SUPERHEATED STEAM IN MARINE PRACTICE. 179 



Clark (i860), Butler (i860), Pullen, Cresswell and Longstaff (i860). The work 

 which these men did, although preliminary, has been of inestimable value to those 

 who have taken up the labor in more recent times. This series of illustrations 

 should not be considered as complete, being intended rather to illustrate the 

 growth towards greater structural value. By structural value is meant those fea- 

 tures which require consideration before the adoption of any apparatus. Among 

 these points are: 



1st. First cost. 



2d. Installation cost. 



3d. Operating cost. 



4th. Maintenance cost. 



28. These four could be subdivided to quite an extent, bvit the writer believes 

 it hardly necessary to consider these subdivisions in this paper. 



29. In the first class (separately fired superheaters), we find that Schmidt, 

 about 1896, built a number of tubular superheaters, and Watkinson, a few years 

 later, constructed several different superheaters of this general type. Figure i, 

 Plate 90, illustrates Watkinson's tubular design, regarding which, in the paper re- 

 ferred to, he says* : — 



"For marine, locomotive, and some other purposes, where the space available 

 is very limited and where it is undesirable to have a large mass of brickwork, the 

 arrangement of superheater shown is preferred. The tubes are of the inverted 

 U form, and they are expanded into an annular tube plate P and this tube plate is 

 bolted to the header H, which is either a steel casting or a forging. The steam 

 enters the outer compartment of the header by the pipe S and leaves the inner com- 

 partment of the header by the pipe S'. A light steel casting C surrounds the super- 

 heater, and the products of combustion flow across the tubes, as indicated by the 

 long arrows. The superheater is shown as arranged for the use of oil fuel, but 

 it can be fired with any kind of fuel burned in an ordinary furnace or in a gas 

 producer. An economizer of the air-heater type is shown at A and by means of 

 this the efficiency of the plant is appreciably increased. The outside diameter of 

 the casing for a superheater of this type for 150,000 pounds of steam per hour is 

 about II feet." 



30. Separately fired superheaters have their advocates and opponents. It is 

 not difficult with such construction to divide the superheater into parts. This 

 makes possible an "initial" superheater with one or more "intermediate" super- 

 heaters. These intermediate superheaters may be termed "reheaters," and there are 

 certain advantages in superheating steam between the different cylinders. On the 

 other hand, such a construction necessitates a very much longer path for the steam, 

 which may result in greater losses in pressure than would be the case in a single 

 high-degree, initial superheater. Separately fired superheaters, on shipboard, re- 



*Institution of Naval Architects, June 24, 1903. 



