GOVERNORS 251 



Relief valves at the turbine case are sometimes employed to 

 obviate the difficulties of long feed pipes, but it is evident that 

 they can be of use only upon the load going off. They can be of 

 no use upon the load going on, for they cannot supply to the 

 moving water column kinetic energy which it has lost and which 

 it must regain before it can flow at the higher velocity required 

 by an increase of load. Standpipes are better; in fact, they are 

 often imperative. If of improper design, or of insufficient capacity, 

 they frequently add to the difficulty of obtaining regulation. If 

 of proper design, they simply result in shortening the closed water 

 column; that is, they bring the turbine nearer to being set under 

 open-water conditions which are the most favorable conditions. 

 Unfortunately, the conformation of the country is often such that 

 a standpipe is unfeasible, and reliance must be placed on relief 

 valves to prevent dangerous water pressures being developed and 

 upon flywheels to liberate or absorb kinetic energy as the closed 

 water column absorbs or liberates it. 



Energy Output of Governor. In order to be of ample capacity 

 to control the gates promptly and still have a margin for speed 

 regulation of the wheels, it is necessary that the governor should be 

 capable of developing an effort in excess of the maximum effort 

 required to merely operate the gates themselves. Practical expe- 

 rience seems to indicate that this margin should be about 100 per 

 cent of the maximum effort required to move the gates. 



Governors are nominally rated in foot-pounds at a given pres- 

 sure, the rated effort being equal to the nominal rating divided by 

 the length of the stroke, expressed in feet. It has, however, been 

 suggested to rate a governor by its maximum torque produced or 

 also by its energy produced per second. This latter term would be 

 an indication of both the power supplied for and the rate of the 

 gate motion to be produced by the governor. 



Arrangement and Operation. The movement of turbine gates 

 requires a relatively large amount of energy and indirect-acting 

 governors are therefore almost exclusively used, employing either 

 mechanical energy as with the so-called mechanical governor or a 

 compressed fluid as with the hydraulic governor. 



Mechanical governors obtain their energy mechanically by 

 belt drive from the prime mover and transmit it by friction coup- 

 lings, etc., to the gate shaft. They are not very sensitive but 

 exposed to considerable wear, for which reason they are only 



