My First One Drum Boiler

When the latest version of our classic design of Rhodesian boiler stopped working, during my teens, I got to thinking about making improvements on this classic design. Time was limited (I wanted a hot bath), and there were neither text books nor the web to assist me in those days.

• A common point of failure was rusting through of the drum where the drum contacted the supporting fencing standards.
• The flue gases had little time to contact the drum before disappearing up the chimney.
• The construction was massive and I had to build this replacement myself.
• I wished to add a fire grate to assist with the firing up procedure and to improve combustion of the fuel.
• The firebox on the classic design is too large - this enables the boiler to be stuffed with an excessive quantity of firewood which results in poor combustion (smoke) and often results in a couple of hours of boiling water showering down from the standpipe.

This is the design I came up with, which I built in its entirety in two days, enjoying a hot bath at the end of my second day of work:

• The drum is placed across the top of the firebox, and rests on the masonry on either side of the firebox at each end (rather than resting on metal fencing standards.) The firebox is thus fed from the side of the drum.
• We had a sheet of heavy steel sheeting lying around - I, therefore, constructed a lid for the boiler from this single sheet of steel, placed directly on top of level walls.
• The drum is fully bricked in on both ends with small holes for the plumbing (these are closed with adobe after being disturbed.) The drum is easily exchanged by removing the steel lid of the boiler.
• I cut a slot for the flue directly above the rising flue gases at the back of the boiler - cooking pots could be placed over this slot (there was no chimney.) A sheet of steel was slipped over this flue when the fire had died down to conserve heat.
• The firebox was restricted to 12" (300mm) wide, and was 12" (300mm) high. 
• The grate was constructed from a row of parallel fencing standards (the front section was later closed with a sheet of metal.)  
• I left a 3" (75mm) annulus around the drum, at both the back and front, and between the top of the drum and the steel sheet. I added a fillet of adobe at the back of the firebox to form a throat (not shown), forcing the hot flue gases into contact with the drum.
• Plumbing enters the boiler from the side, well away from the flue gases (after changing the drum, adobe is packed around the pipes to keep the flue gases away.) Two quick couplings on the cold feed and hot water outlet  assist a speedy replacement of the drum.

My father operated this boiler as built for many years after I left home and it functioned very well, outperforming all of the monstrosities we had endured up to then. Combustion of fuel was complete even in this original configuration (other than whilst being fired up), and little smoke issued forth from the flue. I later moved the flue to the front and added a section of chimney to improve the draw when being fired up, and to lift the smoke further from the ground. I also restricted the flow of gases at the front of the drum by resting a couple of bricks on the drum (not shown) - this prevents the fire migrating toward the opening at the front. The flow of hot gases now rises up the back of the drum, spreads out over the top of the drum and exits via the chimney stack to the front:

Although this simple design works extremely well, there remains the problem of excessive draw from the flue during the cooling down cycle. It is still necessary to place a tile over the top of the chimney stack as soon as the fire has died down, if heat is to be retained overnight during cooler weather. In nearly forty years of use, I have had to replace the liner of the firebox a few times - this is a finicky operation as the walls of the firebox were originally constructed from the same masonry as the reminder of the boiler (burnt brick and lime mortar) as one continuous construction.