Control for hopper loader for granular materials

A control circuit for a vacuum hopper loader of the kind comprising a hopper having an air port at the top of the hopper, a filter extending across the air port, a plurality of material inlet ports located below the filter, individual electrically actuated material fill control valves for opening and closing the material inlet ports, and air supply means for supplying air under pressure to the air port, and evacuation means connected to the air port, comprising:

• blowback timer means for developing a blowback enabling signal for a predetermined time interval T2;
• blowback signal generator means for developing a blowback actuating signal comprising a series of pulses, including means for adjusting the period of such pulses;
• blowback gate means, connected to the blowback timer means and blowback signal generator means and to the air supply means, for actuating the air supply means to apply a series of pulses of air through the filter into the hopper during the time interval T2;
• fill timer means for developing a fill enabling signal for a predetermined time interval T3;
• fill signal generator means for developing a repeating sequence of fill actuating signal pulses, one pulse for each fill control valve, including means for adjusting the relative durations of the fill actuating signal pulses;
• fill vacuum coupling means for actuating the evacuation means to evacuate the hopper continuously during time interval T3;
• fill logic means connected to the fill timer means, the fill signal generator means, and the fill control valves to open the control valves in repeating sequence during time interval T3;
• and control sequence coupling means interconnecting an input of one of the timer means to an output of the other timer means to set the one timer means in response to timing out of the other.