Self-cleaning filter

A filtering apparatus for removing entrained particulate from a stream of fluid, said apparatus comprising:

• a generally tubular filter portion formed from a porous material for removal of particulate from the fluid, said filter portion being formed with upper and lower end portions;
• means for intermittently drawing the fluid radially inwardly through said filter portion and then upwardly through one of said upper and lower end portions;
• and
• first and second rings connected to said upper and lower end portions, respectively, for maintaining said upper and lower end portions in first and second radial positions, respectively;
• said filter portion being sufficiently flexible to collapse inwardly as the fluid flows therethrough such that said lower end portion is simultaneously drawn upwardly;
• the weight of said second ring being sufficient to cause the lower end portion to drop downwardly and thus expand the filter portion outwardly when said fluid stops flowing so as to cause the particulate collected thereon to fall therefrom.

A pre-filtering apparatus adapted for use with a vacuum cleaner, said vacuum cleaner having a canister with a generally open upper end and an inlet opening, a lid closing the upper end of the canister, a filter connected to the lid and extending downwardly in the canister, and a vacuum source connected to the lid for drawing contaminated air through the inlet opening of the canister and then through the filter when the vacuum cleaner is turned on, said apparatus comprising:

• a dust bag having an open top and a generally closed bottom and having a generally tubular filter portion therebetween, said filter portion having upper and lower end portions and being sized to slip over and surround said filter such that the air flows through said pre-filter portion prior to reaching said filter;
• means for removably connecting the top of the dust bag to the lid;
• means for holding said upper end portion in a first radial position;
• and
• means for biasing said lower end portion downwardly and toward a second radial position;
• said filter portion being sufficiently flexible to collapse inwardly as the air flows therethrough such that said lower end portion is drawn upwardly;
• said biasing means generally expanding and straightening said filter portion when the vacuum cleaner is turned off.