Construction and Working Principle of Locomotive Boiler

Locomotive Boiler

Before we learn about the Locomotive Boiler at first we should learn what is it means by this name. 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 railway sector. You may see several Locomotives in historical Hollywood Movie where engine operator 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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Locomotive boiler is a Fire Tube Boiler. It is a horizontal drum axis, multi-tubular boiler. Because this boiler has 116 general fire tube and 38 super-heated fire tube. Locomotive Boiler is a internally fired boiler. That’s means boiler furnace located inside the main boiler shell or barrel. This boiler use 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 marine sector because of its mobility. This boiler has 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 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 boiler. It contains the regulator for regulating the steam produced through the steam pipe when boiler is operational.

Firing point or hole present at the rear end of the boiler. We already know that this boiler use solid fuel in furnace. Solid fuel is inserted and ignited into the furnace by using this hole. After that a fire box 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 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 passes. When hot flue gases passes it exchange the heat with 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 it entering in the boiler fire tubes. There is a pipe called Steam Pipe. 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 super heater and dome. Second steam pipe is connecting the super heater 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 use to super heated before it entering into the cylinder of the steam engine. Because wet steam create is harmful for engine. There is a super heater element pipes by which the steam travels and become superheated.

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 increases above the safety level or critical level. It also prevents 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:

Locomotive boiler uses the 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 boiler. You will find two air in damper to flow fresh air into the combustion chamber.

When hot flue gases passes through the boiler fire tubes 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 super heater 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 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 escapes out form 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 its portable. Because you can take and place this boiler at any place. The price of this boiler is less and it is capable of handling fluctuating demands of steam. This boiler has high steam generation rate. It come with compact in size and easy operates.

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

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