How do vacuum cleaners use water to filter air?

Answer 1

There's a sealed tank that's about half full of water, half full of air. At the top of the tank there is a hole going to the vacuum moter, and a tube going to the bottom of the water on one end, and to whatever is sucking off of your floor on the other. The motor pulls the air out of the top, dropping the pressure inside the tank. Since water won't expand (much), the pressure is equalized by air from the tube which is full of the stuff from your floor. This dirty air enters at the bottom of the water. As it bubbles up to the top, heavier and larger things like dust and dirt remain trapped in the water, and the air comes out clean. That's it in a nutshell. Your vacuum cleaner likely has a series of valves and maybe a one-way respirator (like on some snorkels that only allow water to flow in one direction) to reduce the risk of water damaging the motor. Even though water does an excellent job filtering air, there are probably also some filters at the motor exahaust to catch things the water couldn't trap. Still, none of these are necessary to the basic functioning of a water-based vacuum cleaner. This exact process is used in some industrial air filtering systems, and just like your home water-based vacuum cleaner, creates a nasty sludge which gets flushed into the sewage system.