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  3. Vacuum cleaners and electric brooms are almost as basic today as once were the ordinary broom and dustpan. With or without their

Vacuum cleaners and electric brooms are almost as basic today as once were the ordinary broom and dustpan. With or without their

admin2010-06-18  56
问题    Vacuum cleaners and electric brooms are almost as basic today as once were the ordinary broom and dustpan. With or without their special attachments, these cleaners can handle hardwood floors, wails, carpets, furniture, and draperies, and are an important factor in the maintenance of appliances such as window air conditioners and refrigerators.
   Although vacuum cleaners are available in a variety of sizes and shapes (the two major categories are tank or canister and upright), they all work on the same principle. As for electric brooms, they are in fact lightweight, upright vacuum cleaners with the same working parts.
   At the heart of a vacuum cleaner is an electric motor housed in a compartment. The motor drives a shaft which causes a fan to whir. The fan pulls air through the housing and forces it out through the outlet end of the cleaner.
   All this occurs at a very high rate of speed. Vacuum cleaner motors operate at a very high rate of speed. Vacuum cleaner motors operate at approximately 3000 to 10,000 + revolutions per minute, depending upon design. With this speed, a great quantity of air is moved at once, creating suction.
   As the fan draws air through the compartment, it creates suction at the inlet end of the housing — the end with the pickup attachment. In canister-type vacuum cleaners, the pickup is a long hose equipped with the nozzle (or brush or wand, or other cleaning attachment). In upright Units, the pickup is a brush-equipped roller mechanism (sometimes with a beater bar) that sweeps along the floor or rug.
   The high-speed fan sucks air through the pickup attachment and into the inner compartment. As it docs so, it creates a vacuum -- an empty space from which all air has been removed. The crucial point of a vacuum is that air around it always rushes in to fill the empty space. In other words, an area of high pressure always rushes toward an area of low pressure.
   In a vacuum cleaner, the air that surges in to fill the vacuum carries with it dust, dirt, and lint particles. The air that flows in to fill the vacuum flows on into a container or bag. (One brand of electric broom uses a plastic cup; others, and vacuum cleaners, use a bag. ) Vacuum cleaner bags are made of a special paper or cloth that is porous enough to permit a free flow of air, fight enough to trap most of the dust and dirt, and tough enough to withstand the pressure without tearing. The cloth bags can be cleaned and re-used. Paper bags are discarded when full and replaced with new ones.
   Beyond the bag is a filter that permits air to flow through but which captures finer dust and dirt that was not trapped by the bag. The air -- relatively clean by now -- passes next over the vacuum cleaner motor, cooling it, and then on out through the outlet.
How to Repair a Vacuum Cleaner
   The chief complaint of those who use vacuum cleaners and electric brooms is lack of suction— it won’t "pick up." Sometimes the complaint is based on a real problem; other times, the solution can be a simple one.
   You can check to see if your cleaner is creating sufficient vacuum by scattering some sawdust over the floor. If some of the sawdust remains after you bare swept the vacuum cleaner over it, the suction is not sufficient. The unit needs servicing.
   The most common cause of insufficient suction is a full dust bag or a dirt-clogged filter. Dirt— clogged nozzles, hoses and passages also reduce suction — in fact, anything that cuts down on the free movement of air cuts down the efficiency of a vacuum cleaner.
   If you are having problems with suction, cheek first to see if the dust bag or filter are clogged. Remove both. Place the cleaner in a position where it will not pick up dirt, then switch it on. (Never operate a vacuum cleaner or electric broom in the cleaning position without a dust bag, pickup receptacle or filter.) Dust will be pulled into the motor, where it can clog air passages, causing the motor to overheat and burn out. Hold your hand over the pickup end of the cleaner to check the suction. If it seems stronger without the dust bag and filter, replace them.
   If removing the dust bag and filter does not increase the vacuum (suction), all hoses, nozzles and passages should be inspected for dirt buildup. Pull the power cord from the wall outlet, then clean all parts of the unit. Make sure, too, that hoses are not torn or otherwise damaged. Check gaskets for tears. A bad hose will create an air leak, which will result in reduced vacuum and weaker suction.
What is TRUE about vacuum cleaners?
选项 A、The whirring of the fan does not necessarily occur at a high speed.
B、A vacuum is created as the fan sucks air into the inner compartment.
C、As a vacuum cleaner works, a magnetic field is created, drawing dust, dirt and other particles into the machine.
D、There is a filter in a vacuum cleaner, whose sole function is to permit air to flow through.
答案B
解析
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