154 



WATER CONDUCTORS AND ACCESSORIES 



starting torque and either direct or alternating current motors 

 may be used. The former are mostly compound wound with a 

 sufficient shunt field to limit the speed at light load. With the 

 latter the squirrel-cage induction motor seems to be most widely 

 used for small and medium-size valves, principally on account of 

 its simplicity. It should be designed with a high-resistance 

 rotor to increase the starting torque, and it is generally found 



Remote Control Panel 



__X L__L__L X X_Y __TfL_ JIL__*U. 1 



Series Field 



Limit Switch 



FIG. 80. D. C. One-station Remote Control Equipment. 



necessary to select a motor somewhat larger than what would be 

 the case with a compound-wound direct-current motor to perfor.n 

 the same duty. 



With certain valves it becomes necessary to overcome the 

 sticking due to wedging action when opening, and the drive is 

 therefore provided with a " lost motion " so as to give a hammer- 

 blow. For alternating current motors this is furthermore of value 



