Vacuum cleaners

by Chris Woodford. Last updated: July 14, 2011.

Even when your house is clean, it's absolutely filthy! That's because most of the dust and dirt in your house is way too small to see. Fortunately, most of us can live without knowing this kind of truth about our homes; a quick run around with the vacuum cleaner is enough to keep us happy. Twenty-first century homes are packed with dozens of appliances and gadgets, but vacuums are one of the few most of us simply couldn't live without. We all know vacuums suck up dirt—but how exactly do they work? Let's take a closer look!

Photo: Left: A Dyson cleaner, like this one, shows you just how much dirt it's picking up in its transparent bin. The dust and hair tends to swirl around thanks to the machine's "cyclonic" action. Other popular makes of vacuum cleaner (including Hoover, Miele, and Electrolux) also now make bagless cleaners—the revolutionary idea Dyson popularized in the 1990s.

Vacuum cleaner or suction cleaner?

The name "vacuum cleaner" is a bit of a giveaway when it comes to understanding how your machine works: vacuum cleaners work by suction. ("Suction cleaner" would be a better name than vacuum cleaner, in fact, because there's no actual vacuum involved.) If you've ever tried that cleaning trick with a tissue paper and a comb, you'll know how effective suction can be for removing dirt. If not, try it now! Wrap a piece of tissue paper around a comb. Breath out as far as you can and hold your breath. Place the comb and paper against your mouth. Now lean against a dusty armchair and press your mouth and the comb against it. Breath in sharply so, effectively, you are breathing straight through the comb. Take the comb away from your mouth and inspect the tissue paper. See how dirty it is!

How does a conventional vacuum cleaner work?

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 normal vacuum:

Artwork showing the basic cleaning process in a conventional bag vacuum cleaner.

Electricity outlet supplies energy to the cleaner's electric motor.
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.
Rubber belt powered by electric motor turns brushes and beaters on the roller at the front of the machine.
Vigorous beating and brushing loosens dirt from the carpet or rug.
Fan attached to the electric motor sucks air and loosened dirt in through the front of the machine.
Dirty air travels through to the back of the machine, cooling the electric motor as it passes by.
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).
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.

How do Dyson vacuums work?

Most vacuums used this "suck and bag the dirt" process until the late 1980s, when another British engineer named James Dyson felt it was time to go one better.

The trouble with old-style vacuum cleaners is that they suck in dirty air and blow it directly into the bag. The bag catches the dirt and the relatively clean (but sometimes still dusty) air drifts back into the room. The longer you use a vacuum, the more the bag fills up. As the bag fills up, the amount of empty air it can hold decreases, so its ability to suck in more dirt is gradually diminished. The longer you go without emptying your vacuum, the worse the problem becomes.

The two HEPA filters on a Dyson vacuum cleaner at the bottom and top of the dirt bin.

Goodbye to the bag

Dyson decided to tackle this difficulty by doing away with the bag altogether. By this time, he was already a successful inventor manufacturing his own plastic garden equipment. His factory in England's West Country was plagued with dust, so he designed a "cyclonic" air filtering device to keep it clean. Using a powerful fan, it sucked in dusty air and spun it around at high speed like a centrifuge. Spinning the dusty air was an effective way to separate the dust out of the air. In a washing machine, the same principle is used to spin water from clothes at the end of the wash cycle. As the drum spins at high speed, the clothes fling against the edge of the drum and the water they contain is forced out through the drum's tiny holes. The same idea proved just as effective in Dyson's air filter. Spinning the air forced the heavy dust particles out through holes in the filter where they could be trapped and collected; the cleaned air could then be piped back into the room. Dyson's machine was so efficient and successful that he wondered why vacuum cleaners didn't use the same idea. He resolved to invent a cyclonic vacuum cleaner there and then.

Photo: Right: Vacuum cleaners work just like the comb and paper trick using two, sophisticated HEPA filters. Top: Take the dust-collecting bin off a Dyson and you can see one of the two HEPA filters (beneath the circular grating). Bottom: There's a second filter at the top of the dust bin.

Perfecting the invention

Between the late 1970s and the mid 1980s, Dyson built no fewer than 5,127 prototypes of his cyclonic cleaner. By the late 1980s, he was selling a bright pink cyclonic cleaner called the G-Force in Japan. It was large, clumsy, and expensive, but it earned him enough money to develop a more compact, affordable cyclonic vacuum called the DC01. During the mid-1990s, this new machine won countless design awards and soon became Britain's biggest selling vacuum cleaner—and it is now sold worldwide.

Its secret is simple: because there is no bag to clog up with dust and dirt, the machine always sucks with exactly the same power. You still have to empty the dirt bin every so often, but the cyclonic action means a Dyson with a full dirt bin works equally as well as one that's just been emptied.

All this goes to show that, no matter how good an invention appears to be, someone can always make it better! (Talking of improvements, have you seen robotic vacuum cleaners that clean your home automatically?)

How does a Dyson vacuum work?

Parts of a dyson vacuum cleaner

These are some of the more important parts on a Dyson DC04 upright vacuum:

Brush bar and air intake: The rotating brush under this bar loosens dirt in the rug so the vacuum's suction can pull it in.
Height adjustment: Allows you to use the cleaner on hard floors, rugs, and other surfaces. When the vacuum is upright, the rotating brush is switched off. Air sucks in through an extension hose at the top of the machine instead.
Powerful electric motor: This is effectively a giant fan that sucks in air and pulls it through the machine's cyclone and filters. As you've probably noticed, the motor in a vacuum cleaner gets quite hot after a few minutes; that's why the cool air it sucks in emerges from the other side of the machine somewhat hotter!
Transparent plastic dust collection bin. The bin on this cleaner is absolutely full. One interesting thing worth noting on Dysons is the way their centrifugal, spinning action sorts dust particles into bands of different sizes, much like a centrifuge. You can just about see in this photo that there's a band of grit at the bottom of the bin, followed by a darker band of bigger dirt particles, with lighter fluff sitting on top.
Cyclone: The cyclone is a large yellow plastic cone that points down into the dust bin:

The cyclone is the most important part of a Dyson. You can see from this photo that it's a tapering, cone-shaped piece of plastic with small holes in the top:

As the electric motor sucks air through the cone, it swirls around like a vortex. Dust spins out through the small holes and collects in the clear plastic bin ready for disposal.

Just above the cyclone is the upper dust filter (it's inside the gray cylinder, above the yellow cyclone, in the photo above). There's one filter immediately above the dust collection bin and another one just beneath it.
Air hose: The electric motor sucks air through the Dyson along a network of tubes. Some Dysons have a sticker on them showing how the air moves around through the various parts of the machine: