How does the vacuum pump works?
Answer:
*Following are the two widely used vacuume pumps:
*A rotary vane pump is a positive-displacement pump that consists of vanes mounted to a rotor that rotates inside of a cavity. In some cases these vanes can be variable length and/or tensioned to maintain contact with the walls as the pump rotates. The most simple vane pump is a circular rotor rotating inside of a larger circular cavity. The centers of these two circles are offset, causing eccentricity. Vanes are allowed to slide into and out of the rotor and seal on all edges, creating vane chambers that do the pumping work. On the intake side of the pump, the vane chambers are increasing in volume. These increasing volume vane chambers are filled with fluid forced in by the inlet pressure. Often this inlet pressure is nothing more than pressure from the atmosphere. On the discharge side of the pump, the vane chambers are decreasing in volume, forcing fluid out of the pump. The action of the vane drives out the same volume of fluid with each rotation. Multistage rotary vane vacuum pumps can attain pressures as low as 10-3 Torr.
http://en.wikipedia.org/wiki/rotary_vane...
*The liquid ring pump compresses gases by means of a vaned impeller rotating within and eccentric to a cylindrical casing. Liquid (usually water) is fed into the pump and by centrifugal action, forms a moving cylindrical ring against the inside of the casing. This liquid ring creates a series of seals in the space between the impeller vanes to form compression chambers. The eccentricity between the impeller rotating axis and the casing geometric axis results in a cyclic variation of the volume enclosed by the vanes and the ring.
Gas (or air) drawn into the pump via an inlet port in the end of the casing, is trapped in the space formed by the impeller vanes and the liquid ring. The impeller rotation compresses the gas, which is then discharged through another port in the end of the casing.
Some ring-liquid is also entrained with the discharge stream. This liquid is separated from the gas stream by other equipment external to the pump. In some systems, the discharged ring-liquid is cooled via heat exchanger or cooling tower, then returned to the pump casing. In other systems, the discharged hot liquid (usually water) is treated as a waste stream. In this case, fresh, cool water is used to make up the loss. Environmental considerations are making such once through systems increasingly rare.
http://en.wikipedia.org/wiki/liquid_ring...
Source(s):
http://en.wikipedia.org/wiki/vacuum_pump...
The only 'Vacuum pump' I've seen, associated with a large oil tank, is when the tank has been emptied for cleaning and maintenance. The tank top man-hole is opened.
A large 'Eductor' (Venturi Tube) is used at the bottom manhole, that uses compressed air as its eduction medium.
The velocity of the compressed air through the eductor, gives a 'suction' that causes a draft of fresh air to be drawn through the tank to remove combustible and toxic gases from the tank before maintenance men can enter the tank, even then, they may need to wear breathing apparatus due to, when removing sludge from the tank bottom, its disturbance can release more gases into the tank's atmosphere..
(The vacuum pumps mentioned above are not used with large oil tanks).
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