Evans invented several devices which helped to improve work in a flour mill. He described this in his book “The Young Mill-wright and Millers’ Guide”. To protect his ideas and to earn his living Evans always tried to get patents. So he e.g. got the third U.S. patent.
"The Abortion of the Young Steam Engineer's Guide" as source for the "Drop Valve Engine"
Evans’ book “The Abortion …” is today a very hard to read text. Nevertheless it is the main source for the “Drop Valve Engine”. Some sources say, that the Editor forced Evans to publish the text, though Evans thought it not to be ready yet - so he called it “The Abortion …”
Evans states, that his engine had a cylinder bore of 6 inch [approx. 15 cm] and a stroke of 18 inch [approx. 45 cm]. So it is quite clear that this engine must have used high pressure steam. According to Evans a perfectly safe boiler could be built, which would produce steam at 120 psi [more than 8 bar]. Unfortunately I did not understand at which steam pressure the machine actually ran.
Evans writes, that in 24 hours 400 bushel plaster of paris [14 cubicmeter] could be grinded or 200 feet marble [about 6 m] could be sawed. He describes the engine, details the four valves and gives some figures of the grind-stone. On 35 strokes per minute this would have had 100 revolutions per minute.
In another paragraph Evans uses subjunctive: The engine might do 10 strokes per minute or 100. If the piston diameter would be 8 inch, it could drive 5 grind-stones.
As a reference some data from Watt’s “Lap Engine” (built 1788). Cylinder bore was 19 inches approx. [475 mm]. It had a stroke of 50 inch approx. [1244 mm]. According to Watt nominal power was 7,5 kW, measurements yielded up to 10 kW. Steam pressure was about 22 psi [1,5 bar].
Due to the higher steam pressure needed the boiler was for Evans’ machines even more important than for ordinary machines. There is a coloured redraw of the “Columbian Engine” from 1893 with some dimensions for the boiler in it. Unfortunately not all of these are proper readable. I think the boiler had an OD of 20 inches [ca. 50 cm] and a length of 10 feet [rund 3 m]. According to Evans it was made from whrought ironplates which were riveted together. I am afraid that we can hardly imagine nowadays the difficulties of the production around 1801.
"Columbian Engine" at the Water Works of the City of Philadelphia
With his second machine Evans replaced the four dedicated valves by a single rotary valve. This was the idea of a carpenter, from whom Evans bought the right to use the idea.
There is a model of the “Columbian Engine” in the Franklin Institute in Philadelphia, founded 1824. A label on the model says “From Fairmount Water Works, designed by Oliver Evans; model at Franklin Institute”. The model is said to be made 1815.
With the “Fairmount Water Works” (these are the water works of the city of Philadelphia) another source becomes available. In 1876 the son of the founder os these water works Frederick Graff junior (he took over his father’s job) published some notes:
Graff lists a few engines to be found 1801 in America. All but one are atmospheric, imported from England. The exception is called a small engine “used by Oliver Evans to grind plaster of Paris at the corner of Ninth and Market Streets, Philadelphia”. At least the “Drop Valve Engine” is now mentionend by another and independent source.
Graff has a lot more details about the “Columbian Engine” (my comments in ):
“At this works Oliver Evans erected the first large high pressure engine made by him. It had a steam cylinder 20 inches diameter [50 cm approx.] and five feet stroke [1,5 m approx.], with a rotating steam valve, worked by bevel gear wheels, driven from the main shaft; it had a double acting pump 20 inches diameter and 5 feet stroke; the beam was made of wood, and was suspended at one end upon vibrating standards, the piston rod being attached to the other end of the beam.
The boilers were wrought-iron, 27 feet long [more than 8 m], 27 inches diameter [nearly 70 cm], and four in number, upon which steam was at times raised to 220 pounds to the square inch [more than 15 bar]; they were twice burst, three men being killed by the explosion, first time June 20, 1818, and again October 12, 1821.
On the 15th of May , 1817, this engine was submitted to contract test; she run twenty-three and a-half-hours; filled the reservoir 9 feet 5 inches [nearly 3 m] deep, being equal to 3,666,021 United States gallons, maintained steam from 194 to 200 pounds to the square inch [up to 13,8 bar], and burned 13 cords [47 cubicmeter] of oak wood, running at a speed of 22 revolutions per minute.
The use of both these engines was discontinued January 14, 1822; “
So far Frederick Graff junior writing. It should be mentionend, that there was a second engine in the water works (atmospheric, presumably imported from England). Most of the time Evans’ “Columbian Engine” was running, because she turned out to be more reliable.
The engines were put out of service, because due to the high operating costs Frederick Graff senior had searched an alternative solution. He finally did not use any pumps, but new built reservoirs and the natural water pressure.
I find Frederick Graff notes really trustworthy. I think they prove that the “Drop Valve Engine” really existed and that the “Columbian Engine” was a real success - maybe a little bit later than other sources stated.
Unfortunately there are no sources for another topic, Oliver Evans raises in “The Abortion …”.
Evans writes, that he had on the order of the Board of Health of Philadelphia constructed and built an amphibic digger (he called it “Orukter Amphibolos”). This should use a chain of buckets to bring up the mud. This vehicle had moved on wheels with its own power from his shop to the river. There it had continued as a boat.
The machine, which would this make happen, had according to Evans a cylinder with 5 inches diameter [13 cm] and 19 inches stroke [50 cm].
Professor Steven Lubar, an American historian, with quite a few publications about American history of technology, <a href=http://18.104.22.168/dev-it/print/86629>wrote here 2006</a> about this great story. He points out that this historical event is not being mentionend in the newspapers of those days except in an advertisement Evans himself payed for. Lubar notes, that The Board of Health got $31.10 back for its $4,000 investment, when the machine was sold for parts 1809.
People visiting the Capitol in Washington may get a different picture. There is a ceiling painting showing the “Orukter Amphibolos” just driving into the water …
Evans died 1819. After nearly 200 years gone we hardly can appreciate his merits from a contemporary perspective. Comparing his work to e.g. Watt or Trevithick does not seem to me permissible, because both worked in an industrial environment, where the first steam engine for production purposes had been made approx. 100 years ago. Evans most likely only had craftsmen to help him.
So I think his work may really be called outstanding. Furthermore it is remarkable, that he already saw clearly the chances of using the steam engine for transportation both in the country and on the water.