Control apparatus for advancing web of filter medium through a filtering zone

Claim 1

IN A CONTROL APPARATUS FOR ADVANCING A WEB OF FILTER MEDIUM IN AN AIR FILTER HAVING A REWIND ROLL FOR STORING SPENT WEB FED THROUGH A FILTERING ZONE AND A MOTOR FOR DRIVING SAID ROLL, THE IMPROVEMENT COMPRISING AN ELECTRICAL SYSTEM FOR EFFICIENTLY UTILIZING THE WEB DURING ABNORMAL OPERATING CONDITIONS AND INCLUDING; A SWITCHOPERATING MEANS ACTUATED INDEPENDENCE UPON LINEAR ADVANCE OF SAID WEB, A FIRST SWITCH ACTUATED BY SAID MEANS AND MOVABLE BETWEEN A NORMAL FIRST POSITION AND A SECOND POSITION, FIRST AND SECOND RELAYS HAVING SEPARATE CIRCUITS FOR RESPECTIVELY ENERGIZING SAID ROLL-DRIVING MOTOR; A SELF-RESETTING TIMER FOR TIMING THE SUCCESSIVE NORMAL ADVANCES OF SAID WEB AND COMPRISING A TIMING MOTOR, A TIMER SWITCH MOVABLE BETWEEN A POSITION ENERGIZING SAID SECOND RELAY AND A POSITION DE-ENERGIZING SAID SECOND RELAY, AND A TIMER COIL ADAPTED UPON ENERGIZATION TO MOVE SAID TIMER SWITCH FROM SAID RELAY-ENERGIZING POSITION TO SAID RELAY-DE-ENERGIZING POSITION AND TO RESET SAID TIMER; AND AN OVERLOAD PRESSURE SWITCH FOR ESTABLISHING EMERGENCY CIRCUIT TO SAID ROLL-DRIVING MOTOR, UPON ATTAINMENT OF A PREDETERMINED PRESSURE DROP ACROSS SAID WEB, SAID PRESSURE SWITCH BEING MOVABLE BETWEEN A NORMAL INACTIVE POSITION HAVING NO INFLUENCE UPON SAID RELAYS AND TIMER