Anatomy of a antique traction engine boiler
(locomotive style.)
This boiler is located at Threshermen's Park in Booneville, Indiana.

This is an old boiler that has been cut away to show how they were constructed.
Its construction is typical for most locomotive style boilers commonly used on
farm tractions engines from the 1880's up until the late 1920's. I put this page together
so those who are unfamiliar with the insides of a boiler
can see how one is constructed. 

The fire box in this boiler is totally surrounded by water and is called a wet bottom boiler. Some boilers don't have water under the bottom of the boiler and are called dry bottom boilers. The steam dome is where the steam is collected and trapped to feed the engine. The water level should always cover the crown sheet and flues.

The crown sheet is held into place by the stay bolts. Water must cover the crown sheet at all times and keeps the crown sheet from over heating. If the water level falls below the crown sheet it will become super hot. If water is added while it is super heated it will flash into steam faster than the boiler can handle it. The pressure will spike and usually the boiler will fail. As safety device called a fusible plug is located in the crown sheet. It is designed to melt at a much lower temperature than the crown sheet. When it melts steam will enter the firebox putting out the fire thereby preventing a rupture of the boiler.
The brace here is used to support a flat section of the boiler where stay bolts are not practical to hold the flat surface in place.

A boiler has a lot of stay bolts. Stay bolts are used to hold non-cylindrical parts of the boiler in place.

They are threaded into both pieces they are holding. Without them the steam pressure would cause the plates to separate. The inner plates would collapse and the outer plates would budge. Not something you want to happen.

The firebox typically have two opening. A larger upper opening called the firedoor or firebox door and is used to feed the boiler it's fuel. It is located above the grates where the fuel is burned. The smaller opening located under the grates is used to clean out the ashes and control the amount of draft and is called the draft door. Both of these openings would have doors on them.

This view is from the front of the boiler looking into the smoke box. the smokebox would have a door on it. This shows the front tube or flue sheet. They have holes drilled in them to hold the tubes or flues. There is another flue sheet located in the front of the firebox. Boiler tubes or flues connect the two sheets.

Rivets were used to hold the various different pieces of the boiler together. They were used before the advent of the arc welder.

This boiler is a lap seam boiler, which mean that the seam in the barrel of the boiler laps over itself and is riveted together. This is an older design. Newer (old) boilers used a butt-strap seam, which mean that the edges of the boiler barrel are butted up against each other and are covered with a strap of iron on both the inside and outside of the boiler and then riveted. Butt strap boilers were considered to be 5-15% stronger than lap seam boilers.

Boilers have handholes that are openings used to access the inside of the boiler for cleaning and inspection. Handholes should be left open for air circulation when the boiler is stored. One is shown here just above the large firebox door opening.


The fire box in this boiler is totally surrounded by water and is called a wet bottom boiler. Some boilers don't have water under the bottom of the boiler and are called dry bottom boilers. The steam dome is where the steam is collected and trapped to feed the engine. The water level should always cover the crown sheet and flues.

 


The crown sheet is held into place by the stay bolts. Water must cover the crown sheet at all times and keeps the crown sheet from over heating. If the water level falls below the crown sheet it will become super hot. If water is added while it is super heated it will flash into steam faster than the boiler can handle it. The pressure will spike and usually the boiler will fail. As safety device called a fusible plug is located in the crown sheet. It is designed to melt at a much lower temperature than the crown sheet. When it melts steam will enter the firebox putting out the fire thereby preventing a rupture of the boiler.
The brace shown here is used to support a flat section of the boiler where stay bolts are not practical to hold the flat surface in place.

 


A boiler has a lot of stay bolts. Stay bolts are used to hold non-cylindrical parts of the boiler in place.
They are threaded into both pieces they are holding. Without them the steam pressure would cause the plates to separate.  The inner plates would collapse and the outer plates would budge.  Not something you want to happen.

 


Technically, the flues are tubes but that old-time farm engineers used the misnomer "flues" and the term stuck.  A flue must be larger in diameter and carry the majority of the smoke and hot gases from the fire.  A return-flue Huber boiler offers a good example of a flue.



The firebox typically have two opening. A larger upper opening called the firedoor or firebox door and is used to feed the boiler it's fuel. It is located above the grates where the fuel is burned. The smaller opening located under the grates is used to clean out the ashes and control the amount of draft and is called the draft door. Both of these openings would have doors on them.

 


This view is from the front of the boiler looking into the smoke box. the smoke box would have a door on it. This shows the front tube or flue sheet. They have holes drilled in them to hold the tubes or flues. There is another flue sheet located in the front of the firebox. Boiler tubes or flues connect the two sheets.

 


Rivets were used to hold the various different pieces of the boiler together. They were used before the advent of the arc welder.
This boiler is a lap seam boiler, which mean that the seam in the barrel of the boiler laps over itself and is riveted together. This is an older design. Newer (old) boilers used a butt-strap seam, which mean that the edges of the boiler barrel are butted up against each other and are covered with a strap of iron on both the inside and outside of the boiler and then riveted. Butt strap boilers were considered to be 5-15% stronger than lap seam boilers.



Boilers have handholes that are openings used to access the inside of the boiler for cleaning and inspection. Handholes should be left open for air circulation when the boiler is stored. One is shown here just above the large firebox door opening.

 

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