Method of making zigzag filter element

Claim 1

IN THE METHOD OF MAKING A ZIGZAG FILTER ELEMENT HAVING FILTER SHEETS BETWEEN END PANELS, THE STEPS COMPRISING TRANVERSELY FOLDING A LONG STRIP OF FLEXIBLE FILTERING MATERIAL BACK AND FORTH UPON ITSELF TO FORM A STACK OF SHEETS WHILE SUCCESSIVELY JOINING EACH PAIR ADJOINING SHEETS TOGETHER ALONG A ROW OF LATERALLY SPACED LINES THAT EXTEND LENGTHWISE OF THE STRIP, THE LINES IN THE ROW BEING STAGGERED RELATIVE TO THE LINES IN THE ROWS AT OPPOSITE SIDES OF THAT ROW, PLACING A ROW OF LATERALLY SPACED RODS AGAINST EACH END SHEET OF THE STACK OPPOSITE SAID LINES AT THE OPPOSITE SIDE OF THE SAME SHEET, APPLYING PRESSURE TO SAID RODS TO PRESS THEM INTO SAID STACK AND THEREBY FORM WAVES IN THE END SHEETS AND SHORTEN THEM, JOINING A PAIR OF PANELS TO THE END SHEETS ALONG THE CRESTS OF THEIR WAVES WHILE SAID PRESSURE IS MAINTAINED, REMOVING SAID RODS ENDWAYS FROM BETWEEN THE PANELS AND END SHEETS, AND THEN EXPANDING SAID STACK TO FORM FILTER POCKETS BETWEEN THE SHEETS IN THE AREAS THAT ARE NOT JOINED TOGETHER ALONG SAID LINES.