Engineering reminiscences contributed to "Power" and "American machinist"

by Charles T. Porter

In England, when the steam was worked expansively, it was cut off by a separately driven valve on the back of the main slide valve, the point of cut-off being fixed; and the regulation was effected by means of the throttle. This system was also largely employed in this country.

The compound engine was unknown in the United States. I once saw at some place in New York City, now forgotten, a Wolff engine—a small beam-engine, which had been imported from England. It was visited as a curiosity by several engineers, and I remember Mr. Horatio Allen, then president of the Novelty Iron Works, remarking, “It is only a cut-off.”

In the south of England the Wolff system was used to a limited extent. I was much interested in the McNaught system, devised, I think, by the same Scotchman who first applied a rotating paper drum to the Watt indicator. The cotton and woolen mills, as their business grew, felt the need of additional power, but dared not employ higher steam pressures in their cylinders, because the beam centers of their engines would not stand the additional stress. McNaught provided an additional cylinder to carry a higher pressure, and applied this pressure directly to the connecting-rod end of the beam. The exhaust from this cylinder was taken into the old cylinder at the old pressure. This latter cylinder then exerted the same power it always had done. The stresses on the beam centers were not increased, but the power of the engine was doubled, and only a little more steam was used than before. This method of compounding was known as McNaughting, and became common in the manufacturing districts of England and Scotland.

There was one feature which was common to all engines in America and Europe, both ashore and afloat, and of whatever make or name, except locomotives. That was the piston speed, which varied only from 200 to 300 feet per minute. This last was the maximum speed, to which every new engine, however novel in other respects, was made to conform.

I come now to the turning-point in my career, and the reflection forces itself upon me, how often in the course of my life incidents trivial in themselves have proved afterwards to have been big with consequences; and how events, sometimes chains of events, beyond my control, of which indeed I had no knowledge, have determined my course. The same must be the case in the lives of many persons, and the thoughtful mind cannot look back on them without being impressed by the mysterious interrelations of our being.

One morning in the winter of 1860-61, Mr. Henry A. Hurlbut, of the firm of Swift, Hurlbut & Co., wholesale dealers in hats at No. 65 Broadway, and who was interested in my governor manufacture, called upon me to tell me that a friend of his, Mr. Henry A. Burr, manufacturer of felt hat bodies at the corner of Frankfort and Cliff streets in New York, had been having trouble with his engine. He thought my governor was just what he needed, and asked me to accompany him to Mr. Burr’s office, where he would give me the advantage of his personal introduction. In the interview with Mr. Burr which followed, I did not have an opportunity to say a word. After Mr. Hurlbut had explained the object of our visit, Mr. Burr replied that he had had a great deal of trouble with the regulation of his engine, and had thought seriously of getting a Corliss engine in the place of it; but two or three weeks before the builders of the engine had sent him a very skillful engineer, and since he came there had been no further trouble, so he should not need my governor. He invited us to see his engine, in which—since it had been taught to behave itself—he evidently took much pride. We found a pair of beam-engines of 5 feet stroke, running at 25 revolutions per minute, made by Thurston & Gardiner of Providence. They had the usual poppet valves and the Sickels cut-off. This was made adjustable, and was regulated by the governor. At the time of our entrance, Mr. Allen, the new engineer, was engaged on the scaffold. Mr. Burr called him and he came down, and at Mr. Burr’s request explained to us the variable liberating mechanism and what he had done to make it work satisfactorily. The regulation did not appear to me to be very close, and I made a determined effort to induce Mr. Burr to substitute one of my governors. I showed him a cut of the governor, and pointed out its combination of power and sensitiveness, but all in vain. He was satisfied with things as they were, and I went away crestfallen, having lost not only the sale of a governor, but also an opportunity for a triumph in a very important place. But I did not know to whom I had in fact been talking.

As we were leaving, Mr. Allen asked me if I would call some time and see him—he had something he thought I would be interested in. I called soon after. He told me he had a plan for a variable cut-off with positive movements, which he thought would avoid defects in the liberating gear. He had had it in his mind a good while, but did not think it could be used, because the governor could not handle the block in his link so as to maintain uniform motion, and he had been inclined to abandon the idea; but when he heard me describing my governor to Mr. Burr, it occurred to him that that governor would do it, and he would like to explain his plan to me. He had no drawing, not a line; the design existed only in his mind. He put down his ideas, as he fitly expressed it, with chalk on the engine-room floor, and that rude sketch represented the perfect system.

When his plan came to be analyzed, it was found that everything had been thought out and provided for, with a single exception afterwards provided by Mr. Allen, as will be described. But the wonder did not stop there. Mr. Allen had remedied the defect in the link motion of making a narrow opening for admission when cutting off early, by employing a four-opening admission valve of unique design at each end of the cylinder, and also by greatly enlarging the opening movements.

The four-opening valve required four seats in one plane, and it was important that these should be as narrow as possible. For this purpose Mr. Allen employed the Corliss wrist-plate movement to reduce the lap of the valve, and, by an elegant improvement on this movement, he made it available also to enlarge the openings. This improvement consisted in the employment of two rockers having a common axis and separate driving-arms, as well as driven arms, for each valve. The driving-arms were made to vibrate a long way towards their dead points, and the increased opening movement in arc thus obtained was imparted directly to the valve. This combination of an enlarged opening with a reduced lap was perhaps the most surprising feature of Mr. Allen’s system.

The four-opening equilibrium valve, afterwards invented by Mr. Allen and since 1876 always employed, requires but two seats in one plane. These could therefore be made wider. The division of the driving-arm was then dispensed with, and the enlarged openings were obtained by increasing the length of the driven arms.