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 A copper aspirator. The water inlet and outlet are at the top and bottom, respectively; the air inlet is on the side. |
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| Other names | Eductor-jet pump Injector/Ejector Filter pump |
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| Uses | Vacuum generation Suction |
| Related items | Injector Vacuum pump |
An aspirator, also called an eductor-jet pump or filter pump, is a device that produces vacuum by means of the Venturi effect. In an aspirator, fluid (liquid or gaseous) flows through a tube which then narrows. When the tube narrows, the fluid's speed increases, and because of the Venturi effect, its pressure decreases. Vacuum is taken from this point.
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Operation
The cheap and simple water aspirator is the most common type of aspirator. It is used in chemistry and biology laboratories and consists of a tee fitting which is attached to a faucet and has a hose barb at one side. The flow of water passes through the straight portion of the tee, which has a restriction at the intersection, where the hose barb is attached. The vacuum hose should be connected to this barb.
If a liquid is used as the working fluid, the strength of the vacuum produced is limited by the vapor pressure of the liquid (for water, 3.2 kPa (32 mbar) at 25 degrees Celsius.) If a gas is used, however, this restriction does not exist. The industrial steam ejector (also called the steam jet ejector, steam aspirator, or steam jet aspirator) uses steam as a working fluid.
In order to avoid using too much steam, a single steam ejector stage is generally not used to generate vacuum below approximately 10 kPa (75 mmHg).1 To generate higher vacuum, multiple stages are used; in a two-stage steam ejector, for example, the second stage provides vacuum for the waste steam output by the first stage. Condensers may be used between stages to reduce the load on the later stages. Steam ejectors with two, three, four, five and six stages may be used to produce vacuums down to 2.5 kPa, 300 Pa, 40 Pa, 4 Pa, and 0.4 Pa, respectively.1
The air ejector or venturi pump is similar to the steam ejector but uses high-pressure air as the working fluid. Multistage air ejectors can be used, but since air cannot easily be condensed at room temperature, an air ejector is usually limited to two or three stages.2
Medical aspirators
Medical aspirators are small suction machines used to remove mucus and other bodily fluids from a patient. They are often designed to be portable for use in ambulances and nursing homes, and can run on AC/DC or battery power. Major manufacturers include Allied Healthcare (under the Gomco brand) and Impact.
Insect aspirator
An insect aspirator, often called a pooter, is a device for collecting small insects or spiders using light suction. A motorized device is occasionally used, but normally the suction produced is through the lungs. The most common design is a long, flexible tube held in the mouth, connected to the stopper of a capture vial; the stopper is also fit with a rigid nozzle through which the insect is sucked.
References
- ^ a b High Vacuum Pumping Equipment, B. D. Power, New York: Reinhold Publishing Corporation, 1966, chapter 4.
- ^ Air Ejectors Cheaper Than Steam
See also
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Wikipedia content modification information:
- This page was last modified on 14 October 2008, at 14:44.
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