METHODS TO CYLINDRICAL RETURN TUBULAR BOILERS. 165 



ing more uniformity of design and possibly lead to the adoption of standard designs 

 of boilers. 



A great many of the variations in design met with accomplish no useful pur- 

 pose, and their elimination would prove of benefit. 



It is not intended that this paper should give the impression that the author 

 claims that the proportions outlined herein are the only ones or the best, but the 

 data given have the merit of being based on many actual designs giving satisfactory 

 service and do approximate the mean values of average practice. 



It has been the author's experience that in many cases the specifications writ- 

 ten for boilers were such that, had they been followed literally, the resulting boilers 

 would have been failures, and boilers which have failed to perform satisfactorily 

 are unfortunately not yet a thing of the past. 



In order to obtain a successful boiler two factors of primary importance are 

 more or less dependent one upon the other. These factors are heating surface and 

 steam space. It would appear that the easiest steaming boiler is not always the 

 one which contains the greatest amount of heating surface, and some very satis- 

 factory boilers have contained only a comparatively small amount of heating sur- 

 face for their size. 



On the other hand, optimism as regards the amount of heating surface that 

 can be crowded into a boiler is one of the primary causes resulting in designs 

 wherein the principal characteristics are not properly balanced, and wherein condi- 

 tions affecting accessibility, etc., are neglected. 



We cannot sacrifice steam space indefinitely, nor can a boiler that is inaccessi- 

 ble have a long or satisfactory life. Steam space is undoubtedly one of the primary 

 requisites to the proper performance of boilers, and it would appear that for ocean- 

 going vessels an average practice is to keep the center of the upper row of tubes 

 at one-sixth of the diameter of the boiler above the center line, whereas for coast- 

 wise or harbor vessels this distance is approximately one-fifth of the diameter, and 

 these proportions have been rigidly adhered to in preparing the data for this paper. 



Only two types of Scotch boilers have been considered, i. e., those with separate 

 combustion chambers and those with a common combustion chamber, and while 

 there are other variations they are not by any means common. 



The separate combustion chamber type is more particularly suitable for ocean- 

 going service, whereas the common combustion chamber type is used principally for 

 coastwise and tugboat service. When forced draft is used the separate combustion 

 chamber becomes almost essential. 



Perhaps one of the best reasons for adhering to the separate combustion cham- 

 ber' type of boiler for ocean-going vessels lies in the fact that the interior of this type 

 of boiler is so readily accessible for cleaning purposes, and there can be no doubt 

 that a boiler which is examined and thoroughly cleaned at regular intervals is go- 

 ing to give the best service and have the longest life. 



It is not the intention to discuss in this paper the methods for arriving at the 

 heating and grate surface required to develop a given power, but rather to deter- 



