DISC FKICTION 193 



One or two points which have been brought out by the foregoing in- 

 vestigation would appear to deserve special note in connection with the 

 design of pumps and turbines. 



All clearances, side and radial, should be cut down to the absolute 

 minimum compatible with freely-running surfaces. That this point 

 needs emphasizing will be evident from a consideration of Fig. 306, 

 which is taken from examples of modern high-speed pumps by makers 

 of repute. The manner in which the disc resistance might be reduced 

 without any accompanying drawback is indicated by dotted lines. 



The internal surfaces of all casings should be finished off as smoothly 

 as possible and should be coated with a hard varnish paint or enamel. 

 The same applies to the surfaces of the discs. It would appear, further, 

 that very little is to be gained by machining and polishing a smooth-cast 

 surface as compared with simply painting and varnishing it. 



H.A. 



