248 HYDRAULIC EQUIPMENT 



foot-pounds. The loss of energy is, therefore equal to 205,752 

 18,517 foot-pounds, and this amount will be transferred to the 

 water issuing ^from the gate apertures, which, therefore, will have 

 its velocity increased until the 187,235 foot-pounds of energy has 

 been absorbed. The kinetic energy of the water column will, 

 therefore, be transferred to the water wheel at the very moment 

 when it is desired to reduce the energy produced by the wheel. 

 In the same manner, if the load be thrown on and the gate again 

 instantly opened full, the same amount of energy which the water 

 column gave out on being retarded in the previous case will be 

 absorbed by the water column in accelerating its velocity to 5 

 feet per second. The energy delivered to the wheel will, therefore, 

 be reduced, causing its speed to drop off, just when the opposite 

 is required, and this action cannot be overcome by rapid move- 

 ment of the gate, but, on the contrary, is intensified by more 

 rapid gate movement. It is, therefore, obvious that after the 

 governor has been set in motion by a change of speed, some means, 

 other than the return of the speed, must be provided to stop it 

 when it has moved the gates the amount required by the change 

 of load which was the cause of the change in speed that originally 

 set the governor in motion. The means provided for this pur- 

 pose is a dashpot, known as the " compensating " mechanism, 

 and is an essential feature of all quick-acting water-wheel govern- 

 ors. Compensation may thus be considered the act of stopping 

 and waiting for the result of the gate movement. 



It is a comparatively easy matter to calculate the speed- 

 regulation in cases where the inertia of the moving water column 

 is a negligible quantity, such as with open flumes and short draft- 

 tubes. For such conditions, the following formula applies: 



H P 



^=81-000,000 



, 



where d = percentage temporary change in speed for load 



thrown off; 



H.P.= maximum horse-power capacity of the turbine; 

 T = time in seconds occupied by the governor in moving 



the turbine gates through their range ; 

 WR 2 = weight of rotating parts multiplied by square of 



radius of gyration of generator; 

 N normal speed of rotating parts in R.P.M. 



