Beth,
I knew that Minneapolis made more return flue engines then direct flue engines, but I was not aware that they made the most return flue engines. I would have thought that Huber made the most return flue engines as that is all that they built.
An interesting fact is that the first few years that MTM was in business, they did not manufacture steam engines, but they sold engines. In 1887 they sold 20 Huber steam engines, in 1888 they sold 30 Huber engines and in 1889 they sold 40 Huber steam engines and 20 North Star engines manufactured by Upton of Port Huron, Michigan. On July 1, 1889 MTM finished there first experimental steam engine.
In 1890 a new $30,000 plant was added for the manufacturing of the MTM return flue steam engine and 125 men were added to the workforce and 26 RF engines were made. Until 1892 the boilers were made by E. P. Allis of Milwaukee and Freeman and Sons of Racine, Wisconsin. They also bought the rights to the Woolf reverse and abandoned the more complex link that they had used during the first two years of production. Thanks goes to Gerry Parker for these interesting facts.
As to your question about return flue boiler being prone to exploding I will give you my opinion. I was not around when these boiler explosions occurred so these are simply my observations and opinions. In the early years of the “farm engine”, most of the engines were built with return flue boilers, so any boiler explosion was more likely to be from a return flue boiler. The return flue, or Scotch marine boiler design, is still used today so I do not believe that there is any design flaw in this style of boiler. I would speculate that the number one cause of boiler explosions back in the day was the same as it is today – operator error. You can take a brand new boiler built today and if you run it low on water you run the risk of a boiler explosion. How much training did these boiler operators get in the real early years of the “farm engine”? My second concern is scale buildup in the boiler. Both of the return flue boiler that Jeff bought at the Rynda sale were full of scale under the fire tube. I have seen other return flue boilers with the same condition. Did these boilers get the washouts they needed? I see boilers even today that don’t get proper washouts. They also were stuck using whatever water was available and they didn’t have the water treatment we have today. So it is my opinion that most, if not all of these boiler explosions were caused by low water (operator error) of scale buildup (improper maintenance).
The big complaint on return flue boilers is the external pressure on the large fire tube. The fire tube is surrounded by water so the hottest the fire tube should ever get is saturation temperature of the steam, or about 325-350 degrees in the pressure range that these boilers are operated at. However, if the water level is low, or if the fire tube is scaled over on the water side, the fire tube could be overheated and loose it's strength. The steel will start to loose appreciable strength when it gets over about 500 degrees.
As far as the new boiler goes, it was built to all of the current codes and the steel is 27% stronger then what we assume the original boiler was built with. The new boiler also has welded seams which are 100% efficient instead of the 60-70% efficient seams on the original boilers. As an example, the shell on the new boiler is actually good for 359.7 PSI. I have no concerns about the safety of the new boiler.
It is interesting that many people have a bias against the return flue boiler, but the first thing to let loose in a low water condition in a return flue boiler should be the top row of tubes at the front of the boiler which should not cause a catastrophic failure. In a direct flue boiler the first thing to be exposed is the crown sheet which can, and has, caused catastrophic failures. Bottom line is, keep water in the boiler and keep the boiler clean.
We have been a little distracted in the shop with the installation of a new crankshaft in one of Jeff’s other engines. This is almost completed so we should be able to get back to the canopy very soon. Once we know the plans for the summer, we might get more motivated to get the canopy done.
Tom