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Fire Tube Boilers Detailed Guide

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There are boiler systems around that work quite differently. Each has its advantages and disadvantages in use. In this article, we will consider the fire tube boiler. These boilers, which allow us to produce steam by simply passing hot gases through the tubes, contain many details.

You can read our other contents for Boilers:

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Representative image Boiler room

Type of Boilers

Generally, you can see 2 types of boiler systems. These are divided into two as fire tube and water tube.

Fire tube, as the name suggests, allows the water to evaporate by passing the hot gas through the tubes. The water tube, passes water through the tubes, passing it through the combustion chamber and evaporating the water.

First i will give you some compartments used almost in every boiler systems. I hope it helps you for better understanding.


It is the equipment in charge of producing the heat required to evaporate the water. After all, we need heat for the evaporation process, right? It provides the necessary heat to the combustion area by using fuels such as diesel. Thus, we have a constant source of heat to heat the water.

In fact, most boiler systems come with their own burner, but there are exceptions. Some boiler systems evaporate water by waste heat method. We often faced it on ships, we pass the hot exhaust gas from the main engine through the economizer and generate steam. We can then use this steam power in other parts of the ship.

Safety Valves

If we are going to work with high heat and steam, this is no joke. We all know how important safety is, especially in the ship environment. So, there are equipments called safety valves in different parts of the boiler system. They allow us to evacuate steam in case of high pressure. In routine boiler maintenance, safety valves must be checked.

Pumps on Boiler System

These are the pumps used in different types and numbers according to the system design. They are used to pump cold water (feed water) into the water tank. It is also used to pump the heated hot water back to the water tank to increase the system efficiency.

Diagram of Fire Tube Boiler 

We can show the fire tube diagram as follows.

Diagram of fire tube boiler 

Working Principle

First of all, water is filled into the heating area with the help of pumps. Since the water in the system will decrease as the water evaporates, this process is usually done automatically by the pump.

Make sure that the safety valve and drains are closed so that the pressure in the system can rise. Then the circulation pumps are activated. The burner is made ready for burning. After the burner ignites, the temperature and pressure gauges are monitored.

The combustion gases created by the burner will pass through the tubes and heat the water. Then the excess hot gas goes outside. Meanwhile, the evaporated water comes out of another pipe.

In case of overpressure, safety valves operate and give the pressure to the atmosphere. Actually, I tried to explain it simply, but the system contains too many details.

Fire Tube Boiler vs Water Tube 

The following comparison has been made in general. It is the commonly used comparison for water and fire tube boilers.

Fire Tube BoilerWater Tube Boiler
Rate of steam generation is generaly lowerRate of steam generation is generaly higher
Not suitable for large power plantSuitable for large power plant
Probablity of explosion is lower due to pressureProbablity of explosion is higher due to pressure
Hot gases inside the tubes and
water outside the tubes
Water inside the tubes and hot
gases outside the tubes
Fire tube boiler vs water tube 


How a fire tube boiler works

Simply, there are tubes inside a reservoir filled with water. Hot gases pass through these tubes, thermal conduction occurs and evaporates the water.

What is fire tube boiler 

It is a type of boiler for steam generation. It is used to evaporate water using hot gas passing tubes.

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