Chances are that you probably don’t spend a lot of time contemplating your vacuum cleaner. Either it works well, and you don’t have to think about it, or it doesn’t work well, and you refuse to acknowledge that this $100 to $2000 device fails to pick up so much as a single piece of macaroni.
The wide price range of vacuums seen today generally reflects the presence or absence of new technologies like the self-adjusting vacuum head (found on the Miele S8990 UniQ), or the smooth drive of a ball vacuum (like the Dyson Cinetic Big Ball). However, most people have a regular vacuum cleaner with no extras that's primarily used to clean carpets.
Here’s a thought experiment: Imagine trying to clean a carpet without a vacuum cleaner. Short of ripping out your wall-to-wall carpets every month and beating them with a stick the size of a snowboard, what could you possibly do?
Fortunately, we do have vacuum cleaners. And their cleaning power is all thanks to two simple machines hidden underneath all that plastic molding—the roller brush and the fan.
The Roller Brush
It’s the combination of a belt, a roller, and sometimes a small vacuum head motor that makes it possible to clean carpets of various pile heights. The roller part of this combination is the actual cleaning tool, which has brush bristles attached to it.
The cylindrical shape of the roller brush is harnessed on at least one end by a rubber belt. This belt pushes and pulls the brush to make it spin. The other end of this belt is connected to another roller. This second roller is driven either by the motion of the wheels when you push the vacuum, or by a motor that causes the brush to rotate independently.
Big deal, you say. Who cares about the roller brush? It’s always covered in gross hair and other things you don’t want to investigate too closely. It’s also always the first thing on the vacuum to break or come loose.
Despite its flaws, carpet cleaning would not be possible without the roller brush. It performs two vital functions: Firstly, it agitates the shallower parts of the carpet, allowing debris caught in the carpet fibers to escape from their nylon prisons and more easily come out of the carpet. Secondly, the roller's bristles disturb the carpet fibers to create a more direct path for dirt trapped deep in the carpet to move towards the surface.
Basically, there’s a very good reason why shop vacuums aren’t used on carpet: A vacuum without a roller brush would do a terrible job of cleaning a carpet. The belt/roller combination of the roller brush is really the unsung hero of removing dirt and incriminating forensic evidence from carpets.
The fan is located in the body of the vacuum cleaner and is powered by a motor. When you turn your vacuum on, you’re switching on the motor, which drives the rotation of the fan blades and creates suction. The fan in your vacuum operates under the same principles as your ceiling fan, except that it's much more compact and powerful. The blades of a fast ceiling fan rotate at rates up to about 300 rotations per minute (RPM); a vacuum cleaner fan can get up to about 4800 RPM.
In fact, the fan blows air out through vents in the vacuum cleaner so quickly that it creates a localized area completely devoid of air, also known as a vacuum. Air rushes in just as rapidly to replace the lost air. It is this type of observation (albeit, not with a vacuum cleaner) that caused Aristotle to determine that “Nature abhors a vacuum.”
Since nature wants to fill this low-pressure airless void, vacuum cleaner engineers seal all other access points in the vacuum cleaner head and hose, ensuring that the only available replacement air is located where the vacuum head meets the carpet. Therefore, the “sucking” force of a vacuum is really the continuous flow of air from a high-pressure area (the carpet) to a low-pressure area (inside the vacuum cleaner). This differential causes the replacement air to be pulled in so rapidly that both light debris (like dust and dander) and heavy debris (dirt in the carpet) are pulled into the vacuum cleaner and caught in the filter and bag.
Having read this explanation, you may decide to pull a Tim “The Toolman” Taylor and say, “More power!” on the basis that a bigger vacuum fan will generate more suction and make your carpet rue the day it decided to hide Cheez-It crumbs from you.
Unfortunately, increasing the amount of suction generated by the fan would eventually make it physically impossible to push the vacuum cleaner across the carpet (unless you add extra air intakes on the vacuum head, like on the Kenmore Elite 81714). To clean a carpet, you’d have to get the Hulk to lift the vacuum head up each time and move it to a new spot. This dilemma results in engineers having to strike a balance between raw cleaning power and ease of mobility.
You can thank your vacuum's tiny fan for that powerful suction you're accustomed to, but remember that its coworker—the roller brush—is just as important. Without the roller brush, vacuum cleaners wouldn’t be effective at cleaning carpets. And without the fan, vacuum cleaners wouldn’t clean at all. So the next time you lament having to roll out your vacuum cleaner, just remind yourself that these two simple devices actually make carpet cleaning a lot easier than you think.