Model Marine Boiler and another Koffiekop.
by John
At the recent Geelong Society of Experimental and Model Engineers (GSMEE) meeting, several interesting models were presented, including my Koffiekop engine. And another Koffiekop, this one by Stuart T.
Stuart T is an expert engineer and machinist. He CNC’d most of the components in his engine, and has enough spare parts to make another 6 of them. He says each part takes a couple of hours to draw and program, then 5 minutes of machining to spit out half a dozen.
Another most interesting model is the marine boiler by Rudy pictured below. Rudy was a marine engineer, and some of his ships were steam powered. This model is made from his memory of one of those. The odd external shape is to conform with the ship’s hull, starboard (right hand) side.
Model ship’s boiler. it is approx 300-400mm high. The fire box is stainless steel. The copper boiler and water tank and superheater were TIG welded. The water tubes are silver soldered.
The water tank, water tubes, super heater and boiler.
The water gauge was scratch built by Rudy. The pressure gauge was bought.
Not sure what these attachment points are called, but they look interesting coming off the almost hemispherical ends of the boiler.
Rudy made the nameplate on an engraving machine, then formed the domed shape.
Rudy has pressure tested the boiler to 100psi. He reckons that it would be good for 200psi. He tested it with compressed air, submerged in a barrel of water. That would show any leaks. And if it did happen to blow, the force would be diffused by the water.
johnsmachines 
Looks a bit different to the boilers I was used to.
Even so, the principle looks similar. If that is the case, the lower drum is not the boiler, instead it is the water drum. Heat is not applied to it at all. The tubes rising from the water drum to the steam drum are where the heat exchange takes place. The flame jets are introduced into the space between the water & steam drums in the space surrounded by the tubes.
Interesting fact- as the boiler ages and the tubes get thinner from erosion/corrosion, the boiler becomes increasingly efficient.
The boiler POMM continuously adjust feed water rates (which is likely to be one of the fittings on the back of the water drum) to ensure the amount of water entering is balanced against the amount of steam drawn off. The tubes are kept full, but not to the point that water enters the steam drum (at the top).
The sight glass is used by the boiler POMM – keep the water level at 1/2 way. If the sight glass fills, there is danger that water will carry across to the turbines, who ch can quickly destroy them. If the level is too low, danger that the flame will impact on a dry tube and burn through it exceedingly quickly, blowing the boiler.
While I can understand the additional drum, I hadn’t seen one in practice, and would think it would help protect the turbines from overflow.
Spent days sitting inside the steam drum, cleaning the tubes by shooting wire brushes from the steam drum to the water drum. Mattresses were placed in the water drum to protect it from the brushes shooting out.
The tubes were then inspected by fibre optic.
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