About 35 years ago when my children were quite young I thought it would be interesting and instructive for them, (and me too), to design and build a homebrew steam engine driven electric generator. I had always thought in general terms that the inverse/reciprocal of an air compressor could be run as a steam engine. My hobby workshop in Virginia had just about every Sears Roebuck Craftsman tool in it including overhead saw, drill press, 200 amp arc welder, grinders, oxy-acetylene welder and tanks, impact driver, multiple electric drills, sabre saws, most every Craftsman hand tool, wrenches and sockets, plus a South Bend metal lathe and homebrew metal cutting bandsaw.
I started out with a large Craftsman, single cyclinder air compressor illustrated above. By drilling and taping the rear of the crankshaft for a 3/8 inch bolt and running it outside the compressor's case I had the means to drive a rotary brass valve threaded for one inch water pipe. The idea here was to have the rotary valve open the steam source when the piston was about top dead center which would drive the piston down and when at the bottom turn off the steam source. Hopefully, the system's rotary inertia would then exhaust the steam through a flapper valve until it reached top dead center and started the cycle all over again. Centering and drilling the hole in the air compressor's crankshaft was easily done using my South Bend metal lathe that was in the bedroom of our guest house.
Shown above is a rear view and an expanded sectional view of the air compressor. The bottom held about a quart of oil which as the crankshaft rotated splashed oil on the cylinder walls and all parts that need lubrication when running. The 3/8ths inch bolt coming through the rear of the compressor case came through a fiber washer that prevented oil leakage. This bolt held the cam that rotated the rotary steam valve and can be seen in both views. All the steam input pipes were wrapped with 1/2 inch thick expanded fiberglass insulation to keep heat loss down as much as possible. The sectional view shows the crankshaft's supporting ball bearings on both sides of the compressor's case. Both the crankshaft's throw and counter weights served to splash the oil twice on each revolution.
BUILDING A FLAME TUBE BOILER:
One of my guidelines in this project was that all parts required to complete it be available from the standard Sears Roebuck catalog. I had little spiral bound "how to build it" booklets printed up and advertised them in Popular Mechanics magazine. I think about 200 copies were sold over a year's time which just about paid for the advertisements.
My flame tube boiler was a steel portable air tank from Sears Roebuck that could safely take up to 200 pounds per square of pressure. I sawed about two dozen one inch diameter holes with metal cutting hole saws through each end of the air tank using a 1 horsepower half inch electric drill. This was the nastiest job in the entire project and used up about 6 hole saw blades as the air tank was one piece of really tough steel. The flame tubes were one inch diameter, thin wall, aircaft steel tubing and were brazed into each end of the air tank using my oxy-acetylene torch and lots of flux. This was not at all difficult, but rather tedious with 48 each tube ends to braze. The last boiler job was to braze two threaded one inch pipe flanges onto the top and bottom for water inlet and steam output. The steam out line had the air tanks 200 pounds per square inch pressure gauge and a brass on-off valve installed. The water in line also had a brass on-off valve installed.
THE HEAT SOURCE - FURNACE - SPACE HEATER:
The heat source was a plain vanilla Sears Roebuck coal or wood burning space heater. The sketch above is not quite to exact scale, but close to my recollection of some 35 years ago. It had a cast iron grate for the wood or coal and adjustable air inlets on the bottom. With great anticipation I ordered a half ton of anthracite coal which no one appreciated. The top of the heater had ten inch black metal flue pieces which could be extended as high as one wished.
THE WHOLE THING PUT TOGETHER AND WORKING BEAUTIFULLY:
In the above drawing, the pressure relief valve is on the steam out line to the steam whistle. A steam boiler is no safer than the pressure it has been tested to! I decided to test it to 150 pounds per square inch and then run it at a maximum of 75 pounds per square inch which seemed like an ultra safe bet. I set the whole kit and kaboodle up on the concrete driveway in front of my workshop, and cleared all guests, kids, and onlookers out of the way. The 150 pound per square inch pressure test of my flame tube boiler passed with no explosion or unpleasant surprises. I had somewhere obtained an 18 inch long brass air whistle which could be heard at least a mile away. Three long toots on the whistle announced to my 3 children and all the neighbors' kids that the test was successful and they could return. I then reset the pressure relief valve to 75 pounds per square inch and began adjusting the rotary steam inlet valve for best power output. I found that beginning its opening about 10 degrees or so before the piston reached top dead center was best. Note in the drawing the twelve inch diameter cast iron pulley with about 5 pounds of lead weights added that acted as a flywheel. It is attached to the steam engine's output shaft that drove the 12 volt DC generator. Also note the 15 amp ammeter between the generator and 12 volt battery. About the best the steam engine could do was charge the fully discharged battery at about 4 amps which equals about 50 watts of electrical power. Since 746 watts equals one horsepower I will leave it to the reader to calculate the air compressor steam engine's efficiency and power output at 75 pounds per square inch steam pressure.
WOULD I DO THE STEAM ENGINE PROJECT AGAIN?
Nope! Not in this lifetime. Maybe in the next one? Actually it was a great deal of fun and quite satisfying to see it work as designed. The danger of a steam explosion while running it at much, much higher steam pressures which would have significantly improved its efficiency and power output was just too great to contend with at my home with my children and the whole neighborhood watching. The graphic below illustrates where I tested it at our home in Northern Virginia.