Lancashire Boiler

A Short History of Steam Boilers, cont.



The Lancashire Boiler

The need for smaller more powerful, to say nothing of safer, steam boilers finally led to the Lancashire Boiler design. Basically the same as the Cornish Boiler with its internal furnace design. But vastly improved both in efficiency and safety.

The first advance was in the number of furnaces. Each boiler had two completely separate furnaces sitting side by side. And each furnace had a separate flue system. At first this might seem silly yet the idea behind having two separate fires going at the same time is outstanding.

Everything that burns, wood and coal especially, contains some amount of water and that water must be evaporated before the fuel will burn efficiently. In the time it takes the fuel to be heated, the furnace cools somewhat and that in turn lowers the amount of air being drawn into the furnace. The less air drawn in the less heat created in the furnace. As I said in the article on the Cornish Boiler, this slight cooling allowed the metal flue to contract placing a heavy strain on the ends of the boiler. It also slowed the heating of the water inside the boiler reducing the amount of steam available.

With the Lancashire Boiler each furnace is stoked at a different time. This means that one furnace is always producing maximum heat and that heat creates a powerful draught in both furnaces speeding up the ignition process. Something like blowing on a campfire. It heats things up real fast.

It also means that more air is drawn into the system which allows combustion (burning) of the smoke created by the low burning furnace. This combustion takes place in flue #2 thereby increasing the amount of heating of the sides of the cylinder.

Having one furnace always at full heat also provided a more even tension on the end plates as one flue was always fully expanded.

Like the boilers we have already seen, the Lancashire Boiler has three flues. The first is the metal tube which runs through the water in the boiler. From this the hot gasses moved downward beneath the boiler through flue #2 and then aft again along side the boiler in flue #3 to the chimney.

But the Lancashire Boiler is designed with two separate flue systems. Gasses from the right side furnace remain on the right side of the boiler while hot gasses from the left furnace remain on the left side. They do not combine until they reach the base of the chimney connection. This system provided a very powerful, even and constant draught in both furnaces.

Another major improvement in heat transfer and fuel efficiency was the addition of Galloway Tubes. Hollow metal tubes which traverse (connect both sides of ) the main flue #1. Water in the boiler flowed through these tubes which are subject to heating by the hottest fire and gasses which pass around them.

The number and arrangement of these tubes varied with the individual manufacturer. Those shown are typical and used to give you the idea of how they worked.

Galloway Tubes also acted as stiffeners greatly strengthening the main flue (flue #1) against collapse. As I said above, the use of Galloway Tubes increased the heat transfer to the water and that of course, made more steam and made it quicker, and at greater pressures. A working steam pressure of 175 psi (pounds per square inch) was common. These higher steam pressures allowed for smaller more efficient engines.

The increased efficiency of Lancashire style boilers also allowed them to be smaller. Commonly only seven feet in diameter (side to side) and twenty-seven feet long. A great saving of both space and weight.

Another advantage to the Lancashire style of boiler was the extensive number of internal braces designed to keep the cylinder from rupturing. As seen in the illustration, besides the Galloway Tubes criss-crossing the main flue, a number of metal rods extended through the cylinder and were bolted at each end. Even more, the designers placed several gusset stays (triangle metal braces) at both ends of the boiler. These, the rods and gusset stays, kept the ends from bulging and added much to the overall strength of the boiler.

Yet even the best designed boiler cannot withstand the tremendous pressures created when the water level is allowed to get too low. Should the water level drop below the top of the internal flues, the intense heat of the furnace would quickly burn through the metal. And that would lead to the very unpleasant condition know as the boiler explosion. A massive steam explosion that could completely destroy a steamboat and those aboard her.

To help avoid this type of accident, someone invented the automatic low water safety valve shown in the illustration. A simple enough device which would release excess steam pressure through a pipe when the water level dropped to low. The noise this valve made when it opened would also get the attention of the engineer very, very, quickly.

The low water safety valve was operated by a float which rides up and down with the water level in the boiler. When the water dropped below a predetermined level, the valve would gradually open and release steam pressure. The lower the water level dropped the more the valve would open.

But even this device could not handle all the pressure which would be created by a sever loss of water in the boiler. A second Pop Off Safety Valve can been seen in the illustration at the front of the boiler. These valves operated on steam pressure alone.

Each boiler was equipped with at least one of these safety valves and most often several of them depending on how large the furnace area was.

When the pressure in the boiler exceeded a specified level, these valves suddenly popped wide open, and stayed open, until they were manually reset or replaced. Something of a chore requiring the boiler to be shut down and cooled enough so a man could work on top of it

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