Cochran Boiler

A cochran boiler is a vertical boiler that contains a number of horizontal fire tubes. It is typically used to create steam used to power small machines. It is defined by the multiple narrow fire tubes that run horizontally across it. Some typical applications of Cochran boilers are as donkey or auxiliary boilers that are generally used on ships. Smaller examples of the Cochran boiler, specifically the Robertson type, have been used in the past to power steam wagons. The efficiency obtained using Cochran boilers is much higher than standard vertical boilers, due to the increased heating surface by using more of the horizon fire-tubes.

cochran boiler with fire

How Does A Cochran Boiler Work?

Cochran boilers work very similar to all other fire tube boilers. The fire hole is used to place coal at the grate. Air then enters the combustion chamber and combusts with the fuel at the grate by being sparked through the fire hole. Flue gases that are produced then move into the combustion chamber and then into the fire pipes. From the hot flue gases, heat is transferred into the water within the fire tubes. Steam is released when a certain pressure is reached, and the flue gases are exhausted out through a chimney. This process continuously repeats for as long as the boiler needs to run.

What Are The Different Parts of a Cochran Boiler?

There are many different parts that are used to create a Cochran boiler, some of the main parts are as follows:


This is the main body of the Cochran boiler. It features a hemispherical shape at the top, where steam is kept.

Combustion chamber

This is the room inside of the boiler that is lined with bricks, and prevents the boiler overheating. This chamber is connected to the furnace, and hot gases flow from the flue pipes to the fire tubes in this chamber.


Solid fuel (typically coal) is stored in the grate. It is designed in a way that promotes a lot of air flow through it, therefore making combustion between air and fuel as easy as possible. Ashes then also fall out of the way quite easily because of this design. The grate is where the fire happens.

Fire hole

The fire hole is a small hole at the bottom of the combustion chamber that allows fuel to be placed inside.

Fire tubes

Fire tubes are tubes that have one end connected to the furnace, and the other venting out through the chimney. There are several fire tubes in Cochran boilers, and the more tubes you have, the more heating surface there is.


This allows flue gases to escape from the “smokebox” to the outside.

Fire box (furnace)

The fire box is dome-shaped like the shell, and allows gases to be pushed back until they are forced out through the flue pipes to the combustion chamber.

Flue pipe

This a short passage where gasses flow from the firebox to the combustion chamber.




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