ENGINEERING PROGRESS IN THE U. S. NAVY. 6i 



With the impulse turbine, however, the advance over the original naval 

 turbines of this type, those of the scout Salem, has been rapid. The number 

 of stages has been very much increased, both in battleship and in destroyer 

 turbines, a drum construction has been adopted for the lower-pressure stages, 

 steam balance for propeller thrusts has been provided, cruising nozzles for 

 ^low fractional powers have been fitted, and nozzles for utilization of auxiliary 

 exhaust are now supplied as in the Parsons turbines. 



That these changes in turbines of the impulse type have been accom- 

 panied by increase in economy has been thoroughly demonstrated by experi- 

 ence with the machinery of the destroyers, the economy of the impulse 

 turbine showing up nearly, if not fully, as good as that of the reaction type. 

 No opportunity has as yet been offered to obtain a measure of this economy 

 increase with the battleship types of impulse turbine, nor will such oppor- 

 tunity occur until the Nevada is ready for trial. 



IMPROVEMENTS IN RECIPROCATING ENGINES TENDING TOWARD INCREASED 

 ECONOMY AND REDUCTION IN WEIGHT. 



The steps taken in pursuit of the above objects are — 



1. Increase in steam pressure at engine. 



2. Change in design of engine framing. 



3. Increase in piston speed. 



4. Use of superheat, but to a small degree only. 



5. Reduction of clearances in cylinders. 



6. Decrease of frictional losses through steam ports. 



7. Positive circulation of steam through steam jackets. 



8. Reduced back pressure in low-pressure cylinders. 



9. Increased ratio between low-pressure and high-pressure cylinders, 

 with consequent increased ratio of expansion of steam. 



10. Application of forced lubrication to all journals, crosshead guides, 

 eccentrics and thrust bearings. 



While the following improvements, both with reciprocating engines 

 and with turbines, have been made : — 



1 1 . Improved condensing apparatus resulting in higher vacuum. 



12. Rational designs of feed heaters based upon amount of water to be 

 heated and amount of auxiliary exhaust steam available for heating pur- 

 poses instead of using the old rule of thumb of allowing a fixed number of 

 horse-powers per square foot of heating surface. 



13. Basing steam-pipe design upon actual rate of flow of steam through 

 the pipes as determined by tests in service. 



14. Reduction of feed-pipe losses to a minimum. 



