228 



HANDBOOK OF MECHANICAL DESIGN 



PushbuHon ~^ 

 , 1 .1 i I . 1 



^-~ Pushbuffon 

 for A 



AX. 



Fig. 456. — Illustrating the use of rectifiers in conjunction with magnetic control equipment on relays. Through 

 the use of a rectifier in conjunction with direct-current relay, multiple control can be obtained over a single-control 

 circuit. 



^--J 



Fig. 457. — Showing the use of a pulsating direct current on a vibrating machine. In most instances, frequency of 

 pulsations is important and on hammer shown 25-cycle alternating current is used with a single-wave rectifier. 



Pump 

 motor 

 control 



Time 

 delay 

 relay 



Wheel 

 motor 

 control 



Pump -A^ 

 motor 



Start-s+op 

 pushbuttons 



- Grinding wheet 

 driven by motor 



c 



^—'^^{[^Pump 



Fig. 458. — Large grinders use pumps driven by separate motors. Pump motor need not be in operation when 

 grinding wheel is not running, but it is sometimes desirable to allow wheel motor to coast to rest before shutting down 

 pump motor. This can be done electricallj' by means of time delay relay to permit pump motor to operate for pre- 

 determined time after wheel motor is shut down. For the starting sequence, an arrangement similar to that in Fig. 

 462 may be used. 



