254 HYDRAULIC EQUIPMENT 



bine gate mechanism, and the installation was complete excepting 

 the pumping system. While this arrangement is still in use with 

 small units, it is no longer used for large units. In the latter case 

 the centrifugal control mechanism and regulating valves are now 

 combined and localized in an " actuator " placed in any con- 

 venient position near the unit, and the power element or servo- 

 motor is incorporated in the design of the turbine. By separating 

 these elements, each of them may be located in the most advan- 

 tageous position with respect to the individual function it has to 

 perform. For example, in the case of vertical units, the actuators 

 may be placed on the generator floor and the servo-motors in the 

 wheel pit, directly connected to the gate mechanism. 



Methods of Control. Governors up to about 60,000 foot- 

 pounds capacity are often equipped with mechanical hand con- 

 trol independent of the servo-motor. This is, however, scarcely 

 feasible with larger governors on account of the time that would be 

 required to develop so much power by hand. They are, there- 

 fore, equipped with hand control of the operating pressure only. 

 This control is independent of the centrifugal speed element, 

 and is of great value for adjusting the load on the unit and for 

 synchronizing purposes. In addition to local hand control all 

 governors are now as a rule also equipped with manual remote 

 control. The mechanism is equipped with a small reversible 

 motor electrically connected with a double-throw control switch on 

 the switchboard, and enables the operator to control the load and 

 speed from the switchboard. 



Numerous plants can be found where the units must first be 

 paralleled by hand and the governor " cut in " after the generators 

 are tied into the power system. The reason may be found in the 

 lack of harmony of flywheel effect, the velocity of the water and 

 the length of the pipe line. If one of the three could be properly 

 altered, the trouble could possibly be eliminated. 



Sometimes it is required to carry a fixed load irrespective of 

 the load or speed variation of the system and such fixed loads may 

 be less than that developed at full gate opening. This require- 

 ment necessitates the use of a load-limiting device, which prevents 

 the distributor of the regulating valve from attaining a position 

 beyond the amount desired. A load-limiting device also allows of 

 an adjustment according to the head or quantity of water available 

 at various times, and it should preferably be remote control. 



