Downing, R.D. 1, Box 181, Ellwood City, Pa. 16117.
Thought I would take a minute to drop a line and say how much I liked the article in Sept.-Oct. 1973 I.M.A. on 'Pre-History of Steam' which might also be called just the early history of actual use of steam to do useful work. Anyhow I was in England a year ago and wrote of my experiences in an earlier letter. If anyone missed it I will repeat my advise to plan on at least one full day in the Museum of Science in South Kensington, London. They have many originals of steam power and I don't mean mock-ups or reproductions either. I had never realized that Watt limited pressures to 15 pounds maximum and depended on the separate condenser to raise the effective or differential working pressure to near 30 pounds until my visit there. It is easy to see why the condenser which is rare, except in industrial work here, was so useful in view of the fact that it doubled the working pressure. Many of our antiques could really earn their way again if the boilers could stand double the pressure to feed the cylinders.
In addition to this, Watt was reportedly very fearful of steam at higher pressures probably through sad experiences or his own or his co-workers and verily preached against raising pressures. This set the stage for a hero we don't hear so much about, named Richard Trevithick. He was a Cornishman of courage or to Watt foolishness, and did away with the huge condensers by raising boiler pressure to a horrifying 55 pounds in both stationary and a rail hauling engine he built. They are both very similar looking in general and rather typical of design in that day. The boilers are short cylinders with bolted on heads of lids so that they look a lot like a stew pot laying on its side with the lid bolted on. To stand the fearful pressure the wrought iron is over half an inch thick making the weight more fearful than the pressure on the rail engine. The cylinder vertical as it was feared horizontal ones would wear excessively from the weight of the piston and is mounted down into the boiler to keep it hot. That sounds like a good idea if it could easily be done and English traction engines used steam jacketed cylinders right to the end, but I wonder how they got condensed water out of the bottom of that cylinder? The fire flue was also interesting to me. It was 'U' shaped and mounted in the bolted-on boiler head so that the fire door and bottom of the stack (or chimney) were side by side. The door opening was about sixteen inches in diameter and the chimney about eleven if I recall correctly, making the flue tapered. Quite a job of engineering for the early 1800's. Anyway it was quite enough to make Richard Trevithick the steam hero of Cornwall and a nice statue of him adorns the corner in front of the library at Cambourne and that Scotsman is not so much spoken of there.