GATES AND VALVES 



155 



in that it permits the motor to speed up some and gain in torque 

 before the load comes on, the maximum torque, as a rule, occurring 

 slightly above zero speed. 



Valve motors are generally thrown directly on the line, and 

 the control is accomplished by means of contactors for remote 

 control and large equipments. For hand control of smaller equip- 

 ments, ordinary knife switches are sufficient. Fuses give better 

 protection than automatic circuit breakers, in that they will 

 protect against a stalled motor but will not blow during start or 

 running. 



Limit switches which will open the circuit when the gate has 

 reached its limit of travel should always be provided. Such 

 switches are geared to the valve stem and arranged to open the 

 contactors at a predetermined point of travel of the gate in either 

 direction. Provision is also made so that the open or closed valve 

 positions are indicated on the control board by means of two lamps. 

 When only one lamp burns it indicates open or closed valve posi- 

 tion, as the case may be, 

 while Loth lamps burn in 

 any mid position. 



Connection diagrams for 

 D.C. and A.C. remote-con- 

 trol equipments are shown in 

 Figs. 79 and 80. These are 

 for single-station control, and 

 for multiple-station [control 

 push buttons are substi- 

 tuted for the single-pole 

 double-throw pilot switch. 



Pivot Valve. A type of 

 valve used in a number of 

 large plants for the purpose 

 of shutting off the turbine 

 from the penstock is the 

 pivot or " butterfly " type of 

 valve, illustrated in Fig. 81. 



This type of valve is simple in construction and takes up very 

 little space. The operation is by means of a hydraulic cylinder, 

 having a trunk piston connected to the crank or lever shown. It 

 is reliable in service, but is not as tight agairst leakage as either 



FIG. 81. Pivot Valve. (Built by I. P. 

 Morris Company.) 



