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3.4 Function
3.4.2 Working Principle of Rotary vane pumps
Pressure reduction in a closed system is accomplished by repeatedly removing a portion of the original
volume of gas contained in the system. Removal is performed by the action of the rotating elements of
the pump which cause a given space to be successfully enlarged and diminished. Figure 2 illustrates
a chapter through a typical stage of rotary-vane pump. Note that this figure is not intended to illustrate
exactly the internal components of the pumps; its purpose is to illustrate the general operating principles
of vacuum pumps.
The rotary action of the pump creates a hollow space of chamber (1) which expands as the pump rotates.
As the chamber expands, the pressure in the chamber decreases. As a result, gas is drawn into
the chamber due to the difference in pressure between the chamber and the inlet (4) to the chamber
(The inlet is the only place where gas can flow into the chamber).
Once the vane (3) moves past the inlet (4), it seals the inlet against the chamber (1) and the gas becomes
trapped between the vanes (2 and 3). The chamber (1) formed by the enclosed space between the
vanes then begins to decrease in volume as the rotor revolves, compressing the gas. The pressure
of the compressed gas becomes greater than atmospheric pressure.
When the vane (2) moves past the exhaust port (5) the compressed gas in the chamber is forced out
through the exhaust port. This expansion/compression cycle constitutes one complete cycle of the
pump operation. This cycle is repeated as the vane (2) passes the intake port and seals it against
the atmosphere. Therefore, two pump cycles are performed during each revolution of the pump rotor.
Fig. 2 Rotary vane pump Principle
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DESCRIPTION
