Construction and Working Principle of Locomotive Boiler

Before we learn about the Locomotive Boiler at first we should learn what is it means by this name. The locomotive is a self-propelled vehicle and it can be powered by Diesel, Electricity or Steam. But this type of Locomotive Steam engine was famous in the railway sector. You may see several Locomotives in historical Hollywood Movies where engine operators throwing solid coal inside the boiler furnace.  And boiler is a part of Locomotive where steam is generated to power the Locomotive engine.

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A locomotive boiler is a Fire Tube Boiler. It is a horizontal drum axis, multi-tubular boiler. Because this boiler has 116 general fire tubes and 38 super-heated fire tubes. Locomotive Boiler is an internally fired boiler. That’s means boiler furnace located inside the main boiler shell or barrel. This boiler uses solid fuel like coal.  It is also a forced circulation, mobile or portable type, and medium pressure fire tube boiler. The most common use of this boiler is in railway locomotive engines and in the marine sector because of its mobility. This boiler has a high steam generation rate.

Locomotive Boiler
Locomotive Boiler. Source-Wikimedia

Construction of Locomotive Boiler:

A Locomotive Boiler has several components. First of all, it’s a shell or barrel. Generally, boiler shell diameter is about 8.5m and length is about near 4m. A Steam Dome presents at the top section of the boiler. It contains the regulator for regulating the steam produced through the steam pipe when the boiler is operational.

Firing point or hole present at the rear end of the boiler. We already know that this boiler uses solid fuel in the furnace. Solid fuel is inserted and ignited into the furnace by using this hole. After that, a firebox is present inside the boiler shell where the fuel is burned and generates heat. There is a platform called Grate where solid fuel like coal is kept and burnt.

It is a fire tube boiler and we already know how many fire tubes are present inside this boiler with its types.  The fire tubes in which, the hot flue gases pass. When hot flue gases pass it exchange the heat with the surrounding water. There is a smoke box and it is the only way where smoke is passing through the air. When solid fuel burned inside the furnace it also creates some smoke. This smokes need to exhaust in the environment by the chimney.

There is a fire brick arch placed inclined over the grate. It is responsible for preventing the entry of the ash, burnt fuel, and dust particles into the fire tubes during operation. Brick arch also provides a way to the hot flue gases to travel a definite path before entering the boiler fire tubes. There is a pipe called SteamPipe. By this pipe generated steam passes through. There are two steam pipes in Locomotive Boiler. First one is the main steam passing pipe. It located between the superheater and dome. The second steam pipe is connecting the superheater exit end to the steam engine.

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A blast pipe is provided above the steam engine. By this pipe, the exhaust steam passes. It has an important role during boiler operation.  Generally, a blast pipe is used to create the artificial draft that pushes the smoke out through the chimney. It also creates suction pressure for the hot flue gases. This suction pressure allows the hot flue gases to passes forward and it passes through the boiler fire tubes.

This boiler has a Super-Heater and it superheats the steam to the desired temperature. Steam used to superheated before it enters into the cylinder of the steam engine. Because wet steam creates is harmful to the engine. There are a superheater element pipes by which the steam travels and become superheated.

The safety valve is used for safe working with steam pressure.  This safety valve is responsible for the blows off steam when the pressure of generated steam is increased above the safety level or critical level. It also prevents the blasting of the boiler. There is a Regulator valve present that regulates the steam through the main steam pipe for super-heating. Now come to the final component of this boiler and it is Chimney. It is used to throw out the exhaust smoke and gases to the environment.

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Working of Locomotive Boiler:

The locomotive boiler uses solid fuel like coal. At first, the solid fuel is inserted on the grate. Then it ignites from the fire hole. When the fuel is burning inside the fire hole, it starts to generate necessary hot flue gases. Then a fire brick arch provides the path to flow the hot flue gases to a definite path before it entering into the long fire tubes of this boiler. As we know it also stops entering the burnt solid fuel particles into the fire tubes during the operation of the boiler. You will find two air in damper to flow fresh air into the combustion chamber.

When hot flue gases pass through the boiler firetubes then it heats the water surrounding the fire tubes. Water becomes heated by this continuous process and water becomes saturated steam. Generated saturated steam is collected at the top. Then this saturated steam from the dome (which is present at the top of the boiler) enters into the main steam pipe through the regulator valve. After this stem steam travels through the main steam pipe and reaches to the super-heater header. Form this super-heater header steam enters into another pipe called superheater element pipes. It is the place where saturated steam becomes superheated. Then superheated steam enters into the steam pipe of the smoke box.

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When saturated steam becomes superheated then it goes to the cylinder containing piston. By this superheated steam engine piston moves inside the cylinder. Piston use to connect with the wheels of the steam engine and the wheels start rotating like a locomotive train. Then the exhaust steam from the cylinder enters into the blast pipe. When you are sending steam into the cylinder then only steam will come out as exhaust gas.

Burnt gases and smoke after passing through the fire tubes of the boiler then it enters into the smoke box. Then the exhaust steam coming out from the blast pipe and it pushes the smoke out of the boiler through the chimney. Smoke from burned solid fuel cannot escape out from the boiler by its own. For this reason, an artificial draft is created by exhaust steam which coming out from the steam engine cylinder. This artificial draft also pushes the smoke out of the smoke box and creates suction pressure for the hot flue gases. There is a platform under the Grate called ash-pit where ash is stored after burning of solid fuel.

Application of Locomotive Boiler:

Locomotive boilers are mostly used in railways and marines sectors.  But the efficiency of this boiler is very less. This boiler cannot work in heavy load conditions. Locomotive Boiler is also used in traction engines, in portable steam engines, steam rollers, and some other steam road vehicles.

Related: Fire Tube Boiler

Now come to the Advantage and Disadvantage of Locomotive Boiler:

The best advantage if this boiler is it’s portable. Because you can take and place this boiler in any place. The price of this boiler is less and it is capable of handling fluctuating demands of steam. This boiler has a high steam generation rate. It comes with the compact in size and easy operates.

After all those advantages it has some disadvantages like corrosion and scale formation. This boiler cannot work under heavy load conditions due to its overheating problems.

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