Due to the lack of delicate moving parts and the flow of steam providing somewhat of cleaning action, steam ejectors can handle gas flows containing liquids, dust, or even solid particles that would damage or clog many other vacuum pumps. The industrial steam ejector (also called the "steam jet ejector", "steam aspirator", or "evactor") uses steam as a working fluid and multistage systems can produce very high vacuums. Most are supplied through a ship's firefighting main, and portable models can also be supplied by an emergency pump, provided it can supply sufficient flow to operate the eductor. Sizes, flow ratings, and applications vary, including eductors that are permanently installed (typically used in very large spaces, such as a ship's main engine room), or portable models that can be lowered into spaces by a rope and supplied and drained through firefighting hoses. The size of the debris that can be passed depends on the physical size of the eductor. This makes an eductor especially useful in situations where fitting a debris strainer to the suction port will present more issues than it resolves. Additionally, unlike many mechanical pumps, they can also pass debris as the eductor has no moving parts that can be fouled. Typically referred to as an eductor in these applications, this is preferred over electrical pumps due to their simplicity, compact size, and greatly mitigated risk of explosion in the event that flammable liquids and/or vapors are present. Their use has decreased somewhat as small electric vacuum pumps are far more effective, environmentally safe, and have become more affordable, but the unmatched simplicity and reliability of this device have caused it to remain popular for small labs or as a backup.Īnother, much larger version of this device is used in maritime operations as a device to dewater (drain) areas in a ship that have been flooded in emergency situations. solvent removal), they can violate environmental protection laws such as the RCRA by mixing potentially hazardous chemicals into the water stream, then flushing them down a drain that often leads directly to the municipal sewer. However, they are water-intensive, and depending on what the vacuum is being used for (e.g.
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In the past, water aspirators were common for low-strength vacuums in chemistry benchwork. The vacuum hose should be connected to this barb. 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 cheap and simple water aspirator is commonly used in chemistry and biology laboratories and consists of a tee fitting attached to a tap and has a hose barb at one side.
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If not considering the source of the working fluid, vacuum ejectors can be significantly more compact than a self-powered vacuum pump of the same capacity.Ĭommon types Water aspirator If a gas is used, however, this restriction does not exist.
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The strength of the vacuum produced depends on the velocity and shape of the fluid jet and the shape of the constriction and mixing sections, but 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 or 0.46 psi or 32 mbar at 25 ☌ or 77 ☏). The outer tube then narrows into a mixing section where the high velocity working fluid mixes with the fluid that is drawn in by the vacuum, imparting enough velocity for it to be ejected, the tube then typically expands in order to decrease the velocity of the ejected stream, allowing the pressure to smoothly increase to the external pressure. The fluid leaving the jet is flowing at a high velocity which due to Bernoulli's principle results in it having low pressure, thus generating a vacuum. In an ejector, a working fluid (liquid or gaseous) flows through a jet nozzle into a tube that first narrows and then expands in cross-sectional area. The water inlet and outlet are at the top and bottom, respectively the air inlet is on the side.Ī vacuum ejector, or simply ejector is a type of vacuum pump, which produces vacuum by means of the Venturi effect.