One HP Compound Steam Engine - Introduction


The design actually started in early 2007. Never having designed a steam engine before, there was considerable learning and research to be done. There is more than 100 years of perfecting that has gone in to steam engines. I did not want to loose this valuable knowledge. The plans and drawings are based on this extensive research/investigation. I looked at the designs of several existing engines including:

Model Twin 0.5 X 0.5 X 0.61
Convetry (via Live Steam) 1.25 X 2.25 X 1.5
Reliable 2.5 X 3.75 X 2
Pearl 2.5 X 3
Kelley 2.5 X 4 X 3
Semple 3 X 4
Tiny Power M 3 X 4
Steeple Compound 3 X 6 X 5
Lowe (Navy B) 3.5 X 7 X 5
Navy K 3.75 X 7.75 X 6
Hasbrouck (several engines)

I also talked with many people and learned many things about the design and material to be used in an engine. These people included:

Richard Dean (NY),
Ray Hasbroack (NY),
Carl Kriegeskotte (NY),
Dean Merrill (NY),
Livingston Morris (PA),
Charlie Roth (NJ),
Dave Thorpe (NH),
Will Widner (MA),
and others.

I also read numerous articles and books published from as far back as the 1800s. This has been an interesting and educational experience exploring the thoughts and trials of the early days of steam. Sorting the truth from the published literature has not always been easy. Usually the generally agreed upon knowledge is true. But there are times when working from first principles shows otherwise. There were also many advances during the 100+ years where steam was the primary new power fueling the industrial revolution.

I was told that Pattern Makers were the best of the bunch. I have a much better appreciation for the meaning behind this now that I have made some patterns. First, a pattern maker must deal with ALL the surfaces, not just the ones that later get machined. Second, the pattern has to be used for making a mold. This implies that the pattern has to come out of the mold and also surfaces need to be convex to the molding sand. And then there are the subtleties of draft, symmetry, cooling machineability and fixturing. There is a lot of science and art to good pattern making.

I started out creating a table of sizes of components of several of the engines listed above. This consisted of such dimensions as: cylinder bore and stroke, base size, important bolt sizes, cylinder flange width and height, shaft diameter, tie rod diameter and length, valve dimensions and settings, web thicknesses, bronze/ball bearing size, piston height and various pipe sizes. From this data, I calculated rations of the piston diameter or area to the other dimensions. This gave me a good starting point for my engine dimensions.

The cross sectional area of the cylinder ports had quite a wide variation in the engines that I looked at. There are several tradeoffs on these dimensions. Much of the wasted heat is dissipated through the metal that is heated with high pressure steam and cooled with low pressure steam. The smaller the cross sectional area (and thus surface area) of the cylinder ports, the less heat loss. On the other hand, the smaller the cylinder port, the greater the loss in steam pressure.

It was when I was talking to Ray Hasbrouck that the ratio of the port cross sectional area to piston area all started to make sense to me. Ray said that when the strength of materials got good enough for the boiler pressure to go higher, the port cross sectional area could go down and still make the engine be efficient. It is little bits of knowledge like this that are hard to find in other ways.

Next the patterns were made and sent out for casting. Patterns

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