Vacuum cleaners with bags

Invented in 1901 by a British engineer, the first electric vacuums were simple sucking machines with a brush and suction head at the front, a motor in the middle, and a bag at the back. When you switched them on, the motor whirred into action, sucking in air and dirt and blowing them into the bag.

Think back to the "suck and filter" comb trick and you'll understand straight away how these old-style, bag vacuum cleaners work. In place of your mouth, there's a powerful electric motor attached to a fan that sucks in air. Instead of a tissue paper and comb, there's a dirt bag (sometimes a disposable paper bag inside a fabric bag), which catches the dust sucked in so you can use the cleaner for some time without worrying about where all the dirt is going. The bag isn't completely airtight, as you might think. Air can pass out of it, though not dirt, so it effectively acts as a filter; the air is sucked into the bag and then escapes through it, leaving the dirt behind inside it.

This diagram summarizes what's happening inside a conventional vacuum:

1. Electricity outlet supplies energy to the cleaner's electric motor.

2. In a typical cleaner, the electric motor is rated at about 500–1000 watts, so it uses five to ten times as much energy as an old-style (incandescent) lamp.

3. Rubber belt (blue) powered by electric motor turns brushes and beaters on the roller at the front of the machine.

4. Vigorous beating and brushing loosens dirt from the carpet or rug.

5. Fan attached to the electric motor sucks air and loosened dirt in through the front of the machine.

6. Dirty air travels through to the back of the machine, cooling the electric motor as it passes by.

7. Dirt is trapped in the bottom of the dirt bag (which may be a single fabric bag or a disposable paper bag fixed inside a fabric bag).

8. Relatively clean air emerges out of the back. Note that the outgoing air is much warmer than the incoming air because it's picked up waste heat from the electric motor.