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8 MARINE REVIEW. Accepted Explanation of the Choctaw Accident. The bursting of the steam chest cover on the steel steamer Choctaw, while the vessel was on a trip up the lakes above De- - troit on Wednesday of last week, was undoubtedly due to the practice of making a narrow joint inside of the bolts in the covering, as explained in detail further on in this article, and _ then screwing up the bolts to nearly the breaking strain. Im- _ mediately following the accident, through which Chief Engineer F. B. Smith of Cleveland was seriously injured, and three other Tg members of the crew-lost their lives, expert engineers from the Cleveland Ship Building Company, builders of the steamer, made a thorough examination of the disabled machinery, and they have since been joined in their investigations by other com- petent engineers of Cleveland and Detroit, who have fully agreed - on the cause of the accident, especially as three or four similar cases, with less disastrous results, have been noted on the lakes. Asa result of this investigation, the builders make public the - following letter, bearing upon the accident, which was sent this __ week to representatives of the owners of the vessel: -"H. H. Brown & Co., City-- : Gentlemen: Our attention has lately been called to a dan- - gerous and faulty practice of making steam chest and cylinder- head joints on lake steamers, which we think it would be to your interest to stop on the engines of your fleet. It consists in using - @ narrow tape gasket between the flange and face of the cover, inside of the bolts, substantially as shown on the drawings - which we send you. The danger is, that so long asthere is a leak through the gaskets, instead of taking off the cover and correcting the fault, _ those in charge of the engine will simply heave up on the bolts and continue this practice until either the leaks are stopped or _ the cover is broken. You will readily see by examining the drawings that the narrow tape, which is usually of a hard sub- stance, forms an excellent fulcrum over which to break a cover. We suggest that you cause your people to usea gasket _ covering the whole surface of the flange where it is in contact . with the cover, on both sides of the bolts as shown in the draw- ings, which will entirely remove the liability of breaking the cover in this way. In the past animal oils were used in steam cylinders which attacked the studs and bolts, and the engineers sought to save the waste by making the joints inside of the bolts of tapes as described above. Now that mineral oils are used almost exclusively for this purpose, there is no good reason for _ the continuance of this dangerous practice. THE CLEVELAND SHIP BUILDING COMPANY. | Drawings referred to in the foregoing letter are printed here- with and will be of assistance in discussing the accident. When - the machinery was examined after the boat had been tied to the dock of the Frontier Iron Works at Detroit, it was found that "the rim of the steam chest cover was broken off at the edge of the gasket next to the bolts, with no bolts broken. The valve stem was doubled in the shape of a horse shoe, with the valve, which was not broken, keyed onto it, and the stem broken be- tween the link and the steam chest. 'There was no defect in the casting. 'The gasket was of what is known as asbestos tape. It wasan inch wide by three sixteenth's of an inch thick and was put on inside of the bolts. This is a practice followed in some of the shops on the lakes and by a large number of engineers, although not all of them use this particular kind of a gasket. T'he builders of the boat say they do not permit of this kind of a joint being made in work leaving their shops. In the steam chest there -were thirty-two bolts of 1% inches full thickness and fifteen-sixteenth's of an inch at the bottom of the thread. The tensile strength of these bolts would be about 40,000 pounds to the square inch, and the breaking strain would be 27,600 pounds in each bolt. Suppose the strain on each bolt was one-third of the breaking strain, or 10,000 pounds, (5 tons) it is at once apparent that the strain on the cover must be very great when the gasket is used asa fulcrum. 'The inside measure- ment of the steam chest cover, 17x42 inches, or 375 square inches, multiplied by 160, the steam pressure, equals 117,600 pounds, or over 55 tons, pressure. With this pressure added to the strain already put on the bolts, the only wonder is, in looking at the facts, that any steam chest cover will stand such an excessive strain with a gasket put inside of the bolts only, as in this case. It is apparent that the bending and breaking of the valve stem was caused by the pressure being so suddenly relieved from the back of the valve as it was in the explosion of the chest cover. Running as this steamer was, there would be from 50 to 60 pounds presssure in the receiver between the high and inter- mediate cylinders, and this would find vent back through the ex- haust port of the high pressure cylinder. 'The area of the ex- haust cavity in the valve was 91 square inches, and with 50 pounds pressure behind it, this would exert a force equal to 4,550 pounds, which was more than enough to give momentum to the valve so as to double up the valve stem, which it did. When it is known that the valve stem was bent and had caught on the bottom of the chest, the cause of the break in it, through the downward motion, will be readily understood. 'The very fact that the valve was not broken, and was keyed to the stem, shows that the breaking of the stem had nothing whatever to do with the explosion. On account of this method of making a cylinder-head joint being so common, the ship building company, as well as the en- gineers who have joined in securing an explanation of the ac- cident, are not disposed to in any way blame Mr. Smith, the engineer, who is recognized as one of the most competent men on the lakes. His theory that the valve stem had broken first and "the steam had used the valve as a hammer to break the steam chest" was, of course, advanced without a knowledge of the condition of the machinery after the accident. 'The break- ing of the water glass column from the explosion of the steam chest, was, as had been understood from the outset, the direct cause contributing most to the loss of life. 'This water, escaping under a pressure of 160 pounds, would, on being suddenly liber- ated, almost wholly expand into steam, and as one cubic inch of water will make 1,700 cubic inches of steam, it is fortunate that the results were not even more serious. aomrerennianaicaienhinit SS