Making the Ground Boiler....

We decided to go the simple route for the ground boiler - a classic type fire-tube boiler. The steam is only required at atmospheric pressure, which greatly simplifies the manufacture, because there can be absolutely no danger of explosion.

Some time ago we had the end plates for our ground boiler made. They were quite impressive!

These end plates were made of 6 mm mild steel, about a meter square. Each was pierced with a total of 33x33=1089 holes of 22mm diameter for installation of the boiler tubes. These plates were made with a laser cutting system, the operation of which was most impressive.... A lot easier than trying to drill 2178 22mm holes with a pillar drill!

Our friend Erskine then welded the boiler together for us. The side plates were also made with the laser cutter. Really, it's a marvellous piece of equipment - like computer graphics, but in steel.... it's just so easy, compared to the old-fashioned way of hacking by might and main to get the shape you want..... Kind of "reality graphics" a la Vernor Vinge!

This boiler is a bit of an animal! just the box, without the tubes, weighed about 170 kg. The tubes are 118 cm long, and provide a total heat transfer area (counting the bottom plate) of about 90 square meters. For the tubes, we decided to use standard 22mm plumbing-type copper pipe of 1 mm wall thickness, so the total tube weight comes out to about 700 kg! (to say nothing of the cost).... With manifolding, the final unit is anticipated to weigh just about a ton, dry. The water volume will be about 800 liters.

This photo shows the boiler shell finished and painted! However, "Sans tubes, sans manifolds, sans windows, sans covers, sans everything...."

This side view shows the water supply pipes and the sight gauges for seeing the water level.

This side view shows the steam vents and the inspection hatch.

As you can see, there were no tubes in the shell at this stage....

After welding the boiler shell together and painting the outside, I realized that it was very important to paint the welded seams on the inside with Hammerite in order to inhibit rusting. If I had figured that out earlier I might have made the inspection hatch a bit bigger - it is only 30 cm (one foot) square - but anyway I managed to get through it, and I painted the seams (and myself) very thoroughly....

We hired a truck and crane to lift the boiler shell out of the works and carry it round to the Scout Hall, where the painstaking process of putting in 1.3 km of boiler tube is being undertaken....


The next development was to purchase all the copper pipe for the boiler tubes, and then we were faced with the task of cutting it all up!

These pictures show the boiler with 40% of the tubes fitted.....(yes, I was indeed tired)....




As for the anticipated performance, this boiler is actually considerably bigger than we really need. We will probably need to provide forced draft from a gasoline-powered blower like, perhaps, a standard balloon inflation fan (a propeller mounted on a small Honda engine). (It is desirable to be independent of mains electrical power if possible). With good air supply, it will certainly be possible to get more than two tons of steam per hour from this boiler. That will be adequate for filling quite a large Steam Balloon - it would be enough for a modest Steam Airship, in fact!


For a firebox, we have gone the crude and simple route: just a large steel box, lined with fire-clay and insulated with rock wool. It will be suitable for burning coal or wood; indeed, it could very easily be adapted to a fuel oil burner, if we want to stretch to the expense. Anyway, the use of coal will just enhance the Victorian feeling of the Steam Balloon! We must be sure to keep the stoker's face grimy....





Next you can read here about building the firebox....




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