APPENDIX III 



795 



MEASUREMENT OF QUANTITY OP WATER 



9. The quantity of water discharged from the turbine is to be meas- 

 ured by one of the following methods. It is recommended that whenever 

 possible more than one of these methods be used, the quantity being taken 

 as the average of the results of two or more simultaneous measurements. 



(a) By Weir. When the quantity of water is measured by weir, weirs 

 with suppressed end contractions shall be used. 



The weir or weirs shall if possible be located on the tailrace side of the 

 turbine, and care shall be taken that smooth flow, free from eddies, surface 

 disturbances or the presence of considerable quantities of air in suspension 

 exists in the channel of approach. To insure this condition the weir should 

 not be located too close to the end of the draft tube, and stilling racks and 

 booms should be used when required. The channel of approach should be 

 straight, of uniform cross-section and should be unobstructed by racks and 

 booms, for a length of at least 25 feet from the crest. The racks should be 

 arranged to give approximately uniform velocity across the channel of 

 approach. The uniformity of velocity should be verified by current meter 

 or otherwise. 



The head on the weir should be observed by hook gauges placed in stilling 

 boxes communicating through orifices approximately 1 inch in diameter 

 in the sides of the channel of approach, approximately 1 foot below the level 

 of the crest and a distance of not less than 5 or more than 10 times the head 

 upstream therefrom, the head being observed independently at both sides 

 of the channel. In measuring quantities of water corresponding to the 

 loads on which the turbine guarantees are based, the head on the crest shall 



TABLE OF VALUES OF C FOR VARIOUS HEADS AND HEIGHTS 



OF CREST P 



not be more than two (2) feet or less than one (1) foot, and the velocity of 

 approach shall not be greater than 1 foot per second. 



The discharge shall be computed by the Francis formula in the form given 

 below, using the accompanying table of coefficients. These coefficients are 

 believed to represent the best available information. The values of turbine 

 efficiency resulting from weir tests made in accordance with this code are 



