Vacuum Cleaners
A vacuum cleaner is a device that uses an air pump to create a partial vacuum to suck up dust and dirt, usually from floors, and optionally from other surfaces as well. The dirt is collected by either a dustbag or a cyclone for later disposal. Vacuum cleaners, which are used in homes as well as in industry, exist in a variety of sizes and models— small battery-operated hand-held devices, domestic central vacuum cleaners, huge stationary industrial appliances that can handle several hundred litres of dust before being emptied, and self-propelled vacuum trucks for recovery of large spills or removal of contaminated soil.
Modern configurations
A wide variety of technologies, designs, and configurations are available for both domestic and commercial cleaning jobs.
Upright
Upright vacuum cleaners are popular in the United States, Britain and numerous Commonwealth countries, but very unusual in Continental Europe. They take the form of a cleaning head, onto which a handle and bag are attached. Upright designs generally employ a rotating brushroll or beater bar, which removes dirt through a combination of sweeping and vibration. There are two types of upright vacuums; dirty-air/direct fan (found mostly on commercial vacuums), or clean-air/fan-bypass (found on most of today's domestic vacuums).
The older of the two designs, direct-fan cleaners have a large impeller (fan) mounted close to the suction opening, through which the dirt passes directly, before being blown into a bag. The motor is often cooled by a separate cooling fan. Because of their large-bladed fans, and comparatively short airpaths, direct-fan cleaners create a very efficient airflow from a low amount of power, and make effective carpet cleaners. Their "above-floor" cleaning power is less efficient, since the airflow is lost when it passes through a long hose, and the fan has been optimized for airflow volume and not suction.
Fan-bypass uprights have their motor mounted after the filter bag. Dust is removed from the airstream by the bag, and usually a filter, before it passes through the fan. The fans are smaller, and are usually a combination of several moving and stationary turbines working in sequence to boost power. The motor is cooled by the airstream passing through it. Fan-bypass vacuums are good for both carpet and above-floor cleaning, since their suction does not significantly diminish over the distance of a hose, as it does in direct-fan cleaners. However, their air-paths are much less efficient, and can require more than twice as much power as direct-fan cleaners to achieve the same results.
The most common upright vacuum cleaners use a drive-belt powered by the suction motor to rotate the brush-roll. However, a more common design of dual motor upright is available. In these cleaners, the suction is provided via a large motor, while the brushroll is powered by a separate, smaller motor, which does not create any suction. The brush-roll motor can sometimes be switched off, so hard floors can be cleaned without the brush-roll scattering the dirt. It may also have an automatic cut-off feature which shuts the motor off if the brush-roll becomes jammed, protecting it from damage.
Canister
Canister models (in the UK also often called cylinder models) dominate the European market. They have the motor and dust collector (using a bag or bagless) in a separate unit, usually mounted on wheels, which is connected to the vacuum head by a flexible hose. Their main advantage is flexibility, as the user can attach different heads for different tasks, and maneuverability (the head can reach under furniture and makes it very easy to vacuum stairs and vertical surfaces). Many cylinder models have power heads as standard or add-on equipment containing the same sort of mechanical beaters as in upright units, making them as efficient on carpets as upright models. Such beaters are driven by a separate electric motor or a turbine which uses the suction power to spin the brushroll via a drive belt.
Drum
Drum or shop vac models are essentially heavy-duty industrial versions of cylinder vacuum cleaners, where the canister consists of a large vertically positioned drum which can be stationary or on wheels. Smaller versions, for use in garages or small workshops, are usually electrically powered. Larger models, which can store over 200 litres (53 US gallons), are often hooked up to compressed air, utilizing the Venturi effect to produce a partial vacuum. Built-in dust collection systems are also used in many workshops.
Wet/dry
Wet or wet/dry vacuum cleaners are a specialized form of the cylinder/drum models that can be used to clean up wet or liquid spills. They are generally designed to be used both indoors and outdoors and to accommodate both wet and dry soilage; some are also equipped with a switch or exhaust port for reversing the airflow, a useful function for everything from clearing a clogged hose to blowing dust into a corner for easy collection.
Robotic
In the late 1990s and early 2000s, several companies developed robotic vacuum cleaners, a form of carpet sweeper usually equipped with limited suction power. Some examples are Roomba, picaBot, Robomaxx, Intellibot, Trilobite, FloorBot and Dyson. These machines move autonomously, usually in a mostly chaotic pattern ("random bounce") across a floor, collecting surface dust and debris into a dustbin. They usually can navigate around furniture and come back to a docking station to charge their batteries, and a few are able to empty their dust containers into the dock as well.
Most robotic vacuum cleaners are designed for home use, although there are more capable models for operation in offices, hotels, hospitals, woodshops, etc. Most models are equipped with motorized brushes that sweep debris from the floor into a collection bin. Additionally, some – such as the Roomba – are equipped with an impeller motor to create an actual vacuum to collect finer dust particles.
The Dyson robotic vacuum cleaner (DC06) was too expensive for home use, due to its high technical specifications. Thus, it was never released, although it is claimed that it would have been the first robotic vacuum cleaner sold. In December 2009, Neato Robotics launched the world's first robotic vacuum cleaner which uses a laser-based range-finder to scan and memorize its surrounding. It then cleans the floor methodically with the strongest impeller among robotic vacuum cleaners, pulling in 140CFM of air at 18.6 m/s velocity. It is claimed that the Neato XV establishes a new benchmark for performance of a robotic vacuum cleaner.
Cyclonic
Portable vacuum cleaners working on the cyclonic separation principle became popular in the 1990s. This dirt separation principle was well known and often used in central vacuum systems. Cleveland's P.A. Geier Company had obtained a patent on a cyclonic vacuum cleaner as early as 1928, which was later sold to Health-Mor in 1939, introducing the Filter Queen cyclonic canister vacuum cleaner.
In 1979, James Dyson introduced a portable unit with cyclonic separation, adapting this design from industrial saw mills. He launched his cyclone cleaner first in Japan in the 1980s at a cost of about US$1800 and in 1993 brought out the Dyson DC01 upright in the UK for £200. Critics expected that people would not buy a vacuum cleaner at twice the price of a conventional unit, but the Dyson design later became the most popular cleaner in the UK. Cyclonic cleaners do not use filtration bags. Instead, the dust is separated in a detachable cylindrical collection vessel or bin. Air and dust are sucked at high speed into the collection vessel at a direction tangential to the vessel wall, creating a fast-spinning vortex. The dust particles and other debris move to the outside of the vessel by centrifugal force, where they fall due to gravity.
In fixed-installation central vacuum cleaners, the cleaned air may be exhausted directly outside without need for further filtration. A well-designed cyclonic filtration system loses suction power due to airflow restriction only when the collection vessel is almost full. This is in marked contrast to filter bag systems, which lose suction when pores in the filter become clogged as dirt and dust are collected.
In portable cyclonic models, the cleaned air from the center of the vortex is expelled from the machine after passing through a number of successively finer filters at the top of the container. The first filter is intended to trap particles which could damage the subsequent filters that remove fine dust particles. The filters must regularly be cleaned or replaced to ensure that the machine continues to perform efficiently. Since Dyson's success in raising public awareness of cyclonic separation, several other companies have introduced cyclone models. Competing manufacturers include Hoover, Bissell, Eureka, Electrolux, Filter Queen, etc., and the cheapest models are no more expensive than a conventional cleaner.
Central
Central vacuum cleaners, also known as built-in or ducted, are a type of canister/cylinder model which has the motor and dirt filtration unit located in a central location in a building, and connected by pipes to fixed vacuum inlets installed throughout the building. Only the hose and cleaning head need be carried from room to room, and the hose is commonly 8 m (25 ft) long, allowing a large range of movement without changing vacuum inlets. Plastic or metal piping connects the inlets to the central unit. The vacuum head may be unpowered, or have beaters operated by an electric motor or by an air-driven turbine.
The dirt bag or collection bin in a central vacuum system is usually so large that emptying or changing needs to be done less often, perhaps a few times per year for an ordinary household. The central unit usually stays in stand-by, and is turned on by a switch on the handle of the hose. Alternately, the unit powers up when the hose is plugged into the wall inlet, when the metal hose connector makes contact with two prongs in the wall inlet and control current is transmitted through low voltage wires to the main unit.
A central vacuum typically produces greater suction than common portable vacuum cleaners because a larger fan and more powerful motor can be used when they are not required to be portable. A cyclonic separation system, if used, does not lose suction as the collection container fills up, until the container is nearly full. This is in marked contrast to filter-bag designs, which start losing suction immediately as pores in the filter become clogged by accumulated dirt and dust.
A benefit to allergy sufferers is that unlike a standard vacuum cleaner, which must blow some of the dirt collected back into the room being cleaned (no matter how efficient its filtration), a central vacuum removes all the dirt collected to the central unit. Since this central unit is usually located outside the living area, no dust is recirculated back into the room being cleaned. Also it is possible on most newer models to vent the exhaust entirely outside, even with the unit inside the living quarters. In addition, because of the remote location of the motor unit, there is much less noise in the room being cleaned than with a standard vacuum cleaner.
Technology
A vacuum's suction is caused by a difference in air pressure. An electric fan reduces the pressure inside the machine. Atmospheric pressure then pushes the air through the carpet and into the nozzle, and so the dust is literally pushed into the bag.
Tests have shown that vacuuming can kill 100% of young fleas and 96% of adult fleas.
Exhaust filtration
Vacuums by their nature cause dust to become airborne, by exhausting air that is not completely filtered. This can cause health problems since the operator ends up inhaling respirable dust, which is also redeposited into the area being cleaned. There are several methods manufacturers use to control this problem, some of which may be combined together in a single appliance. Typically a filter is positioned so that the incoming air passes through it before it reaches the motor, and then the filtered air passes through the motor for cooling purposes. Some other designs use a completely separate air intake for cooling.
It is nearly impossible for a practical air filter to completely remove all ultrafine particles from a dirt-laden airstream. An ultra-efficient air filter will immediately clog up and become ineffective during everyday use, and practical filters are a compromise between filtering effectiveness and restriction of airflow. One way to sidestep this problem is to exhaust partially filtered air to the outdoors, which is a design feature of some central vacuum systems. Specially engineered portable vacuums may also utilize this design, but are more awkward to set up and use, requiring temporary installation of a separate exhaust hose to an exterior window.
Bag: The most common method to capture the debris vacuumed up involves a paper or fabric bag that allows air to pass through, but attempts to trap most of the dust and debris. The bag may be disposable, or designed to be cleaned and re-used.
Bagless: In non-cyclonic bagless models, the role of the bag is taken by a removable container and a reusable filter, equivalent to a reusable fabric bag.
Cyclonic separation: A vacuum cleaner employing this method is also bagless. It causes intake air to be cycled or spun so fast that most of the dust is forced out of the air and falls into a collection bin. The operation is similar to that of a centrifuge.
Water filtration: First seen commercially in the 1920s in the form of the Newcombe Separator (later to become the Rexair Rainbow), a water filtration vacuum cleaner uses a water bath as a filter. It forces the dirt-laden intake air to pass through water before it is exhausted, so that wet dust cannot become airborne. The water trap filtration and low speed may also allow the user to use the machine as a stand alone air purifier and humidifier unit. The dirty water must be dumped out and the appliance must be cleaned after each use, to avoid growth of bacteria and mold, causing unpleasant odors. Ultra fine air filter: Also called HEPA filtered, this method is used as a secondary filter after the air has passed through the rest of the machine. It is meant to remove any remaining dust that could harm the operator. Some vacuum cleaners also use an activated charcoal filter to remove odors.
Ordinary vacuum cleaners should never be used to clean up asbestos fibers, even if fitted with a HEPA filter. Specially designed machines are required to safely clean up asbestos.
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