APPENDIX III 793 



not exceeding 10 per cent of the latter, the speed of operation of the tur- 

 bine shall be adjusted to correspond to the head under which the test is 

 made. The principle is recognized and accepted that if the speed is changed 

 in proportion to the square root of the head, the horse-power output will 

 change in proportion to the three-halves power of the head, and the turbine 

 efficiency will remain the same; that is, when the head differs from the 

 value specified in the contract, the contract guarantees shall be considered 

 to apply if the hydraulic equivalents of the power and speed of the turbines 

 are substituted for the power and speed enumerated in the contract. The 

 hydraulic equivalent of the speed is equal to the specified speed multiplied 

 by the square root of the ratio of the effective head existing during the test 

 to the specified effective head. The hydraulic equivalent of the horse- 

 power is equal to the specified horse-power, multiplied by the three-halves 

 power of the ratio of the effective head existing during the test to the specified 

 effective head. 



The test shall not be carried out if the head differs from the contract 

 value by more than 10 per cent either above or below, or if, due to an excess 

 of the head above the contract value, or to a reduction in tailwater eleva- 

 tion, the total draft head approaches within 5 feet of the limiting value 

 corresponding to the barometric height. By total draft head is meant the 

 height of the centerline of the distributor of vertical turbines, or of the 

 highest point of the discharge space of the runner of horizontal turbines 

 above tailwater, added to the velocity head at the point of minimum internal 

 diameter of the runner band. 



If during the test it is not practicable to adjust the speed, or if the 

 final calculation should show the speed to have been incorrectly adjusted 

 to suit the head, provided that the discrepancy in speed does not exceed 

 2 per cent either way from the correct value, the values of power and efficiency 

 shown by the test shall be corrected on the basis of the test curves, of the 

 same or a homologous turbine, made at a testing flume or on a wheel tested 

 in place according to the methods of this code, when such curves are available. 



(a) Encased Turbines. In turbines having closed casings the head is 

 to be measured by at least two, and when possible not less than four pie- 

 zometers located in a straight portion of the penstock near the turbine casing 

 intake, and by two or more rod or float gauges in the tailrace, placed at points 

 reasonably free from local disturbances. 



Such board, rod or float gauges are to be free of velocity effects, and if 

 this is not obtainable when the gauges are set in the open channel, they shall 

 be placed in properly arranged stilling boxes. 



Ah 1 piezometers shall be connected to separate gauges. The conditions 

 of measurement, including velocity distribution, length of straight run of 

 penstock, and conditions of piezometer orifices shall be such that no piezom- 

 eter shall vary in its readings by more than 20 per cent of the velocity head 

 from the average of all the piezometers in the section of measurement. The 

 piezometer orifices shall be flush with the surface of the penstock wall, the 

 passages shall be normal to the wall, and the wall shall be smooth and parallel 

 with the flow in the vicinity of the orifices. The piezometer orifices shall 

 be approximately 1 inch in diameter. If any piezometer shall be obviously 



