In order to adequately control dust exposures during mortar removal, vacuum cleaners need to exhaust 80 cfm from an exhaust hood on the grinder and maintain this air flow while collecting as much as 35 pounds of debris in the vacuum cleaner. A laboratory study was conducted to evaluate how mortar debris affects air flow and pressure losses through a vacuum cleaner's filters. Four vacuum cleaners were tested. Two of the vacuum cleaners used vacuum cleaner bags as a prefilter while the other two vacuum cleaners used cyclones to reduce the amount of debris which hits the filter. To conduct the testing, a contractor provided mortar removal debris that had been collected during actual mortar using grinder hood and a vacuum cleaner which involved cyclonic pre-separation. The vacuum cleaner fan curves were obtained experimentally to learn how pressure loss affects vacuum cleaner air flows. Then, 35 pounds of mortar removal debris was sucked into the vacuum cleaner in 5 pound increments. Before and after adding each five pound increment of debris, vacuum cleaner air flows were measured with a venturi meter and vacuum cleaner static pressures were measured at the inlet to the vacuum cleaner motor, before each filter and after each filter. The vacuum cleaners equipped with cyclonic pre-separation were unaffected by the mass of debris collected in the vacuum cleaner. These vacuum cleaners were able to maintain air flows in excess of 70 cfm throughout the testing program. As debris accumulated in the vacuum cleaners that used vacuum cleaner bags, air flow decreased from 80 cfm to as little as 30 cfm. This air flow loss is caused by the increased air flow resistance of the vacuum cleaner bags which increased from less than 0.1 inches of water per cfm to 2 inches of water/cfm which is 60 inches of water at an airflow of 30 cfm. Apparently, vacuum cleaners using vacuum cleaner bags should be used in applications where adequate dust control can be achieved at air flows less than 30 cfm. Where higher air flows are needed, vacuum cleaners should incorporate cyclonic pre-separation in an effort to prevent debris from reaching the vacuum cleaner final filters.
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