FLOW (3F WATER IN CHANNELS AND PIPES. 65 



about 34 in. high. In precisely the same way water 

 will stand in theory to about 34 ft., which in practice 

 28 ft. is considered the outside limit. Now in fig. 

 50 the vertical pipe in the well constitutes the short 

 leg of the syphon and the rest of it the long leg. 

 When the pipe is quite airtight and the end of the 

 lower leg is somewhat lower than the level of water 

 in the well, then if the short leg is immersed in water 

 and air is exhausted from the pipe, water will flow 

 right through it and continue to do so till the water 

 falls below the bottom of the short leg, or air finds 

 its way into the pipe, when the vacuum must be 

 again started. The highest point of the pipe line 

 must not be more than 28 ft. above the lowest water 

 level, while the difference of level between the lower 

 end of the pipe and the top water level must be at 

 least equal in value to that found in equations 13 

 and 1 6 added together. For satisfactory working 

 the long leg must fall gradually throughout its length, 

 and its hydraulic gradient must be drawn, and it 

 must not rise above this line at any point. In the 

 figure the full line shows a properly constructed 

 syphon, and the dotted one a syphon which would 

 not work. At the very top point of the pipe line 

 a valve should be placed from which water can be 

 poured into the pipe. When this is done and the 

 stop valve on the lower end closed, water will rise 

 up to the filling point. This valve is then closed 

 and will not be in use again till the apparatus fails 

 from some cause or other, and when the lower valve 

 is opened a continuous flow of water should result. 

 The closing of the lower valve will not break the 

 vacuum. 



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