WATER CONDUCTORS 131 



example during the shut-down of a unit. This may be obtained 

 from the following formula by Boucher: 



Where 



Q = Water discharge in cubic meters per hour; 

 T a = Lowest air temperature in degrees Centigrade; without 



negative sign; 

 T w = Water temperature in degrees Centigrade' (may be taken 



as lC.); 

 S = Exposed surface of penstock in square meters. 



Wooden-sta: e Pipe. 1 This kind of pipe is extensively used 

 in the West where redwood or fir is cheap and plentiful. It is 

 admirably adapted for heads up to about 200 feet, and for high- 

 head developments it is often used for the upper sections. For 

 heads above 200 feet, steel pipe is preferable, as the spacing of 

 the bands for wooden-stave pipe becomes so close that the cost 

 of the pipe may equal or exceed that of steel. 



Wooden-stave pipe has a greater carrying capacity than steel 

 pipe on account of the smooth surface of the planed wood, and its 

 carrying capacity will not decrease with age, as deposits will not 

 adhere to the inside of the pipe. 



A wooden-stave pipe should always be in use so that the staves 

 are thoroughly saturated. Under these conditions they will not 

 decay and leakages are prevented. Provisions are, however, 

 made so that the staves may readily be drawn firmly together by 

 tightening the bands. 



Continuous wood-stave pipe is constructed in place and 

 should preferably be located above ground and free from all 

 contact with it, cradles being provided at certain intervals for 

 the support (Figs. ^4 and 65). 



In erecting the pipe the staves are assembled and put together 

 to form a circle of the diameter of the pipe and the bands put 

 around the outside and tightened to hold the staves together. 

 The end joints in the staves should be broken by a lap of not less 



1 An excellent treatise on wood-stave pipe is found in Bulletins Nos. 155 

 and 376 U. S. Dept. of Agriculture. 



