Spacer rings for dust collector bags

Claim 1

FILTER APPARATUS COMPRISING: (A) UPPER AND LOWER STRUCTURES IN VERTICALLY SPACED RELATIONSHIP, (B) A DUST-COLLECTING FILTER BAG OF ELONGATED TUBULAR CONSTRUCTION AND MADE OF FLEXIBLE GAS-PERVIOUS FIBER GLASS MATERIAL, (C) FIRST MEANS ATTACHING THE ENDS OF SAID BAG RESPECTIVELY TO SAID UPPER AND LOWER STRUCTURE HOLDING SAID BAG IN TENSION BETWEEN SAID ENDS, WITH AT LEAST ONE END OF SAID BAG BEING NORMALLY OPEN TO THE FLOW OF GAS TO BE FILTERED INTO SAID BAG AND OUTWARDLY THERETHROUGH, (D) A PLURALITY OF RIGID RINGS HAVING AN OUTSIDE DIAMETER SLIGHTLY LESS THAN THE INSIDE DIAMETER OF THE BAG EXTENDING ANNULARLY ABOUT THE LONGITUDINAL AXIS OF SAID BAG AND BEING LONGITUDINALLY SPACED APART BETWEEN THE ENDS OF SAID BAG, (E) SECOND MEANS CONNECTED TO SAID UPPER STRUCTURE AND EXTENDING LONGITUDINALLY OF SAID BAG WITHIN THE PERIPHERY OF SAID RINGS FOR POSITIONALLY ATTACHING SAID RINGS WITHIN SAID BAG, (F) SAID BAG INTERMEDIATE THE ENDS THEREOF BEING FREE OF ATTACHMENT TO SAID RINGS, AND (G) SAID FIRST AND SECOND ATTACHING MEANS (C) AND (E) BEING OPERATIVELY INDEPENDENT OF ONE ANOTHER; THE CONSTRUCTION AND ARRANGEMENT BEING SUCH THAT DURING NORMAL FILTERING OPERATION OF SAID APPARATUS, WITH GAS TO BE FILTERED FLOWING INTO SAID BAG UNDER PRESSURE, SAID BAG IS SUBSTANTIALLY OUT OF CONTACT WITH SAID RINGS; AND UPON ANY REVERSAL OF TTHE DIRECTION OF GAS FLOW THROUGH SAID BAG, SAID RINGS ENGAGE SAID BAG TO HOLD THE SAME AGAINST COMPLETE COLLAPSE.