184 SUPERHEATED STEAM IN MARINE PRACTICE. 



49. In starting-up, particularly with new engines, or if new liners or rings 

 have been applied, nearly all superheater manufacturers recommend that saturated 

 steam be used for a short time. After the engines are well heated, the mixing-pipe 

 valve may be partly closed and the temperature of the steam in the high-pressure 

 chest gradually raised. When the vessel is on a run, some hours should elapse be- 

 fore the full degree of superheat is used. In this way the wearing surfaces will 

 have an opportunity of taking on a smooth finish and will afterwards work with- 

 out difficulty. 



50. Lubrication is probably the most prominent point in mind when first con- 

 sidering the use of superheated steam. In reality this need not cause apprehension. 

 With low degrees of superheat, it is not always necessary to use any oil internally. 

 This may be explained by the fact that the superheat is not sufficient to carry the 

 steam through the high-pressure cylinder without condensation. Where condensa- 

 tion occurs oil lubrication may not be necessary, and this is particularly true when 

 low pressures are carried. Low superheat really does little more than eliminate 

 part of the initial condensation. With moderate degrees of superheat opinions 

 differ as to the necessity for the use of oil. Cases are on record where superheat 

 of more than 100° has been successfully taken care of without internal oil lubri- 

 cation. It seems probable, however, that in such cases heavy swabbing of rods was 

 resorted to. When high degrees of superheat are considered, lubricating oil 

 should certainly be applied internally. The quantity of oil needed to satisfactorily 

 take care of 150 or more degrees of superheat is probably imagined as being 

 greater than what is actually required. The average of a large number of boats 

 using high degrees of superheat shows that very favorable results were obtained 

 with about 0.3 gallon of oil per 1,000 horse-power per 24 hours. One case has been 

 reported of a 2,800-horse-power ship that used but 20.5 gallons of oil on a 42-day 

 voyage. This is just about 0.5 gallon per day, or 0.167 gallon per 1,000 horse- 

 power per 24 hours. Gray in his paper* referred to above, speaking of the lubrica- 

 tion required, says : — 



"On the Port Augusta, of 2,000 I. H. P., 1.5 gallons per day of cylinder oil 

 were used at first for internal lubricating and swabbing of piston rods of both main 

 and auxiliary engines ; on the Port Lincoln and Port Macquarie, of 4,000 I. H. P., 

 about 2 gallons per day, this being gradually reduced until now only 0.5 to 0.75 

 gallon is required." 



51. The keynote of the lubrication question with highly superheated steam is 

 that a regular supply rather than a large quantity of oil is required. The oil fur- 

 nishes the lubrication previously afforded by the water present in the saturated 

 steam, but it does not follow that a regular supply of oil means a large quantity of 

 oil. 



♦Paper before Institution of Naval Architects. 



