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June, 1916 of a core, causing the steam to flow in a thin layer between the core. and the pipe. The outer surface of the pipe has also been provided with cor- rugations, for the purpose of protect- ing the pipe against corrosion, and of affording greater heat absorbing surface. Improvement in the means for attaching pipes to the header is likewise provided in this design. It should be noted that the introduction of the core causes two changes in the steam section in each unit. . It would appear that still further im- provement is possible in this respect, by making the core continuous through the length of the element. Fig. 2 shows the Lovekin “superheater boil- er’, which is of the waste-gas, cellu- lar type. Live-gas superheaters, which were first brought out by Schmidt in 1898, are illustrated in Fig. 4. This par- ticular design is termed the ‘“fire-tube type”, as the superheater unit is intro- duced into the boiler tube. It is claimed that more than 1,500,000 horse- power of marine engines are being supplied with highly superheated steam from apparatus of this design. Considering the location of the units in this design, any desired degree of steam temperature could be obtained. The Babcock & Wilcox superheater has been especially designed for, and applied to, many forms of water-tube boilers. Its construction is quite sim- ilar to the Watkinson and Foster de- signs, so far as its basic principles are concerned and the writer assumes that it could, if desired, be applied as a waste-gas superheater to fire- tube boilers. Engine Conditions With Superheated Steam Reference was briefly made above to the handicap under which the older en- gineers labored in not having suitable materials for superheater construction. They had further obstacles to over- come in not having suitable designs of various engine parts. Among the details, aside from the superheater, which require investigation if super- heated steam is to be used, are steam pipes, valves and fittings, steam chest valves, engine cylinders, liners, etc., piston rings, rod packings and cylin- der ratios. Steam pipes, stop valves and fittings should contain no copper or brass. Many governmental regula- tions also prohibit cast iron and mal- leable iron. The rules of the United States steamboat inspection service require steel, where “pressures of more than 300 pounds and a tempera- ture of more than 425 degrees Fahr.” are used. This requirement is ad- hered to in the practice, both here THE MARINE REVIEW and = abroad. Steam “pipes and flanges should be well insulat- ed. this: “is; of: course; good practice whether the steam is saturat- ed. or superheated, but lack of such insulation, when an investment has been made in the superheater, is a cause of wastefulness that ought not to be tolerated. The main stop-valve should have a cast-steel body, and the valve spindle should be of steel. Affects Design of Valves Steam chest valves on the _ high- pressure cylinder should be of the piston type with rings, wherever the degree of superheat is sufficient to eliminate all condensation through the first cylinder. Balanced slide valves on high-pressure chests have been, in some instances, satisfactorily operated, 4—SCHMIDT FIRE-TUBE SUPER- HEATER FIG. but, as a rule, if the temperature of the steam is 500 degrees or more, piston valves are generally recom- mended. For the intermediate chest of triple and quadruple engines, or the low pressure of compounds, piston valves are desirable, but well-bal- anced slide valves, if properly provid- ed with grooves for oil lubrication, have been successfully used. For the low-pressure chest of triple and quad- ruple engines, it would appear safe to use slide valves. The steam tem- perature, even with high initial super- heat, to which the low-pressure valves will be exposed is but little, if any, above saturated steam operation. Engine cylinders and liners must be of first-class, close-grained cast iron, as hard as can be worked. Iron, as a material, for these details has been proven to be entirely suitable for high superheat. It is well known that cast 201 iron does not lose strength, but on the contrary the strength increases slightly when exposed to temperatures up to about 800 degrees Fahr. It is probable that under exceptionally high temperatures, cast iron may “grow”, but, within the range of temperatures to which steam chests and cylinders are subjected with superheated steam, no appreciable change will be found. If this were really a serious matter the number of superheated steam marine plants would not be increasing at the present rate. No fear need be entertained, therefore, that there will be deterioration of these parts, due to steam temperatures up to 650 de- grees or 700 degrees. That this is borne out by facts will be indicated by the satisfactory operation of steam- ships and locomotives using superheat in. excess of 200 degrees, as referred to above. In these instances, steam chests, cylinder bushings and cylin- ders are made of cast iron. Further- more, in American locomotives, cast iron is almost exclusively used for the steam pipes leading from the superheater headers to the steam chest. Type of Piston Rings Required Piston rings cylinder packing should be of strong, hard cast iron. There are several designs of piston packing rings on the market which are report- ed as giving good satisfaction on marine engines using 200 degrees of superheat. These designs are also ap- plicable for valve rings. Rod pack- ings, for high-pressure piston and valves, as now arranged are durable and satisfactory. Trouble was hith- erto experienced in obtaining the proper designs of rod-packing, but this is no longer the case. It is the author’s understanding that there is a growing tendency towards the use of soft cast iron instead of white metal in these rod packings, and it is claimed to meet all the requirements. If such is the case our ideas of this de- tail may have to be revised. Cylinder ratios to be suitable for use with highly superheated steam require consideration, on account of the steam characteristics. The pub- lished dimensions of English and Ger- man superheated steam ships show that a lower cylinder ratio is used. This is generally accomplished by increasing the diameter of the high- pressure cylinder, the intermediate and the low-pressure diameters, on a triple job, remaining as before. In quadruple engines, the high and first intermediate-pressure cylinders are in- creased in diameter, while no change is made in the second intermediate and low-pressure cylinders. In con- verting saturated engines to the use