SYNCHRONOUS GENERATORS 339 



bearings will at all times be supplied with continuous streams of 

 cool, clean oil. 



The lubrication of pressure bearings requires a positive dis- 

 placement type of pump such as a triplex pump, preferably directly 

 geared or chain-driven from the turbine shaft. As a continuous 

 supply is absolutely essential two pumps are sometimes installed 

 for each unit, one being motor driven. A central oil supply may 

 also be used in starting up or in case of emergency. The inter- 

 connection of the thrust bearing and the governor oil-supply sys- 

 tem by the use of one set of pumps is not to be recommended. 



For the lubrication of thrust bearings, requiring no pressure, 

 a central oiling and filtering system of the gravity type, as shown 

 in Fig. 201, is generally employed. Clean oil is stored in over- 

 head reservoirs, then is distributed to the thrust and guide bear- 

 ings on each unit by means of a suitable system of piping. After 

 passing through the thrust and guide bearings the used oil flows 

 by gravity to filters located in the basement, where it passes 

 through the filtering medium and over cooling coils, and the puri- 

 fied oil is then returned by automatically controlled pumps to the 

 overhead reservoirs ready for re-use. 



The oil piping should be laid out carefully to permit of readily 

 draining and cleaning the pipes, and air pockets should be avoided. 

 Return drain should be amply large and properly pitched to rapidly 

 and thoroughly remove used oil. It is better to err on the safe 

 side and have the returns a size or two too large rather than too 

 small with consequent flooding of machines and wastage of oil. 

 All feed pipes should be of brass or reamed steel pipes. All joints 

 should be carefully reamed and the piping blown out with steam 

 or compressed air as they are installed. Arrangement for a tem- 

 porary connection from the feed pipes to the return drains at the 

 machines is advisable. This allows of thoroughly flushing out all 

 dirt by kerosene or oil before any oil is fed to the bearings. The 

 piping should be equipped with valves and unions to permit 

 readily disconnecting a machine for repair work. 



All bearings should be equipped with sight feeds or some sim- 

 ilar arrangement to show when the oil is feeding profusely. This 

 should preferably be in the return as this indicates that oil is 

 actually going through the bearings. Also the oil temperature for 

 each bearing can be measured when necessary. There are many 

 indicators on the market for this purpose. One of the best schemes 



