186 SUPERHEATED STEAM IN MARINE PRACTICE. 



ing fall in boiler pressure; in other words, acts as a danger signal as regards 

 pressures. 



56. A small diameter mixing pipe is generally provided, so that saturated 

 steam can be taken from the boiler directly to the main steam pipe leading to the 

 engines. The use of this pipe has been criticized in some quarters on the ground 

 that the proportion of steam flowing through the pipe, if adjusted for a certain 

 condition of maximum load, will, at other loads, permit a difl^erent quantity of 

 steam to flow through the pipe, and the temperature of the engines will fluctuate. 

 It is further contended that at light loads too much steam will pass through the 

 mixing pipe, having a tendency to short circuit the superheater, in which case the 

 superheater pipes may become overheated. Consideration should be given to these 

 objections. The mixing pipe, if it can be properly applied, is of value and should 

 not be condemned without careful study of its advantages. Probably its greatest 

 use is that it permits of tempering the superheated steam at the engine within very 

 narrow limits. 



57. Auxiliary Machinery may be more economically operated when super- 

 heated steam is available. Pipes for accomplishing this may be arranged so that 

 the desired amount of superheated steam can be led to the auxiliary steam line, the 

 quantity depending on the kind of machines to be operated, the distance of these ma- 

 chines from the mixing pipe, and the severity of weather. If auxiliary machinery 

 is fitted for the full degree of superheat obtainable, maximum economies are, of 

 course, possible. If the machines are not arranged for superheated steam, there 

 is still opportunity of effecting considerable saving by feeding enough high-tem- 

 perature steam into the auxiliary line, to carry practically dry or even slightly 

 superheated steam up to the auxiliary engines. With long pipe lines leading, for 

 instance, to steam winches operating in cold winter weather, the economy in steam 

 which is obtainable will be very readily appreciated. Winches thus provided will 

 use steam instead of a very high proportion of hot water. In fact, the percentage 

 of economy, by using thoroughly dry steam, in auxiliary machinery will be greater 

 than obtained on the main engines. In converting existing vessels to use super- 

 heated steam, it is probable that the auxiliaries will not be capable of operating with 

 more than a low superheat. New ships now being turned out are, in many cases, 

 being provided with auxiliary machinery capable of operating with a considerable 

 superheat. 



TURBINES USING SUPERHEATED STEAM. 



58. The combination of turbine engines and highly superheated steam should 

 meet with much more favorable reception than has been accorded, until recently, 

 to highly superheated steam in reciprocators. This may be attributed to the fact 

 that internal lubrication, piston rings, valve rings, rod packings, filters, etc., do not 

 require consideration, due, of course, to the character of the prime mover. It is 

 understood that a large percentage of the turbine ships now under construction 

 abroad are equipped for superheated steam, To the writer's knowledge, there are 



