160 THE APPLICATION OF SMALL STEAM TURBINES 



Turbines can also be effectively used on bilge pumps. Other applications 

 are for auxiliary condenser, sanitary service, fire and ballast pumps. Plate 8i 

 shows the latest design of three-bearing turbo circulating pump for destroyer 

 work, and Plate 82 a special pumping unit for grading the banks of the Mississippi 

 River. 



DETAIL DESIGN OF SMALL TURBINES. 



It is only natural to expect that small turbines as designed for land work 

 need certain modifications to conform with marine practice. However, in the large 

 majority of cases, as for instance where comparatively low speeds are required, 

 practically no modifications, or at most very slight modifications, are required from 

 standard stationary practice. 



For forced-draft blower sets on board torpedo-boat destroyersc a special ver- 

 tical design of machine had to be developed for this work. The first design 

 accepted by the Bureau, and which has been standard up to a year or two ago, con- 

 sisted of a three-bearing unit, a steady bearing being considered necessary at the 

 outboard end of the fan, or, in other words, secured to the intake duct. As this 

 steady bearing could not conveniently be made integral with the main turbine 

 frame and had to be supported from the light steel work composing the intake 

 duct, a certain amount of difficulty was experienced in keeping this machine in line. 

 This difficulty, however, has not been as serious as would be at first imagined, 

 and some builders still favor this arrangement. In order to overcome this, how- 

 ever, later designs have been fitted with only two bearings with a very stiflf, hollow 

 shaft eliminating the necessity for this outer bearing. 



For low and moderate speeds, such as that required for pumps, horizontal 

 blower sets, etc., standard ring oil bearings have proven perfectly satisfactory. In 

 land practic'e it is considered that for ring oil bearings a PV (pressure in pounds 

 per squarg inc^ times rubbing velocity in feet per second) of 450 or 500 is per- 

 fectly- safe. In marine work, however, a considerably lower limit should be used, 

 especially in sm?'l boats, owing to the rocking of the vessel and the uncertainty of 

 a uniform supply of oil being delivered by the rings. It is therefore becoming 

 universal practice to supply all such apparatus as generator sets with their own 

 forced feed system. It is advisable to still retain the oil rings (in addition to pro- 

 vision for forcecl lubrication) for starting up and as a safeguard against accident 



to the oil pump. 



The glands (^^ stuffing boxes of small turbines should be of such a type as to 

 require absoluteb/ "^o lubrication, in order to eliminate any necessity for oil or grease 

 separation in th'^ feed-water heater. In all small turbine work the critical speed 

 of the rotor should be well in excess of the maximum running speed. This point 

 is of more than particular importance in marine work where units are required 

 to run through r^ large variation of speed. 



