THE FLOW OP WATER IN WOOD-STAVE PIPE. 65 



Moritz suggests the extensive use of air valves in some form. The 

 best air outlet is probably a "chimney" rising above the hydraulic 

 gradient. There should be several connections to the siphon, either 

 normal to the pipe or, better, pointing shghtly upstream. These 

 may be independent of each other or all may connect to a common 

 pipe extending along the top of the siphon, the upper end passing 

 through the head wall of the intake chamber so that any water that 

 blows out with the air wiU fall back into the pipe. The last connec- 

 tion should be at a lower elevation than the water surface in the out- 

 let chamber so that, with a small discharge, the air entrained will be 

 collected and passed off. As a rule low discharges entrain more air 

 than does a full discharge, since the water rushes down the initial 

 reaches of pipe in a turbulent condition. On the other hand, the 

 upper air vents are necessary to care for air entrained and compressed 

 during discharges approaching maximum capacity. These vents 

 may be from 1 to 12 inches in diameter, depending on the size of the 

 wood pipe, and should be so assembled that they may be taken 

 apart, as debris collects in such vents and must be periodically 

 removed. If excessive air troubles are present, a collecting chamber 

 may be attached to the siphon at each vent, the air pipe being at- 

 tached to the top of the chamber rather than directly to the siphon 

 pipe. 



FRICTION LOSSES. 



The loss of head necessary to overcome internal resistances within 

 the pipe is proportional to the length of the pipe but is independent 

 of the static pressure in the pipe. That is, the loss necessary in the 

 conveyance of a given quantity of water through a siphon pipe will 

 be the same whether the low point is, say, 10 feet or 150 feet, below 

 the hydraulic grade line, the other factors remaining unchanged. The 

 influence of temperature upon the frictional resistances was found 

 by Saph and Schoder to be considerable in small brass pipes but has 

 not been studied in connection with tests on large wood pipes. It is 

 doubtful whether the influence of temperature could be differen- 

 tiated from that of friction alone in tests on large pipes in commercial 

 service. 



In order to determine the size of pipe and the loss of head neces- 

 sary to overcome the frictional resistances in the conveyance of a 

 given quantity of water, two estimate diagrams and a table have 

 been prepared. Two examples of typical pipe problems are given. 

 In these the use of the diagrams only is explained, as the table is 

 considered seK-explanatory. The factors of safety given below 

 should be considered in each problem, as a study of Plate VII shows 

 that an averaging formula, accepted literally, can not assure the 

 desired discharge for a given loss of head. 

 42463°— Bull. 376—16 5 



