How does a vacuum cleaner carry dust away?

A vacuum cleaner can make crumbs race along the floor and disappear into a hose. Inside the machine, the crumbs have not vanished. They have taken a ride in moving air, which is then separated from the dirt before returning to the room.

An electric motor turns a fan. The fan moves air onward through the cleaner, keeping pressure lower on the inlet side than in the room. Room air flows into that lower-pressure opening. Its motion can lift and carry loose dust. A rotating brush in some floorheads helps loosen material caught among carpet fibers so the air can carry it along.

The hose leads into a collecting space. In a bagged cleaner, the dusty air enters a porous bag. The bag lets air pass through while its material traps many particles. Dust stays in the bag as air continues toward the fan and outlet. Additional filters can catch particles that pass earlier stages. The design needs both an air route and a way to keep captured dust from escaping through leaks.

Bagless cleaners often give the air a curved, swirling path through a cyclone. Particles do not follow every tight turn of the air easily, so many separate toward the outer wall and collect in a bin. Filters then handle particles that remain in the airflow. A cyclone and a bag use different methods, but both separate carried material from its moving air.

The distinction between pressure and flow explains an odd possibility: a blocked opening can have a pressure difference without a continuing stream of air through it. Dust collection needs that moving stream. A vacuum cleaner's useful trick is not merely making low pressure; it is maintaining a connected journey for air while giving the dust a place to stop.