STEAM-PIPE DIAGRAMS. 



THE effect which a running-engine has upon the pressure in 

 the steam pipe, as shown by an indicator diagram taken from 

 the pipe, is a matter which not only possesses interest from an 

 engineering point of view, but it has a bearing on an important 

 question relating to steam-pipe design. The fluctuations of 

 pressure in the pipe caused by the intermittent flow of steam 

 into an automatic cut-off engine is sufficient to set up vibrations 

 in the pipe ; and these extend from the engine through the 

 whole distance back to the boiler unless the pipe is well an- 

 chored, and sometimes in spite of what appears to be good 

 anchorage. When we consider the relatively small weight of 

 the substance which is traveling through the pipe, it is difficult 

 to realize the powerful effect which these fluctuations have upon 

 its stability. It is not, however, the substance itself which is 

 the potent factor in the matter, but the effect of the unbal- 

 anced pressure acting between the two ends of a section of pipe 

 produced by the sudden and intermittent reduction of pressure 

 at the end nearest the engine. If the reduction is 10 Ibs. and 

 the diameter of the pipe is 8", there is an unbalanced pressure 

 of 10 Ibs. per square inch upon an area of about 50 square 

 inches, or a total force of 500 Ibs. acting in the direction of the 

 length of the section. Such a force would have in a measure 

 the effect of a 500 Ib. blow upon the pipe, which, of course, is 

 a serious matter. These fluctuations can be overcome to some 

 extent by avoiding short right-angle elbows, and employing 

 long-turn bends in their place. They can be overcome more 

 effectually by introducing in the steam pipe as near as possible 

 to the engine a reservoir having considerable volume relative 

 to the size of the cylinder, and passing the steam through the 

 large space thus provided. The fluctuations will then occur 



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