SUPERHEATED STEAM IN MARINE PRACTICE. 181 



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. 



38. Watkinson, about 1903, brought out a tubular live-gas superheater shown 

 on Fig. 9, Plate 94. This is similar in most respects to the design shown on Fig. 

 6, except that the gases, after leaving the superheater, pass to the combustion 

 chamber, and from there through the boiler tubes. No provision is shown in this 

 construction for shutting off the gases from the superheater or controlling them, 

 but it is probable that a damper of some kind was provided. 



39. Another interesting design, brought out in 1906 by Pielock, is shown in 

 Fig. 10, Plate 94. This construction is cellular, and consists of a box surrounding 

 a majority, or all, of the boiler tubes, for a portion of their length. Steam is ad- 

 mitted to, and taken out of, this box by suitably arranged pipes. The gases, flow- 

 ing in the regular manner, impart heat to the steam while passing through that 

 portion of the tube which is in the superheater chamber. It is understood that 

 this construction was used by Pielock on locomotives for a time, but that this de- 

 sign has been supplanted by the Schmidt fire-tube design. In the Pielock super- 

 heater the steam loses part of its superheat in passing through the outlet pipe 

 that is surrounded by water and saturated steam. While the heat lost by the super- 

 heated steam goes, of course, into the saturated steam, yet it prevents the full de- 

 gree of superheat which the apparatus would give, being obtained in the steam pipe 

 outside the boiler. The lack of opportunity for inspection, and the difiiculty of 

 keeping the tubes tight where they pass through the wall of the superheater cham- 

 ber, appear to offer objections to this construction. 



40. The Babcock & Wilcox superheater has been especially designed for, and 

 applied to, many forms of water-tube boilers. Its construction is quite similar to the 

 Watkinson and Foster designs shown in Figs. 3, 4 and 5, Plate 91, so far as its 

 basic principles are concerned, and the writer assumes that it could, if desired, be ap- 

 plied as a waste-gas superheater to fire-tube boilers. 



ENGINE CONDITIONS WITH SUPERHEATED STEAM. 



41. Reference was briefly made above to the handicap under which the older 

 engineers labored in not having suitable materials for superheater construction. 

 They had further obstacles to overcome in not having suitable designs of various 

 engine parts. The following are details, aside from the superheater, which re- 

 quire investigation if superheated steam is to be used : — 



1st. Steam pipes, valves and fittings. 



2d. Steam chest valves. 



3d. Engine cylinders, liners, etc. 



4th. Piston rings. 



5th. Rod packings. 



6th. Cylinder ratios. 



