USING REVERSE-MOTION AS A BRAKE.
Numerous attempts have been made to utilize the reversed engine as a brake for stopping the train, and even by this means to save some of the power lost in stopping. Chatelier, a French engineer, experimented for many years on this mechanical problem. He injected a jet of water into the exhaust-pipe, which supplied low-tension steam to the cylinder, instead of hot gas or air coming through the smoke-box. This was pumped back into the boiler on the return stroke. Thus the act of stopping a train was used to compress a quantity of steam, converting the work of stopping into heat, which was forced into the boiler and retained to aid in getting the train into speed again. Modifications of this idea produce the car-starters that pass so frequently through our Patent Office.
As a means of conserving mechanical energy, the Chatelier brake was not a success; but, in the absence of better power brakes, it met with some applications in Europe. Some of our mountain railroads use it, under the name of the water-brake, as an auxiliary to the automatic brake.
CHAPTER XVIII.
THE SHIFTING LINK.
EARLY REVERSING MOTIONS.
In the engineering practice of the world, before the locomotive and marine engines came into use, there was no need for devices to make engines rotate in more than one direction. When the need for a reversible engine first arose, it was met by very crude appliances. Locomotives were kept at work, earning money for their owners, which were reversed by the man in charge stopping the engine, and by means of a wrench changing the position of the eccentric by hand. A decided improvement on the wrench was the movable eccentric, which was held in forward or back gear by stops; the operation of reversing being done by a treadle or other attachment located near the engineer’s position. A serious objection to this form of reversing gear was, that the abrasion of work enlarged the slot ends, and wore out the stops, leading to inaccuracy and frequent breakage. A somewhat better form of reversing motion was a fixed eccentric, with the means at the end of the eccentric-rod for engaging with the top or bottom of a rocker-shaft, which operated the valve-stem. This was the form of reversing motion used on the early Baldwin engines. Numerous other appliances, more or less defective, were experimented with before the double fixed eccentrics were introduced. Till the link was applied to valve-motion, the double eccentrics—an American invention—were the most important improvement that had been made on the locomotive valve-motion since the incipiency of the engine. The V hook, in connection with the double eccentrics, made a fair reversing motion in comparison to any thing that had preceded it. The objection to the hook was, that, when the necessity arose for reversing the engine while in motion, much difficulty was experienced in getting the hook to catch the pin. As a simple, prompt, and certain reversing motion, the link was readily acknowledged to be far superior to any thing that had previously been tried.
INVENTION OF THE LINK.
There is no doubt but the link was first applied to a steam engine by William T. James of New York, a most ingenious mechanic, who also invented the double eccentrics. James experimented a great deal about the period from 1830 to 1840, with steam carriages for common roads; and it was in this connection that he invented the link. His work having proved a commercial failure, the improvements on the valve-motion were not recognized at the time; although the probability is, that Long, who started the Norris Locomotive Works of Philadelphia, and brought out the double eccentrics upon the locomotives built there, was indebted to James for the idea of a separate eccentric for each direction of engine movement.