Newcomen) za pokretanje pumpe za vodu u rudnicima ugljena.

Želio je iskoristiti pogonsku snagu stroja da zamijeni konje koji su se koristili za pokretanje primitivnih mehanizama pumpi vode u rudnicima. Konji su bili skupi a ugljen jeftin.

Newcomenov parni stroj je bio poprilično jednostavan i sastojao se od cilindra sa klipom. Na slici je prikazan presjek parnog stroja jednostavne konstrukcije.

![ Parni stroj Thomasa Newcomena](https://strapi.metrikon.io/uploads/Parni_stroj_Thomasa_Newcomena_430c3a962e.png)
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Slika: Parni stroj Thomasa Newcomena ([Izvor](https://www.britannica.com/biography/Thomas-Newcomen))

Atmosferski tlak bi pritisnuo klip prema dolje nakon što se vodena para kondenzirala u cilindru i stvorila vakuum. Tako dobivena snaga se prenosila dalje preko mehanizma

Za grijanje vode i nastanak pare koja će pokretati klip Newcomenovog parnog stroja također je bila potrebna velika količina ugljena.

Kako su rudnici postajali sve veći, trebalo je ispumpavati sve više vode. Newcomenov parni stroj svojim radnim kapacitetom tome nije bio dorastao.

Održavanje strojeva i opreme je u 18.stoljeću bio nepoznat pojam.

Voda je je u rudnicima  stalno poplavljivala parni stroj bi tada prestajao sa radom što je dovodilo do obustave rudarenja.

[James Watt](https://en.wikipedia.org/wiki/James_Watt) je 1764. već bio poznat po svojoj vještini izrade i popravaka mehaničkih uređaja poput kompasa, vaga i kvadranta, malih mehaničkih igračaka i glazbenih instrumenata.

James Watt je također bio vrlo frustriran i nervozan što učestalo mora popravljati oštećene Newcomenove parne strojeve koje su mu donosili vlasnici rudnika u sjevernoj Engleskoj.

Nakon svakog popravka Newcomenog parnog stroja, kao svaki savjestan mehaničar, James Watt bi stroj pustio u probni rad da provjeri njegovu ispravnost.

Parni stroj bi jedva radio.

## Kako je James Watt unaprijedio parni stroj

Iznimno nervozan što sav njegov trud oko popravka postojećeg parnog stroja rezultira smiješnim napretkom, James Watt  je krenuo sa eksperimentima.

Pritom je otkrio da se ugrubo 75% toplinske energije troši na grijanje cilindra tijekom svakog radnog ciklusa.

Toplinska energija se trošila jer se kasnije u ciklusu ubrizgavala hladna voda da se kondenzira para kako bi se smanjio tlak.

Takvim uzastopnim grijanjem i hlađenjem cilindra parni stroj je imao nisku učinkovitost jer se većina toplinske energije trošila na grijanje umjesto da se pretvori u iskoristiv mehanički rad.

Shvatio je da najveći nedostatak Newcomovog parnog stroja čini količina izgubljene latentne topline do koje dolazi prilikom promjene agregatnog stanja vode iz tekuće faze u parnu fazu.

Zato se kondenzacija vode mora odvojiti od parne faze u [zasebnu komoru](https://www.britannica.com/video/180124/James-Watt-steam-engine) koja je povezana sa parnim cilindrom. James Watt je nastojao poboljšati postojeći parni stroj i tako je dobio ideju da izradi odvojeni kondenzator. Dimenzija cilindra je bila 127 cm a visina čitavog stroja 7 m.

![Parni stroj Jamesa Watta ](https://strapi.metrikon.io/uploads/Parni_stroj_Jamesa_Watta_9eba0d02f7.png)
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Slika: Parni stroj Jamesa Watta ([Izvor](https://www.worldhistory.org/Watt_Steam_Engine/))

Zbog stalne prisutnosti od eksplozije parnog kotla koji je bio vrlo primitivno reguliran te česte pojave kvarova kao što je propuštanje i nastanak kamenca, James Watt je ograničio svoj stroj tako da radi samo upotrebom pare na atmosferskom tlaku.

Uz to je dodao i brojna druga poboljšanja: rotirajuće vratilo, ventil za regulaciju tlaka te regulator brzine vrtnje.

Dobio je patent 1769. ali nije se dalje trudio da svoj izum komercijalizira.

Sada na scenu stupa Matthew Boulton, bogati tvorničar i vlasnik tvornice za proizvodnju pribadača, kopči i jednostavnih alatki.

Strojeve u njegovoj tvornici pokretala je hidroenergija, što se pokazalo posebno problematičnim tijekom ljeta kada se količina vode u rijeci smanjivala.

Posljedično time, proizvodnja se morala prilagođavati količini raspoložive energije.

Matthew Boulton je shvatio da bi primjena parnog stroja za prepumpavanje vode ili za pokretanje strojeva omogućila potreban proizvodni kapacitet i kontinuirani rad.

James Watt i Matthew Boulton postali su poslovni partneri u zajedničkoj kompaniji, pri čemu je Watt bio zadužen za tehnički dio i razvoj parnog stroja a Boulton za financije.

Angažirali su majstora ljevača Johna Wilkinsona koji je bio vrlo uspješan u lijevanju topova da
izradi parni cilindar.
Jamesu Wattu je bilo jako važno da odljevak cilindra ne sadrži nečistoće niti poroznosti kako bi prijenos topline bio što bolji i kako bi se rizik od nastanka eksplozije sveo na minimum.

Stroj je bio 4 puta snažniji u usporedbi sa Newcomenovim.

Kompanija je kupovala strojne dijelove od brojnih dobavljača i potom su djelatnici sastavljali parne strojeve pod nadzorom inženjera.

Profit je ostvaren temeljem razlike od skoro 30% u količini ugljena koju je koristio manje efikasan Newcomen parni stroj u usporedbi sa efikasnijim Wattovim parnim strojem.

Kupci parnih strojeva su bili vlasnici rudnika u kojima je trebalo stalno ispumpavati vodu te vlasnici tvornica za proizvodnju tekstila.

Svestranost primjene parnog stroja se pokazala toliko velikom da ga je Matthew Boulton kasnije iskoristio za pokretanje strojeva za kovanje novčića.

U Velikoj Britaniji je u periodu 1783-1800 proizvedeno i koristilo se preko 500 parnih strojeva.

## Funkcioniranje parne lokomotive i glavni dijelovi

[William Murdoch](https://en.wikipedia.org/wiki/William_Murdoch) zaposlenik je bio Watt-Boulton kompanije, zadužen za ugrađivanje i popravljanje parnih strojeva u tvornicama i rudnicima kupaca.

Neprestano radeći na mehanizmima parnih strojeva napravio je određena poboljšanja koja su toliko oduševila Jamesa Watta i Matthewa Boultona da su ga uzeli za trećeg partnera u kompaniji.

William Murdoch je došao na ideju da parni stroj koristi za transport i tako je izradio prototip prve parne lokomotive. Kasnije su brojni drugi unaprijedili i razradili ovaj izum.

Tijekom 19.stoljeća parni stroj se uvelike koristio za pogon lokomotiva kojima su vlakovi počeli prevoziti teret i putnike na veće udaljenosti.

Iako su danas parne lokomotive muzejski primjerci, još uvijek nas mogu naučiti i podsjetiti osnovama strojarskih konstrukcija i termodinamike.

Prilikom posjete tehničkom muzeju vidjela sam i proučila jedan od najvećih izložaka, parnu lokomotivu s otvorenim parnim kotlom zbog uklonjene oplate i otvorenih cilindara te pomoćnih sustava.

Radi se o pruskoj lokomotivi model S 10 koja se proizvodila u razdoblju između 1910. i 1914. kada su izradili ukupno 202 lokomotive.
Na sljedećoj slici vidi se lokomotiva model S kojoj je uklonjena vanjska oplata. 

![Screenshot 2024-02-03 at 20.08.35.png](https://strapi.metrikon.io/uploads/Screenshot_2024_02_03_at_20_08_35_1726636f1e.png)
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Slika: Parna lokomotiva kojoj je uklonjena oplata, poprečni presjek parnog stroja  (Izvor: Arhiva autorice)
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Ispod oplate odnosno čeličnog cilindričnog plašta vidi se **poprečni presjek parnog kotla** i cijevi, parnog cilindra s klipom, prednjeg dijela kotla za dimne plinove te prijenosnog mehanizma.

Na idućoj slici vidi se lokomotiva s druge strane pri čemu je oplata parnog kotla čitava, te dio pogonskog mehanizma spojenog sa 3 para pogonjenih kotača.

![Parna lokomotiva sa cjelovitom oplatom](https://strapi.metrikon.io/uploads/Parna_lokomotiva_sa_cjelovitom_oplatom_59036c3181.png)
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Slika: Parna lokomotiva sa cjelovitom oplatom (Izvor: Arhiva autorice)
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Parna lokomotiva **model P8** proizvedena je 1919. za pokretanje teretnih i ekspres putničkih vlakove se koristila do 1970-tih.

Na sljedećoj slici je otvorena portela ili poklopac lokomotive modela P8.

Vidljiva je prednja strana kotla dimnih plinova u kojem su **cijevi izmjenjivača topline**.

![Prednja strana lokomotive](https://strapi.metrikon.io/uploads/Prednja_strana_lokomotive_c001341556.png)
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Slika: Prednja strana lokomotive (Izvor: Arhiva autorice)
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Tijekom proteklih 200 godina princip rada parnog stroja i pretvorbe energije za pokretanje željezničkih lokomotiva se nije mijenjao iako je sama konstrukcija lokomotiva doživjela brojne izmjene.

Svaka parna lokomotiva se u osnovi sastoji iz 2 dijela: **parnog kotla** (ložište, cijevi, predgrijač, ventili) i **pogonskog stroja** (cilindri s klipovima, klipnjače, prijenosni mehanizam, kotači).

Na slici prikazan je pojednostavljeni poprečni presjek lokomotive i glavni dijelovi.

Osnovno djelovanje svake parne lokomotive je da para pod tlakom od 14 bar do 22 bar ulazi u prostor cilindra s klipom, ekspandira i odgurava klip.

![steam-engine.webp](https://strapi.metrikon.io/uploads/steam_engine_0805c3feb6.webp)
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Slika: Dijelovi parne lokomotive ([Izvor](https://straction.wordpress.com/how-the-steam-engine-of-the-locomotive-works/))
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**Klip povezan s klipnjačom** prenosi translacijsko gibanje na križnu glavu pogonskog mehanizma spojenu s pogonskim kotačima.

Tako dolazi do prijenosa translacijskog gibanja u rotacijsko tj. dolazi do pokretanja kotača i gibanja lokomotive.

Para ekspandira u **cilindru** sve dok ne dostigne atmosferski tlak.

Na dnu ložišta parnog kotla nalazi se rešetka gdje dolazi do izgaranja goriva. Nastaju topli plinovi izgaranja koji odlaze prema gornjem dijelu ložišta tj. u komoru izgaranja.

**Ložišta** u kojima izgara ugljen imaju tave na dnu u koje odlazi nastali pepeo tako što se pomoću poluge protrese rešetka.

**Dimni plinovi** napuštaju komoru izgaranja uz turbulentno strujanje kroz sustav cijevi u kotlu ispunjenom vodom.

Toplina dimnih plinova zagrijava vodu sve do isparavanja.

Nastaje para koja se pod tlakom uzdiže prema kupoli i odatle odlazi prema parnim cilindrima sustavom paralelno položenih cijevi.

Količina pare se regulira pomoću regulacionog ventila smještenog u kupoli.

Drugi sustav cijevi **prenosi paru do pregrijača** gdje se para dodatno zagrijava na višu temperaturu prije odlaska u parne cilindre.

Korištenje pregrijane pare u usporedbi sa suhozasićenom parom povećava učinkovitost rada parne lokomotive za 25% do 30% (prisjetite se Mollierovog h-s dijagrama za vodenu paru).

Kada malo detaljnije promotrimo samo kotao sa cijevima, podsjeća li vas na preteču današnjih suvremenih [cijevnih izmjenjivača topline](https://en.wikipedia.org/wiki/Shell-and-tube_heat_exchanger)?

Nadalje, kotao parne lokomotive je zapravo posuda pod tlakom čiji rad treba pažljivo regulirati.

Sigurnosni ventili su konstruirani i podešeni tako da automatski otvaraju i ispuštaju paru ako tlak u parnom kotlu prijeđe dozvoljenu granicu.

Prostor iznad ložišta mora cijelo vrijeme biti ispunjen vodom. Ako razina vode padne ispod visine vrha ložišta (desna strana slike), dolazi do pregrijavanja kotla i povećava se rizik nastanka eksplozije kotla.

**Mjerači razine vode ili nivokazna stakla** se postavljaju za praćenje razine vode.

Para prolazi kroz parne cijevi i ulazi u parne cilindre gdje se događa ekspanzija i pomicanje klipova.

Kada je para predala energiju i postigla koristan rad pokrećući klipove, sustav ventila propušta pothlađenu paru nižeg tlaka kroz ispušnu cijev smještenu u kotlu ispunjenom dimnim plinovima.

Gibanje kotača lokomotive nastaje kao posljedica prijenosa gibanja klipova preko stapajice i križne glave, gibanje pogonskog mehanizma se kontrolira polugom smještenom u kabini strojovođe u stražnjem dijelu lokomotive.

Preko iste poluge se upravlja smjerom kretanja lokomotive te ubrzanjem ili usporenjem kretanja.

Jednom kada je para pokrenula klip do kraja cilindra, sustav stapajice, klipnjače i spojne osovine kotača pretvara translacijsko gibanje klipa (naprijed-natrag) u kružno okretanje kotača.

Protuutezi ili kontra utezi postavljeni na suprotnim krajevima spoja osovine i kotača omogućavaju održavanje ravnotežnog položaja tijekom kretanja.

Prvobitne lokomotive su imale po 1 par pogonjenih kotača, tek kasnije su razvijeni kompleksniji mehanizmi sa većim brojem kotača pri čemu je najveći broj kotača pogonjenih iz pojedinačnog sklopa cilindara bio šest (6) para.

Zbog velikog promjera i potrebe za fleksibilnošću kretanja, brojne lokomotive su imale po 2 parna stroja i po 2 seta pogonjenih kotača.

Raspored, broj i konstrukcija kotača i pogonskog mehanizma ovisili su o namjeni lokomotive.

Nakon što para preda energiju u cilindrima, izlazi kroz ispušnu cijev i miješa se s dimnim plinovima.

Pritom nastaje propuh koji dodatno povlači dimne plinove kroz cijevi u prednji dio kotla.

Svježi zrak ulazi u ložište kroz otvore ili portele na prednjoj i donjoj strani ložišta.

Pomiješana ispušna para i dimni plinovi izlaze kroz dimnjak uz brzo, turbulentno strujanje.

Strujanje nastale mješavine ulazi u cijev dimnjaka i pritom dolazi do naglog smanjenja brzine, pri čemu nastaje poznati zvuk lokomotive.

Budući da količina ispušnog plina ovisi o potrošenoj pari koja napušta cilindre, mora se predvidjeti ispuh vrućih plinova ili dima kada strojovođa zatvori ventil.

Za ovu svrhu služi skupina malih mlaznica tkz. propuhača za usmjeravanje pare, smještenih u prednjem dijelu kotla dimnih plinova.

U kotlu dimnih plinova se također sakupljaju djelomično izgorjele čestice ugljena koje su došle iz ložišta u smjesi dimnih plinova.

Kada se nakupi količina čestica dovoljna da ometa strujanje plinova, tada započinje vrtloženje čestica i njihovo izbacivanje u obliku ugaraka kroz dimnjak zajedno sa smjesom pare i dimnih plinova.

## Koji dijelovi parne lokomotive su najviše podložni kvarovima?

Parni kotao može **eksplodirati** ako para prijeđe maksimalno dozvoljeni tlak.

Parni kotlovi su se spajali zakovicama do otkrića zavarivanja i masovne primjene u spajanju metalnih materijala.

Spojevi izvedeni zakovicama imaju manju čvrstoću u odnosu na kvalitetno izvedene zavare, stoga je porastom tlaka pare raslo opterećenje zakovičastih spojeva.

Osim toga, tlačne probe kao način [ispitivanja posuda pod tlakom](https://narodne-novine.nn.hr/clanci/sluzbeni/2020_07_75_1450.html) ušle su u masovnu primjenu tek u 20. stoljeću pa je upitno koliko su prvobitni parni kotlovi bili ispitivani i provjeravani prije puštanja u rad.

**Požari** u ložištu su još jedna od potencijalnih opasnosti, kad bi došlo do pregrijavanja i manjka vode u prostoru iznad ložišta.

Prvobitne lokomotive nisu imale nikakve protupožarne sustave.

**Lomovi dijelova prijenosnog mehanizma** bi se javili uslijed nekvalitetne proizvodnje ili nekvalitetnog materijala izrade prijenosne osovine, križne glave, klipnjače ili stapajice.

**Pucanje cijevi** kroz koje prolaze dimni plinovi se javljalo kao posljedica zamora materijala cijevi ili zbog učestalog prisustva plinova previsoke temperature.

**Otkazivanje sigurnosnih ventila** ili gubitak funkcionalnosti je još jedan od potencijalnih kvarova, s obzirom da u ono vrijeme nisu postojale zakonske regulative redovitog servisa i ispitivanja sigurnosnih ventila.

Ostali **potencijalni problemi** u radu lokomotiva s kojima su se susretali strojovođe su: smanjena učinkovitost izgaranja zbog ugljena loše kvalitete te lošija iskoristivost, veliki mehanički gubici, toplinski gubici uslijed nedovoljnog iskorištavanja pare, nedovoljno pregrijavanje pare, previše krute ili popucale opruge, propuštanje vode iz parnog kotla, začepljenje parnih cijevi te smanjeni prijenos topline zbog naslaga kamenca na površinama cijevi.

## Zaključak

Izum parnog stroja revolucionaran je za industrijsku proizvodnju i doveo do temeljitih promjena u svim sferama društva.

Parna lokomotiva je sjajan praktičan primjer kako je parni stroj unaprijedio i razvio transport ljudi i tereta, a brojni strojni mehanizmi našli su primjenu u različitim industrijskim granama.

Velika Britanija je odala počast dvojici svojih velikana Wattu i Boultonu koji su udarili temelje moderne industrije, prikazavši njihove portrete na poleđini novčanice od 50 funti (50 £).

![Matthew-Boulton-and-James-010.png](https://strapi.metrikon.io/uploads/Matthew_Boulton_and_James_010_af2472c4d4.png)

Slika: Poleđina novčanice od 50 funti sa portretima Matthewa Boultona i Jamesa Watta ([Izvor](https://www.theguardian.com/business/gallery/2013/apr/26/banknotes-winston-churchill-predecessors-in-pictures))

Ispod njihovih portreta stoje citati:

_Gospodine, ja ovdje prodajem ono što čitav svijet želi imati – SNAGU (Boulton, na lijevoj strani)_
_Ne mogu razmišljati ni o čemu drugome osim ovog STROJA (Watt, na desnoj strani)_

Mjerna jedinica SI sustava za [snagu](https://hr.wikipedia.org/wiki/Snaga) je u čast Jamesu Wattu dobila naziv Watt i definira se kao omjer rada od 1 Joula koji se obavi u 1 sekundi. Ekvivalent je 1/746 konjske snage (hp) za određivanje mehaničke i električne snage.

Vodena para nije čudo, ali je njena toplinska energija stvorila čuda pokrećući parni stroj, izum što je revolucionirao industriju.

Strojarka susreće parni stroj - Saznajte sve o parnoj lokomotivi

Wasserdampf ist kein Wunder, aber seine thermische Energie hat Wunder geschaffen, indem sie die Dampfmaschine angetrieben hat, eine Erfindung, die die Industrie revolutioniert hat.

Maschinenbau trifft auf Dampfmaschine - Erfahren Sie alles über Dampflokomotiven

Mechanical Engineer Meets Steam Engine - Learn All About Steam Locomotives

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Mechanical Engineer Meets Steam Engine - Learn All About Steam Locomotives

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