CHAPTER XVIII
Demonstration to the Judges of Action of Reciprocating Parts. Explanation of this Action. Mr. Williams’ Instrument for Exhibiting this Action.
The subject of the equalizing action of the reciprocating parts of the engine was not considered in the report of the judges. Indeed, the speed of that engine, 125 revolutions per minute, was not sufficient to develop this action to any important extent. But there was another reason behind that. I invited the judges directly after the close of the fair, but before making their report, to witness a demonstration of this action in my little shop engine, which invitation was accepted by them, and the following exhibition was made, but this was not alluded to in their report, the reason of which will be given on a later page.
The engine had a 5-inch cylinder by 12 inches stroke, and its regular speed was 300 revolutions per minute. I kept Saturday afternoon holiday, one of the good things I had brought from England, and so on Saturday afternoon I had a clear field for this exhibition.
I had previously prepared two governor pulleys to speed the engine up to the increased speeds required, which speeds had been ascertained by calculation. I was so certain of the correctness of this calculation that I did not make any preliminary trial, did not think of such a thing.
President F. A. P. Barnard
After running the engine for a short time at its usual speed, I changed the governor pulley for the smaller one of the two I had prepared, by which the speed would be increased to about 400 revolutions per minute, and loosened the crank-pin brasses so that they were slack fully a thirty-second of an inch. On starting the engine in this condition, of course, it pounded violently on the crank-pin. As the speed was gradually permitted to increase the knock softened, and just before the governor rose it disappeared entirely, and at the calculated speed the engine ran in entire silence.
After running in this manner for a while I prepared for the second part of my show. I put the crank-pin brasses back to their usual running adjustment, loosened the brasses of the cross-head pin fully a thirty-second of an inch, and put on a larger governor pulley, which, if I remember rightly, ran the engine at about 550 revolutions per minute. Under these conditions we utilized only the inertia of piston, rod and cross-head, without that of the connecting-rod.
On starting, the engine of course pounded heavily on the cross-head pin. As the speed increased the same decrease in the noise was observed as on the first trial, only later in the course of the acceleration, and again just before the governor rose the pounding had completely died away, and at the calculated speed the engine ran again in entire silence.
Like everything else, this action seems mysterious until it comes to be understood, when it is seen to be quite simple, as the following explanation will show.